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SWP27 May Creek
\\\�\\\•\ King ® County Surface Water Management Everyone liver downstream N May Creek Current and Future Conditions Report August 1995 Prepared by Foster Wheeler Environmental Corp. King County Surface Water Management Division King County Department of Public Works Surface Water Management Division 700 Fifth Avenue Suite 2200 Seattle, Washington 98104-2637 (206) 296-6519 City of Renton Surface Water Utility City of Renton Building/Planning/Public Works Department Surface Water Utility Municipal Building 200 Mill Avenue South Renton, WA 98055 (206) 277-6200 Text will be made available in large print, Braille, or audiotape as requested G:\WP\4248\MAYCREEK\08244A ♦ 9-1-95 King County Executive City of Renton Mayor Gary Locke Earl Clymer King County Council City of Renton Council Maggi Fimia, District 1 Randy Corman Cynthia Sullivan, District 2 Robert Edwards Louise Miller, District 3 Kathy Keolker-Wheeler Larry Phillips, District 4 Toni Nelson Ron Sims, District 5 Timothy Schlitzer Bruce Laing, District 6 Richard Stredicke Pete von Reichbauer, District 7 Jesse Tanner Greg Nickels, District 8 Kent Pullen, District 9 Building/Planning/Public Works Department Larry Gossett, District 10 Gregg Zimmerman, Administrator Jane Hague, District 11 Ronald Olsen, Utility Systems Director Brian Derdowski, District 12 Ron Straka, Stormwater Utility Supervisor Christopher Vance, District 13 Contributing Staff (Renton) Department of Public Works David Jennings, Project Manager Paul Tanaka, Director Carolyn Boatsman, Water Quality Specialist David Christensen, Wastewater Supervisor Surface Water Management Division Jennifer Henning, Senior Planner Jim Kramer, Division Manager William Hutsinpillar, Parks and Recreation Director Ken Guy, Assistant Division Manager Gail Reed, Airport Supervisor Keith Hinman, Basin Planning Program Manager Patricia Stoddard, Production Assistant Neil Watts, Plan Review Supervisor Contributing Staff (King County) Richard Rutz, Ph.D., Project Manager Contributing Staff (Consultant) Clint Loper, Senior Engineer Foster Wheeler Environmental Corp. (formerly, Ebasco Susan Kaufman, Senior Water Quality Engineer Environmental) Derek Booth, Ph.D., Geologist John J. Brueggeman, Project Manager David Hartley, Ph.D., Hydrologist Ellen Hall, Ph.D., Project Manager Robert Fuerstenberg, Senior Ecologist Bruce Stoker, Geomorphologist Ruth Schaefer, Senior Ecologist John Knutzen, Aquatic Ecologist Todd Bennett, Engineering Technician Elizabeth Ablow, Aquatic Ecologist John Adams, Program Analyst Clayton Antieau, Wetland Ecologist Brad Liljequist, Community Planner Roger Kadeg, Environmental Engineer Julie Shibuya, Community Planner Kathleen Gilligan, Toxicologist Karen Goto, Senior Engineer Thomas Martin, Water Resources Modeler Mary Harenda, Senior Ecologist Kenneth Johnson, Ph.D., Geohydrologist Martha Bray, Resource Planner Katherine Godtfredsen, Environmental Chemist Ruoxi Zhang, Planning Graphics Supervisor Ron Tressler, Terrestrial Ecologist Fred Bentler, Planning Support Technician Ken Winnick, GIS Specialist Ted Krause, Planning Support Technician Donna Hawley, GIS Technician Laurel Preston, Planning Support Technician David Barber, Technical Editor Wendy Gable, Graphics Technician Aqua Terra Citizens Advisory Committee Douglas Beyerlein, Hydrologist Julie Bonwell Joseph Brascher, Hydrology Technician Robert Cugini Ginger and Richard Dickson The Quinn Company Thomas Drummond Julie Quinn, Land Use Planner William (Ed) Horne Susan Larson -Kinzer Fisheries Consultants John Richardson Kerry Tappel, Fisheries Biologist Richard Spence Mick Zevart Inca Engineers Andrew Duffus Robert Custer, Surveyor John Affholter Ben Peterson, Surveyor Carl Johanson, GIS specialist G:\WP\4248\MAYCREEK\08244A ♦ 9-1-95 CONTENTS List of Figures and Tables x List of Maps xiii Chapter 1 Executive Summary 1-1 Chapter 2 Introduction 2.1 Background and Purpose of Basin Planning 2-1 Background 2-1 Purpose 2-1 Political Jurisdictions and Interactions 2-2 Earlier Planning Efforts 2-3 2.2 Organization of this Report 2-3 Subarea Delineation 2-3 Contents of this Report 2-5 Chapter 3 Land Use and Land Cover 3.1 Introduction 3-1 3.2 Land Use and Land Cover Concepts 3-1 3.3 Data Collection and Analytical Methods 3-2 Mapping Categories 3-2 Existing Land Use/Cover 3-2 Future Land Use/Cover 3-4 3.4 Basinwide Conditions 3-5 Physical Overview 3-5 Historical Landscape and Settlement Pattern 3-6 Current Conditions 3-7 Future Conditions 3-9 3.5 Conditions by Subarea 3-11 Lower Basin 3-11 May Valley 3-13 East Renton Plateau 3-14 Highlands 3-14 3.6 Key Findings 3-15 Chapter 4 Geology and Groundwater 4.1 Introduction 4-1 4.2 Data Collection and Analytical Methods 4-1 4.3 Regional History and Stratigraphy 4-1 Bedrock Lithology and Structure 4-1 Ice Occupation of the Basin 4-3 4.4 Postglacial Processes and Deposits 4-5 Deglaciation and Landscape Changes 4-5 Basin Soils 4-6 4.5 Groundwater in the May Creek Basin 4-6 4.6 Geologic Hazard Areas 4-7 v CONTENTS (continued) Prehistoric Period 4-7 Historic Period 4-8 Future Seismic Hazards 4-8 4.7 Key Findings 4-9 Chapter 5 Hydrology 5.1 Introduction 5-1 5.2 Hydrologic Concepts 5-1 Rainfall and Weather 5-1 Runoff 5-1 5.3 Data Collection and Analytical Methods 5-3 Introduction 5-3 Data Collection 5-3 HSP-F Simulation Model 5-5 Statistical Analysis Procedures 5-15 5.4 Basinwide Conditions 5-17 Pre -Development Conditions 5-18 Current Conditions 5-22 January 1990 Storm 5-24 Future Conditions 5-31 5.5 Conditions by Subarea 5-33 Highlands 5-33 East Renton Plateau 5-37 May Valley 5-40 Lower Basin 5-44 5.6 Key Findings 5-49 Chapter 6 Flooding 6.1 Introduction 6-1 6.2 Flooding Concepts 6-1 6.3 Data Collection and Analytical Methods 6-2 Data Sources 6-2 Analytical Methods 6-2 6.4 Basinwide Conditions 6-5 Current Conditions 6-5 Future Conditions 6-8 6.5 Conditions by Subarea 6-9 Lower Basin 6-10 May Valley 6-15 Highlands 6-22 East Renton Plateau 6-24 6.6 Key Findings 6-26 W • CONTENTS (continued) Chapter 7 Sediment Erosion and Deposition 7.1 Introduction 7-1 7.2 Watershed Processes 7-1 Hillslope Processes 7-2 Stream Channel Processes 7-3 7.3 Data Collection and Analytical Methods 7-8 Hillslope Conditions 7-8 Channel Conditions 7-8 7.4 Basinwide Conditions 7-9 Historic Conditions 7-9 Current Conditions 7-10 Future Conditions 7-17 7.5 Conditions by Subarea 7-18 Lower Basin Subarea 7-18 May Valley Subarea (May Creek RM 3.9 to 7.0) 7-34 Highlands 7-35 East Renton Plateau Subarea 7-50 7.6 Key Findings 7-53 Chapter 8 Water Quality 8.1 Introduction 8-1 8.2 Water Quality Concepts and Regulations 8-1 Water and Sediment Quality Concepts 8-1 Beneficial Uses 8-5 Standards 8-6 8.3 Pollutant Sources 8-9 Nonpoint Sources 8-9 Point Sources 8-28 8.4 Water Quality Data Collection and Analysis 8-29 Data Collection and Methods 8-29 Water and Sediment Quality Data Analysis 8-33 8.5 Nonpoint Modeling Approach 8-54 8.6 Conditions by Subarea 8-66 Lower Basin 8-66 May Valley 8-69 Highlands 8-70 East Renton Plateau 8-72 8.7 Key Findings 8-72 Chapter 9 Aquatic Habitat and Fish 9.1 Introduction 9-1 9.2 Landscape and Habitat Concepts 9-1 Landscape Age 9-1 Buffering Elements 9-2 vii CONTENTS (continued) Riparian Vegetation 9-4 Salmonids and the Hydraulic Environment 9-5 May Creek Fisheries 9-8 Lakes and Wetlands 9-16 9.3 Data Collection and Analytical Methods 9-20 Stream Habitat 9-20 Wetland Habitats 9-21 9.4 Significant Resource Areas 9-22 9.5 Basinwide Conditions 9-26 Historic Conditions: Basin Vegetation 9-26 Historic Conditions: Stream Habitat 9-27 Current Conditions (1936-1993): Basin Vegetation 9-28 Current Conditions: Stream Habitat 9-29 Future Conditions 9-30 9.6 Conditions by Subarea 9-31 Lower Basin 9-31 May Valley 9-49 Highlands 9-52 East Renton Plateau 9-59 9.7 Key Findings 9-64 Fish Resources 9-64 Wetlands 9-65 Vegetation 9-65 Chapter 10 Current and Future Conditions by Subarea 10.1 Introduction 10-1 10.2 Lower Basin Subarea 10-1 Description 10-1 Current and Future Lower Basin Conditions 10-2 10.3 May Valley Subarea 10-4 Description 10-4 Current and Future May Valley Conditions 10-4 10.4 Highlands Subarea 10-7 Description 10-7 Current and Future Highlands Conditions 10-7 10.5 East Renton Plateau Subarea 10-8 Description 10-8 Current and Future East Renton Plateau Conditions 10-9 Chapter 11 Coordination and Planning 1 1 .1 Introduction 11.2 Private Sector Actions 11-1 viii CONTENTS (continued) 1 1 .3 Role of Government and Public Agencies 1 1-6 Local Governments 1 1-6 State, Federal and Tribal Agencies 1 1-7 11.4 Related Plans, Programs, and Regulations 1 1-8 King County Growth Management Planning Policies 1 1-8 King County Comprehensive Plan Update 1 1-8 King County Zoning Code Revisions 1 1-9 King County Public Benefit Rating System 1 1-9 King County Parks, Recreation, and Open Space Comprehensive Plan 1 1-9 King County Code and Community Plan Amendments 1 1-10 King County Surface Water Management Stewardship Program 1 1-10 City of Renton Comprehensive Plan 1 1-10 City of Renton Groundwater Management Planning 1 1-10 City of Renton Comprehensive Park, Recreation, and Open Space Plan 1 1-1 1 City of Renton Sensitive Area Ordinances 1 1-1 1 City of Renton Comprehensive Surface Water Utility Plan 1 1-1 1 Honey Creek and May Creek Interceptors 1 1-1 1 City of Newcastle Incorporation 1 1-12 City of Newcastle Comprehensive Plan 1 1-12 East King County Coordinated Water System Plan 11-12 Washington Department of Ecology Stormwater Permitting 1 1-12 Washington State Department of Transportation Highway Planning 1 1-13 Chapter 12 References 12-1 APPENDICES A Observed Conditions Summary B Maps C Hydrology D Flooding E Water Quality ix LIST OF FIGURES AND TABLES Land Use and Land Cover Table 3-1 May Creek Basin Existing Land Use/Land Cover Mapping Categories 3-3 Table 3-2 Existing Land Use/Land Cover by Subarea 3-8 Table 3-3 Future Land Use/Land Cover by Subarea 3-12 Geology and Groundwater Table 4-1 Description of Geology Map Units 4-2 Hydrology Figure 5-1 Flow Chart of May Creek and Tributary Inputs for HSP-F Model 5-7 Figure 5-2 Distribution of Current and Future Land Cover Types in the May Creek Basin and Subareas 5-10 Figure 5-3 Relative Contribution of Runoff per Unit Area 5-19 Figure 5-4 25-Year Flow at Selected Locations in May Creek 5-20 Figure 5-5 Increase in Tributary Flow with Changing Land Use 5-21 Figure 5-6 Simulated Hydrographs for the January 1990 Storm 5-27 Figure 5-7 Simulated January 1990 Storm Hydrographs for the Upper Basin of May Creek 5-28 Figure 5-8 Simulated January 1990 Storm Hydrographs for the Lower Basin of May Creek 5-30 Table 5-1 Streamflow Gaging and Calibration Results at Two Locations on May Creek 5-13 Table 5-2 Mean Annual Flows in May Creek and Tributaries (Current Conditions) 5-25 Table 5-3 Simulated January 1990 Flood Results for May Creek and its Tributaries (January 9, 1990) 5-29 Table 5-4 Mitigation Effectiveness in May Creek and its Tributaries (Based on 10-year Flows) 5-32 Table 5-5 Highlands Flow Frequencies Show that the Highlands Subarea Streams are the Largest Flow Contributors to May Creek 5-35 Table 5-6 East Renton Plateau Flow Frequencies Show that These Streams are Moderate Flow Producers 5-38 Table 5-7 May Valley Flow Frequencies Show that Floodplain Storage in the Valley Attenuates Downstream Peaks 5-41 Table 5-8 Lower Basin Flow Frequencies Demonstrate that Urbanization Affects both Current and Future Flows in the Subarea 5-47 Flooding Table 6-1 Culvert Capacity Analysis for May Creek Tributaries 6-7 Table 6-2 May Creek Roadway and Flood Elevations Based on HEC-2 Results 6-17 Sediment Erosion and Deposition Figure 7-1 Profile of May Creek, Selected Tributaries to May Creek and Lake Washington 7-4 Figure 7-2 Estimated Flood Flows Along May Creek 7-11 x LIST OF FIGURES AND TABLES (continued) Figure 7-3 Channel Stability Index and Field Observed Channel Conditions for Creeks in the May Creek Basin 7-12 Figure 7-4 May Creek Channel Parameters 7-14 Figure 7-5 Gypsy Creek Channel Parameters 7-22 Figure 7-6 Honey Creek Channel Parameters 7-25 Figure 7-7 Newport Hills Creek Channel Parameters 7-29 Figure 7-8 Boren Creek Channel Parameters 7-32 Figure 7-9 Unnamed Creek (0287D and 0287E) Channel Parameters 7-37 Figure 7-10 Long Marsh Creek Channel Parameters 7-39 Figure 7-11 Country Creek Channel Parameters 7-42 Figure 7-12 Cabbage Creek Channel Parameters 7-44 Figure 7-13 North Fork May Creek Channel Parameters 7-47 Figure 7-14 Greene's Creek Channel Profile Along the Existing Channel 7-51 Water Quality Figure 8-1 Flows and Phosphorus Loads Supplied to Lake Washington by Six Stream Systems 8-42 Figure 8-2 Water Temperatures are Cooler both Upstream and Downstream of the May Valley 8-47 Figure 8-3 Total Suspended Solid Loads by Subcatchment 8-57 Figure 8-4 Total Phosphorus Loads by Subcatchment 8-58 Figure 8-5 Zinc Loads by Subcatchment 8-59 Table 8-1 Definitions, Significance and Possible Sources of some Water Quality Parameters that are used in Evaluating the Health of a Water Body 8-2 Table 8-2 Summary of Standards and Recommended Threshold Values for Common Water Quality Parameters for Class AA Freshwater Streams such as May Creek 8-6 Table 8-3 Guidelines for May Creek Basin Planning for Water Quality Thresholds for Several Parameters that do not have Established Numeric Criteria 8-7 Table 8-4 Calculated Values for Metal Toxicity for May Creek based on WAC Criteria and Measured Water Hardness 8-8 Table 8-5 Livestock Densities by Farm Size in the May Creek Basin 8-16 Table 8-6 Pasture Conditions on Farms in Nine King County Watersheds 8-18 Table 8-7 Underground Storage Tank Inventory in the May Creek Basin 8-26 Table 8-8 Number of Samples with Metal Concentrations that Exceed Dissolved (State) or Total (Federal) Criteria 8-36 Table 8-9 Total Metals Concentrations in May Creek Baseflow and Stormflow 8-38 Table 8-10 Metals Concentrations in May Creek Stormflow Compared to Median Urban Site Values 8-38 Table 8-11 Baseflow and Stormflow Concentrations of Total Suspended Solids (TSS), Nutrients, and Fecal Coliforms in May Creek Basin 8-39 Table 8-12 Annual Phosphorus Loadings to Lake Washington from Six Selected Basins 8-43 A LIST OF FIGURES AND TABLES (continued) Table 8-13 Fecal Coliform/Fecal Streptococci Ratios Determined from Storm Samplings in May Creek 8-44 Table 8-14 May Creek Water Temperature Ranges 8-46 Table 8-15 Ranges of Water Quality Measurements in Lake Kathleen and Lake Boren 8-49 Table 8-16 Locations where Contaminant Concentrations exceeded WDOE Freshwater Sediment Guidelines 8-53 Table 8-17 Percent Increase in Water Quality Parameter Loadings from Current Conditions 8-60 Table 8-18 Parameter Loadings from May Creek Water Quality Modeling 8-62 Table 8-19 Lower Basin Subarea Water Quality Issues 8-67 Table 8-20 May Valley Subarea Water Quality Issues 8-70 Table 8-21 Highlands Subarea Water Quality Issues 8-71 Table 8-22 East Renton Plateau Subarea Water Quality Issues 8-72 Aquatic Habitat and Fish Figure 9-1 May Creek Sockeye (1992), Cutthroat (1993), and Steelhead (Total 1984 through 1987) Redds (Steelhead Surveyed from RM 0.3-3.9) 9-14 Table 9-1 Distribution of Anadromous and Adfluvial Salmonid Species and Habitat 9-9 Table 9-2 Summary of May Creek 1992-1993 Spawning Surveys 9-12 Table 9-3 Steelhead and Cutthroat Escapement Data for Lower May Creek (RM 0.0 to 4.0 or 4.5) 9-15 Table 9-4 Wetland Summary 9-23 Table 9-5 Large Pool Habitats in the Mainstem of May Creek (0282) 9-32 Table 9-6 Slow Water Habitat Types in the May Creek Mainstem Channel 9-33 Table 9-7 Relative Habitat Composition and Large Woody Debris (LWD) per Mile for the Mainstem of May Creek and Selected Tributary Reaches 9-34 Table 9-8 Fast Water Habitat Types in the May Creek Mainstem Channel 9-35 Table 9-9 Riparian Conditions for May Creek and its Tributaries 9-37 Coordination and Planning Table 11-1 Government Agency Roles in Managing Resources of the May Creek Basin 11-2 xii LIST OF MAPS (all maps are in Appendix B) Map 1 Water Features Map 2 Subarea Boundaries Map 3 Planning Area and Urban Growth Boundaries Map 4 Existing Land Use/Land Cover Map 5 Future Land Use/Land Cover Map 6 Geology Map 7 Groundwater Potential Recharge Areas Map 8 Subcatchment Boundaries Map 9 Sewer Service Map 10 Septic Systems Map 11 Small Farms and Livestock -keeping Locations Map 12 Hazardous Waste Generators and Underground Storage Tanks Map 13 Stormwater Sampling Locations Map 14 Lower Basin Conditions Map 15 May Valley Conditions Map 16 Highlands Conditions Map 17 East Renton Plateau Conditions Map 18 May Valley 100-year Floodplain xui Executive Summary Executive Summary The May Creek Current and Future Conditions Report provides a comprehensive assessment of the current conditions and predicts future trends in the May Creek basin. Its primary purposes are to identify significant conditions and issues to be addressed in the May Creek Basin Plan, and to serve as a resource for future agency actions. The Basin Plan will recommend solutions and management programs to address significant and often interrelated flooding, sediment erosion and deposition, water quality, and wetland and stream habitat problems. May Creek basin encompasses a 14- square-mile area located in King County, southeast of Lake Washington between the Cedar River, Coal Creek, and Issaquah Creek drainages. The basin lies primarily within unincorporated King County, but the western and southwestern portions of the basin (approximately 12 percent of the total area) are within the City of Renton, and the northwestern 20 percent is in the City of Newcastle. There is a diverse mix of land use and land cover types ranging from the developed communities in Renton and around Lake Boren, Honey Creek, and Lake Kathleen to more sparsely settled rural residences and small farms in May Valley and the large regional park on Cougar Mountain. The surface -water system of May Creek and its tributaries includes 26 miles of mapped streams, two small lakes, and over 400 acres of wetlands. As was the case for many drainages in the Puget Sound region, in the years since the European settlement many activities, such as logging and forest removal, coal mining, and agricultural activities occurred without much consideration of long-term consequences. These actions led to denuded slopes, channelized streams, and encroachment on floodplains, which in turn resulted in erosion, sediment deposition in the stream channels, flooding of structures, and destruction of fish habitat on a large scale. In recent decades, the basin has experienced the pressures of growth and continuing urban and suburban development, as well as impacts from some continuing rural uses such as quarry mining and livestock management. This development replaces forest cover and other vegetation with hardened and impervious surfaces (roads, buildings, parking lots and others). The land with plant cover allows much of the rainwater to soak into the soil, supplying plants with water and replenishing aquifers, whereas the hardened surfaces let the stormwater run off the land and overwhelm the natural ability of the surface -water system to adequately convey peak stormwater discharges, sustain Chapter 1 Executive Summary 1-1 healthy aquatic habitat and fish resources, and maintain water quality. The future will bring more development to the basin, and will While the May Creek basin has suffered many impacts, it still retains high quality natural resources and attributes. The May Creek Basin Plan will provide information and guidance to address some of the basin's more pressing problems and improve watershed management to protect its current resources. The choices regarding future actions will be complex and difficult to make because many problems are interrelated: improving matters in one place may worsen them in another. Also, there are physical and monetary limitations, as well as regulatory and social factors to address. Restoring and protecting the basin's resources will require the collective commitment of the interested parties to implement an effective basin plan. SUMMARY OF KEY FINDINGS Land Use and Hydrology A wide diversity of land uses may be found in the May Creek basin, ranging from urban residential and commercial areas in and near the cities, to forest, farmlands, and residences in the eastern part of the basin. Wetlands account for over five percent of the basin, and more than half of this acreage is contained in several large wetlands in the May Valley that are closely associated with the floodplains. After a century of development, forest vegetation is still the largest cover category in the basin, with nearly 51 percent of the area. However, two-thirds of this forest cover is likely be removed as a consequence of future residential development. The second largest cover category is Residential use: this currently occupies about 35 percent of the basin but is expected to double in the future. The urban western portion of the basin will develop to high densities, while the eastern part of the basin will retain a substantially rural character with low -density development (but with some significant inclusions of higher -density development, especially on the East Renton Plateau). The developed, urbanized portion of the basin will have the lowest increases in future peak streamflows: much of the increase due to development has already occurred in this area, and the new development will be at high densities that will have more extensive requirements for mitigation of stormwater runoff effects. The Highlands subarea is the least urbanized portion of the May Creek basin, and flows to date have increased only a relatively small amount from pre -development conditions (less than 20 percent in most cases). However, this area of relatively high rainfall, thin soils, and steep terrain contributes disproportionately large peak flows, storm volumes, and sediment loads. Due to future development and removal of forest cover, flood peaks and volumes in this subarea could increase from 20 to 50 percent, and contribute to a future increase in flooding in the May Valley. Storage of floodwaters is the dominant hydrologic factor in the May Valley. 'This storage occurs in the valley floodplain and results in long -duration flooding; however, the long residence time of floodwater in the valley directly contributes to reduced peak flood flows Chapter 1 Executive Summary 1-2 downstream. Simulation of the January 1990 flood showed that the tributaries in the basin peaked some 8 to 14 hours prior to the mainstem of May Creek, and that the lower mainstem (canyon and mouth) peaked slightly earlier than upstream May Creek in May Valley. Removal of the substantial storage in the May Valley would cause downstream flood flows to increase. Current drainage requirements for new development in areas zoned for low -density will not prevent significant increases in tributary flood flows and delivery of water to May Valley because R/D ponds or other measures are not required for most low -density residential development. But even if R/D ponds were required for all future development, their effectiveness in reducing May Valley floods would still be limited because the May Valley problem is primarily controlled by volume, and the R/D ponds would delay but not greatly reduce the total volume of storm runoff delivered to May Valley. Flooding and Drainage The most extensive flooding problems in the May Creek basin are found in the May Valley. This valley is a natural floodplain that was frequently inundated with floodwaters even before settlement began. Development, dredging and filling within the May Creek floodplain have since greatly altered drainage patterns and reduced natural storage areas, and placed structures in the path of floodwaters. Cessation of dredging and the gradual infill of the channel with sediment has also reduced the channel capacity and increased the frequency of overbank flow. Extensive flooding of pastures and other open land occurs annually during the winter, with extensive ponding of long duration in several locations. Approximately six homes and a commercial business and several other structures are located in the 100-year floodplain of May Creek, and two other homes are affected by tributary flows. Runoff due to future development will increase the flood volumes that will be delivered to the valley, resulting in longer durations of floodwater inundation, greater frequency of flooding, and slightly greater flood depths. However, the width of the 100-year floodplain, and therefore the number of homes in it, is not expected to increase significantly under future conditions. Localized drainage problems throughout the basin are primarily related to alterations to natural stream channels, filling of natural detention areas, undersized conveyance systems, development with inadequate mitigation, or improper installation of drainage measures that cause an increase of runoff to downslope properties. Most current drainage problems are concentrated in the more urbanized portions of the basin, although the Highlands subarea is expected to have the largest percentage increase from future development. Several road bridges and culverts throughout the basin have also been identified as inadequate for conveyance of 25-year flows. Chapter 1 Executive Summary 1-3 Sediment Erosion and Deposition Sediment is naturally generated by erosion in many locations in the basin, such as in the May Creek canyon. This erosion is accelerated by the increased stormflows that result from development and land cover changes. Mitigated future stormflows will be higher than current flows, and will result in additional erosion and sediment deposition. The deposition of transported sediment has been gradually reducing the capacity of the formerly dredged channel of May Creek in the May Valley. This gradual accumulation has contributed to the worsening of flooding problems in the valley. In the May Creek canyon downstream, sediment fills instream pools and degrades fish habitat. It also deposits at the mouth of the creek at Lake Washington, where it interferes with commercial business and must be removed biennially by dredging. Many of May Creek's tributary channels show evidence of downcutting and sediment production above natural levels. Several stream channels, including those of Honey Creek, Gypsy Creek, and Greene's Creek, exhibit considerable downcutting. Future stormflows will be greater, and additional downcutting is expected. Several other stream reaches are currently relatively stable but are predicted to undergo increased or severe channel erosion as flows increase with future development. These include lower May Creek, Boren Creek, Cabbage Creek, and the North and East forks of May Creek. The May Creek canyon and lower Honey Creek are the major sources of the sediments deposited in Lake Washington at the mouth of the creek. In addition to stormwater, other major sources of erosion and sediment -laden water include poor livestock practices which lead to streambank trampling and loss of riparian vegetation, as well as poor construction practices and quarry runoff. Water Quality Dispersed human activities are the major contributors of pollution to the surface waters of the May Creek basin. Major sources of this nonpoint pollution in the basin include road runoff, quarry outflow, runoff from developing sites and commercial operations, animal -keeping practices and grazing in riparian areas, and leaking septic tanks. Nonpoint pollution concentrations are projected to increase in the future as more of the basin urbanizes, most dramatically in the Country Creek, Newport Hills Creek, and other drainage areas where large increases in development are anticipated. Consistently high fecal coliform counts were found in the May Valley and upper basin areas. Poor livestock practices (best management practices were not in place on half to two-thirds of the farms surveyed, animal densities exceeded the carrying capacity of many pastures) and failing septic tanks both contribute to these high coliform counts. However, locally high concentrations of fecal coliforms were also found at the mouths of Honey Creek and China Creek, indicating that urban sources of fecal coliform such as failing septic systems and pet wastes may be important contributors to downstream May Creek fecal coliform counts. Water quality in Lake Boren and Lake Kathleen is currently Chapter 1 Executive Summary 1-4 moderate to good; however, continued input of high total phosphorus and fecal coliform levels to Lake Boren may threaten its popular recreational uses in the future. Aquatic habitat values and fish use are affected by poor water quality in several ways. High water temperature due to lack of riparian vegetation and shade is a serious limit to fish use and survival in the May Valley reach of May Creek in the late summer months. High metals levels after storm events in some areas pose risks to aquatic life: the more urbanized tributaries such as Honey Creek have more exceedances of toxic metals criteria than do the less -developed tributaries. Heavy sediment loads in the upper basin can cause fish stress or death, as well as limit the survival of eggs. Stormwater phosphorus loading is an important concern in this basin and in others that contribute to Lake Washington. Current stormwater phosphorus concentrations for May Creek already well exceed EPA guidelines for streams that discharge to lakes, and the concentrations are high enough that they are also a concern for the health of the stream itself. Moreover, phosphorus levels are expected to increase in the future as develop proceeds in the basin. However, the relative contribution from May Creek to Lake Washington is low when compared to the load contributed by other tributaries to the lake. Groundwater data for the basin are very limited. Best management practices should be emphasized for all possible sources of groundwater contamination, especially in areas of high potential aquifer recharge. Aquatic Habitat and Fish Historically, development activities including logging, agriculture, mining, home-building and commercial development have significantly degraded the stream and wetland habitats of the basin. This has occurred through the filling of wetlands, increase of stormwater runoff and peak streamflows, addition of sediment and pollutants to the water, and removal of the conifer forest that is the source of large woody debris (LWD), a critical feature of healthy aquatic habitats. Given the location deep within the urban and urbanizing area, the lower four miles of May Creek are in comparatively good condition and support five species of salmonids, but high sediment loads and a lack of current and future sources of LWD limit the potential use of this reach. Coho salmon and steelhead trout, key native fish species, have decreased in abundance because of larger Lake Washington system problems but also because the complex habitat structure typical of undisturbed streams has been greatly reduced throughout the May Creek basin. Sockeye salmon and adfluvial cutthroat trout can better tolerate the less complex, disturbed habitats currently found in May Creek and its tributaries, and consequently may not be decreasing. The lack of adequate quantities of LWD is a major cause of the loss of habitat complexity, and accounts for the relative scarcity of pool habitats in much of the basin. The lack of LWD also accelerates downcutting in the stream channels, and decreases trapping of suspended sediment. Land -use projections suggest that much of the Chapter 1 Executive Summary 1-5 remaining forest cover will be removed by future development: thus, active efforts will be necessary to increase the amount of instream LWD. The basin has a moderate diversity and sizable base of wetland resources, including the extensive 200-acre May Valley wetland. However, virtually every known wetland in the basin has been disturbed by deforestation, filling, draining, agricultural disturbance, and/or buffer removal, and much disturbance has occurred since the wetlands were first inventoried in 1983. Field investigations for this study also discovered additional small class-2 wetlands that were not included in the 1983 inventory: these uninventoried wetlands are particularly vulnerable to damage because of the lack of awareness of their existence. Without proper controls, existing uses and new development will continue to damage stream, wetland, and lake habitats. Streams and wetlands will suffer from increasing stormflows and sediment loading, buffer area clearing and loss, livestock trampling of banks, and nonpoint pollution. Chapter 1 Executive Summary 1-6 Chapter 2 Introduction Chapter 2 Introduction 2.1 BACKGROUND AND PURPOSE OF BASIN PLANNING BACKGROUND May Creek is a small stream that has its origins on the high ground of Cougar and Squak mountains, and the East Renton Plateau. In its seven -mile length it flows through rural, suburban, and urban settings, through forest and horse pastures and commercial areas, through floodplain and wetlands and a deep canyon until it meets Lake Washington. The creek and its tributaries together form the May Creek surface -water system, and this system together with the surrounding land forms the 14-square-mile May Creek basin. Early use of the basin for fishing and hunting was supplanted by intensive extraction of timber and coal, and farming of the rich soils. More recently, land use in the basin has been shifting substantially to urban and suburban communities and their supportive services, with significant livestock use in the more rural areas. The western third of the basin is now incorporated within the cities of Renton and Newcastle, with the remainder in unincorporated King County: with urbanization and development has come an increase in the amount of impervious surface and associated impacts on the surface - water system and habitats of the basin. Historically, the May Valley has experienced periodic and occasionally extensive flooding, with prolonged ponding of water in some locations. The valley is a natural floodplain in which flooding has worsened because of floodplain development, filling of wetlands, and increased stormwater runoff. Naturally high erosion and sedimentation rates in the basin have also been exacerbated by development and consequent increases in stormwater runoff. Water quality is affected in various locations by pollution from agricultural and livestock practices, gravel pit operations, septic tank failures, small commercial businesses, highway runoff, and other sources. Most streams and wetlands have experienced extensive modifications including filling or dredging, grazing, and others that have seriously degraded both their habitat quality and function, including impairment of flood storage. Salmonid fish use in May Creek has been reduced because of habitat loss and degradation, deteriorating water quality, and increasing water temperatures. Many of these effects are anticipated to worsen in the future and affect not only the natural environment but also the quality of life for those who live and work in the basin unless steps are taken to address runoff and other problems. PURPOSE The complex and interrelated nature of surface water problems in the May Creek basin requires comprehensive assessment in order to identify the forces affecting the basin and to define the problems and formulate long-term solutions. This basin planning effort includes several steps: 1) evaluation of current and future basin conditions; 2) Chapter 2 Introduction 2-1 identification of surface water problems; 3) analysis of issues and solutions; and 4) development of specific recommendations and actions for the basin. This document, the Current and Future Conditions Report (hereafter, Conditions Report), completes the first two steps. It describes the current and expected future condition of the basin's water -related resources and defines specific problems that have been identified in the basin. These include: increased urbanization and the resulting increase in impervious surfaces and stormwater runoff, water quality degradation, flooding, loss of fish and wildlife habitat, erosion and sedimentation, poor domestic livestock practices, failing septic systems, and inadequate controls and enforcement of regulations on quarry operations. The report is based on extensive field work throughout the basin and information gathered from previous City and County plans and other agencies. The next steps in the basin planning process include the analysis of potential solutions to problems and development of specific recommendations. Responsive measures will be developed to address current drainage and water quality problems (such as flooding, erosion and sedimentation, and non -point water pollution), protect and rehabilitate aquatic resources, and avoid or minimize future problems, damage, and financial impacts on taxpayers. The draft May Creek Basin Plan is scheduled to be published for public comment in late 1995 or early 1996. It will be revised based on public and agency comment, and in 1996 a final plan will be forwarded to the King County Council and the City of Renton Council for their review and adoption. The adopted plan will then be implemented through capital improvement projects, regulations, development permits, educational programs, and other programs administered by management and resource agencies. POLITICAL JURISDICTIONS AND INTERACTIONS The City of Renton and King County are working together to prepare the basin plan for the Cedar River basin to the south of May Creek, and are cooperating and sharing costs for the preparation of the May Creek Basin Plan. Renton is responsible for about 12 percent of the study area in the southwestern corner of the May Creek basin, the new city of Newcastle in the northwest portion of the basin incorporates approximately 20 percent of the study area, and King County administers the remainder. Each jurisdiction has its own adopted codes and policies for regulating land use and surface water run-off, but recognizes as well the importance of coordinating this planning effort and implementing solutions to problems of the basin. In 1979 King County and several suburban cities (including the City of Renton) agreed on a sphere of influence boundary (Huckell/Weinman, 1993) to recognize each jurisdiction's interests and to help define their ultimate growth boundaries. All but the easternmost portion of the basin lies within the Renton sphere (the easternmost area is in the sphere of influence of the City of Issaquah). A significant modification to this arrangement occurred in November 1993, when the northwestern 20 percent of the basin, together with adjacent areas outside of the basin Chapter 2 Introduction 2.2 to the north, voted to incorporate under the interim name of Newport Hills. The new city formally incorporated on September 30, 1994, and shortly thereafter voted to rename itself as the City of Newcastle. In addition to these political jurisdictions, portions or all of May Creek basin fall within the areas of authority or management for a number of governmental agencies, and within the Usual and Accustomed Area of the Muckleshoot Indian Tribe. These agencies and tribe and treir-authorities and responsibilities are discussed in more detail in Chapter 11: Coordination and Planning. EARLIER PLANNING EFFORTS There have been several earlier water resource planning efforts for the basin. A 1960's Flood Control Zone District and drainage plan failed in a bond vote due to opposition to a fee on new development and to elements of the drainage plan, including disposition of dredge spoils; disagreement about the appropriateness of dredging as a long-term solution; fears that flood -proofing would encourage additional development in the valley, and fears that dredging easements would be required to provide public access. In the early 1970's an intergovernmental environmental management group explored five alternative drainage concepts with May Creek residents. The citizens preferred two of these concepts: (1) clear, widen or deepen the channel of May Creek and (2) control runoff from new development onsite. However, the committee had no implementing authority for these proposals, and they were not acted upon. In the late 1970's some of the first surface water and stormwater utilities were being formed to respond to stormwater runoff. In response to such runoff concerns and also to concerns about developing information necessary for the consideration of sanitary sewer development in the basin, King County in 1980 prepared a drainage basin plan for the May Creek basin. The analysis for this plan proceeded in cooperation with the development of the Newcastle Community Plan for the area. The 1980 plan outlined a basinwide approach for controlling stormwater and improving the water quality of lakes and streams, with the primary emphasis on structural solutions. Unfortunately, the hydrologic and flooding predictions of the models did not correspond well with flooding observed in 1979, and the plan was not adopted by the King County Council. However, a portion of the plan's recommendations was implemented in the area zoning adopted in 1983 to support the Newcastle Community Plan. The current planning effort will develop and utilize better models and a more comprehensive group of techniques and solutions to address the problems of the basin. 2.2 ORGANIZATION OF THIS REPORT SUBAREA DELINEATION To aid in the consideration of conditions and problems, and to facilitate discussion in this report, the May Creek basin has been divided into four subareas: the Lower Basin, May Valley, Highlands, and East Renton Plateau (see Map 2 in Appendix B). Each subarea Chapter 2 Introduction 2.3 has been defined so as to include lands with common natural and developmental characteristics. Lower Basin Subarea The Lower Basin extends from the mouth of May Creek at Lake Washington upstream to RM 3.9, above the Coal Creek Parkway SE crossing. The principal features of the Lower Basin are the canyon through which May Creek flows, the delta downstream of the canyon, Lake Boren, and the two principal tributaries of Honey Creek and the Boren Creek system. Other major tributaries in the Lower Basin are Gypsy Creek and Newport Hills Creek. The Lower Basin is wholly contained within the Urban Growth Area, and has extensive high -density residential and commercial development. May Valley Subarea The May Valley is the best known and most identifiable feature in the basin, being the floodplain of upper May Creek and adjacent lower valley areas from RM 3.9 to the hydrologic divide to the east. The land in the valley bottom is quite flat, and much of it is wetlands. The subarea includes the lower portions of the three headwater forks of May Creek, as well as the confluences and alluvial fans of a number of small tributary streams to the north and south of the creek. Highlands Subarea The Highlands subarea lies north of May Valley and east of the Lower Basin, and includes the steep southern slopes of Cougar Mountain and the southwest portion of Squak Mountain. Thin, till soils characterize much of the area, drained by tributaries that include Long Marsh Creek, Country Creek, Cabbage Creek, and the North and East forks of May Creek: part of the Cougar Mountain Regional Wildland Park is within this area, and contains the largest forested area in the basin. Though this subarea has been slower to develop than others, much of the non -park land has in recent years been platted for residential homes at low and medium densities. East Renton Plateau Subarea The East Renton Plateau is shared between the May Creek and Cedar River basins. The May Creek basin portion of the tableland lies south of May Valley and east of the Lower Basin subarea. The terrain is relatively flat (except where it slopes sharply down to the May Valley) and capped with relatively impervious till soils. Development in the subarea has been very uneven, with intermixed pockets of suburban and urban -density housing, highways and commercial establishments, and working farms. Major tributaries that drain the subarea include the South Fork of May Creek, Tributary 0291A, and Greene's Creek. Lake Kathleen is situated at the subarea's southeastern end. Chapter 2 Introduction 2-4 CONTENTS OF THIS REPORT The following seven chapters (Chapters 3-9) describe the current and future conditions in the surface -water systems of the May Creek basin through several disciplinary perspectives. These disciplines include land use, geology and groundwater, hydrology, flooding, erosion and sediment deposition, water quality, and aquatic habitat. Conditions are discussed from basinwide and subarea points of view. Each chapter also includes a description of concepts needed to understand the issues, data collection and analytical methods, and key findings. Chapters 10 and 11 summarize conditions by subarea, and address the public and governmental entities affecting the basin's resources. References used in preparing this report, appendices and maps follow. Chapter 1: Executive Summary Summarizes the key findings of this report Chapter 2: Introduction Discusses the background and purpose of the report, and its organization Chapter 3: Land Use Describes how past changes in land use have created the landscape we see today, and how current and expected future development will continue this process Chapter 4: Geology and Groundwater Describes the effect of geology, glacial history, seismic conditions, and groundwater resources on basin conditions Chapter 5: Hydrology Discusses streamflow conditions in relation to current and future land use, as analyzed using a continuous flow simulation model Chapter 6: Flooding Identifies areas currently prone to flood damage, where flood damage is expected in the future, and causal factors Chapter 7: Sediment Erosion and Deposition Describes the effects of current and future stormflows on conditions in the tributary systems and on erosion and sediment deposition patterns in the May Creek mainstem Chapter 8: Water Quality Describes water quality conditions, current and anticipated future nonpoint source pollution problems, and water quality impacts on aquatic habitat Chapter 9: Aquatic Habitat and Fish Discusses landscape processes in relation to fish population trends and habitat, describes current and future conditions of stream, riparian, and wetland habitat, and identifies significant habitats Chapter 2 Introduction 2-5 Chapter 10: Summary of Current and Future Conditions by Subarea Summarizes the findings of Chapters 3-9 by subarea, including how each discipline interacts with others Chapter 11: Coordination and Planning Discusses the underlying factors affecting conditions in the basin and the roles of private individuals and public agencies in managing natural resources, including development activities and regulatory programs References Lists, by chapter, the references used in compiling this report Appendix A: Observed Conditions Summary Lists the problems and issues identified in each subarea from staff observations, model results, and citizen complaints Appendix B: May Creek Basin Maps Includes all maps referenced in the document Appendices C-E These include additional detailed material referred to in Chapters 3-11 Chapter 2 Introduction 2-6 Chapter 3 Land Use and Land Cover Chapter 3 Land Use and Land Cover 3.1 INTRODUCTION May Creek basin (see Map 3 in Appendix B) is located within the 49-square-mile Newcastle Community Planning area, southeast of Lake Washington between the Cedar River, Coal Creek, and Issaquah Creek drainages. The 14-square-mile drainage basin is characterized by a mixture of land uses ranging from more dense urban areas in the west to lower -density rural, agricultural and forestry lands in the central and eastern part of the basin. Within the basin are two incorporated cities: the City of Renton is located in the southwestern portion of the basin and covers about 12 percent of the land area, and the City of Newcastle, located in the northwestern portion, includes about 20 percent of the basin. Land use in the cities varies from medium -density single-family residential areas to commercial and industrial uses. In addition to the commercial development within the City of Renton, there is a small commercial area in the City of Newcastle along Coal Creek Parkway SE near Lake Boren, and two neighborhood -scale centers in unincorporated King County at 164th Avenue SE and SE Renton -Issaquah Road (SR-900), and at SE 128th Street and 164th Avenue SE. Major areas of residential identification in the basin include Sierra Heights/Honey Creek in the southern part of the Lower Basin subarea, Newcastle, Lake Boren and China Creek in the northern part of the Lower Basin subarea, the May Valley, the East Renton Plateau south of May Valley, and the Lake Kathleen locality in the southeast corner of the East Renton Plateau subarea. The current population in May Creek basin is estimated at approximately 16,200, based on the 1990 King County 1:100,000 Population Dot Map. The population is increasing and is expected to continue to do so as a result of growth trends and land use policies in the basin and surrounding areas. Between 1980 and 1991, for example, population in the Newcastle Community Planning area increased 26 percent, to a total of 82,000 (King County, 1992). 3.2 LAND USE AND LAND COVER CONCEPTS As an area develops, the uses of the land become more intense and densely packed. The vegetative cover of the land also changes: forest and other highly vegetated areas are replaced by grass and impervious surfaces (e.g. roads, parking lots, roofs, and sidewalks). This conversion of vegetation has important consequences for surface water management, because forest and other dense vegetation types intercept more water and hold it longer. Greater forest and vegetative cover allow more water to evaporate back into the air; the vegetation also impedes the flow of water across the ground surface, and allows more water to soak into the ground. When the vegetation is cleared and removed, the greater volume and rate of stormwater runoff results in increased streamflows and flooding, and increases in erosion and sedimentation, habitat degradation, and non -point water pollution problems. Chapter 3 Land Use and Land Cover 3-1 The changes in vegetative cover more directly predict changes in surface water runoff than do changes in land uses. Basin planning uses land cover in the hydrologic model to evaluate current surface water runoff and predict future changes (see Chapter 5: Hydrology). Decisions about the appropriate mixes of land uses and zoning in a basin continue to be the province of the comprehensive land use and development plans of the County and the cities (see also the Future Land Use discussion, below). 3.3 DATA COLLECTION AND ANALYTICAL METHODS MAPPING CATEGORIES The mapping categories for the current and future land use/cover maps are determined by the amount of impervious surface per unit area, vegetative cover, and the presence of wetlands (Table 3-1). For convenience and because of the rough correlation of level of development with amount of impervious surface, the cover types are fit to existing land —use names. The percentage of impervious surface therefore determines the category assignment for a given area. For example, any area that contains 35 to 45 percent impervious surface will be mapped within the single-family high -density type: if an area of duplexes (a multifamily type of land use, in zoning terms) had 40 percent impervious surfaces, it would be mapped using the single-family high -density category. The mapping categories and maps of existing and future land use/cover (Maps 4 and 5 in Appendix B) are designed to provide information about surface water runoff, and are not land use development guides. Land use development guidance is provided by the comprehensive land use and development plans, mapping and zoning of the City of Renton and King County. EXISTING LAND USE/COVER The existing land use/land cover data were derived from aerial photographs taken in 1992; U.S. Geological Survey (USGS) 1:25,000 digital topographic maps; King County Wetlands Inventory (King County, 1990a); King County Sensitive Areas Map Folio (King County, 1990b); City of Renton Critical Areas Maps (Geo Engineers, 1991); Soil Conservation Service maps; and field investigations. Existing land use in the basin was mapped according to the dominant features of the landscape and the amount of impervious surface per unit area that characterizes each land use type. Areas of similar land use and impervious surface content were grouped on aerial photographs (scale 1:12,000) taken February 16 and September 10, 1992. All wetlands listed in the King County Wetlands Inventory and those identified by the City of Renton were visited in the field during February and March of 1993 and their boundaries were verified. Additionally, other potential wetlands observed on aerial photographs but not listed in the inventory were visited to determine the presence and estimate the extent of wetland. Chapter 3 Land Use and Land Cover 3-2 Table 3-1. May Creek Basin Existing Land Use/Land Cover Mapping Categories. Land Use Category Impervious Surface (percent) Minimum Mapping Unit (acres) Commercial/Institutional 90-100 1 (Pavement, compacted soil, sidewalks, buildings) Multifamily (trailer parks, densely spaced buildings) Single family —high density (housing developments) Single family —low density grass (widely scattered houses surrounded by grass) Single family —low density forest (widely scattered houses surrounded by u, trees) Quarry Grass Forest Clearcut Wetland (emergent, scrub -shrub, forested and aquatic beds) Open water 60-70 35-45 3-13 3-13 90 0-3 0-3 0-3 0-3 C�7 1 1 2.5 2.5 2.5 2.5 2.5 2.5 1" 1/ All wetlands greater than one acre were mapped. Wetlands smaller than one acre that were observed in the field were also mapped. FUTURE LAND USE/COVER As is noted above, basin planning does not determine how much or what kinds of development are appropriate for a watershed, but rather evaluates and addresses the current and anticipated future surface water effects of development, which may include making recommendations about land use where appropriate to address or prevent surface water problems. Land use plans prepare policies for guiding future development in the community, city, or county, and may address many development issues such as traffic congestion and maintenance of open spaces. Basin plans provide information and guidance for land -use planning and in turn receive such guidance from the land use plans. Several local land -use plans were used in developing this Conditions Report, including the City of Renton Comprehensive Plan and zoning map (1992), King County Comprehensive Plan (1985, and 1994 revisions), and Newcastle Community Plan and Area Zoning (1983). King County Comprehensive Plan The 1985 King County Comprehensive Plan designated almost all of the May Creek basin as Urban, excepting only the easternmost portion together with the May Valley floodplain of May Creek. This reflected the location of the basin within the urbanizing Lake Washington area, and envisioned that almost all of the basin would eventually develop residential, commercial, and industrial areas at urban densities. Both the City of Renton and King County revised their land use plans and policies in 1994 pursuant to the Washington State Growth Management Act. As part of this updating, the County and the interjurisdictional Growth Management Planning Council defined a new Urban Growth Area (UGA) boundary (Map 3, Appendix B) that reflected goals and needs for accommodating projected growth. Future land use/cover modeling is greatly influenced by the location of the UGA boundary, because the Comprehensive Plan assumes that land use in the areas west of the UGA boundary will ultimately proceed to high -density residential or other urban densities and uses, unless there are environmental or legal constraints. Community Plans King County has used the community planning process to develop policies to guide land development in each of the 13 planning areas in the county. It provided an opportunity for the County to look at each area in the context of county -wide policies such as growth management and environmental protection. The plans include policies on land use, residential densities, commercial and industrial needs, sewer and water service, transportation networks, park and recreational needs, and environmentally sensitive areas. Chapter 3 Land Use and Land Cover 3-4 The 1983 Newcastle Community Plan recognized the potential impact of development on the environmentally sensitive May Valley subarea and recommended low residential densities there. In most of the Highlands and East Renton Plateau subareas the plan recommended suburban -level residential densities. Additional policies related to surface water and flood problems were developed for other key areas in the basin and have been implemented during review of development permits. City Planning The City of Renton's land -use planning process is similar to King County's. Renton also updated its comprehensive plan as required by the State's Growth Management Act, and defined the extent of its future growth areas. The City's new comprehensive plan underwent significant public review by both City and County residents, and was adopted on June 7, 1993. The new plan addresses land use densities, sensitive areas, services and facilities, and transportation. Portions of two subunits, Kennydale and the East Renton Plateau, are in the May Creek basin study area. The new City of Newcastle (see Map 3 for the portion in May Creek basin) formally incorporated in 1994, and has adopted its own interim comprehensive plan and land use and drainage codes. 3.4 BASINWIDE CONDITIONS PHYSICAL OVERVIEW The May Creek basin is a rectangularly shaped watershed that is nestled between the Coal Creek, Issaquah Creek, and Cedar River basins at the southeast corner of Lake Washington in the southeast region of the Puget Sound Lowland. The entire basin is within King County and drains 14 square miles. The basin has been divided into four subareas (see Chapter 2: Introduction, and Maps 1 and 2 in Appendix B). Moderate temperatures are characteristic of the basin. Stream flows are highest during periods of high precipitation, generally from November to March. The elevation is low enough that most of the precipitation is received as rain. The basin is centered on a glacial outwash channel, the May Valley, which is shared with McDonald Creek in the Issaquah Creek basin. Three headwaters creeks meet near the hydrologic divide of May Valley to form the main channel of the creek, which then flows down the center of the May Valley subarea. At the downstream end of the May Valley the creek enters a narrow canyon area with steep bluffs. May Creek emerges from the canyon and is conducted by a channel to one side of the industrial development on the alluvial fan at the outlet to Lake Washington. Two major tributaries enter May Creek in the Lower Basin subarea, Boren Creek and Honey Creek. Boren Creek receives water from Lake Boren and China Creek, and part of the Newcastle Hills. Honey Creek drains a residential and commercial area mostly within the City of Renton to the south of May Creek. In the Highlands subarea several Chapter 3 Land Use and Land Cover 3-5 north -side tributaries drain the steeper uplands of Cougar Mountain and southwestern Squak Mountain. Several small tributaries from the southern side of the basin drain the northern portion of the East Renton Plateau. The second of the basin's two lakes, Lake Kathleen, is located in the southeastern corner of the basin and is drained by the South Fork of May Creek. Lake Boren has public access through Lake Boren Park and the public boat ramp, but there is no public access to Lake Kathleen. There are 14 inventoried Class -land -2 wetlands, and an additional 47 previously uninventoried wetlands were identified during the field studies for this report (see Map 1). The largest and most prominent wetland is the 208-acre Class-1 riparian wetland that is located along much of the valley floor of the May Valley subarea. HISTORICAL LANDSCAPE AND SETTLEMENT PATTERN The Newcastle area, which encompasses the May Creek basin, has a long and diverse history. The Indian peoples of the Puget Sound area had loose regional or ethnic identities that were derived from their geographic location and the resources they relied upon (Buerge, 1984). In the Lake Washington area these people were generally known as hah-chu-AHBSH, "the lake people." The lake people fished for anadromous salmonids and for resident fish species such as peamouth; they hunted waterfowl and other animals, and gathered plants such as wapato and cattail for food and other life needs. House sites were clustered at the mouths of important salmon -spawning streams around the periphery of the lake. Two longhouses of the shu-bahl-tu-AHBSH, "the drying house people," were located near the mouth of May Creek, with a burial ground near Pleasure Point. The settlement of the area by people of European lineage initially occurred slowly, and only a few hardy settlers were present when coal was discovered in 1863 (King County, 1979). Coal seams were soon found at Coal Creek, Newcastle, and Squak Valley, and investors from Seattle and San Francisco formed several companies to exploit the resource, including the Lake Washington Coal Company, Seattle Coal Company, and the Pacific Coast Coal Company. Between 1868 and 1890, approximately 150,000 tons of coal were produced each year. The towns of Newcastle and Coal Creek (just north of the basin) sprang up to house the miners. "At one time the combined populations of Newcastle and Coal Creek exceeded that of Seattle. During those 'boom' years Newcastle coal helped pull Seattle out of the Depression of 1884, and with the rebuilding of the city after the fire of 1889" (Fish, 1969). The coal mines in the May Creek basin and surrounding areas eventually began to play out, and were eventually destroyed by both fire and flooding. When the mines closed, logging and lumber mills remained for a time as major industries in the basin, for the area had an abundance of timber and was close to both Lake Washington and Lake Sammamish. Large areas of the basin were cleared within a relatively short period: the west side of Cougar Mountain was harvested around 1917, and by the early 1920s the area that now includes Somerset, Newport, and Horizon View had been logged. As was the case for coal, the timber resources were exhausted, and the prime logging years ended by the late 1920s. Chapter 3 Land Use and Land Cover 3-6 At the same time that coal and timber resources were being developed, farmers were also settling in the basin, clearing the flat valley floor and some of the uplands south of May Creek. Agricultural use expanded over time until, by the 1930s, May Creek had been channelized and nearly all of the land in the valley was intensely cultivated. Small farms and truck farming, with some livestock raising, was the dominant pattern through the 1950s. Residential settlement in the early 1900s concentrated near the town sites. Large -lot residential tracts near Lake Washington were particularly popular. Typical of these was Hazelwood, which began to develop around the turn of the century. C.D. Hillman, a realtor from Seattle, offered five -acre tracts for sale in the Kennydale and Hazelwood area. An advertisement in a newspaper of August 1904 states "Millions of brook trout nearly a foot long run up May Creek in this Garden of Eden. Here a person can purchase a four room cottage and five acres of fine land on Lake Washington for $775, $25 down, and $10 a month, with a fine view of the mountains and a car line close by." Development in Newcastle stagnated when the coal and lumber industries ceased in the late 1920s. This stagnation was prolonged by the Depression of the 1930s and by World War Il. The character of the basin changed considerably in the 1950s, partly due to the "post-war boom" and the increased popularity of suburban development. Increasingly, new residences housed commuters who traveled to the central cities for daytime jobs. Coupled with this trend were the decline of the agricultural use of the valley, and an increase in the numbers of commercial and recreational livestock: many former agricultural fields now serve as pasture for livestock. The trend of suburban residential growth has continued to the present time. CURRENT CONDITIONS Existing land use in the May Creek basin ranges from the urban residential areas in and near the cities of Renton and Newcastle to forests, pastures, and scattered residences in the eastern part of the basin (Map 4). In general the greatest amount of impervious surface occurs in the western third of the basin in the Lower Basin subarea, where industrial, commercial, and single-family high -density and multi -family residential areas are most common. Even after the large removal of the forest cover in the early part of the century, forests still cover the largest total area of any cover type within the basin with nearly 4,600 acres (51 percent) (Table 3-2). These forest areas consist of stands of second- or even third —growth coniferous and hardwood (broadleaf) trees, with the largest stands concentrated on the slopes of the mountains and in the May Creek Park. While there are still a few woodlot areas in the basin, most cutting permits are now associated with clearing preparatory to development. Wetlands occupy another large area, over 400 acres (five percent) of the basin. Most of these are small, perched wetlands, but significant acreages are contained in several large wetlands. In particular, the May Valley is dominated by a large emergent wetland that is associated with the floodplain. It is heavily grazed by livestock and is also used for low -intensity agricultural practices. The current wetland acreage, like the forest Chapter 3 Land Use and Land Cover 3-7 Table 3-2. Existing Land Use/Land Cover by Subarea. a m Total Lower Basin May Valley Hiahlands East Renton Plateau Land Use/Land Cover Acres Percent Acres Percent Acres Percent Acres Percent Acres Percent r Q. Commercial/Institutional 169.8 2 142.8 4 2.9 0 1.3 0 22.8 1 CO Multifamily 39.1 0 27.9 1 7.9 1 0 0 3.3 0 co Single family - high density 1,581.3 18 1,184.7 37 18.9 3 14.7 0 363.0 18 a Single family - low density 1,472.8 17 327.2 10 192.5 31 429.1 13 524.0 26 a Quarry 89.9 1 0 0 10.8 2 61.8 2 17.3 1 C� CD Grass 562.6 6 241.6 8 78.5 13 57.4 2 185.1 9 Forest 4,582.0 51 1,194.0 37 65.7 11 2,578.2 81 744.1 38 Clearcut 14.9 0 0 0 0 0 14.9 0 0 0 w Wetland 410.7 5 77.4 2 242.6 39 29.8 1 60.9 3 00 Open water P 65.6 1 17.1 1 0 0 0 0 48.5 2 Totals 8,988.7 100 3,212.7 100 619.8 100 3,187.2 100 1,969.0 100 acreage, reflects losses from past activities, in this case the partial or complete filling of a number of wetlands during the past several decades. Most existing wetlands are strongly correlated with the remnants of forest cover, particularly in the more developed western portion of the basin. Single-family high -density family residential is the second most common land category. It occupies nearly 1,600 acres (18 percent), mostly in the western and urbanized part of the basin. A close third in total area is the single-family, low -density residential category, most of which is in the eastern, more rural portion of the basin. The dominant feature of the central and eastern portions of the basin is the May Valley with its large central wetland and floodplain. To the north are Cougar Mountain and Squak Mountain, which currently still retain much second -growth conifer and deciduous forests but also have scattered single-family low -density residential areas. The uplands to the south of the May Valley are composed of a mixture of grasslands (pastures), small areas of single-family high -density and multi -family residential development, and single-family low -density residential areas with a large amount of grass cover. Four active sand and gravel quarries are located near the eastern end of the basin along SR- 900. Surface water and stormwater runoff from the three eastern subareas converge on the May Valley (Map 2). While the eastern part of the basin still has a very rural "feel" to it, significant amounts of development and impervious surface can be identified in a number of locations (Map 4). This is consistent with the observation of many residents that development has been increasing in the basin, and also reflects the assignment by the 1985 King County Comprehensive Plan of most of the basin to the urban growth area. This suggests that more stormwater runoff is being generated in the eastern basin than might be expected simply based on the rural impression the area gives. Most such runoff makes its way to the May Valley; this water, together with the contributions of the Lower Basin subarea, is then conducted through the canyon to Lake Washington. FUTURE CONDITIONS The future land use/cover map (Map 5) illustrates conditions in which build -out has occurred. That is, the map portrays the highest level of development that could be implemented within the limits of current zoning and land -use designations. Thus, this scenario would yield the highest potential stormwater flows that could result under current zoning. The map was constructed using zoning designations and guidance for the City of Renton provided by the City's zoning adopted in June 1993, and for the unincorporated County and Newcastle areas by the King County Newcastle Community Plan zoning (1983, as amended), and the Growth Management Planning Council's recommended revised Urban Growth Area (UGA) boundary. Where existing development or vested platting already exceeded the planning area designations, the existing development and vesting took precedence. The County Comprehensive Plan assumes that land use in the unincorporated areas west of the UGA boundary (see Map 3 in Appendix B) will ultimately proceed to high - density residential or other urban densities and uses, unless there are environmental or Chapter 3 Land Use and Land Cover 3-9 legal limitations. This assumption is incorporated in the modeling for the Conditions Report. In addition, areas that were identified by the City of Renton as urban separators were modeled as proceeding to medium density. In the discussions prior to adoption of the 1994 revisions to the County Comprehensive Plan an interim UGA boundary was identified by the Growth Management Planning Council, together with four Technical Review Areas (TRAs). With minor revisions the interim UGA boundary was adopted in the final revised Comprehensive Plan. The revised UGA boundary differs considerably from the 1985 boundary, for it moved westward in May Creek basin, removing two large areas north and south of the May Valley floodplain from the urban area and placing them in the rural portion. Had the UGA boundary been retained at its old (1985) location, the new rural areas would have remained in the urban area and have been modeled as future high -density development (except in wetland and other constrained locations); instead, because the boundary was relocated, new rural area was created, the majority of which was represented as future low -density residential (see Map 5 in Appendix B). Because the hydrologic modeling for this report occurred before the final adoption of the revised UGA boundary, County and City staff developed the model based on the interim UGA boundary and anticipated changes to that boundary. For hydrologic purposes only, the TRAs were allowed to be modeled using land -use densities that could differ somewhat from then -current City or County zoning. The staff assignments were, in most cases, relatively good approximations of the UGA boundary and land -use assignments in the final revisions to the Comprehensive Plan. TRAs NC-3 and R-2 were included in the urban growth area, but were modeled as urban separator areas and thus assigned wholly to the single-family medium -density designation. In 1994 almost all of TRA NC-3, and a small portion of TRA R-2, were incorporated into the City of Newcastle. In the city's Interim Comprehensive Plan, most of the City's development and density assignments correspond well with the County and City of Renton staff assignments made earlier. For modeling purposes, TRA R-1 was split between single-family low- and high -density residential use, based primarily on existing platting patterns. The adopted Comprehensive Plan divided the area in this manner, with minor deviations from the modeled alignment. TRA R-3 was wholly assigned during modeling to the rural area and to the single-family low -density designation; the final UGA boundary placed the southern quarter -section of TRA R-3 inside the urban area, resulting in a higher future density for approximately 80 acres than was modeled. For the future conditions map, the West Village area located east of Lake Boren was assigned a different density than current zoning allowed. The Newcastle Community Plan designated three village sites for future urban development, of which only two would be allowed to develop. In 1994, one village had been built, and staff determined that it was reasonably likely that the West Village would be the other developed site. Within the West Village area some single family development has already occurred, and in 1994 an application was submitted to rezone the remaining area (about 100 acres of which is in the basin) from growth reserve to the appropriate urban zones. Based on the most current development plans at the time of modeling, staff assumed that Chapter 3 Land Use and Land Cover 3-10 approximately 70 percent of the acreage would become single-family high -density developments, and 30 percent would be multi -family units or equivalent density. The future conditions map also assigned a different density to the Newcastle Landfill than current zoning would have allowed. The current owners of the landfill are in the process of closing it and complying with the conditions of the EIS. They have preliminary approval for an 18-hole golf course development: for modeling purposes, based on the likely amount of impervious surface to be developed, this area is portrayed as single- family low -density on the future conditions map. Residential uses (low-, medium-, and high -density single-family residential, and multi- family) will double from the current 35 percent of the basin to 70 percent in the future. At present this is divided approximately evenly between low and high densities, and roughly even proportions will likely also be seen in the future. The entire lower portion of the basin, that is, everything within the UGA boundary, will eventually develop to suburban (medium) and urban (high) densities. New development in the rural areas outside of the cities will be limited to existing platting or to single-family low -density residences, small farms, and forestry and quarry activities, but may add considerable amounts of impervious surface. With the exception of designated natural areas and unbuildable sites, the forested area of the basin will gradually be removed, and its total area will be reduced by almost two-thirds. Interstate 405 and SR-900 will expand, with the SR-900 being of particular interest because of its addition of considerable amounts of impervious surface into the middle and upper basin. These changes, if realized and unmitigated, would introduce additional runoff into the May Valley, the Honey Creek and Lake Boren tributaries, and the downstream May Creek canyon. 3.5 CONDITIONS BY SUBAREA LOWER BASIN The Lower Basin subarea is now largely incorporated in the cities of Renton and Newcastle (Map 3). It is characterized by the presence of large areas of single-family high -density residential development interspersed with smaller tracts of lower -density housing, pastures and undeveloped forest, commercial and industrial sites, heavily disturbed lands, and the 120-acre Renton/Newcastle/County May Creek Park in the canyon. Wetlands in the western portion of the basin are mostly restricted to forested areas, with the exception of two relatively large, emergent and shrub wetlands near Lake Boren (Map 4). The majority of the Lake Boren area has been developed in the past decade under the existing zoning. Significant commercial activity occurs near Honey Creek. Public services and facilities are readily available in the Lower Basin and this area is expected to continue to develop. Tables 3-2 and 3-3 illustrate the expected changes in Lower Basin land use. Most striking are the increase in single-family medium- and high -density residential uses (from 37 percent of the area currently to 69 percent in the future). These increases in residential housing density come at the expense of forest land conversion (from 37 Chapter 3 Land Use and Land Cover 3-11 c� a Table 3-3. Future Land Use/Land Cover by Subarea. m w Total Lower Basin May Valley Highlands East Renton Plateau jLand Use/Land Cover Acres Percent Acres Percent Acres Percent Acres Percent Acres Percent a C Commercial/Institutional 367.5 4 234.4 7 43.0 7 28.3 1 61.8 3 n i Multifamily 79.3 1 73.0 2 3.3 1 0 0 3.0 0 a Single family - high density 2,003.0 22 1,622.1 50 13.6 2 10.5 0 356.8 18 r- v a Single family - medium density 1,335.1 15 603.3 19 50.0 8 394.0 12 287.8 15 o Single family - low density 2,869.3 32 155.0 5 202.9 33 1,382.4 43 1,129.0 57 CD Quarry 39.2 0 0 0 0 0 39.2 1 0 0 Grass 122.0 1 56.1 2 38.1 6 17.2 1 10.6 1 Forest 1,703.0 19 374.6 12 29.4 5 1,287.6 40 11.4 1 w N Wetland 404.6 5 77.2 2 239.4 39 27.9 1 60.1 3 Open water 65.6 1 17.1 1 0 0 0 0 48.5 2 Totals 8,988.6 100 3,212.8 100 619.7 100 3,187.1 100 1,969.0 100 percent currently to 12 percent in the future) and residential infilling (single-family low - density housing declines from ten percent currently to five percent in the future). In general, the area is urban or urbanizing, in keeping with its Urban area designation. The future conditions map also incorporates some additions to city and county parks, as indicated in planning documents for King County and City of Renton. The City of Renton and King County Department of Metropolitan Services (Metro) are currently considering a new sanitary sewer interceptor line for the Honey Creek area, to connect to the Metro trunk line near Lake Washington Boulevard via a connecting Metro interceptor line. The two principal groups of alternatives are 1) a gravity -line that would construct the Metro interceptor line in the May Creek canyon downstream from Honey Creek, and 2) a force -main route over the Renton Highlands that would use existing lines for most of its length and would require pumping, but would avoid the sensitive areas of the May Creek canyon. The canyon route could link with and help service parts of the District 107 sanitary sewer system; however, current District plans envision using a route down the Coal Creek drainage, and this would be used if a Renton Highlands interceptor route were chosen. The WSDOT has recently made improvements to 1-405 for High Occupancy Vehicle (HOV) lane development. In connection with this project and others, old drainage problems near the May Creek crossing are being investigated and addressed by WSDOT and the City of Renton. MAY VALLEY The May Valley subarea supports pasture and low -intensity agricultural uses, small farms, and scattered single-family residences. Currently, 31 percent of the area is in single-family low -density uses (Table 3-2). The subarea has several large wetlands and floodplain areas, forming 39 percent of the subarea. Increased stormwater flows, periodic flooding and extended ponding of water, poor water quality, and impacts to fish are all well documented problems in the subarea, in part due to practices in the area and in part a result of surface water inflow from other subareas. Through the Open Space Program, King County has proposed a hiking trail connection along the Puget Power transmission line right-of-way from the Cedar River to Cougar Mountain. Most of the subarea has been allocated to the rural designation in the County's Comprehensive Plan. Much of it also has special p-suffix development conditions applied under the Newcastle Community Plan (although the protections provided by p- suffix conditions may be provided in the future by zoning code changes or other land - use tools). Under the rural designation, residential development in the valley will continue to be limited to rural uses and minimum 5- or 10-acre lots. Agricultural uses, including domestic livestock grazing, may continue, but new, more intense activities will be limited by zoning, rural designation, and sensitive area restrictions on much of the land. If currently zoned commercial sites in the subarea are developed, the amount of land in the commercial/institutional category will increase from almost zero to seven percent of the area (Table 3-3). Chapter 3 Land Use and Land Cover 3-13 EAST RENTON PLATEAU The uplands to the south of May Creek are composed of a mixture of grasslands and pastures, small areas of high -density single-family and multi -family residential development, and low -density single-family residential areas with a large amount of grass cover. Lake Kathleen and its adjacent wetlands are located in the southeast corner. As Chapter 4 (Geology and Groundwater) discusses, the East Renton Plateau subarea is capped with till soils which allow less infiltration of water than do many other soil types. Development of the plateau could thus be expected to create a number of situations where water would collect and pond, which is consistent with experience in the subarea. Forest land (38 percent) and single-family residential development (26 percent) are currently the largest categories in the May Creek basin portion of the East Renton Plateau. However, nearly 20 percent of the area is already in the single-family high - density category. Some locations in May Creek basin, but particularly inside the Cedar River basin, illustrate the extension of suburban and urban densities and public services to formerly outlying areas. With the westward movement of the Urban Growth Area boundary in the revised County Comprehensive Plan, rural -designated areas now begin as far west as 148th Avenue SE, south of May Creek, and north of SE 128th Street, including the area around Lake Kathleen. Future development in this area will be subject to the revised zoning that will implement the designation. Despite the redesignation of much of the subarea to rural, the East Renton Plateau subarea is expected to experience the greatest percentage loss of forest land in the future, with over 700 acres to be converted to medium- and low -density single-family residential uses. If realized and unmitigated, this would have consequences for the May Valley (see Chapter 5: Hydrology). HIGHLANDS Forest is currently the largest cover category in the Highlands subarea, forming 81 percent of the total (Table 3-2). Much of this forest area is located in the Cougar Mountain and Squak Mountain park areas, and will continue to be present in the future. But future development of other holdings will result in the loss of about half of the forest land (more than 1,200 acres) in this subarea. King County is considering the purchase of several additional parcels and trail connections in the area to add to the Cougar Mountain Regional Park system, which could slightly reduce the amount of forest loss. In the revised County Comprehensive Plan, much of this subarea was placed in a rural designation. This designation nevertheless will allow much of the forested area to be converted to single-family low -density residential use. Low -density housing is anticipated to increase from 13 to 43 percent of the subarea. Some building activity is currently occurring along the hillsides, such as the Ellenswood area and Licorice Fern subdivision. Chapter 3 Land Use and Land Cover 3-14 The Washington State Department of Transportation (WSDOT) has proposed widening SR-900, easterly and northerly from Duvall Avenue within the Renton city limits to 1-90 in Issaquah. The WSDOT published a Design Analysis Study in 1992 that included three different project concepts; while no specific decisions have been made to date, evaluations of future land use/cover for this Conditions Report assumed that widening to at least four lanes will occur. The realignment of the intersection of SR-900 and SE May Valley Road, and the crossing of May Creek, will be completed in 1995-6. For the larger future project, the area of greatest environmental concern in the basin is the drainage of the North Fork of May Creek. In this subcatchment, the widening and realignment of SR- 900 will affect Class-1 and -2 wetlands and Class-2 streams with salmonids, and spatial constraints will force hard choices for the locations of the roadbed and the creek. 3.6 KEY FINDINGS After a century of development, forest vegetation is still the largest cover category in the basin, with 50 percent of the area. However, two-thirds of this total is likely be removed as a consequence of future residential development. Residential use is the second largest cover category at the present time, occupying about 35 percent of the basin. This land use/cover category is expected to increase substantially in the future, eventually occupying as much as 70 percent of the area. Chapter 3 Land Use and Land Cover 3-15 r Chapter 4 Geology and Groundwater Chapter 4 Geology and Groundwater 4.1 INTRODUCTION The May Creek basin consists of three regions with distinct geological characteristics: the bedrock foothills of Cougar Mountain, Squak Mountain, and Newcastle Hills that form the uplands north of May Valley; the gently rolling plateau that is south of May Valley; and the valley itself, which divides the uplands and the plateau. The foothills north of May Valley are a bedrock upwarp in the earth's crust. South of May Creek the bedrock of the uplands drops away rapidly: this downwarp in the crust has been infilled with sediment deposits left by the continental ice sheet that occupied the region about 15,000 years ago. The ice sheet deposited a sequence of unconsolidated sediment that is 200 to 500 feet thick below May Valley. May Creek is an underfit stream flowing in the wide valley that was carved by drainage during that glacial age. This section describes the geologic processes that formed these geologic regions and describes how the soils and other features now found in the basin interact with surface water and groundwater. These interactions are discussed in this and subsequent sections in terms of how they affect certain processes in the basin, such as flooding, erosion, and sediment deposition. 4.2 DATA COLLECTION AND ANALYTICAL METHODS The geology of the surface materials of the May Creek basin, referred to as the surficial geology, has been partially mapped by several geologists (Booth and Minard, 1992; Luzier, 1969; Mullineaux, 1965; Rosengreen, 1965; and Liesch et al., 1963). Additional sources include maps of the adjacent Cedar River basin (King County, 1993). In preparing this Conditions Report, these maps were compiled onto one base map for the May Creek area. The base map was revised and expanded based on field work in January and March, 1993, using road cuts, construction excavations, well logs, and stream -bank exposures to identify soils and their characteristics. Table 4-1 describes the map units (adapted from Booth and Minard, 1992) that were used to produce the Geology Map (see Map 6 in Appendix B) of the May Creek basin. The subsequent discussion makes frequent reference to both Table 4-1 and Map 6 to describe how the advancing and retreating ice sheet produced what we see today. 4.3 REGIONAL HISTORY AND STRATIGRAPHY BEDROCK LITHOLOGY AND STRUCTURE The foothills north of May Valley are a bedrock upwarp in the earth's crust, bounded on the north by a possible fault (Bucknam et al., 1992; Booth and Minard, 1992; Gower et al., 1985; Walsh, 1990) and on the south by the southern flank of the Newcastle Hills Chapter 4 Geology 4-1 Table 4-1. Description of Geology Map Units Holocene Period Deposits m Modified land —Sand and gravel as fill or extensively graded natural deposits that obscure or substantially alter the original geologic deposit. Mapped areas include fill areas for 1-405, filling on the May Creek delta, and gravel mining areas. Qls Landslide Deposits —Landslide areas and landslide debris shown where sufficiently thick and continuous to obscure underlying material. Landslides are common on the May Valley and tributary creeks' inner canyon walls, and are most common downslope from the contact between units Qva and Qtb between May Creek RM 3.3 to RM 3.7. Numerous unmapped areas of mass -wastage deposits occur elsewhere in the basin in equivalent topographic and geologic settings, but are too discontinuous or too poorly exposed to show at map scale. Deposits, both mapped and unmapped, include abundant discrete landslides from 1 to 10 meters wide. Qaf Alluvial/Debris Fan Deposits —Boulders, cobbles, and sand deposited in a lobate form where streams emerge from confining valleys and the reduced gradients cause some of their sediment loads to be deposited. Gradational with unit Qyal. Qyal Younger alluvium —Moderately sorted cobble gravel, pebbly sand, and sandy silt mapped along the major stream channels. Also includes sediments of similar texture and age forming the May Creek delta. Pleistocene Deposits of the Vashon stade of the Fraser glaciation of Armstrong and others (1965) Qvr Recessional outwash deposits —Mainly stratified sand and gravel, moderately to well sorted, and less common silty sand and silt. Mostly exposed on the upland plateau in the southern part of the basin, along the south -trending outwash channels that carried glacial meltwater under the ice, and outwash from meltwater flowing eastward through May Valley, and westward from glacial Lake Snoqualmie during ice retreat (the "Kenneydale Channel" of Rosengreen (1965) and Booth and Minard (1992)). Deposits in the valleys display cross bedding and ripples reflecting alluvial channel deposition. Outwash on the plateau is typically well sorted sands to weakly stratified gravely sands. Qvt Till —Compact diamicton containing subrounded to well-rounded clasts, glacially transported and deposited. Generally forms an undulating surface a few meters to a few tens of meters thick. Generally very compact, with low infiltration and relatively high runoff rates. Qva & Advance outwash deposits —Well -bedded sand and gravel, deposited by streams and rivers issuing Qpf from the front of the advancing ice sheet. Generally unoxidized; almost devoid of silt or clay, except near the base of the unit. Well exposed along much of the May Valley sidewall, where its high susceptibility to water erosion has resulted in large prehistoric ravines and rapidly expanding new gullies that have been caused by runoff from recently urbanized areas. At map scale, also includes silt, clay, sand, and an older till unit associated with early Fraser to pre -Fraser glacial and nonglacial deposits. Puget Group Bedrock Tr Renton Formation (Tertiary)—Nonmarine sandstone and claystone containing abundant coal beds. Tt Tukwila Formation (Tertiary)—Andesitic volcanic sandstone, tuff, mudflow breccia, and minor lava flows. Typically massive; only local sedimentary interbeds indicate structure. Chapter 4 Geology 4-2 anticline, or by a possible fault. The bedrock of the uplands drops away rapidly south of May Creek. This downwarp in the crust has been subsequently infilled with sediment (Yount et al., 1985; Hall and Othberg, 1974; Luzier, 1969). The entire east -central Puget Lowland is underlain by Eocene (about 40 million years old) volcanic and sedimentary rocks. In the May Valley area these rocks are exposed at the surface in the uplands north of the valley, with only one possible bedrock outcrop on the south side of the creek (Map 6). This sequence of rocks, which is many thousands of feet thick, has been regionally folded along a northwest -trending horizontal axes. The dominant fold affecting the basin is the Newcastle Hills anticline, whose axis and corresponding bedrock uplift trend west-northwest to form the Newcastle Hills, Cougar Mountain, and Squak Mountain. The May Creek drainage basin lies on the southwest limb of that fold. Beneath May Creek and to the southwest, away from the anticline axis, the bedrock is buried progressively deeper by glacial sediment and is not exposed at the surface. The overall form of the May Creek basin is determined by the bedrock on the north side and the downwarp and glacial erosion of the bedrock on the south half of the basin. The underlying rock surface forms a much larger subsurface valley extending southeast out of the nearby Issaquah Creek basin, running beneath what is now the plateau of Cedar Hills, Lake Kathleen, and Maplewood, at a maximum depth of over 500 feet below ground level (Hall and Othberg, 1974; Yount, et al., 1985). The southern part of the May Creek basin lies on the southwest flank of that valley, possibly an infilled arm of an ancestral Puget Sound. ICE OCCUPATION OF THE BASIN Early Glacial Advances Multiple invasions of glacial ice into the Puget Lowland have left a discontinuous record of Pleistocene glacial and interglacial periods. Originating in the mountains of British Columbia, this ice was part of the Cordilleran ice sheet of northwestern North America. During each successive glaciation it advanced into the Lowland as a broad tongue called the 'Puget lobe" (Bretz, 1913). May Valley near the mouth contains exposures of multiple glacial advances. A typical stratigraphic section mapped at the big bend in May Creek at River Mile (RM)1.3 shows the general sequence common to the area. Loose sandy recessional outwash of various thickness, from 0 to about 33 feet (10 meters), is common near the surface. Below the recessional outwash is the very compact Vashon till with a thickness from 3 to 33 feet (1 to 10 meters). The uppermost till lies at or very near the ground surface of the upland plateau south of May Valley and is found near the surface plastered on the bedrock on the uplands north of May Valley. The upper till was derived from the most recent glacial advance, named the "Vashon" by Armstrong et al. (1965). The Vashon till was deposited about 15,000 years ago (Booth, 1987). Below the Vashon till at the big bend in the creek is a compact silt lake deposit that lies above a second thin till layer at about 160 feet (50 meters) elevation, included in unit Chapter 4 Geology 4-3 Qva & Qpf on the geologic map of the basin (Map 6). Below the till to the bottom of the section at 80 feet (25 meters) elevation is compact silt and fine sand, probably outwash deposits that were waterlain in a variety of environments. Their thicknesses vary from a few feet to tens of feet, and none can be traced continuously for more than a mile or two (and most for much less). Most are clearly associated with glacial streams, because the clasts are a wide mixture of different rock types, indicating transport from outside the river basin. But some reflect lowland nonglacial conditions, with fine sediment and peat beds. Most of the valley walls of May Valley display a mixture of these coarse- and fine-grained sediments, which render the exposed slopes very susceptible to landsliding and impedes the vertical descent of percolating groundwater. The Vashon Ice Advance Approximately 16,500 years ago, advancing ice during the Vashon stade had flowed south into Puget Sound far enough to block off drainage through the Strait of Juan de Fuca. Large lakes and rivers formed in the Puget Sound region, including the May Creek basin area, as the regional drainage was forced to the south. Large and numerous meltwater rivers flowed from the Vashon ice as it slowly moved south. Sediment was deposited in the proglacial lakes, first laying down fine-grained clay and silt lake -bottom sediments well ahead of the ice. In the May Creek basin these lake bottom deposits are found in the lowest portion of the geologic section along the base of the valley walls in the deeply incised valley of May Creek and some of its tributaries. These deposits are included in unit Qpf & Qva. They consist of compact to very compact, massive to thinly laminated silts and clay. When these sediments were deposited they were loose, saturated, unconsolidated sediments draped over the existing topography in the region. As is common in loose lake sediments, some will slump off the steeper areas, forming turbidity currents and lake bottom deposits of non -stratified clay and silt with sparse matrix -supported pebbles. When the Vashon glacier finally ran over the area, the lake sediments were consolidated and sometimes slightly folded by the weight of about three thousand feet of ice. As the ice approached closer to the May Creek basin, coarser lake bottom and river deposits were laid down. About 15,000 years ago (Booth, 1987) the front of the ice was right in the area of May Creek basin. Coarse river alluvium was deposited near the ice margin. These deposits, consisting of boulders and blocks in a sandy gravel matrix, can be seen at the top of many of the advance outwash outcrops just beneath the glacial till. The Vashon glacial front moved over the water -laid deposits, expanding as far south as the Olympia area aver the next 1000 years. Below the glacier, lodgment till (a compact, poorly sorted mix of clay, silt, and gravel, Qvt) was deposited. This till layer, which is typically 5 to 30 feet thick in the May Creek basin, is draped over the layers of pre -glacier sediments. Chapter 4 Geology 4-4 The Vashon Ice Retreat As the ice receded from the May Creek basin area, a layer of loose, gravely, oxidized brown sands were left behind from the melting stagnant ice and from rivers flowing off the ice (Qvr). As the Vashon glacier receded from the May Creek basin area, various drainage channels were occupied. These channels carried the flow from the melting glacier and the drainage from the Stillaguamish, Skykomish, and Snoqualmie valleys that were still blocked by the ice farther north. Together, these flows formed the wide May Valley. Water flowing from the region eroded into the glacial deposits to a base level of about 100 meters, which forms the present-day elevation of upper May Valley and many remnant terraces along the lower May Valley walls. By about 13,600 years ago the Vashon glacier had receded north of the Strait of Juan de Fuca, allowing the Southern Puget Sound drainages to flow north out the Strait of Juan de Fuca. This allowed Puget Sound to lower to its approximate present-day base level. It was at this time that May Creek started to erode down through the glacial deposits, forming the canyon section of May Creek. The channel eroded deeper and the main eroding section (the "knickpoint") migrated up -valley. Tributaries to the canyon section try to keep up with the eroding canyon section, with their respective knickpoints moving up -valley as well. Abandoned terraces scattered along the May Creek and tributary valley walls show the old creek levels. May Creek continued to erode down through the glacial sediments, but at a much slower rate than when the entire foothills region drained through the area. The present day May Creek delta and alluvial fans began to form at about this time. As May Creek eroded up the valley, it may have encountered bedrock in the region of RM 3.5 to 4.0. The field evidence is equivocal: rock is exposed in the bed of lower Boren Creek near its confluence with May Creek but none is actually observed in the channel of the mainstem. This bedrock, if present, may have slowed the creek's progress of eroding farther up the valley. 4.4 POSTGLACIAL PROCESSES AND DEPOSITS DEGLACIATION AND LANDSCAPE CHANGES In the May Creek drainage basin, emptying of the regional glacial -age lake occupying the Puget Sound and Lake Washington basins was an event of major geomorphic, and ultimately human, importance. As a result of that lake drainage, May Creek incised through the sequence of glacial and non -glacial deposits, leaving high and steep valley sidewalls that line both sides of the river valley. Flanking the stream, the valley sidewalls are the scene of particularly severe landsliding and erosion, a consequence of their steep gradient and complex stratigraphy. Valley -side erosion and stream incision also are common in this basin. Almost any discharge over the lip of the steep valley walls is erosive. Where sandy deposits of either the Vashon advance outwash or older deposits are encountered, severe erosion results. The major prehistoric ravines of the basin, such as Honey and Gypsy creeks, are testament to this process in the natural environment. In the human -affected environment, increasing runoff has yielded even more rapid erosion in these and some of the other basin tributaries. Chapter 4 Geology 4-5 BASIN SOILS On the surrounding uplands, soil formation has proceeded slowly but with profound hydrologic consequences. Bare, unweathered till absorbs water only very slowly; in contrast, the several feet of soil that has developed on that surface since deglaciation has high infiltration capacities and a large capacity to store and slowly release subsurface runoff (see Chapter 5: Hydrology). This till -derived "Alderwood" soil blankets the majority of the uplands on the south side of May Valley. Its hydrologic properties differ dramatically from its underlying parent material, and so the compaction or removal of that soil during typical urban or suburban development can result in large hydrologic effects. Scattered occurrences of Everett series and Ragnar series soils formed from glacial outwash in the May Creek basin. These soils form well drained to excessively drained gravely sandy areas. Towards the western and southwestern portions of the basin outwash sands forming Indianola loamy fine sand soils are formed in sandy recessional stratified drift that is draped over the landscape. The indianola soils are well drained to excessively drained soils. Water that infiltrates the loose to medium compact sandy areas of the basin encounters the compact tills, lake sediments, or bedrock and migrates laterally to the tributary creeks and May Valley walls where it drains from springs, dispersed valley edge wetlands, or heads in swales or tributaries. In developed areas of the basin rainfall that would normally infiltrate these sandy units is now intercepted by impervious areas and piped via storm drains to the nearest creek or swale where soil erosion can occur. 4.5 GROUNDWATER IN THE MAY CREEK BASIN Characteristics of the surface and subsurface deposits control the infiltration, movement, and storage of groundwater. Infiltration at the surface depends on the permeability of the surface sediments and the accessibility of those sediments to precipitation. Thus outwash deposits, consisting of silt, sand, and gravel, provide the best opportunities for infiltration where they are exposed at the ground surface. Till, in contrast, has a much higher percentage of silt and clay and so offers significantly more resistance to flow. The soil layer that has developed on top of the till has much greater infiltration, but the movement of water is largely restricted to that thin upper soil zone. Although groundwater exists by definition in all saturated geological materials, it is accessible for water use or discharge to surface -water bodies only where it can move freely through subsurface deposits. These freely transmitting deposits are characterized by relatively large pores and are known as aquifers. In the May Creek basin, the various outwash deposits of the last glaciation form the most common aquifers. In contrast, deposits that restrict the movement of groundwater —typically till —are called aquitards. The outwash units predominate in May Valley and in the southwest portion of the basin, while aquitards occur at or near the surface in the Vashon till areas of the basin (Map Chapter 4 Geology 4-6 6). Additional aquitards occur at depth in the sequence of glacial deposits on the south side of May Valley. The presence and also the sequence of layered aquifers and aquitards affects groundwater movement. Aquifers exposed at the surface provide not only areas of easy infiltration but also shallow zones of groundwater storage and movement. If shallowly underlain by an aquitard, then the groundwater is "perched" above the deeper zones and may locally appear at the ground surface as springs or wetlands. Aquifers at greater depth may have less direct access to surface waters, with recharge occurring only by slow percolation through overlying aquitards. Discharge from these deeper aquifers is most common at hillside springs and along hillside drainage courses, where the groundwater re-emerges along the exposed edge of the deposit. During the course of a year, that discharge may fluctuate as the water level in the aquifer rises and falls with seasonal precipitation patterns. Conversely, aquifers that are well -isolated from surface recharge areas may show very little seasonal variation in either water -table level or baseflow discharge, because the rate at which water reaches the aquifer is so slow. Surficial geology and soil type are two of the factors that contribute to the recharge potential (Map 7). For example, the till areas (Qvt) on the uplands to the south of May Valley (Map 6), or the rocks of the Tukwila Formation (Tt) to the north, are surface aquitards that impede inflow to any near -surface aquifers and result in those areas being categorized as having low recharge potential. As is discussed in Chapter 8 (Water Quality), the recharge potential methodology used here is designed to be a screen ing level method only, and to be consistent with that used in other areas of the county. It is limited both by data availability as well as by its simplification of the complicated groundwater flow system, such as in not taking into account any deeper aquifers or aquitards or other geologic layers. The direction of flow in the aquifers, and their possible interaction with the adjacent Cedar River basin, is discussed in Section 8.4. 4.6 GEOLOGIC HAZARD AREAS PREHISTORIC PERIOD Another aspect of the May Creek basin's geologic history is related to seismic (earthquake) hazards. In recent years multiple sources of evidence indicate great earthquakes (Magnitude 8 and greater) have occurred in western Washington in prehistoric times (Heaton and Hartzell, 1987; Bucknam et al., 1992; Atwater and Moore, 1987, 1992; Karlin and Abella, 1992; Schuster et al., 1992; Jacoby et al., 1992). Large earthquakes appear to have triggered slumping on the steep Lake Washington valley wall (Karlin and Abella, 1992). Evidence suggests that three earthquakes may have occurred in the Lake Washington region in the past 3,000 years, with the latest occurring between 1,000 and 1,100 years ago (Jacoby et al., 1992). Near simultaneous slumping occurred in at least three separate locations, two of which contain submerged forests (Karlin and Abella, 1992). One of the submerged forests is on the southern end of Mercer Island opposite the May Creek delta front. The bathymetric contours shows lobes of the known slump material that are similar to other lobes along the May Creek delta front. Some of the lobes on the May Creek delta front are likely to be old wave -cut terraces but some, especially the deeper lobes, could be slumps. Chapter 4 Geology 4-7 HISTORIC PERIOD The documented seismic history of Washington State dates to the early 1880's. Most historical seismicity in the region occurred in two diffuse clusters. The most active area is in the vicinity of Puget Sound. This seismicity is a result of the subduction of the oceanic Juan de Fuca plate beneath the continental North American Plate. A second zone of seismicity is located near Mount St. Helens and is primarily related to volcanic activity. Other areas of seismicity are scattered throughout the region and are not unequivocally associated with known geologic structures. The Puget Lowland is one of the more seismically active areas of the United States, but historically the earthquakes in this region have typically been of relatively small magnitude. No earthquake in the past 150 to 200 years west of the Cascades has exceeded magnitude 7.5 on the Richter scale (Hopper et al., 1975). A review of earthquake damage reports indicates that the most severe historical earthquakes in the Puget Lowland occurred in 1949 and 1965 (Noson et al., 1988). Both of these earthquakes originated near Puget Sound. The April 13, 1949 magnitude 7.1 earthquake was felt over 594,000 square kilometers (Noson et al., 1988). The April 29, 1965 magnitude 6.5 earthquake was felt over 500,000 square kilometers with the greatest intensities reported in Issaquah and portions of Seattle. Based on this information, the maximum historical intensity of earthquakes reported for the May Creek basin vicinity is moderate, corresponding to peak horizontal ground motions of about 0.13g (horizontal acceleration of 0.13 times gravitational force) and 0.25g, respectively. These values suggest the potential for moderate damage resulting from ground motion levels. A recent USGS study (Algermissen et al., 1990) found that the May Creek basin area has a 90-percent probability of not exceeding, in 250 years, a horizontal acceleration of 0.51g and horizontal velocity of 42 cm/second. In 50 years, the same probability is associated with a horizontal acceleration of 0.27g and horizontal velocity of 23 cm/second. The May Creek basin is located within Zone 3 of the Uniform Building Code (Noson et al., 1988). FUTURE SEISMIC HAZARDS The May Creek basin area is considered to have a high long-term seismic risk potential (i.e., for large events with recurrence intervals longer than 100 years) because of known earthquake epicenters in the region (Heaton and Hartzell, 1987; Noson et al., 1988; Gower et al., 1985) and thick unconsolidated sediments in an area of observed seismic - induced mass wasting (Bucknam et al., 1992; Atwater and Moore, 1992; Karlin and Abella, 1992; and Jacoby et al., 1992). Seismic hazards in the May Creek basin are primarily related to seismic -induced landslides, ground breakage of unconsolidated sediments, and liquefaction. The greatest damage in a future large earthquake would occur on the May Creek delta. Sliding and generation of turbidity currents are natural processes occurring off deltas like the May Creek delta. Slides and resultant slide -induced waves have occurred on the Chapter 4 Geology 4-8 south side of Mercer Island across from the May Creek delta (Jacoby et al., 1992; Karlin and Abella, 1992). Lobes and terraces on the bathymetry of the delta indicate the presence of wave cut terraces and possible slumps (USGS Bellevue South Topographic Map, 1983). On a geologic time scale (thousands of years) the May Creek delta is a high seismic risk area because of the potential for seismic -induced landslides and slide - induced waves. Farther up the May Creek delta, the sediment is more confined relative to the delta front; the chance of settling and ground fracturing exists but the threat of slide -induced mass wasting is reduced and slide -induced waves would be partly buffered by the old railroad grade and highway fills. Areas throughout the May Creek basin that are greater then 40 percent slope or in a potential landslide runout area are considered to have a moderate seismic risk. Other areas in the May Creek basin are considered to have a low seismic hazard risk.. while they could experience some ground shifting and local damage, the likelihood of severe seismic -induced mass wasting, ground breaking, or wave damage is relatively low even in the long term. 4.7 KEY FINDINGS • May Creek is an underfit stream. The wide, flat valley in which it flows was originally produced by vastly greater flows during glacial retreat. This underfit condition led to the development of a meandering stream within the broad wetland - dominated floodplain of May Valley, in which sediment tends to collect and water is discharged only slowly. • The north side of the May Creek basin is dominated by bedrock uplands. The bedrock drops away rapidly south of May Creek. This low point in the bedrock has been infilled with 200 to 500 feet of sediment that are highly susceptible to the erosive power of May Creek and its tributaries. • Groundwater infiltration in the basin occurs most rapidly in parts of the Lower Basin where erosion by glacial meltwater or the downcutting of May Creek and its tributaries have pierced the overlay of compacted glacial till soils and have exposed coarse (sandy and gravelly) glacial layers like outwash at the ground surface. Some deeper aquifers in the southern portion of the May Creek basin appear to be continuous with aquifers in the Cedar River basin. Chapter 4 Geology 4-9 Chapter 5 Hydrology Chapter 5 Hydrology 5.1 INTRODUCTION This chapter describes the hydrologic conditions of the May Creek basin, including the properties and circulation of water in the atmosphere, on the land surface, in the soil, and in May Creek and its tributaries. Particular emphasis will be given to how changes in the way land is used affect the rate and manner in which rainfall becomes streamflow. Some of these changes cause flooding, or make existing flood conditions worse. Hydrology of the May Creek basin was modeled using the Hydrologic Simulation Program - Fortran (HSP-F) (AQUA TERRA Consultants, 1991). As described below, the HSP-F model used May Creek recorded streamflow data, rainfall data, and land use and channel geometry information to make long-term hydrologic simulations. Predevelopment (forested), current, future, and mitigated future land -use scenarios were modeled to evaluate the effects of land -use changes on hydrologic conditions in the basin. 5.2 HYDROLOGIC CONCEPTS RAINFALL AND WEATHER Elevations in the basin range from near sea level (Lake Washington) to a maximum of 1,600 feet at the summit of Cougar Mountain on the north side of the basin. Average annual precipitation generally increases in the upstream direction (east) with increasing elevation, with recorded levels varying from 44 to 49 inches. Precipitation increases with elevation because storm clouds drop their moisture as they rise over land barriers (a phenomenon referred to as orographic effects). Rainfall gaging information for the May Creek basin is discussed in more detail later in this chapter. The amount of increase in precipitation occurring at the highest elevations in the basin is unknown, as no rain gage is located on Cougar Mountain. The weather pattern for this area is characterized by long -duration, low -intensity storms traveling from the southwest and producing fairly uniform precipitation throughout the Puget Sound lowlands (which includes the May Creek basin). Most of the precipitation falls in the form of rain, although snow occasionally falls at higher elevations during the winter months. The relatively rare snowfall has no significant impact on the hydrology of the basin. RUNOFF Runoff can be divided into several related, yet distinct, components. Precipitation that percolates to the water table and reaches the stream slowly is called groundwater or baseflow. Hillslope runoff that causes high flows in the stream channel within hours or a Chapter 5 Hydrology 5-1 LA day of rainfall is usually classified as storm runoff. This runoff can be generated by one or a combination of several mechanisms: Horton overland flow, saturation overland flow, or shallow subsurface flow (interflow). Groundwater Flow Groundwater flow is generated by the infiltration and transport of precipitation via subsurface flow paths. These flow paths are much longer than those used by shallow subsurface flow. Groundwater is the dominant runoff form in areas where permeable soils are underlain by glacial outwash. The flow rate is proportional to the slope of the water table, which is generally low in outwash deposits. The long flow paths, low driving gradients, and generally large storage capacities result in slow, attenuated flow responses compared to the stormwater flows described below. Stormwater Flow Horton Overland Flow. Horton overland flow is generated when the rainfall intensity is in excess of the current infiltration capacity of the soil. Infiltration capacity or rate is a function of soil type and the pre -rainfall moisture content of the soil. Over the Puget lowlands, the highest one -hour rainfall expected an average of once every 100 years is about one inch per hour. Most undisturbed, vegetated soils in this area have a limiting infiltration rate of two to six inches per hour. As a result, under natural conditions Horton overland flow rarely occurs, because the minimum infiltration rate usually exceeds the maximum rainfall intensity. However, once the land surface has been disturbed by removal of vegetative cover and the permeable surface soil layer, infiltration capacity decreases. This results in an increased likelihood that Horton overland flow will occur. Saturation Overland Flow. Saturation overland flow is produced by rain falling directly on saturated soils. In this case, unlike Horton overland flow, the water is failing to soak into the ground because the ground is already full of water, not because the soil has low permeability. This situation commonly occurs under moderate to wet antecedent conditions. Saturation overland flow occurs on soils in topographic hollows and wetlands and adjacent to stream channels, where the land surface becomes saturated by a rising water table. The soil cannot absorb any additional precipitation, regardless of soil infiltration rates, and all additional water flows over the land surface as storm runoff. Interflow. InterFlow is shallow subsurface flow generated by the rapid infiltration of rainwater and subsequent movement of this water through near surface soil layers. This runoff mechanism is commonly associated with hillslopes underlain by nearly impermeable substratum (typically glacial till or bedrock) covered by shallow, much more permeable soils. The flow rate is proportional to the slope of the restricting layer. At breaks in slope or topographic convergence, water can reemerge to the surface (return flow), resulting in an increase in flow velocity. Chapter 5 Hydrology 5-2 5.3 DATA COLLECTION AND ANALYTICAL METHODS INTRODUCTION Data collection and review of data are important components of any analytical method to ensure the validity of the method and the accuracy of the results. When important decisions will be made and money spent based on the analysis, it is critical that high quality hydrologic and meteorologic data and accompanying land use information be collected in the study basin. The analytical methods used in the hydrologic analysis are also important. Hydrologic data (streamflow, stage, etc.) must be analyzed for a range of conditions to fully understand the impacts of human activities and changes in the basin. This is done by analyzing long time series of data using a number of statistical procedures developed for hydrology. DATA COLLECTION Survey The routing of streamflow through individual channel reaches is based on stage - discharge -storage information for each reach. This information is computed from the geometry of the stream channel and floodplain. As a result, it is important to have accurate information on the stream channel cross-section geometry and channel slope and channel roughness for each reach. Surveyors collected this information for the entire mainstem of May Creek. They also measured stream channel cross section information for the tributaries entering May Creek, and for the stream outlets from Lake Boren and Lake Kathleen. Stream channel stage -storage -discharge tables are critical components in hydrologic modeling, as they describe the relationship between the storage available in a stream reach, and the flow at the outlet of the reach. This determines the amount of attenuation of stormwater flows that occurs in each portion of the drainage system. The stage - storage -discharge tables were generated for the mainstem of May Creek using cross sections obtained from INCA Engineering and the HEC-2 model created for use in a 1989 FEMA study (FEMA, 1989), together with Manning's equation. Where possible, these tables were checked against existing rating curves. Streamflow Gaging Streamflow data from two locations on May Creek were used in the hydrologic modeling. The longest period of record for streamflow on May Creek is near the mouth, just downstream of Lake Washington Boulevard. This gage station is currently maintained by King County and is designated Station 37A. At Station 37A 15-minute flow data were available for the period from November 1988 through April 1993. Chapter 5 Hydrology 5-3 The second May Creek streamflow gage is located near the Coal Creek Parkway SE crossing of May Creek. Recorded 15-minute streamflow data were available at this station (37B) for the period from November 1990 through April 1993. For both of these gages, significant gaps in data existed during the period of record. These gaps somewhat limited the extent and completeness of the calibration effort. The extent and quality of the gaging data is described in detail in the May Creek Basin Plan HSP-F Calibration Report (AQUA TERRA Consultants, 1993). These recorded data were used primarily for comparison of individual flood events where recorded data existed. No comparison of annual volumes or flow durations could be made. Rainfall Gaging For a basin the size of May Creek (approximately 14 square miles), storm events tend to cover the entire drainage area. Precipitation patterns are fairly uniform throughout the basin. As mentioned above, the only important precipitation variability in the basin results from orographic effects. Precipitation is measured at two locations in the May Creek watershed by King County; this locally measured precipitation data is used in calibration of the model, which is described in detail later in this chapter. It is important to generate precipitation data for the entire calibration period, which is essentially the period of streamflow gaging. In order to do this, two additional gages from outside the basin were used to fill in the data gaps for the calibration period. The Lower May Creek precipitation station (37U) is located near stream gage 37B. Fifteen -minute data are available at this station starting in October 1990. Precipitation data are available to March 24, 1993. For water years 1991 and 1992 the mean annual precipitation at 37U is 43.9 inches. For the calibration period prior to Water Year 1991, a rainfall gage from the adjacent Cedar River watershed was used to fill in. Data from this gage, the Renton Highlands precipitation station (31 U), required adjustment prior to its use in the May Creek model. The mean annual precipitation at 31 U for water years 1991 and 1992 is 41.1 inches. By comparison, for this two-year period of record 37U receives approximately 7 percent more rainfall than 31 U. Therefore, the 31 U record was multiplied by 1.07 for water years 1989 and 1990 prior to using it to extend the 37U data. The second May Creek watershed precipitation station is 37V, located in the upper valley near the stream's crossing of SR-900, at an elevation of 330 feet. The mean annual precipitation at 37V for water years 1991 and 1992 is 49.1 inches. The annual precipitation at 37V is approximately twelve percent greater than 37U. This is the result of orographic influences of the surrounding hills on precipitation in the upper valley. Station 37V was used to represent the precipitation in the eastern portion of the watershed and higher elevation areas on the north side of the valley. A few miles to the east of 37V (and outside of the May Creek watershed) is another precipitation station near McDonald Creek in the Sunset Valley Farm development. This Chapter 5 Hydrology 5-4 station, 25V, was used by King County to fill in missing periods of record in the 37V data. Mean annual precipitation at 25V for water years 1991 and 1992 is 48.9 inches. A comparison of annual precipitation at 25V and 37V shows that while there are some minor differences in annual precipitation between the two stations in specific years, over a long period of time these differences balance out and the two stations exhibit nearly identical mean annual precipitation records. Thus, no attempt was made to modify the 25V data when it was used. HSP-F SIMULATION MODEL General Model Structure HSP-F is a continuous simulation hydrologic computer model designed to produce synthetic streamflow data that reproduce measured streamflow at any location within a basin. Surface runoff, interflow, and groundwater can be simulated and routed as discharge into a drainage system of stream channel reaches. The basin is divided into a number of subcatchments drained by a network of channel reaches. This division of the basin into subcatchments is based on topography, hydrologic characteristics, the stream channel network, and locations of desired model output. Runoff from each individual subcatchment is treated as a composite of the runoff from all of its hydrologic land class areas; that is, smaller areas with relatively homogeneous runoff characteristics. For the overall basin, a limited number of hydrologic land classes are defined, and each is assumed to be homogeneous in terms of soils, vegetation, topography, and precipitation. Thus, a particular land class produces the same unit area runoff response to a specific rainfall event regardless of its location within the basin. Runoff from a particular subcatchment represents the sum of the runoff from each individual land class within the subcatchment, with its respective acreage. Flows from each subcatchment are then combined and routed through the stream channel drainage network. For each stream channel reach the relationship between depth, surface area, volume, and discharge must be known. Flow can be routed through stream channels, lakes, retention/ detention ponds, and reservoirs, and flows can be computed at all the defined points of interest, basically, the outlets of each subcatchment. Application to May Creek Basin Application of the HSP-F model to the May Creek basin required several steps, including division of the basin into subcatchments, selection of appropriate pervious and impervious land classes, calibration of the model to replicate measured streamflow in the basin, and long -period simulation of basin streamflow for statistical analyses. In addition, evaluation of alternative land use conditions using long -period simulation required knowledge of how to represent these conditions as changes to the HSP-F model of May Creek. Chapter 5 Hydrology 5-5 Step 1: Channel Reach Delineation and Subcatchment Definition. May Creek's stream channel and its tributaries (both natural and storm sewer systems) are the major pathways by which flood flows and pollutants are transported through the basin. For the May Creek basin, channel -reach delineation into areas called subcatchments is based on tributary basin boundaries, stream channel geometry and flow travel times, streamflow gaging locations, and sites of special interest. Sites of special interest can consist of lakes, wetlands, high value fisheries habitat, known problem sites, or hydraulic constrictions such as road crossings. A total of 27 subcatchments, with accompanying channel reaches, were used to represent the movement of the runoff through the main stream channel, its tributaries, upland lakes, and major storm sewers. Ten reaches represent the mainstem of May Creek from the mouth at Lake Washington to the confluence of the three eastern branches: the South, North, and East Forks of May Creek. Each of these has a subcatchment associated with it. Seventeen reaches represent the major tributaries, and accompanying subcatchments represent their drainage areas. Included in these 17 tributary reaches are reaches to represent Lake Kathleen and Lake Boren and a separate reach to represent a major wetland in the uplands tributary to Lake Boren. Other valley wetlands have been represented by the reaches on the mainstem of May Creek between Coal Creek Parkway SE and State Route-900 (SE Renton -Issaquah Road). The configuration of the HSP-F model is shown in Figure 5-1, and the actual subcatchment delineation is shown on Map 8 in Appendix B. Step 2: Hydrologic Land Type Classification. The purpose of defining hydrologic land classes within the basin is to determine which individual land areas tend to respond similarly to rainfall; that is, they produce a homogeneous runoff response. Each land class can then be assigned a set of model parameter values, that will assure a uniform runoff response. Where the weather patterns vary across a basin it is necessary to also divide the hydrologic land classifications based on variations in precipitation, in order to accurately reflect spatial meteorologic variability and its effect on the hydrology of the basin. Runoff within a subcatchment can then be computed, based on its composite land class areas. Twenty land classifications were defined for the May Creek basin. Eighteen of these vary in terms of how precipitation infiltrates into the soil. These are called pervious land segments (PERLNDS) and they reflect variations in soil (till, outwash, and saturated), vegetation (forest and grass), slope (flat [0-5%], moderate [5-15%], and steep [> 15%]), and rainfall (Station 37U in the western part of the basin and Station 37V in the eastern portion). In addition to the 18 pervious land classes, two impervious classes were used to represent areas for which there is no infiltration, only surface runoff. These impervious land classes represent the effective impervious area in the May Creek basin. The two impervious classes differ only by the amount and distribution of rainfall they receive. Chapter 5 Hydrology 5-6 Figure 5-1. Flow Chart of May Creek and Tributary Inputs for the HSP—F Model. Highlands Subarea (North Fork) CAC (Cabbage Creek) COU (Country Creek) May Valley Subarea M (Long Marsh Creek) — LBL LBU NHC (Newport Hills Creek) WT4 GYP (Gypsy Creek) EFK (East Fork) East Renton Plateau Subarea (Tributary 0291A)C (Greenes Creek) 1:H] Lower Basin Subarea (Honey Creek) �iJ HCM HCL KEY Subarea 0 Subcatchment Reach Bold typestyle indicates May Creek mainstem. Chapter 5 Hydrology 5-7 Selection of appropriate pervious and impervious land classes for the May Creek basin was based on runoff characteristics. There are three major types of runoff characteristics that determine the hydrologic response of the May Creek basin. These characteristics are based on soil, land cover, and land surface slope. Soils. The May Creek basin soils were described in detail in Chapter 4: Geology and Groundwater. For the purposes of the HSP-F model they are divided into three types: till, outwash, and saturated. Till soils contain large amounts of silt or clay mixed in with sand; this mixture is often overlain with loamy soil. Because of the high fraction of silts and clays these soils have low percolation rates compared to outwash soils. As a result only a small fraction of infiltrated precipitation reaches the groundwater table. The rest of the water moves laterally (as shallow subsurface flow) through the thin surface soil above the compacted till layer and often reemerges at the base of hillslopes. Till soils may become saturated in large storms and produce high amounts of surface runoff. The peak runoff rate from till areas is much higher than from outwash soils. Outwash soils consist of sand and gravel deposits that have high infiltration rates. Rainfall in these areas is quickly absorbed and percolates to the groundwater table. Creeks draining outwash deposits often intersect the groundwater table and receive most of their flow from groundwater discharge, unless the channel bed is located above the water table. Even during the largest storms, streamflow response is slow, with peak flow often lagged up to several days after the rainfall ends. Saturated soils (also called wetland soils) remain saturated throughout much of the year. The runoff from saturated soils/wetlands depends on the underlying geology, the proximity of the wetland to the regional groundwater table, and the bathymetry of the wetland. Generally, wetlands provide some base flow to streams in the summer months and attenuate storm runoff via temporary storage and slow release in the winter. Land Cover. Land cover plays a major role in the speed and volume of surface runoff reaching the stream channel. Land covered by trees produces much less surface runoff than land covered by asphalt. For the May Creek hydrologic computations, land cover was divided into three major categories: forest, grass, and impervious. Individual areas within each land cover category are based on zoning maps, aerial photos, and field reconnaissance. A summary of this information is provided in the May Creek Basin Plan HSP-F Calibration Report (AQUA TERRA Consultants, 1993). Forest represents portions of the basin covered by evergreen and deciduous trees that provide a contiguous canopy cover above the underlying land surface. Forested areas generate the least amount of surface runoff. Forest cover is most significant in regions of glacial till where the vegetative root system breaks up the soil structure, allowing for increased infiltration. Forest litter provides additional soil water storage and protects against compaction of near surface soils. Interception of rainfall by leaves and needles and removal of soil water by evapotranspiration is also greater in forested areas than in the other cover categories. Chapter 5 Hydrology 5-8 Grass includes both natural grasslands and urban areas where grass has been introduced to replace the natural vegetation. Grassed areas produce more surface runoff than forested areas. When forest vegetation is removed to create grassed areas, surface soils are generally compacted during clearing, reducing infiltration capacities. Furthermore, because grass is shallow rooted, it does not provide as many infiltration pathways as forest. As a result, in large storms grassed areas saturate more quickly and produce more surface runoff than forested areas. Impervious areas consist of roads, rooftops, sidewalks, parking lots, driveways, and other constructed surfaces. They produce the most surface flow of all cover categories. The infiltration rate in impervious areas is zero and water storage in surface depressions is minimal. This results in virtually all rainfall running directly off to the stream to produce high peak flows. As noted earlier, impervious land classes represent the effective impervious area (EIA) within the catchment. The EIA is the impervious surface area connected directly to the drainage system. Impervious land class areas are usually the result of development activities within a basin that result in the construction of impervious surfaces (roads, roofs, parking lots, etc.). As a basin develops, the size of the EIAs increases. The relationship between impervious area and other land cover types in each of the basin's subareas is shown in Figure 5-2. Standard King County land use densities and corresponding impervious area percentages were used to determine the amount of impervious area in the May Creek basin. Table C-1 in Appendix C shows the relationship between land use density, total impervious area, and effective impervious area. Areas that were identified from land cover maps to contain some fraction of impervious area are assumed to have their pervious fraction covered by grass. An exception to this assumption is made for low - density residential areas (less than one dwelling unit per acre) where the forest cover has not been removed. Slope. Land surface slope influences the speed at which surface runoff travels to a conveyance system and eventually to the creek or one of its major tributaries. In the May Creek basin land surface slopes are grouped into three broad categories: flat (0 to 5 percent), moderate (5 to 15 percent), and steep (greater than 15 percent). The land surface slope is most important in areas where there is a large proportion of surface runoff. As discussed above, this is true for till soils, but not for outwash and saturated soils. In outwash and saturated soils groundwater flow rates are proportional to the slope of the water table, but the water table is usually only mildly sloping in these deposits. As a result, no slope classification is used for outwash and saturated soils. Other Factors. Stream channels and lakes also affect the runoff characteristics from a given area. These open water bodies receive rainfall directly and are not included in the land type characteristics discussed above. Within the May Creek basin the total surface area of the stream channel network is relatively small. For this reason no attempt was made to separate out this area. Instead, the stream channel surface area is included in the land type characteristics of the adjacent land areas. However, the two lakes (Lake Chapter 5 Hydrology 5-9 Figure 5-2. Distribution of Current and Future Land Cover Types in the May Creek Basin and Subareas. Page 1 of 2. 27% Current Conditions .01% 7% 5°) 60% Highlands Subarea Current Conditions 4% 1% 1 no/ 36% 85% Future Conditions 12% 9% 53% Future Conditions 3% 3% East Renton Plateau Subarea Current Conditions Future Conditions 7% 11 ° 4% /0 1 s o/ 5% 5% 49% 35% 62% 58% Land Cover Type: g Forest pGrass ®Saturated mLakes 0 Effective Impervious Area Chapter 5 Hydrology 5-10 Figure 5-2. Distribution of Current and Future Land Cover Types in the May Creek Basin and Subareas. Page 2 of 2. 27% Current Conditions Future 4% 10% 1 n0/ Conditions 9 59% 60% Lower Basin Subarea Current Conditions Future Conditions 14% 14% 1 3% 41% 4 1% 3% 59% Land Cover Type: ■Forest 0Grass ®Saturated (0Lakes (3 Effective Impervious Area Chapter 5 Hydrology 5-11 Kathleen and Lake Boren) have relatively large surface areas (49 and 17 acres, respectively) and are modeled separately from the surrounding land. The Geographic Information System (GIS) was used to overlay the soils, land cover, and slope information for the basin. Background information on the sources and development of this information is provided in Chapter 3: Land Use and Land Cover, and Chapter 4: Geology and Groundwater. The overlay resulted in the identification of 18 unique pervious land classes and two impervious land classes in the basin. Within each subcatchment, the size of each pervious and impervious land class area was measured. Tables C-2 and C-3 in Appendix C summarize this information by subcatchment for current and future land use. This information was then used in the calibration and subsequent long -period simulation of the May Creek basin. Step 3: Model Calibration Calibration is the process by which the model's parameter values are adjusted so that the model accurately reproduces the streamflow measured in the basin. Two streamflow measurement stations are operated in the May Creek basin and were used in the HSP-F calibration. Full details of the calibration process and a comparison of the simulated and recorded streamflows can be found in the May Creek Basin Plan HSP-F Calibration Report (AQUA TERRA Consultants, 1993). Final calibration parameter values are included in Table C-4 in Appendix C. The initial calibration used parameter values determined in a regional study of King and Snohomish County basins by the U.S. Geological Survey (Dinicola, 1990). These parameter values were then modified, where appropriate, to better fit conditions observed in the May Creek basin. In addition to modification of the USGS regional parameter values during the calibration process, model assumptions were reviewed. This included analysis of the runoff behavior of the steep till soils on Cougar Mountain on the north side of the basin. These soils are found to produce more surface runoff than originally simulated and their calibration parameters were modified accordingly. In addition, Cougar Mountain is believed to experience higher precipitation amounts than those measured in May Valley, but no confirming data exist. A test run was made using a conservative estimate of the possible precipitation difference, but this did not improve the calibration results. Thus, the issue of increased precipitation on Cougar Mountain was not explored any further, and no adjustment was made for this possible difference. Flow times through May Valley upstream of Coal Creek Parkway SE were investigated; this revealed that the initial Manning's n values were too low for all stream channel reaches in the upper watershed. The calculated flow values for a given depth of water in these stream reaches were two to five times too high compared to field measurements. Substantial vegetation, principally reed canary grass, was found in and adjacent to the stream channel, which increases channel and overbank roughness. Field measurements of flow rate and velocity suggested increases in the Manning's n value for the channel Chapter 5 Hydrology 5-12 from 0.04 to 0.08 and the floodplain from 0.1 to 0.15. These changes improved the computations. Calibration of HSP-F to represent the hydrology of the May Creek watershed was an iterative process. Simulated results were compared with recorded data to see how well the simulation represented hydrologic processes observed in the watershed. By changing specific calibration parameter values the simulation results were improved until a good comparison of simulated and recorded data was made. The calibration for May Creek primarily focused on correctly simulating the major flood peaks. The selected calibration run was judged to be the best calibration based on two major categories: (1) simulation of peaks for major flood events and (2) simulation of average daily flows for major flood events. A comparison of recorded and simulated peak flows and stormwater volumes for the four largest events is shown in Table 5-1. Table 5-1. Streamflow Gaging and Calibration Results at Two Locations on May Creek. Instantaneous Peak Flow Two Day Peak Volume Date of Recorded Peaks for Existing Record Recorded Simulated % Recorded Simulated % Data Rank Quality (cfs) (cfs) Diff. (acre-ft (acre-ft) Diff. Station 37A - Mouth of May Creek December 4, 1989 4 Fair 246 300 22 756 893 18 January 9, 1990 1 Fair 600 521 -13 1,543 1,583 3 November 24, 1990 3 Poor 425 419 -1 1,148 1,138 -1 April 5, 1991 2 Poor 451 464 3 1,240 1,289 4 Station 37B - May Creek at Coal Creek Parkway SE March 4, 1991 3 Fair 98 128 31 n/a n/a n/a April 5, 1991 1 Poor 354 298 -16 873 865 -1 January 29, 1992 2 Fair 142 131 -8 486 444 -9 In addition to selecting the four peak flood flow events for calibration, an effort was made to reproduce observed low flows. The results of the low flow calibration were good, and are summarized in the aforementioned calibration report. As noted above, many gaps existed in the recorded streamflow data. This reduced the effective calibration period to less than three years. The incomplete calibration data set has somewhat limited the ability of this model to represent the possible wide range of hydrologic responses found in the basin. However, for flood flow analysis for the purposes of a planning study such as this one, the final calibrated model is judged to accurately represent the hydrology of the May Creek basin. Chapter 5 Hydrology 5-13 Step 4: Streamf/ow Simulation. With the HSP-F model calibrated to represent the hydrology of the May Creek basin, long -period simulations of alternative land use conditions are possible. These long - period simulations generate a sufficiently long period of streamflow upon which to base flood frequency and flow and stage duration analyses. Long -period simulations for each subcatchment were made for four different land use scenarios: (1) current, (2) predevelopment (forest), (3) future, and (4) future with mitigation. Current land use conditions reflect existing land use as of 1992 and are described in more detail in Chapter 3: Land Use and Land Cover. Predevelopment land use simulates basin conditions prior to immigrant settlement in the 1800s. For the purposes of the HSP-F modeling, predevelopment conditions are assumed to be forest throughout the basin. Since no data or information is available on the channel system prior to the 1930s, no attempt was made to modify the existing stream channel system or basin topography for predevelopment conditions. Aerial photos from the 1930s show that major alterations to the drainage of May Valley had already been made and the channel looked as it generally looks today. Future land use conditions are based on the assumption of full build -out in the basin, subject to existing and proposed development rules and regulations. Future conditions are discussed in more detail in Chapter 3: Land Use and Land Cover. Land cover was changed from forest to impervious and grass cover where development is expected. No changes were made in the stream channel system. For the purpose of identifying the worst case situation, future flood flow results were simulated without any detention/retention mitigation. Future flood flows were also simulated with mitigation in the fourth scenario studied. Mitigation was added to the simulation of future conditions by adding a stream reach/reservoir in each subcatchment. This new reach represented a new detention/ retention pond to mitigate the impacts of additional runoff from proposed future development areas in each of the 27 subcatchments (see Table C-5 in Appendix C). The new, proposed King County standards were used to size the ponds for the simulation. The King County Runoff Time Series (KCRTS) computer program was used to compute the necessary information for each new reach using these proposed standards. These new reaches and accompanying information were added to the future conditions stream channel system to simulate future mitigated conditions. Specific assumptions of what future mitigated conditions might be like are necessary for the model. These assumptions were made based on knowledge and experience with current and proposed mitigation regulations and their application. For the purposes of the HSP-F modeling, the following assumptions were made with regard to mitigation: Chapter 5 Hydrology 5-14 Surface water retention/detention is based on the KCRTS methodology; 2. Development at densities greater than single family low density residential must include mitigation to reduce flow to predevelopment (current) conditions; 3. No mitigation is required for single family low density residential development; 4. Mitigation is based on the 2-year and 10-year flood events; 5. Mitigation requirements in each subcatchment are modeled using one appropriately sized surface water retention/detention facility (a total of 27 facilities were added for the 27 subcatchments); and 6. Twenty percent of the development runoff that should be mitigated is not mitigated but flows directly to the stream because of poor site design, flow bypass, multiple drainages, and other reasons. These assumptions were built into the HSP-F future mitigated conditions model. The surface water retention/detention facilities designed for each subcatchment are listed in a Table C-6 in Appendix C. STATISTICAL ANALYSIS PROCEDURES Following construction of the four land use scenarios, 42 years of Sea-Tac Airport precipitation data and Puyallup evaporation data were used by the HSP-F model to create 42 years of hourly streamflow data for each subcatchment for each scenario. To evaluate flood flows in the May Creek basin for predevelopment, current, and future conditions, several statistical analysis procedures were then used. These procedures include analysis of mean annual and mean monthly flow, flood frequencies, and flow duration. To be meaningful, these analyses must be based on streamflow records of sufficient detail, consistency, and length. To meet these requirements the 42-year simulated hourly streamflow data generated by HSP-F was used. From this 42-year-long period, simulated streamflow record annual peak flows were selected for flood frequency analysis. The flood frequency analysis uses a Log -Pearson Type III distribution and the standard methodology specified in Bulletin #17B (U.S. Water Resources Council, 1981). Detailed flood frequency results are included in Table C-7 in Appendix C. Relevant data from this analysis will be referred to throughout this chapter, with emphasis given to recurrence intervals from 2- to 100-years. The recurrence interval of a flow is based on the percentage chance that it will occur in any given year. The 100- year flow, for example, has a one percent chance of occurring in any given year. Thus it is important to realize that a 100-year flow does not necessarily occur once every 100 Chapter 5 Hydrology 5-15 years, but over the course of a long period of time, if land use conditions remained constant, it would occur on average once every 100 years. The 2- and 10-year flows are generally good indicators of stream and floodplain morphology, stability and erosion potential. They occur often enough that, over the course of time, flows of those magnitudes tend to create the form, shape, and channel size of the streams. The larger these flows, the larger the stream channel. Increases in these streamflows due to changes in land use cause the stream channel to erode and enlarge. As these flows are actively increasing due to basin development, the channels are not in equilibrium; erosion is greater than historically, and rapid changes in channel configuration occur more often, leading to significant and observable drainage, erosion, and water quality problems in the basin. These flows also have the most direct impacts on aquatic habitat. The 100-year flow is a relatively rare event, and is a good indicator of the characteristics of a large flood. Because of its size and lower probability of occurrence, the 100-year flood is more important than the 2- or 10-year events in evaluating risks to public safety and public and private property damage on lands adjacent to streams. Another way to characterize flood -flow behavior is the Unit Area Discharge (UAD). The UAD is the peak flow in cubic feet per second, divided by the drainage area in square miles. Any of the computed peak flows can be utilized for this comparison; however, in this text, the 25-year has been selected, as it is most representative of the entire range of flood flows. Thus, by using the UAD as a measure, the flood response of a single subcatchment under different land uses can be easily compared, as can the responses of different subcatchments of different sizes. Generally, higher UAD values correspond to "flashier" streams—i.e., ones that respond to rainfall and reach their peak streamflow more quickly. The flashiness of the response to rainfall is a function of the land characteristics (soils, vegetation, and slope), the amount of effective impervious area in the drainage area tributary to the stream, and the amount of flood storage that takes place (in lakes, wetlands, or other reservoir areas). For each tributary, the mitigation effectiveness percentage has also been computed, as a measure of how successfully the current mitigation requirements will reduce future flows back to their current levels. The 10-year peak flow has been used as the indicator for this analysis. The percentage is the amount of flow reduction caused by mitigation (that is, the difference between the unmitigated peak and the mitigated peak), divided by the total unmitigated flow increase from current conditions. Thus, 100 percent effectiveness would mean that future mitigated flows are the same as current conditions. Zero percent effectiveness means that future flows are the same for both mitigated and unmitigated conditions. The results of this analysis are discussed in the Basinwide Conditions section (see below). Mean Annual Flow was computed for each point of interest in the model as well; that is, at the outlet of each tributary and mainstem subcatchment. Mean Annual Flow is simply the arithmetic mean discharge at a given point in the stream system over the entire period of record. Chapter 5 Hydrology 5-16 Streamflow duration analyses were also made for each appropriate stream reach. These analyses used the entire 42 years of hourly simulated data and were based on a series of threshold flow levels keyed to different size low and high flow events. The low flow thresholds used were one-half of the low monthly mean flow, three -fourths of the low monthly mean flow, low monthly mean flow, and mean annual flow in cubic feet per second (cfs). The low monthly mean flow was computed by taking the mean of all of the January flows for the 42-year simulation period, then all of the February flows, and so on for each stream reach. This resulted in twelve mean flow values, one for each month. The lowest of these twelve values was selected as the low monthly mean flow. This provides a useful estimate of an average low summer or autumn flow in a given stream reach under a given land use. The high flow thresholds are based on forested (predevelopment) land use conditions. The events used for the high flow thresholds are one-half of the 1.05-year flood, 1.05- year flood, 2-year flood, 10-year flood, 25-year flood, 100-year flood, and 5 times the 100-year flood. The 1.05-year flood (probability of occurrence equals 0.95) was the smallest flood for which Log Pearson Type III flood frequency results could be computed for all stream reaches. Stage duration analyses were performed for the two lakes (Kathleen and Boren) and May Valley. Stages (elevations) were computed for each of the low and high flow thresholds used in the flow duration analyses. In addition, stage durations were computed for the current land use 2-year flood stage and the current 10-year flood stage. These stage duration analyses are a useful way to examine changes in flooding conditions at a ponding area in the stream system, such as a lake. Results of these duration analyses are not fully reported on in the text of this chapter. However, stage duration was a useful tool in considering flooding impacts in the May Creek basin; these results are discussed in Chapter 6: Flooding. Additionally, for some streams where the findings were conclusive and significant, some detail regarding durations and/or base flows is given. More complete results are available in Appendix C. 5.4 BASINWIDE CONDITIONS This section will provide an overview of the hydrologic conditions within the May Creek basin, with further discussion of many of the themes in the subarea discussions that follow. The entire range of flows is useful in identifying conditions affecting the May Creek stream system; however, for discussions of erosion, stream morphology, and some other parameters, the 2- and 10-year flood events are most useful (see Chapter 7: Sediment Erosion and Deposition). Flow mitigation for new development is typically only designed for the 2- and 10-year flows, and the mitigated future modeling constructed for this report is based on this assumption. On the other hand, floodplain management is often based on flows on the order of the 100-year event. At various points in this chapter, many of these flow thresholds will be discussed. In this basinwide discussion, the 25-year flood has often been used as an indicator of the changes in flood flow taking place in the basin, because the 25-year flow level provides Chapter 5 Hydrology 5-17 a balance between the large flood flows used for floodplain management, and the smaller flows that affect channel size and erosion potential. A number of graphs are included in this section, to illustrate how the 25-year flows, and the unit area discharges that are based on them, vary from location to location for a given land use condition, and with different land use conditions for a given location (see Figures 5-3, 5-4, and 5-5). PRE -DEVELOPMENT CONDITIONS Even in pre -development times the land surface in the May Creek Basin produced runoff, though at a much lower rate than today. Different portions of the basin had different natural tendencies for runoff, depending on a number of factors —the steepness of their slopes, the type of soils, the number, size, and location of natural wetlands. Prior to development in the basin the vegetation was primarily forest cover. These forested conditions tended to minimize the amount of runoff from precipitation events. Much of the rainfall was captured in the forest canopy and evaporated back into the atmosphere, or infiltrated into the soil and reached the stream as groundwater flow. As a result of this slow movement of the water to the stream channel, the occurrence of flows large enough to alter channels and move sediment was less frequent than today. Still, floods did occur, and when flows were great enough to fill channels and flood valleys, they tended to cause erosion. The system was "dynamically stable," though, in that the streams themselves adapted over time to the predevelopment flow regime. This is discussed in more detail in Chapter 4: Geology and Groundwater, and Chapter 9: Aquatic Habitat and Fisheries. The Unit Area Discharge (UAD) methodology, described in the Statistical Analysis Procedures section above, is useful in comparing the tendency of various portions of the May Creek basin to produce runoff and peak streamflow under a variety of land use conditions. The predevelopment hydrologic model suggests that these runoff tendencies varied greatly throughout the landscape and stream system. UAD values for all the tributaries in the basin, as well as two points of interest along May Creek, are shown in Figure 5-3. Note that values for the mainstem of May Creek are much lower than for nearly all the tributaries. UAD values are the result of all the factors that influence flood flows in a stream system, and the mainstem has a much more dampened response than its tributaries, due to floodplain storage, travel time to the mainstem, and the low gradient in the May Valley. Of the four subareas, the Highlands tributaries are the highest runoff producers, with UAD values in excess of 100 cfs per square mile, even under predeveloped land use conditions. In contrast, none of the other areas in the basin show predevelopment UADs of greater than 60. The Highlands subareas are characterized by extremely steep slopes, thin till soils over bedrock, and high precipitation amounts due to the orographic effects of Cougar and Squak Mountains. All of these contribute to a high runoff tendency, even with forest cover. Removal of this forest cover significantly increases flows in these tributaries beyond their already high natural UAD values. This finding is of great importance to the May Valley, because the majority of tributary flow in the upper half of the watershed is from these streams. Chapter 5 Hydrology 5-18 Figure 5-3. Relative Contribution of Runoff per Unit Area. May Creek Tributaries East Fork North Fork co a Cabbage Creek TU y c _m Country Creek L r Long Marsh Creek South Fork Trib. #0291A o � � Greenes Creek _m a w Boren Creek c Newport Hills Creek Gypsy Creek FMIIIIIIIIIIIIIIII Co 3 Honey Creek p Future o J May Creek Mainstem []Future Mitigated E Current at Coal Creek Parkway IIIIIIIIIIIIIIIIIIIIIIIIIIIII ID Forest at Lake Washington (Mouth) 0 50 100 150 200 250 Unit Area Discharge [25-Year Flow(cfs)/Drainage Area(sq. mi.)] Figure 5-4. 25-Year Flow at Selected Locations in May Creek. 25-Year Flow (cfs) 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 ..A N N � W 3 co (J1 Lake Wash ton Blvd b ❑ oney Creek q 5 � d O ri ❑ C Dt5 Boren Cree I Coal Creek Parkway SE � e❑ �f {fix 148th Ave E D ❑ � d d i 164th Ave E Figure 5-5. Increase in Tributary Flow with Changing Land Use. East Fork I i North Fork cn I � Cabbage Creek o r rn Country Creek Long Marsh Creek I South Fork I � a� is a Trib. #0291A o c a� 0' in t7, CU Greenes Creek n� f15 w -------------------- Boren Creek Newport Hills Creek - --�- CU m ® Forested 0° aU Gypsy Creek N Current 3 0 1 � ❑ Future (( ❑ Mitigated Future Honey Creek 0 50 100 150 200 250 300 25-Year Peak Flow (cfs) Chapter 5 Hydrology 5-21 Storage of floodwaters in various stream reaches also impacted streamflow significantly prior to development. Even under current conditions, the May Valley, with its low gradient and extensive wetlands, provides substantial storage. But under predevelopment conditions, the storage effects of the valley were likely even greater, because the May Creek channel was much more sinuous, with extensive side channels and wetland complexes throughout the valley floor. The storage provided in the valley, and the changes from predevelopment to the present day, are discussed in more detail in the May Valley subarea section. Figure 5-4 depicts the changes in flood flow throughout the mainstem of May Creek. In the valley, flood flows are reduced because of the storage and attenuation that occurs. In the central valley immediately downstream of 164th Avenue SE, flood flows actually decrease in a downstream direction. Another stream that had and still has a significant amount of storage is the South Fork of May Creek. This is due to the presence of Lake Kathleen, which, at 49 acres, is the largest lake in the basin. The lake provides considerable capacity for dampening of outflows, so that flows at the mouth of the South Fork are much less per unit area than in the other two forks at the head of the May Valley. Under forested conditions, the UADs for the North Fork, East Fork, and South Fork, respectively, are 116, 110, and 23 cfs per square mile. Even with significant land use changes in the South Fork subbasin, flows will continue to be dampened, so that this stream is not a major contributor to May Valley storm flows. The other tributaries to May Creek, in the East Renton Plateau and Lower Basin subareas, tend to have moderate flow responses, with nearly all other predevelopment UADs between 30 and 50 cfs per square mile. Boren Creek is among this group, despite the presence of Lake Boren, which provides limited active storage and much less flow dampening capability than Lake Kathleen. Some predevelopment UADs may be slightly overestimated because storage in the basin's natural wetlands may be underrepresented. While the model assumes a predevelopment land cover (forest), no attempt has been made to represent predevelopment hydraulic conditions, including the extensive natural wetlands that formerly occupied much of the tributary headwater systems, and the meandering, braided channel in the May Valley. These features stored runoff and dampened flows, even more than today. However, these wetlands have been so impacted by past development practices that it is impossible to gauge their original extent. Nevertheless, the forested land -use condition represented in the HSP-F model sufficiently represents predevelopment flow conditions for the purposes of basin planning, and the resulting low runoff response for these tributary streams provides a useful indicator of the magnitude of the changes that have taken place since development began. CURRENT CONDITIONS Clearing of forested areas results in significant flow increases, whether the conversion is to impervious surfaces, such as rooftops, roads, and parking lots, or to grass areas. Most types of development actually result in a mixture of land cover types. Chapter 5 Hydrology 5-22 Development activities to date have changed the hydrologic conditions in the May Creek basin. The amount of effective impervious area (EIA) in the basin has increased from zero percent under predevelopment conditions to a basin -wide average of 7 percent under current conditions. Most of this impervious surface is in the Lower Basin subarea. Similarly, the amount of grass cover has increased from zero percent to 27 percent. The basin is still 60 percent forested; five percent saturated (or wetlands), and one percent open water lakes cover the remainder. Changes in land cover types for the four subareas are shown in Figure 5-2. Grass cover produces more runoff than forest because grass intercepts and stores less rainfall prior to the start of runoff than does forest cover. The forest transpires more soil moisture to the atmosphere than does grass. This keeps the soil drier in the winter and reduces runoff. In addition, forest soils tend to be less compacted than soils that have been stripped of their forest cover and duff and have been altered by development activities. Impervious surface has virtually no capacity for interception or infiltration, so the hydrologic changes are even more profound than with grass. These changes impact not only flood flows but also erosion and sedimentation in the basin (see Chapter 7: Sediment Erosion and Deposition). The change from a predominantly forested basin to one with a high percentage of grass cover and impervious surface has had significant implications hydrologically. The amount of stormwater runoff has increased dramatically throughout the basin. Flood flows have increased as well, resulting in additional erosion of the hillsides above May Valley, flooding and sediment deposition in the valley, erosion in the canyon downstream of the valley, and flooding and deposition near the mouth of May Creek. The magnitude of the change from predevelopment to current land use conditions differs throughout the basin, and is described in more detail in the various subarea discussions. The most urbanized portion of the basin, the Lower Basin subarea, is experiencing significant increases in stormflow. UAD values have increased dramatically in the Lower Basin tributaries; most have doubled. In the Highlands tributaries, which produce the most streamflow and therefore most significantly affect flows in May Valley, urbanization's impacts have thus far been insignificant. UAD values in all the Highlands tributaries have increased by less than 16 percent. Increasing flows with changing land uses are depicted in Figure 5-5. This small change in the Highlands tributaries has led to only moderate flow increases in the May Valley as well. Recent, frequent, widespread flooding has led to the perception that upland development has already resulted in significant increases in May Valley flood flows. However, the analysis actually suggests that May Creek flood flows in the May Valley have increased less than 20 percent to date for all computed flow frequencies, at nearly all points of interest. Twenty percent is not insignificant, but it also clearly suggests that the level of flooding currently experienced is not much greater than before any development of the basin. The valley between 164th and 148th Avenues SE becomes largely inundated at approximately 280 cfs (current conditions 10-year level), and further flow increases result in only small changes in depths and floodplain widths. Thus, the lateral extent of flooding has not changed much with changing land use. This will be discussed further in Chapter 6: Flooding. Chapter 5 Hydrology 5-23 Flood volumes and durations have changed more dramatically than peak flows. The increased runoff from the hill slopes drains very slowly from the May Valley, so that the length of time the valley is above flood stage increases more noticeably than the flood depths. It is also worth noting that several large rainfall events occurred in the late 1980's, as upland development was taking place. These large rainfalls would have produced extensive runoff and flooding under any land use condition. High flows in this stream system have thus been very visible recently, and have increased the local perception of flooding problems. Mean Annual Flows and Permitting Implications The current conditions analysis has also yielded some useful information on mean annual flows throughout the basin. Mean annual flow is a measure of the average flow in a stream over the period of record; it thus represents the entire range of streamflow, from high flood flow events to summertime baseflow. Several permitting agencies use a stream's mean annual flow to determine the level of permit required; this has resulted in several significant "flow thresholds." A 20 cfs threshold is used by the State of Washington's Shorelines Program, and all streams and rivers with mean annual flows greater than 20 cfs are considered "Shorelines of the State." Streams exceeding this flow level are also designated as Class 1 under King County Sensitive Areas Ordinance regulations, and as Type 1 under the King County Surface Water Design Manual. Each of these designations carries certain development standards with it. A 5 cfs threshold is used by the U.S. Army Corps of Engineers to determine whether a 404 permit is necessary for filling of a wetland adjacent to a waterway. The HSP-F model for the May Creek basin is a useful tool for determining where in the basin these standards apply. Based on the current conditions analysis, May Creek has a mean annual flow greater than 20 cfs below the confluence of Honey Creek; from that confluence to the mouth at Lake Washington, the channel is designated a "Shoreline of the State." Mean Annual Flow values for major points of interest in the basin are given in Table 5-2. Above the Honey Creek confluence the mean annual flow in May Creek is less than 20 cfs, but greater than 5 cfs, all the way upstream through the May Valley. The filling of wetlands adjacent to the May Creek channel requires a 404 permit. However, none of the tributaries in the May Creek basin have mean annual flows equal to or exceeding 5 cfs. JANUARY 1990 STORM Prior to a discussion of the expected future conditions hydrology of the basin, it is worthwhile to discuss the response of the mainstem of May Creek and its many Chapter 5 Hydrology 5-24 Table 5-2. Mean Annual Flows in May Creek and Tributaries (Current Conditions). Location Mean Annual Flow (cfs) Highlands Subarea North Fork 4.6 East Fork 1.6 Country Creek 1.3 Cabbage Creek 1.9 Long Marsh Creek 1.8 East Renton Plateau Subarea South Fork 2.2 Tributary 0291A 1.6 Greene's Creek 1.5 May Valley Subarea: May Creek 148th Ave. SE 8.6 Lower Basin Subarea: Tributaries Honey Creek 3.6 Boren Creek 4.0 Newport Hills Creek 0.6 Gypsy Creek 0.8 Lower Basin Subarea: May Creek Coal Creek Parkway SE 13.6 Mouth 25.6 tributaries to the major flow event of January 1990, for which some empirical information is available as well. On January 9, 1990 a major rainstorm swept through the Puget Sound region. In the May Creek basin this storm produced 3.6 inches of rain over a 19-hour period, with 2.3 inches falling between 5 and 11 A.M. Although the relative size of rainfall and streamflow events do not have a one-to-one correspondence, it is worth noting that this was a rare rainfall event; the six -hour total was greater than a 100-year rainfall. The stream gage near the mouth of May Creek recorded a peak flow of approximately 600 cfs during this storm. This is the only gaging location for which measured streamflow data are available for this time period. However, the HSP-F model of the basin has allowed reconstruction of the flood flows at all subcatchment locations, so that the behavior of the basin during a large event can be ascertained. The following description is based on this reconstruction of the January 1990 event. The high streamflows in January 1990 were the result not only of the rainfall on January 9, but also of the antecedent conditions; that is, the saturation and flow levels in the basin and its stream system resulting from wetter than average conditions in the Chapter 5 Hydrology 5-25 preceding days. On the 6th of January, 0.7 inches of rain were recorded at the 37V rainfall gage. This was followed by an additional 0.9 inches on the 7th, and another 0.7 of an inch on the 8th. This was sufficient for the basin's soils to become largely saturated, and for flows in the tributaries and mainstem to begin to rise substantially. The rain continued during the early morning hours of the 9th. By 5 am, 0.6 inches had fallen in the lower portion of the basin and greater amounts occurred at higher elevations. Between 5 and 11 am the heaviest rainfall hit the basin with over 2 inches of rain in 6 hours. The largest hourly value was 0.5 inches between 7 and 8 A.M. The tributaries throughout the basin peaked first in response to this downpour. Several hydrographs have been included to illustrate the timing of the peaks. Figure 5-6 depicts the overall reaction of May Creek to the January 1990 storm; simulated flow information from two mainstem locations is shown, along with data from the North Fork, May Creek's major upper basin tributary. Figure 5-7 shows the major tributaries in the upper half of the watershed, along with two locations in the May Valley, during the two-day flood peak. Most of the upper basin tributaries reacted similarly to the North Fork, in that they peaked long before the valley. The South Fork, which drains Lake Kathleen, is the major exception to this. Despite its drainage area size, it contributed little to flood waters in the valley. This is typical of this stream, which has a highly dampened response. Except for the streams affected by lakes and major wetland areas, all of the tributaries reached their peak flow by 8 A.M. on the 9th (Table 5-3). While the tributaries peaked in the morning of the 9th during the heaviest rainfall, the mainstem of May Creek did not peak until some 8 to 14 hours later. The upper end of May Valley received flows from the South Fork, East Fork, North Fork, and Cabbage and Country creeks. This tributary inflow resulted in some valley flooding during the morning of the 9th, but the large amount of valley floodplain storage resulted in a relatively small peak flow (approximately 100 cfs) moving down through the valley at that time. A large portion of the flood volume was retained in the valley until the afternoon of the 9th, when the flood waters in the May Valley began to recede. This was the time of peak flow, and flood flows in the Coalfield area (SR-900 to 164th Ave SE) exceeded 340 cfs, which is in the range of a 10- to 25-year flood for this portion of the stream. The flood flow at 148th equalled that of 164th (341 cfs), and was also in the range of a 10- to 25-year flood. At the downstream end of May Valley at Coal Creek Parkway SE, the peak flow grew to 420 cfs by 11 PM. This is equivalent to a 10- to 25-year flood. Flood flows in the canyon reached their peak about an hour before the valley flood peak reached the upstream end of the canyon. The Lower Basin tributaries, as well as Greene's and Long Marsh creeks, which also directly affect the May Creek canyon, had already peaked, and this combination of flows was traveling through the canyon before the peak response from farther upstream was experienced. In Figure 5-8, it is evident that the lower mainstem experienced two separate peaks, one driven by the Lower Basin tributaries and the early part of the stormflow from farther upstream, and one driven more directly by May Valley flood flows. This spread out the time of peak or near -peak discharge in the canyon and at the mouth, rather than concentrating the flood volume with a consequent higher peak. Chapter 5 Hydrology 5-26 Figure 5-6. Simulated Hydrographs for the January 1990 Storm. a 0.0 — — _ 700 o. � 1 U L Rain Gage 37V a ` 600 T .... O = 0.6 500 May Creek at Mouth May Creek at Coal Creek Parkway 400 N `u . I o t 300 LL t 200 North Fork 100 i . ........................ 0 N 17 O 1n O n m O O N C2 O t0 tp n N M C C C C C C C C C A > Chapter 5 Hydrology 5.27 Figure 5-7. Simulated January 1990 Storm Hydrographs for the Upper Basin of May Creek. 0.0 - .. c O y a 0 Rain Gage 37V o_ c r� 0 0 2 0.6 ' m m E E N (O May Creek at 164th Avenue SE May Creek at Coal Creek Parkway 400 350 300 250 200 0 U. 150 -.North Fork 100 50 South Fork ....................... . '-• ---- --_ rn rn o 0 0 0 > > m A m m --> N f0 M A a a W t0 �2 W Chapter 5 Hydrology 5-28 Table 5-3. Simulated 1990 Flood Results for May Creek and its Tributaries (January 9, 1990). Tributary Peak Flow (cfs) Time of Peak Flow Flood Recurrence Interval (yrs.) Highlands Subarea North Fork 250 8 A.M. 25- 50 East Fork 87 8 A.M. 25 -50 Country Creek 54 8 A.M. 10-25 Cabbage Creek 85 8 A.M. 10-25 Long Marsh Creek 81 8 A.M. 10-25 East Renton Plateau Subarea South Fork 27 8 A.M. 10-25 Tributary 0291A 71 8 A.M. 50- 100 Greene's Creek 57 8 A.M. 25-50 May Valley Subarea: May Creek 164th Ave. SE 341 4 P.M. 10 -25 148th Ave. SE 341 11 P.M. 10-25 Lower Basin Subarea: Tributaries Honey Creek 102 8 A.M. 50 Boren Creek 77 12 noon 25 Newport Hills Cr. 22 8 A.M. 10-25 Gypsy Creek 30 8 A.M. 25 Lower Basin Subarea: May Creek Coal Cr. Pkwy. SE 420 11 P.M. 10-25 Mouth 598 10 P.M. 10-25 This relationship between flood response in the upper and lower portions of the mainstem is typical: downstream flows in the canyon and at the creek's mouth tend to be reduced due to the significant flood storage that occurs in the May Valley, and the consequent delay of flood peaks. Elimination of this storage would increase peak flows farther downstream. Flood peaks in the canyon and at the mouth were in the range of a 10- to 25-year flood. The simulated flood peak at the mouth was 598 cfs; the recorded flood peak at this location was 600 cfs. In summary, the tributaries peaked some 8 to 14 hours prior to the mainstem. The lower mainstem (canyon and mouth) peaked slightly earlier than the flows in the valley further upstream. As a result, system -wide flooding was spread out over 24 to 48 hours, with flooding at individual locations occurring at different times and for varying portions of that period. Chapter 5 Hydrology 5-29 Figure 5-8. Simulated January 1990 Storm Hydrographs for the Lower Basin of May Creek. 0.0 650 `o — c w u u Rain Gage 37U ! 600 y L I o ` f 550 a �- 0 xo 0.6 ! 1500 May Creek at Mouth 1450 i � 400 \\\ 350 May Creek at Coa \,\ c Creek Parkway 300 .2 250 200 150 100 .................... Honey Creek '— --- _ ..................... 50 Boren Creek 0 rn c m c m c — o 0 0 E N t0 E aD E 7 W N N fD a W V N Chapter 5 Hydrology 5-30 FUTURE CONDITIONS Future land use conditions are based on the assumption of full build -out in the basin, subject to existing and proposed development regulations. Future full build -out in the basin will result in an increase of the EIA from seven to twelve percent. In addition, future land use conditions are expected to reduce forest cover from 60 percent to 29 percent of the basin. Grass cover increases from 27 percent to 53 percent (Figure 5-2). Development will continue to occur throughout the basin, at varying densities; this is described in detail in Chapter 3: Land Use and Land Cover. Although development in the Lower Basin will result in the greatest increase in impervious area in the future, the development in the Highlands tributaries may be much more important in terms of systemic effects. The amount of impervious surface and cleared land in the Highlands is expected to remain relatively low, but the increase in flood flows resulting from these changes will be extremely significant. The Highlands subarea has a high natural tendency for runoff, as described above, and when cleared of tree cover, the increased runoff will result in extremely high flows and volumes in the tributaries. All of this water is discharged directly into the May Valley, and eventually flows through the May Creek Canyon in the Lower Basin as well. Future conditions flows have been modeled two ways, with and without mitigation requirements (see the Streamflow Simulation subsection of this chapter). With mitigation, the impact of future development on the hydrology of May Creek will be somewhat lessened, but not alleviated altogether. Future flows without mitigation provide a "worst -case" estimate of flood flows in the basin, assuming no major changes to zoning. Mitigated future flows, on the other hand, represent the most reasonable estimate of future flows. It is important to realize, however, that mitigation requirements could change in the future, and that these flows could increase or decrease, depending on those changing requirements. In discussing future land use hydrology in this chapter, more emphasis will be placed on these mitigated flows, as they are considered the best estimate of the future. Where current mitigation requirements result in unusually ineffective mitigation, this will be pointed out. As implied above, mitigation, based on the assumptions used in the modeling, does not totally prevent future damage to the stream and its habitat. Three factors are instrumental in this: (1) no mitigation is currently required for development at low densities, as in short plat subdivisions; (2) no additional retention/detention storage is required beyond the 10-year event (that means that storage is not sized for the 100-year event); and (3) some portion of the additional runoff associated with development is typically not mitigated, due to poor site design, flow bypass, multiple drainages, and other reasons (for the purposes of modeling, this portion has been estimated at 20 percent). In addition, mitigation is most successful at lessening peak flows in tributaries and their catchment areas. Detention ponds result in a delayed release of the runoff volume, at a lower peak discharge. The runoff volume is eventually released to the stream system, though, and then combines with flows from other parts of the basin. Two portions of the May Creek system, the May Valley and Lake Kathleen, are large natural storage areas (Lake Boren provides some natural storage as well, but is not large enough for the Chapter 5 Hydrology 5-31 storage effect to be significant). Flooding conditions in these two areas are driven more by flood volumes than by peaks, and flow through these areas is naturally delayed. Mitigation of increased development upstream is largely ineffective at reducing flood volumes in these areas. In the May Creek basin, current mitigation requirements are most effective at reducing future flows in the western portions of the basin, where current zoning allows relatively high density development patterns. Mitigation is least effective in Cabbage Creek and the North and East Forks of May Creek. In these tributary areas, future development will largely be of the low -density single-family type that currently has no detention requirement. For all three of these tributaries, mitigation as currently required would be less than 20 percent effective at reducing future flows to current levels (Table 5-4). Table 5-4. Mitigation Effectiveness in May Creek and its Tributaries (Based on 10- year Flows). Tributary Current Future Mitigated Future Unmit. Mitigation flow (cfs) Flow (cfs) Flow (cfs) Effectiveness (%) Highlands Subarea North Fork 199 242 248 12 East Fork 68 99 101 6 Country Creek 46 63 85 56 Cabbage Creek 81 124 132 16 Long Marsh Creek 75 78 85 70 East Renton Plateau Subarea South Fork 26 30 31 20 Tributary 0291A 51 62 68 35 Greene's Creek 42 51 66 63 May Valley Subarea 164th Ave. SE 285 348 359 15 148th Ave. SE 285 347 339 13 Lower Basin Subarea: Tributaries Honey Creek 85 90 101 69 Boren Creek 62 76 86 42 Newport Hills Cr. 20 22 34 86 Gypsy Creek 25 29 39 71 Lower Basin Subarea: May Creek Coal Cr. Pkwy. SE 357 429 438 11 Mouth 556 652 706 36 Mitigation is also ineffective at reducing flows in May Creek itself. In the high -storage portions of the valley, mitigation reduces 10-year flows less than 15 percent of the difference between current and unmitigated levels. Downstream at the mouth, this Chapter 5 Hydrology 5-32 effectiveness increases to 36 percent. In all cases, mitigation is even less effective for larger floods such as 25- or 100-year recurrence level. (One reason for this is that detention ponds are designed to only a 10-year level.) In short, proposed mitigation measures lessen, but do not prevent, future increases in flows. They do not fully prevent major land -use changes from causing further increases in damage to May Creek, its resources, and residences. 5.5 CONDITIONS BY SUBAREA HIGHLANDS The Highlands Subarea lies to the north of May Valley, and drains the south -facing slopes of Cougar Mountain. These slopes are steep and covered mostly by forest on a thin till soil. Surface runoff drains quickly from these slopes and provides streamflow for the northern tributaries that empty into May Creek. Major Highlands tributaries include Long Marsh Creek (0289), Country Creek (0292), Cabbage Creek (0293), and the North Fork of May Creek (0294). The East Fork of May Creek (0297) is also a Highland tributary, but drains the western slopes of Squak Mountain instead of Cougar Mountain. Steep slopes, till soils, and high precipitation volumes characterize the Highlands Subarea. As a result of these natural conditions, runoff flow rates and volumes were substantial from this subarea even under predevelopment land use conditions. Under predevelopment conditions, Unit Area Discharge values for the East Fork, North Fork, Cabbage Creek, Country Creek, and Long Marsh Creek range from about 100 to 130. These UAD values under predevelopment conditions exceed those for most of the other subcatchments even under future non -mitigated conditions. None of these streams is highly urbanized; the percentage of effective impervious area currently ranges from 0.4 percent in the Country Creek subcatchment to 1.5 percent in the East Fork subcatchment. Even under future conditions, all of these tributary areas will have EIAs of less than five percent. Much of the future development will occur at low densities, though, for which current mitigation requirements do not apply. Future land - use conditions in the Highlands Subarea will see an increase in these single-family low - density residences on the lower slopes of Cougar Mountain. The upper portion of Cougar Mountain will be protected in the Cougar Mountain Regional Park and will remain in its current forested condition. In these streams, even small amounts of urbanization tend to increase runoff peaks and volumes substantially. Under current land -use conditions, UAD values in these streams have only increased from predevelopment by 16 percent or less. In the future, this increase will be as much as 60 percent, due to the effects of future forest clearing with no required mitigation. Because of the Highlands' location as the headwaters for May Creek, as well as the size and high runoff tendencies of these streams, any impacts to these tributaries will also impact May Valley and the Lower Basin. Chapter 5 Hydrology 5-33 Under nearly all modeled land use conditions, the five Highlands tributaries are the five highest runoff producers per unit area in the basin. They are characterized by high rainfall, steep slopes, and shallow soils. In addition, the drainage areas are sufficiently large that these streams tend to be among the highest contributors of runoff volume to May Creek. Each of these streams is discussed below in more detail, with particular emphasis placed on the ramifications of changes in land uses in each of these tributaries. These changes have caused flows to increase and this trend will continue in the future, with impacts to both the tributary streams themselves, and to May Creek. North Fork of May Creek The North Fork is the largest of the three forks at the head of May Valley, and in fact is the largest tributary to May Creek anywhere in the basin. Like all of the Highlands tributaries, the North Fork produces extremely high flows per unit area. Despite its size, the North Fork is flashy and tends to peak quickly during a storm. Slopes are steep, and precipitation is higher here than anywhere in the basin. The stream is channelized for significant portions of its route, further increasing its flashiness and velocity. Urbanization of the North Fork drainage area has been minimal to date, but will increase somewhat in the future. This future urbanization will include expansion of SR-900 to four or five lanes, thereby increasing the impervious surface in the drainage area, in this case immediately adjacent to much of the stream corridor. Characteristic flood flows are shown in Table 5-5 for the 2- and 100-year recurrence intervals. Future increases will be significant, and this will impact both the North Fork itself and the May Valley. Current mitigation requirements are ineffective because most development projects are expected to be of too small a scale to exceed thresholds that trigger mitigation requirements for retention or detention. Ten-year mitigated future flows would only be reduced twelve percent of the way back to current levels. East Fork of May Creek Unlike the other Highlands tributaries, the East Fork of May Creek drains the western slopes of Squak Mountain. The lower third of the East Fork subcatchment is much flatter than most of the Highlands tributary areas; in effect, it forms the upper end of the May Valley. Still, the slopes of Squak Mountain are steep, and the runoff tendency is high, and East Fork peak flows are among the highest in the basin. East Fork flows are expected to increase significantly with future development, and mitigation would be less effective here than in any other of May Creek's tributaries (25—year flows will increase from 70 cfs under forested conditions, to 81 cfs for current, to 116 cfs for future mitigated). The East Fork's location at the head of May Valley means that this additional runoff must travel through the entire valley, contributing to increased flooding there. In addition, the 66 percent increase from forested to future mitigated flows is quite significant to the East Fork itself, and can result in altered stream Chapter 5 Hydrology 5-34 Table 5-5. Highlands Flow Frequencies Show that the Highlands Subarea Streams are the Largest Flow Contributors to May Creek. 2-yr 100-yr Tributary For. Cur. Fut. For. Cur. Fut. Comments Mit. Mit. North Fork of 105 123 169 268 296 328 This is the largest May Creek tributary in the basin. It contrbutes large flows at the head of May Valley. East Fork of 35 42 67 89 102 141 This stream also May Creek contributes large flows to May Valley. Mitigation of future increases is less effective here than anywhere else in the basin. Cabbage 43 46 78 126 133 193 Second largest flow of Creek any tributary in basin; highest UAD values. Future stormflow is anticipated to be significantly higher, on the order of 60 cfs for the 100-yr. event, by far the largest increase in the basin. Country Creek 24 26 35 70 77 108 Mitigation is moderately effective here, more so than for most Highlands tributaries. Future increases are still significant for both the stream itself and for May Valley. Long Marsh 40 42 43 118 125 130 This stream will be the Creek least built -out under future conditions. Flow input to May Creek is very large, but current and future increases will be minimal, and mitigation is effective. Chapter 5 Hydrology 5-35 channels. The magnitude of this percentage increase is greater here than in any of the other Highlands tributaries. Smaller floods, such as the 2- and 10-year, which are more instrumental in determining stream erosion trends, are expected to increase even more dramatically. This is discussed in detail in Chapter 7: Sediment Erosion and Deposition. Cabbage and Country Creeks Cabbage and Country creeks also produce high flows per unit area. Cabbage Creek, in particular, has the highest UAD values of any tributary in the May Creek basin under all computed land -use conditions. Development in these two tributaries has been minimal to date, but is expected to increase in the future. Several plats have been filed, and limited construction has begun on these slopes. Clearing of land and addition of impervious area will significantly increase runoff peaks and volumes in these two streams. Although the allowable amount of development under current zoning is much less here than in Lower Basin tributaries, the implications are far greater here, due to the naturally high predilection for runoff. Flows in Cabbage Creek are also expected to increase significantly (25-year flows have increased from 96 cfs under forested to 101 cfs for current conditions, and will increase further to 150 cfs for mitigated future conditions). Mitigation is extremely ineffective here, because the development is proceeding in short plats that usually do not require stormwater detention under current regulations. The zoning currently in place will encourage this trend to continue. Cabbage Creek's location near the head of May Valley means that this additional runoff will travel through most of the valley, contributing to increased flooding there. Like in the East Fork, these flows may overwhelm the natural stream's ability to adapt. The percentage increases in Cabbage Creek are the next highest in the subarea. None of these impacts have been witnessed yet, as nearly all of this total flow increase will occur in the future, as the parcels are cleared and built upon. Changes in Country Creek are not expected to be as significant, though they will still have ramifications on the total volume of water discharged to the May Valley during large flow events. Increased impervious area will be greater here than elsewhere in the subarea; however, mitigation is expected to be somewhat more effective, due to a higher density of subdivision development, with accompanying higher stormwater detention requirements. Also, Country Creek is the smallest of the Highlands tributaries, and one of the smallest in the entire May Creek basin; thus, it has less impact on May Valley. It is important to note that Cabbage Creek was artificially channelized to enter Country Creek just below SE May Valley Road, and above the confluence with May Creek. Thus, the two streams contribute flow to May Valley at the same outlet. Timing of these two streams tends to be similar, as they're both flashy in nature. Together, they contribute more discharge to May Creek during flood events than any single tributary in the basin, except the North Fork. Chapter 5 Hydrology 5-36 Long Marsh Creek Long Marsh Creek is the westernmost of the streams included in the Highlands subarea. Like all of the Highlands tributaries, Long Marsh is steep, and dominated by shallow till soils underlain by bedrock. Long Marsh peak flows are among the highest in the basin, particularly under forested land use conditions. The majority of the Long Marsh tributary area is located in Cougar Mountain Regional Park, and thus this stream is the least urbanized in the basin, under both current and future conditions. The only Regionally Significant Resource Area in the May Creek basin is located near the headwaters of Long Marsh Creek (see Chapter 9: Aquatic Habitat and Fisheries). Increases in peak flows in Long Marsh are quite minimal, and these limited increases are mitigated very well by current requirements. This stream tends to peak very quickly, and discharges near the lower end of the May Valley, and thus is one of the contributors to the flashy nature of the May Creek canyon. Peak flows from Long Marsh are not stored for long in the valley, but rather flow into the canyon before flows from the other Highlands tributaries. EAST RENTON PLATEAU The East Renton Plateau Subarea lies to the south of May Valley. The plateau drains the north -facing slope of the ridge between the Cedar River and May Creek. The upper plateau is fairly flat; however, a steep valley slope connects it with the May Valley. Along this valley wall surface runoff drains quickly and provides streamflow for the southern tributaries that empty into May Creek. The major Plateau tributaries are the South Fork of May Creek, Greene's Creek (0288) and Tributary 0291A. The tributaries of the East Renton Plateau do not produce significant streamflow compared to the Highlands tributaries across the valley. Slopes are flatter, and precipitation is lower in this subarea. Predevelopment Unit Area Discharge values for the plateau tributaries range from 23 for the South Fork to 52 for Tributary 0291A. By comparison, Highlands tributary values exceed 100 under predevelopment conditions. As a result, the predevelopment flood flows from the plateau only minimally impacted May Valley and the Lower Basin. Development in these drainage areas is not as important in terms of flood volumes discharged to the May Valley. However, streams here are more urbanized, and will become even more so in the future. Urbanization will continue both in existing urbanized areas, and on undeveloped plats. The Plateau has no forest reserve, like Cougar Mountain, to assure that some land remains in open space. Thus, percentage increases in flood flows are higher here than in the Highlands, and will be even greater in the future. Changes in the 2- and 100-year flows with changing land uses are shown in Table 5-6. The ability of the natural tributaries draining the Plateau to adapt to these increasing flows will continue to be in question. The effects of these flows on erosion are discussed in Chapter 7: Sediment Erosion and Deposition. In addition, local drainage on the flat Chapter 5 Hydrology 5-37 plateau is sometimes poor, leading to several problems discussed in Chapter 6: Flooding and in the Observed Conditions Summary table (see Appendix A). Much land has already been cleared and paved in the drainage area of these tributaries. Current conditions EIA ranges from one percent to nine percent. Future development will cause this impervious area to increase to between four percent and 16 percent. For Greene's Creek and Tributary 0291A, these land use changes result in expected increases in flood flows. Conversely, the South Fork is significantly affected by Lake Kathleen, which lies at the eastern end of the East Renton Plateau. At 49 acres, this is the largest lake in the basin. The lake significantly attenuates peak flows, so that the South Fork, its outlet stream, has the lowest UAD values in the May Creek basin. The South Fork reacts to precipitation differently than any other stream in the upper half of the May Creek basin; it peaks much more slowly, and flood volumes are released over a greater period of time. Table 5-6. East Renton Plateau Flow Frequencies Show that These Streams are Moderate Flow Producers. 2-yr storm 100-yr storm Tributary For. Cur. Fut. Mit. For. Cur. Fut. Mit. Comments South Fork 11 17 19 24 36 47 Flows are extremely of May dampened and delayed by Creek the detention provided by Lake Kathleen: in terms of contributing watershed area, peaks in this reach are the lowest in the basin. Tributary 17 33 39 42 76 85 Moderate flow production 0291 A from a moderately urbanized area. Greene's 10 26 32 31 68 82 Moderate flow production; Creek moderately developed area. South Fork of May Creek The land around Lake Kathleen is relatively flat and marshy, and development has been limited to single family residential areas of a variety of densities. A number of small tributaries enter the lake; however, these have not been modeled separately. The outlet of the lake is at its north end, where the rate of outflow is controlled by two culverts under SE 134th Street. The South Fork then flows through a wetland prior to dropping down the steep hillside to May Valley, where it joins the East Fork upstream of SR-900. Less development has occurred in this lower half of the tributary area. Chapter 5 Hydrology 5-38 The South Fork subcatchments do not show as much impact from current development as do the subcatchments further west on the plateau. Lake Kathleen has a large surface area (49 acres) relative to the surrounding tributary area (304 acres). Small fluctuations in the lake's elevation provide sufficient storage to significantly dampen the effects of flood flows entering the lake. Model calculations indicate that flood flows leaving the lake through the two partially submerged culverts have never exceeded 20 cfs over the simulated period of record. These low flood flows give the South Fork the lowest Unit Area Discharge values for a May Creek tributary for all computed land use conditions, with a current conditions UAD value of 35 cfs per square mile. Although peak flows from the South Fork are not very high, the tributary area is the fourth largest of the basin's twelve tributaries, and the mean annual flow from the tributary is correspondingly high. Flow is released much more slowly than in many of the other tributaries, though, so that base flow is higher, and storm flow is relatively low. Attenuation is so extreme that even storm volumes are less than for other tributaries. Tributary 0291A and Greene's Creek Tributary 0291A and Greene's Creek are flashier than the South Fork. They respond to precipitation more quickly, and peak in a similar time frame to the Highlands tributaries across the valley. These two streams have moderate UAD values for all modeled land uses, and their peak flows are in the bottom two-thirds of all May Creek tributaries. Thus, their impacts to May Valley are not significant. Land use changes can significantly affect the conditions of these streams themselves, though, particularly with regard to localized flooding and stream erosion and degradation. These effects are discussed in more detail in Chapters 6: Flooding, and 7: Sediment Erosion and Deposition. Changing land uses actually seem to affect Greene's Creek hydrology more than nearly every other May Creek tributary. Effective impervious area in the Greene's Creek tributary area is currently 8.6 percent; this will increase to 15.7 percent under future conditions. Current conditions 25-year flows are 126 percent greater than forested, while future mitigated flows are 170 percent greater than forested (mitigation in this catchment is moderately effective; future unmitigated flows would be 252 percent greater than forested). More common floods in the 2- to 10-year range would increase even more. Only Gypsy Creek in the Lower Basin experiences comparable flow increases (Figure 5- 3). These flows may be quite deleterious to the Greene's Creek channel morphology; a result of this increase in the size of peak flows is additional scour of the steep slopes between the plateau and the mainstem of May Creek. This is causing increasing sediment movement into May Creek and is resulting in property damage due to gully erosion and culvert blockage. The actual flow values in Greene's Creek are low enough (due to the small size of the drainage area and moderate slopes) that the effects on May Creek will be only moderately significant. Greene's Creek enters May Creek near the head of the canyon, Chapter 5 Hydrology 5-39 and does not contribute flow to May Valley, like Long Marsh Creek, it adds to the flashiness and early flood peaking tendency of the May Creek canyon. Tributary 0291A is similar hydrologically to Greene's Creek in many ways —soils, slopes, and precipitation, as well as drainage area size; however, the impacts of urbanization are somewhat less. Tributary 0291A has a substantial headwater wetland complex, which includes a regional stormwater detention pond, and is less developed than Greene's, under both current and future conditions. Thus, the increases in flood flows are less in Tributary 0291A. Mitigation is expected to be somewhat less successful in Tributary 0291A due to allowed development patterns. MAY VALLEY The May Valley Subarea is the May Creek floodplain and adjacent lower valley areas between Coal Creek Parkway SE to the west and SR-900 to the east. This subarea is characterized by extremely flat land in the valley itself, much of which is regularly inundated from May Creek overflowing its channel banks and from tributary flood flows. The valley floodplain provides extensive storage volume for floodwaters; flows remain in the floodplain for a long time period, and rise and recede slowly. This results in attenuated peaks (smaller and delayed), and longer durations. Significant as this storage is, it was probably much greater prior to valley development, as the natural floodplain was heavily vegetated, and the stream was highly meandering, with beaver dams and ponds, and an even milder gradient than now. Floodwaters would have moved through the predevelopment May Valley extremely slowly. Lateral movement of the stream channel across the valley floodplain is evident by the geologic remains of historic oxbows and peat soils in the valley (see Chapter 4: Geology and Groundwater); this evidence supports the contention of additional valley flood storage. The major tributaries of the Highlands and East Renton Plateau subareas, discussed above, flow into the mainstem of May Creek in the May Valley. Hydrologic impacts of changing conditions in these upland tributary systems have significant implications for flows in the May Valley. The Highlands tributaries, in particular, contribute substantial flood volume to the valley. Nearly 80 percent of the flood volume in the May Valley during large flow events comes from these steep mountain hillsides. Because the May Valley subarea does not directly include any tributaries, the format of the discussion is somewhat different here than in the previous two sections. The stream will be discussed by reach, with some emphasis given to the tributary inputs to each significant stream reach, as well as to the storage and attenuation that occurs there. Current condition peak flows in May Valley have increased from predevelopment conditions by roughly 15 to 20 percent for the 2-, 10-, and 100-year peak flows (Table 5-7). Tributary flood flows entering the valley from the north and south hillslopes generally show greater percentage increases from predevelopment to current conditions, although this varies by subcatchment and depends on the amount of development in each subcatchment. Peak 25-year flows in the May Valley are graphed in Figure 5-4, this figure shows how these flows vary over the length of the stream, as well as the location of the most significant roads and tributary inputs. Chapter 5 Hydrology 5-40 Table 5-7. May Valley Flow Frequencies Show that Floodplain Storage in the Valley Attenuates Downstream Peaks. 2-yr storm 100-yr storm Location For. Cur. Fut. Mit. For. Cur. Fut. Mit. Comments 164th Ave. 151 170 193 396 461 590 Largest tributary inputs SE are upstream from above here; large flow volumes inundating valley. 148th Ave. 141 165 188 397 468 562 Effects of valley storage SE are seen here, as flows are somewhat less than farther upstream despite increased contributing area; mitigation of peak discharge is ineffective in volume -driven stream such as May Creek in May Valley. Coal Creek 173 208 243 482 582 706 Flows have increased Parkway SE towards head of canyon; Long Marsh Creek input is felt in the Lower Basin subarea. The relatively constant percentage increase in the 2-, 10-, and 100-year peak flows for the valley is because of two factors. The first is that the upper portion of the basin (which drains to May Valley) is relatively undeveloped at present. The percent increase in the 2-year flood from predevelopment to current conditions is largely controlled by the increase in impervious area (pervious surfaces absorb much of the rainfall for these smaller flood events). This is less true for the 100-year flood, which results from large runoff volumes from all land types (both impervious and pervious) in the basin. The second factor is that the low channel slope in the valley and the relatively large adjacent floodplain combine to slow down and spread out peak flood flows. In this situation flood volume is more important than peak flow as a factor in evaluating flooding impacts. Future development in May Valley will occur primarily outside the valley's floodplain and accompanying wetlands. Under current conditions, effective impervious area is approximately four percent in May Valley (Figure 5-1). This is expected to increase to about ten percent. However, ten percent is still low for the future full build -out condition, compared to other parts of the basin. In addition, the valley subcatchments are fairly small compared to the upland tributary systems in the Highlands and the Plateau. As a result, future contributions to increased flood flows from within the valley itself will be Chapter 5 Hydrology 5-41 relatively insignificant. Most of the increased flooding impacts in the future in May Valley will stem from development on the hills that surround the valley. Mitigation will be ineffective at reducing flood peaks and volumes in May Valley. The mitigation effectiveness percentage for the 10-year flood is expected to be less than 15 percent (Table 5-4). Most of the expected development in the upper portions of the basin that drain to May Valley will be single family low density housing (less than one dwelling unit per acre), and no mitigation is currently required for this development density. In addition, even where detention is required, its success in reducing May Valley flooding would be somewhat questionable. May Creek in the valley peaks long after the contributing tributaries. Delayed flows from these steeper streams would still contribute substantial flood volumes to the valley; depending on the timing of the releases, this could delay but not significantly reduce the flood peaks in the valley. This effect will require further study in the basin plan, as it will be an important part of determining the potential success of any solutions to May Valley flooding. Above the SR-900 Crossing The three major forks of May Creek join together in the valley floodplain above the SR-900 crossing. The East and South forks join first, in the floodplain and wetland bounded by SR-900 to the west, and by SE May Valley Road to the north. The timing of these two major tributaries differs; the East Fork peaks quickly during flood events, while the South Fork flows are extremely delayed and attenuated by Lake Kathleen. Less than one -tenth of a mile further downstream, and immediately above SR-900, the North Fork merges with the other two streams. The North Fork is flashy like the East Fork. The contributing drainage area above this confluence is 3.3 square miles, 23 percent of the basin total. It is here that the significant May Valley storage begins to considerably attenuate flows. The travel time down the valley from this point is considerable during major storms, allowing high volumes from the other upper basin tributaries to combine with these flows to produce high stream volumes in May Creek; these volumes then reside there for a prolonged period. Many of the reported flooding problems in this upper valley area relate to flat topography and ineffective localized drainage; this is discussed in more detail in Chapter 6: Flooding. SR-900 to 164th Avenue SE In the reach from SR-900 to 164th Avenue SE, two additional major tributaries add flood volume to May Creek during storms. Cabbage and Country creeks combine just below SE May Valley Road, and flow as one stream into May Creek at RM 6.5. Additional runoff from Hendrix Creek and other minor tributaries and swales also enter May Creek above 164th. Of the high runoff -producing Highlands tributaries, only Long Marsh Creek has not entered the mainstem by 164th. The total contributing area to May Creek at 164th Avenue SE is 5.62 square miles, 40 percent of the basin total. Chapter 5 Hydrology 5-42 Flow peaks through this reach are significantly attenuated by the substantial storage of floodwaters in the valley floodplain. This storage reduces flood peaks, and dampens the increase in peaks that occurs with changing development. However, the volumes being contributed from the headwater areas (principally the Highlands streams, but also the East Renton Plateau) increase significantly as development occurs. These volumes fill the valley in these low gradient reaches, and require a long time to recede. Thus, the duration of flood flows increases substantially. At 164th Ave. SE, water begins to exceed the capacity of the channel at an elevation of approximately 317.5 feet (at a flow equivalent to a forested 1.05-year flood event). Under current conditions, the expected amount of time this elevation would be exceeded increases 34 percent from predevelopment conditions. Under future mitigated conditions, the duration increases another 43 percent (total increase of 77 percent over predevelopment). Thus, the number of hours that flooding of this portion of the valley occurs has increased dramatically, and will increase much further in the future. This increase in duration is much more significant than the increase in peak flows. Similar increases in flood durations are experienced for higher flows; these flooding durations are described further in Chapter 6: Flooding. Flow durations provide a useful means of examining the relative behavior of different tributaries in the basin, as well as May Creek itself. The forested 25-year flow threshold provides a useful example of this. Current conditions streamflows along the tributaries in this reach do not exceed their forested 25-year flow values for more than 6 hours over the entire period of record, except for Lake Kathleen which exceeds its threshold for a total of 38 hours. This relatively small number of hours exceeded for the East Fork, the North Fork, Cabbage Creek, and Country Creek demonstrates the flashiness of these streams in response to rainfall. They rise and fall very quickly. By contrast, in May Creek the forested 25-year flow threshold is exceeded for 44 hours under current conditions. This longer period of high flow on the mainstem compared to the tributaries also demonstrates the attenuation effects of the floodplain. The floodplain storage slows down the flood flows and spreads them out over a longer period of time. This is in contrast to the flashy response of the above -mentioned tributaries to rainfall. This is significant in that, during a storm event, the tributaries will often tend to peak long before May Creek —the mainstem peaks in response to the maximum volumes contributed by the tributary streams over the course of a storm event (e.g., a two-day or longer period). 164th Avenue SE to 148th Avenue SE In the reach between 164th Avenue SE and 148th Avenue SE, the dominant characteristic is again the low gradient floodplain that provides significant storage of floodwaters. As discussed above, most of the major tributaries to the May Valley have already contributed their flows by 164th. In this reach, Tributary 0291A and Long Marsh Creek enter May Creek. The first of these contributes far less flow volume than the Highlands streams on the other side of the valley. The second, Long Marsh, is one of the largest flow -producers in the basin, but its confluence with May Creek is just above 148th, so it has little affect on most of this reach. In addition, Long Marsh is the least Chapter 5 Hydrology 5-43 urbanized of all the May Creek tributaries and will remain that way under future land use conditions, so it has extremely little impact on changing flooding conditions in May Creek. The storage that occurs in the valley both above and below 164th Avenue SE leads to increased flood durations as described above, but it is important to remember the significance of the dampening effect on downstream flood flows. Flood peaks actually increase very little in the reach from 164th to 148th (sometimes they -even decrease). 148th Avenue SE to Coal Creek Parkway SE The reach from 148th Avenue SE to Coal Creek Parkway SE is the transition from the May Valley to the canyon below it. The area around 148th is still low gradient with substantial storage, but the channel steepens and becomes confined as it approaches the Coal Creek Parkway SE crossing. The only significant tributary in this reach is Greene's Creek, which contributes relatively minor flow quantities to the valley floodplain. The upstream flooding and resultant storage leads to extremely dampened flood peaks in this part of the valley. For instance, the number of hours exceeding the forested 25- year flow threshold increases as floods move down the valley. The number of hours at or above this flow level is 14 percent greater at 148th Ave. SE than at 164th Ave. SE, and increases 20 percent further at Coal Creek Parkway SE. This increase in the number of flood hours in the valley is the result of the floodplain storage which serves to spread out the peak flows. This results in longer periods of inundation in the valley but smaller downstream floods through the canyon and at the delta in the Lower Basin. Removal of significant valley storage would result in higher flood peaks in the canyon and at the delta. LOWER BASIN The Lower Basin consists of the mainstem of May Creek downstream of May Valley, and its highly urbanized tributaries. May Creek itself flows through a confined canyon prior to dispersing into the delta area, which begins just downstream of Interstate 405, and eventually to its mouth at Lake Washington. The major tributaries that join May Creek in the Lower Basin are Honey Creek (0285), Boren Creek (0287), Gypsy Creek (0284) and Newport Hills Creek (0286). The UAD values for the Lower Basin's tributaries show that under forested conditions the flood flows in this subarea were relatively small (30 to 46) compared to other parts of the May Creek basin. This resulted from a combination of less precipitation in the Lower Basin and a relative abundance of outwash soils, which have a high capacity for infiltration. The predominance of outwash makes this area particularly sensitive to land use changes, as previous mitigation requirements (especially pre-1990) have not effectively replicated this high infiltration capability if lost to development. Chapter 5 Hydrology 5-44 The Unit Area Discharge values for current and future conditions reflect this sensitivity to land use change. UAD values for the tributaries are significantly greater than under predevelopment conditions; for instance, current land use conditions have resulted in values between 50 and 90. The amount of cleared and impervious area has increased tremendously to date in this part of the basin. The eight largest subcatchments (of fourteen) have EIA's over 9%. In the future, these flows will increase even further, although not by as much of a percentage as elsewhere in the basin. Much of the significant urbanization has already occurred here, and future development will be at sufficiently high densities that mitigation will be required, and this mitigation is expected to be reasonably successful at maintaining current flows. An exception to this is in the Lake Boren tributary area. Mitigation tends to be ineffective in stream systems that are already highly dampened, like Lake Boren. The required retention and detention lessens peak flows by delaying the release of flood volumes into the stream system and the lake. Since the lake delays flows anyway, the additional reduction in the peaks due to mitigation is not sufficient to reduce flows downstream of the lake substantially. The natural dampening of the lake tends to reduce future flow increases anyway though, so Boren Creek flow increases are less than in other Lower Basin tributary systems. May Creek itself in the Lower Basin is in a steep confined canyon that has few buildable sites, and thus very little impervious area. The Canyon subcatchments, however, also include the local drainage to May Creek from above the canyon walls, and these areas are highly urbanized. Thus, increased flows in this part of May Creek are a result of all these upstream inputs, from the Lower Basin tributaries and localized drainage, as well as the entire upper half of the May Creek basin. Honey Creek The area draining to Honey Creek forms the second largest tributary area in the May Creek basin, and the largest draining to the May Creek canyon. The stream drains major commercial areas along Sunset Boulevard NE in the City of Renton. The upper portions of the Honey Creek drainage are located on the flat, upland area south of the canyon, and lower Honey Creek flows through a deep canyon itself prior to its confluence with May Creek. The hydrologic conditions of upper Honey Creek are very similar to the streams that drain the plateau farther to the east. The Honey Creek tributary area is highly developed, and the canyon it flows through shows evidence of the stream's increasing flood flows. The Honey Creek canyon was likely more stable under predevelopment conditions than it is today, due to a variety of dampening upstream effects, such as wetlands on the plateau that have now largely been eliminated. Honey Creek cuts through an outwash area on its way to join May Creek in the canyon, and its channel is highly erodible, so it is particularly susceptible to the effects of altered hydrology. Chapter 5 Hydrology 5-45 In the Honey Creek subcatchments the current condition effective impervious area ranges from 13 to 31 percent, with the middle subcatchment the highest at 31 percent. Within the May Creek basin this high EIA value is equalled only by the subcatchment at the delta alluvial fan. All flood flows have already increased dramatically in Honey Creek, as compared to forested conditions (see Table 5-8), this has led to changes in stream morphology, as described in Chapter 7: Sediment Erosion and Deposition. Four streams in the May Creek basin have seen their Unit Area Discharge values more than double; Honey Creek is the largest of these. The area draining to Honey Creek is closer to its full buildout land use than most of the basin, and the future development that does occur in the Honey Creek subcatchments is expected to be at high enough densities to require mitigation. Thus, Honey Creek future mitigated flows are not much higher than current conditions flows. Mitigation is expected to be relatively successful here in minimizing future peak flow increases in the Honey Creek subcatchments; however, it will not reverse the current flow increases that are already extremely significant compared with predevelopment conditions. The ultimate percentage of developed land in the Honey Creek tributary area will be higher than in any other May Creek tributary, with EIA eventually over 30 percent in the entire tributary area. Much of the additional development, especially in the middle Honey Creek subcatchment, the most urbanized of the three, will be single family high density and commercial building. No other tributary will have an EIA over 20 percent. Boren Creek The Boren Creek system, which includes Lake Boren and China Creek, enters the May Creek canyon from the north side. China Creek drains Newcastle Hills and the western slope of Cougar Mountain prior to discharging to Lake Boren, a small lake (17 acres), located near the May Creek basin boundary, south of Coal Creek. The land around the lake is relatively flat and highly developed. The lake's outlet at its south end is called Boren Creek (0287). Boren Creek cuts down through the hillside to reach the May Creek canyon approximately 0.2 miles downstream of the Coal Creek Parkway SE crossing of May Creek. The Lake Boren subcatchments also have high effective impervious area values. The Boren subcatchment EIA values range from 9 to 13 percent, primarily due to development around the lake. This development has caused major impacts to the lake and downstream properties. Boren Creek is not entirely built out, and mitigation may not be as effective for anticipated future development as elsewhere in the Lower Basin. Large flow increases have already taken place as a result of land use changes, and further increases are expected. Unit Area Discharge values have increased from 30 cfs per square mile to 50 at the mouth of Lake Boren, and are expected to increase to 64 in the future. These values are among the lowest in the May Creek basin, so given the size of its contributing area, Boren Creek does not experience very high flows. These flow increases have direct implications for the stream morphology, though, as well as drainage and flooding problems. These effects are described in Chapters 6 and 7. Chapter 5 Hydrology 5-46 Table 5-8. Lower Basin Flow Frequencies Demonstrate that Urbanization Affects both Current and Future Flows in the Subarea. 2-yr storm 100-yr storm Tributary/ For. Cur. Fut. For. Cur. Fut. Comments Location Mit. Mit. Honey Creek 20 63 69 59 109 113 This stream delivers the largest stormflow to May Creek in the Lower Basin. It is highly urbanized, and current flows show large stormflow increases. Relatively little additional increase is expected in the future. Boren Creek 21 36 42 60 103 137 This is a significant, and already highly urbanized tributary. Significant areas remain to be developed in the subbasin, and consequently large flow increases are anticipated for the future. Newport Hills 6 12 14 16 31 34 This is the smallest modeled Creek tributary in the basin. Flow increases are large, but the volume is small and will have only a minimal effect on May Creek. Gypsy Creek 6 16 18 16 38 44 Another small tributary. Its flow increases are large, but again the volume is small and will only have a minimal effect on May Creek. May Creek at 173 208 243 482 582 706 These flows in the upper canyon Coal Creek have been attenuated by storage Parkway SE in May Valley. May Creek at 223 341 391 636 835 1,059 As in the upper canyon, mouth stormflows here are diminished by the significant storage and attenuation provided in May Valley. Inputs from Lower Basin tributaries are important in determining the peak flows. Chapter 5 Hydrology 5-47 Lakes typically dampen downstream flood flows due to their relatively large storage volume compared to the inlet and outlet stream channels. Some dampening effect is provided by Lake Boren, but this is not as evident as with Lake Kathleen, due to the much smaller surface area (and active storage volume) relative to the size of the contributing area. As a result, the downstream channel (Boren Creek) shows only a slight decrease in UAD values compared to the upstream area. At Lake Boren the current condition UAD value is 52; downstream at the confluence with May Creek it is 50. This minor dampening effect is due to the lake's small surface area (17 acres) and the additional runoff from land downstream of the lake that drains into Boren Creek. Boren Creek also experiences some natural flow dampening compared to the neighboring Highlands tributaries, due to the moderate slopes that predominate, the wetland complex of the Wetland 4 subcatchment, and the outwash soils of the lower stream. Newport Hills and Gypsy Creeks Newport Hills and Gypsy creeks are the two smallest modeled tributaries in the basin. They lie in narrow drainages to the west of Boren Creek, and enter May Creek in its canyon. Both streams are short and steep, and tend to peak very quickly during storm events. Peak flows on these streams have only a marginal effect on flood flows in the Lower Canyon, as they peak prior to the May Creek flood peak, and they contribute little volume. The headwaters and tributary areas of these streams are quite urbanized, though, and the streams have experienced significant percentage increases in flood peaks; Unit Area Discharge values for both streams have doubled from forested to current conditions. These values are expected to increase somewhat further with increased development, although mitigation is expected to be more effective here than in any other part of the May Creek basin. May Creek Canyon The May Creek canyon and the delta below it are the eventual recipients of all the runoff that occurs throughout the basin. Flows in the canyon are the result of a complex set of factors, including the extensive storage of floodwaters in the May Valley, which dampens and delays peak flows from the upper half of the basin, and the relatively fast response of the tributaries of the Lower Basin itself, including the highly urbanized Honey and Boren creeks. As described above in the discussion of the January 1990 storm, it is not uncommon for flows in the canyon to peak before those in the May Valley, so that the flood wave is already receding as maximum flows from above begin to cycle through the canyon. Prior to any development in the basin, the stream channel through the canyon was probably well-defined and stable compared to current conditions. This was due to less fluctuation in the streamflow through the canyon, together with stabilizing influences Chapter 5 Hydrology 5-48 such as the existence of large amounts of woody debris from fallen trees, stable vegetation in the basin, and upstream wetlands in May Valley that dampened downstream flood flows even more than today. As a result of these stabilizing influences, large and widespread erosion was much less common. Downstream of the canyon area May Creek spreads out across a delta. The area of the delta available to the stream was much larger in predevelopment times, and was a zone of active channel movement, with the stream migrating from north to south before entering Lake Washington. Peak flows were dissipated as they spread out across the fan. It was not possible to represent this situation in the predevelopment HSP-F model. Although the hillslope areas outside of the canyon have experienced extensive urban development, in some ways, the canyon itself has not changed much from its predevelopment condition. It is too narrow, and its side walls too steep and unstable, to accommodate much development. However, increased peak flows from the tributaries that cut through the side walls have increased erosion in the canyon. This sediment has been moved by the stream to the delta near its mouth, where it settles out along the Lake Washington shoreline. Increased canyon erosion means increased sediment deposition at the mouth (see Chapter 7: Sediment Erosion and Deposition). Dredging at the Barbee Mill property has provided temporary reductions in this sediment accumulation; however, this is very maintenance -intensive, and requires a large ongoing commitment of resources. The majority of the development that has occurred to date in the Lower Basin is in the Boren and Honey Creek tributary areas and on or adjacent to the delta. The additional runoff produced by the development on the delta adds a relatively small amount to the peak flows traveling down the mainstem of May Creek. As a result, development in this portion of the subarea causes few hydrologic and flood -related problems to the mainstem of May Creek. However, localized flooding outside of the creek's floodplain does occur due to an undersized local conveyance system; drainage of this local runoff to May Creek or Lake Washington is inefficient. This situation will be discussed in more detail in Chapter 6: Flooding. Future development in the Lower Basin will be limited to areas outside of the canyon. Consequently, any expected increases in flood flows will result primarily from increased peak flows entering the canyon from May Valley and the two major Lower Basin tributaries, Boren Creek and Honey Creek. Medium and high density single family developments are expected in the Lake Boren subcatchments. High density single family and commercial development are planned for the Honey Creek subcatchments. Some additional development is also expected for the delta area downstream of the canyon. 5.6 KEY FINDINGS • The Highlands tributaries drain twice as much surface area as those on the East Renton Plateau, yet contribute four times as much flood volume to May Valley. In spite of its currently high percentage of forest cover, this area of relatively high Chapter 5 Hydrology 5-49 rainfall, thin soils, and steep terrain contributes disproportionately large peak flows, storm volumes, and sediment loads. • In the future, flood peaks and volumes generated by the Highlands subarea are expected to increase substantially (from 20 to 50 percent) as a result of the replacement of roughly half of the current 81 percent forest cover by low -density rural development. These increases in flood peaks and volumes are expected to significantly increase the frequency and duration of flooding in May Valley. • Storage of floodwaters in the May Valley is extremely important in the hydrologic functioning of the basin. The valley floodplain fills in response to incoming floodwaters from its tributaries, but peak flows are highly delayed due to the low gradient and substantial storage. During a storm, this flow volume builds up slowly in the Valley until May Creek eventually reaches its flood peak, as much as half a day after the tributaries. Floodwaters in the Valley then take a similarly long time to recede. This long residence time of floodwaters in May Valley also directly contributes to reduced flow levels along the lower mainstem of May Creek in the canyon and at the delta. Removal of substantial storage in May Valley would cause downstream flood flows to increase. • Current drainage regulations for new development will not prevent significant increases in tributary flood flows because they do not require R/D ponds for most low -density single-family residences, or for conversion of forest land cover to grass. Thus, peak flows will increase as much as 70 percent for a 2-year event in tributary subbasins that will undergo substantial low -density rural development. • Increases in May Valley flooding that would be caused by future land development with no R/D mitigation can only be reduced by about 15 percent if R/D ponds are required under current regulations. But even if R/D ponds were required for all future development, their effectiveness in reducing May Valley floods would still be limited because R/D ponds would not reduce the volume of storm runoff delivered to May Valley. • Future flow increases in the lower tributaries are not expected to be large because much of the potential development (and resultant flow increases) has already occurred, and the remaining development is expected to be at high density and include R/D mitigation. • Under current conditions all of the tributaries to May Creek have mean annual flows less than five cfs. The mainstem of May Creek from the SR-900 crossing at the upper end of May Valley downstream to the mouth has a mean annual flow greater than five cfs. May Creek has a mean annual flow greater than 20 cfs below the confluence of Honey Creek. Chapter 5 Hydrology 5-50 Chapter 6 Flooding Chapter 6 Flooding 6.1 INTRODUCTION The flooding discussion presented in this chapter is based on the hydrologic and hydraulic analyses of the May Creek mainstem, analysis of the capacity of important tributary culverts, and a review of flooding problems identified by the public, government agencies, and project staff. Much of the discussion builds on the results of the hydrologic analysis presented in Chapter 5: Hydrology. The results of the analysis confirm that several homesites in the May Valley are flooded frequently enough to be considered significant from a County -wide perspective. Poorly located development and loss of floodplain storage, together with silting of the dredged drainage channel, are identified as the principal causes of current problems, but increased runoff due to new development will be the principal contributor to increased and new problems in the future. 6.2 FLOODING CONCEPTS In human terms, flooding is usually considered an unusual, high flow occurrence accompanied by damage. However, in geologic terms, flooding is a cyclical, predictable process that helps to define a river or stream's characteristics. Flooding is not naturally hazardous. Flooding becomes a hazard only when it threatens public safety or damages structures, roads, or other human -built objects in its path. Flooding is essential to the health of the natural system that has evolved in May Creek's floodplain habitat, providing a source of nutrients to the stream's plants and animals, as well as the energy needed for the stream to change its shape and location to more efficiently provide a stable environment between floods. Further discussions of the stream's habitat and flooding's impact on it are provided in Chapters 7: Sediment Erosion and Deposition and 9: Aquatic Habitat and Fisheries. There are two types of flooding observed in the May Creek Basin. "Drainage problems" are localized, generally affect only a few property owners, and are directly related to components of the constructed drainage system; that is, the pipes, ditches, and culverts that convey water to the streams. This type of problem can be caused by short, high intensity rainfall that produces runoff. Upstream development, with its accompanying increase in cleared areas and impervious surfaces, increases the amount of runoff beyond that which would naturally occur. As a result, natural surface drainage paths are insufficient to handle the volume and rate of runoff. In many cases, designed storm sewer systems (ditches, pipes, and culverts) are also inadequate to handle the additional runoff. Properties in low spots and adjacent to drainage systems flood as a result of the excess water spilling out of these drainage ways. Damage is relatively minor, and public facilities (roads, bridges, etc.) are rarely threatened by these drainage Chapter 6 Flooding 6-1 problems. Such drainage problems are distributed throughout the entire basin, and are usually associated with areas that have high levels of development. The second type of flooding is regional flooding. Regional flooding affects numerous properties and has a higher potential for causing significant damage. Regional flooding typically results from long periods of heavy rainfall throughout the basin, and produces large quantities of runoff in all of the tributaries to May Creek. The tributary flows combine as they join May Creek, and can exceed the capacity of the mainstem's channel and cause flooding across May Valley. The entire valley floor is affected by this type of flooding. Eventually the floodwaters move through the valley and down the canyon, causing additional damage before entering the delta at the stream's mouth and flowing into Lake Washington. Regional flooding occurs less often than localized drainage problems, but results in greater damage. In the May Creek basin, regional flooding is limited primarily to the May Valley and the canyon in the Lower Basin Subarea; although there is some potential for flooding in the vicinity of Lakes Kathleen and Boren. Road overtopping due to an undersized bridge or culvert can be considered either a drainage or a flooding problem, depending on whether the affected road is an important transportation route. For consistency in this chapter, culverts are discussed as drainage problems. 6.3 DATA COLLECTION AND ANALYTICAL METHODS DATA SOURCES Information regarding flooding in the May Creek basin was gathered from a variety of sources. These sources include public complaints about flooding problems reported to the King County SWM Division's Drainage Investigation and Regulation (DIR) and Facilities Maintenance units, and to the City of Renton Stormwater Utility; Washington State Department of Transportation (which identified existing and potential drainage problems along State Route 900—WSDOT, 1992); Federal Emergency Management Agency (FEMA) flood insurance claim records; and other sources. This information has been summarized in the table in Appendix A. In addition, project team members walked the mainstem of May Creek and much of the tributary streams. Information was compiled at all locations where flooding problems were known or suspected. This information was added to the data sources noted above. ANALYTICAL METHODS Description The mainstem of May Creek was hydraulically modeled using the HEC-2 Water Surface Profiles computer program (U.S. Army Corps of Engineers Hydrologic Engineering Center, 1991), which is a one -dimension backwater model. Results are dependent on Chapter 6 Flooding 8-2 the accuracy of the input survey data, cross section locations, assumptions regarding flow intensities and timing, and the selection of roughness coefficients and entrance and exit losses. The model cannot represent the effects of time -varying flows, lateral flow, or the effects of overbank storage. Where possible, the HEC-2 model was constructed using information collected for FEMA's flood insurance study of May Creek (FEMA, 1989) and supplemented with additional field surveys conducted in 1993 (INCA, 1993; King County, 1993). The additional field surveys were cross sections of the floodplain, taken perpendicular to the direction of flow. Two distinct HEC-2 models have been created for this study, one for the May Valley, and one for the lower reaches of May Creek, through the delta and the lower part of the canyon. The Lower Basin model begins at the mouth and extends upstream, past the Gypsy Creek confluence to RM 2.0. Between RM 2.0 and Coal Creek Parkway SE, May Creek is too steep to be modeled using HEC-2. The model for May Valley begins at the upper end of the canyon at Coal Creek Parkway SE, continues to the confluence of the North, East, and South forks of May Creek above SR-900, and then follows the North Fork upstream to SE 109th St. This modeled portion includes May Valley and is the part of the basin most susceptible to property damage from flooding. In addition to predicting and helping to describe and analyze flooding, the HEC-2 results were also useful in studying sediment transport and impacts to riparian habitat. The model generates a variety of output information, including water surface elevations, flow velocities, stream cross section area, and the horizontal extent of the floodplain for any given streamflow. May Creek tributaries were not modeled using HEC-2 because they have relatively steep slopes and do not suffer from backwater flooding. Most flooding in the tributary areas results in localized drainage problems outside of the stream channel system and will be discussed separately from the HEC-2 results. Capacities of culverts at the major road crossings in the basin were determined, using standard culvert analysis methods. Data and Model Sources For the analysis of the May Valley, FEMA cross sections were used where possible. Where FEMA surveys were not sufficient or there were concerns that a cross section may have changed since the FEMA survey, additional surveys were conducted by INCA Engineers. The locations of these sections are listed in Table D-1 in Appendix D. The survey included the geometry of bridges and road embankments, so that the effects of these structures could also be computed. For the lower portion of May Creek, from the mouth through the canyon of the Lower Basin, the HEC-2 model used in the FEMA flood insurance study was unavailable. The model utilized here was therefore created especially for this study, based on survey data collected by INCA and SWM. Chapter 6 Flooding 6-3 Peak streamflows at various locations along May Creek were entered into the HEC-2 models based on HSPF-computed results. HEC-2 was then used to compute flood elevations along the stream channel, for both current and future land use conditions: a detailed summary of the results is included in Tables D-1 and D-2 in Appendix D. The HEC-2 model was used to compute water surface elevations throughout the floodplain for several recurrence intervals, from 2- to 100-years. In the May Valley Subarea, where FEMA's original HEC-2 model was used, but modified to reflect the information described above, the modifications were relatively minor and should be viewed as refinements to the original FEMA work. Additional data required for hydraulic modeling includes estimates of the channel and floodplain roughness (resistance to flow), in the form of roughness coefficients (Manning's "n" in the Manning's flow equation), as well as contraction and expansion coefficients. Appropriate coefficients were selected based on field observations and literature values. Additional information came from topographic maps, field notes, and photographs of vegetation and bank conditions. Calibration Measured high water marks along May Creek were unavailable for use in calibrating the HEC-2 model. When available, such measurements are useful in checking the model's ability to correctly compute water surface elevations based on the local floodplain conditions. Calibration of the model is conducted by increasing or decreasing the channel and floodplain roughness coefficients (Manning's n values) to raise or lower water surface elevations. Contraction and expansion coefficients can also be varied to better approximate actual bridge and culvert entrance and exit losses in order to match backwater conditions at these locations. Although it was not possible to calibrate the HEC-2 model, there was verification that the original FEMA HEC-2 model (for the May Valley) contained no gross errors or mistakes. The original HEC-2 model was developed for the flood insurance study by an independent contractor, and then reviewed by FEMA prior to acceptance of its results. The FEMA model was considered sufficiently accurate at that time for flood insurance determinations, and for floodplain management. The revised model created for this study has been improved through the incorporation of HSP-F flow data and more recent cross sections in some locations. In addition, this revised model incorporates both current and future land use information, and can therefore be used to examine the relative differences in floodplain width and elevation between different land use scenarios. For the lower basin model, a sensitivity analysis was performed, to examine the effects of changes in roughness coefficients and other modeling parameters on computed water surface elevations. Based on this analysis, the results should be considered accurate to plus or minus one foot, for the range of flows that were used. Chapter 6 Flooding 6-4 6.4 BASINWIDE CONDITIONS In this chapter, the term "flooding" is used to specify situations where May Creek, one of its named tributary streams, or one of the two major lakes in the basin, has been observed or is predicted to overflow the channel banks and inundate adjacent properties. Flooding is most commonly observed in May Valley when streamflow in May Creek exceeds its channel capacity and spreads out across the valley floodplain. As described above, in situations where localized flooding is caused by surface runoff, or natural and/or artificial drainage conveyance systems such as minor unnamed tributaries, ditches, pipes, and culverts, the phrase "drainage problem" is used in place of "flooding." This is done to distinguish stream or lake flooding that affects many properties from localized problems that may impact only a few properties. CURRENT CONDITIONS Development activities to date have increased the number and extent of observed flooding and drainage problems in the basin. As discussed in Chapter 5: Hydrology, additional runoff from clearing and increased impervious areas in all parts of the basin has resulted in an increase in the number and size of reported problems due to overflowing streams and overburdened drainage systems. In addition, modeling and observation suggest that the May Valley is an historic floodplain that was commonly inundated even under predevelopment conditions. Thus, the past practice of filling and building in the natural floodplain is a principal cause of many of the problems in the May Valley. Valley Flooding The major flooding problem in the May Creek basin is along the mainstem of May Creek in the central valley. The valley is a natural floodplain that was commonly inundated even before any development took place. Historic construction in this area, with placement of residences and properties in the valley wetland/floodplain complex, has resulted in occasional damage to private structures and flooding of pasture land. In addition, development has occurred on the hillsides surrounding the valley, in the East Renton Plateau and Highlands subareas. This development, and the accompanying replacement of vegetation with hardened surfaces, has resulted in additional stormwater running off of the landscape and flowing into the valley. Thus, flooding conditions have worsened over time. However, analysis indicates that peak flows in the valley itself have increased only moderately since development of the uplands has begun. Flow increases from predeveloped to current conditions are only on the order of 15 to 20 percent in the May Valley (as compared to 30 to 50 percent in the May Creek canyon in the Lower Basin). Flooding in the valley, however, is not solely determined by the size of the peak flows. It is also a function of floodwater volumes and flow durations. Several properties experience pasture flooding and ponding of long duration (sometimes on the order of Chapter 6 Flooding 6-5 months) nearly every winter. The valley floor becomes saturated, and the low gradients of the floodplain overbanks do not permit drainage to occur efficiently. Similarly, when major storm -related flooding occurs, the floodwaters recede very slowly. It is this duration and frequency of even low -depth flooding. rather than the size of flood peaks, that has increased substantially over the years as development of the upland areas has occurred. Thus, there are two categories of flooding in the valley: occasional storm -driven inundation, which is widespread; and chronic localized ponding of long duration. These two categories are different but interrelated. Effects of Development and Alterations to Natural Drainage Systems Drainage problems can be found throughout the basin wherever natural drainage pathways have been altered, obstructed, or overloaded. Many of these drainage problems are further compounded by uphill development and accompanying replacement of vegetation with hardened surfaces. This results in additional runoff that overflows existing drainage systems. The excess water can inundate residential yards and basements prior to reaching a stream channel. This type of drainage problem is usually localized, and only a few private properties may be affected. Often, the effects of the altered downstream system do not become significant until upstream development creates increases in flow delivery. This combination of circumstances often results in an observable problem that increases in size and frequency, often leading to a citizen complaint. Culverts Another category of drainage problem is water backing up behind undersized or plugged culverts. A review of the drainage complaints received by the County and City shows that this is not a common problem, but does exist where relatively small drainage courses cross roads. The ponding of water that results usually impacts only one or two adjacent properties and in some situations there is flow over the road surface. Frequent roadway flooding can become an access or public safety issue and should receive a high priority for resolution. Where the ponding does not affect public safety, analysis and management recommendations should focus on the relationship between the storage provided by the ponding area and the capacity of the downstream drainage system. The problem created by the existing ponding must be compared with the potential problem caused by removal of the constriction, and accompanying loss of storage and faster release of the flood volume to the downstream system, where it could add to the existing flood problems of May Creek. A culvert capacity analysis has been done for all of the culvert locations for which a stage -storage -discharge table was created in the HSPF modeling (see Chapter 5. Chapter 6 Flooding 6-6 Hydrology). The results of this capacity analysis are shown in Table 6-1 and are discussed in each subarea section of this chapter. Table 6-1. Culvert Capacity Analysis for May Creek Tributaries Recurrence Interval River Culvert Capacity Current Future Tributary Mile Road Crossing Types/ (cfs)21 (years) (years) North Fork 0.1 SE May Valley Rd. box >328 >100 >100 Cabbage Creek 0.1 SE May Valley Rd. CMP 104 25 5 Country Creek 0.2 SE May Valley Rd. fiberglass 145 >100 >100 Long Marsh Cr. 0.1 SE May Valley Rd. CMP 177 >100 >100 South Fork 8.1 SE 134th Street two CMP 6 5 2 South Fork 7.2 SE 122nd Street two CMP 119 >100 >100 Greene's Creek 0.7 SE 100th Place CMP 43 10 5 Boren Creek 2.5 147th Ave. SE CMP 42 >100 100 Honey Creek 1.7 138th Ave. SE RCP 72 >100 50 1/ CMP = Corrugated Metal Pipe; RCP = Reinforced Concrete Pipe 2/ cfs = cubic feet per second Stream Channel Alterations The last major category of drainage problems is more commonly found in the large -lot rural areas than in the more highly developed urban and suburban parts of the basin. In these rural areas alterations to stream channels and other natural drainage pathways are sometimes made without permits or consideration of impacts to other properties. These alterations often block or alter natural flow paths, usually in order to "improve" drainage of the land for pasture or residential use. Other times these modifications are made in order to improve access or protect against future flooding of the property. Usually these alterations do not solve the problem, instead relocating it onto another property, and sometimes intensifying it. Related Conditions Secondary concerns associated with flooding and drainage problems include erosion and sediment deposition. Erosion results from higher runoff velocities and depths removing and transporting soil with the flow of water. When this happens the removal of soil damages properties over which the water flows and, in rare situations, may cause roadway or bridge failure and destruction. Eventually sediment eroded from the land Chapter 6 Flooding 8-7 surface and stream channel is deposited at locations of low velocity. These locations are found at the two lakes (Kathleen and Boren), May Valley (especially at the confluences of tributary streams), and at the delta at the mouth of May Creek in the Lower Basin. Upstream ends of culverts are also sometimes prone to deposition if floodwaters back up behind the culvert in a low -velocity pool. This sediment deposition fills in the stream channel or drainage system, clogs culverts, and otherwise damages stream habitat. Increased flooding often results from sediment deposition. Stream channel erosion and sediment deposition are discussed in detail in Chapter 7: Sediment Erosion and Deposition. Other secondary problems include water quality and fish passage problems. Water quality problems are often related to erosion problems, because sediment particles are a major form of transport for many pollutants. Additional water quality problems result from illegal dumping of debris into stream channels and flooding of septic drain fields and animal grazing areas. In each case pollutants are picked up by the flood waters and transported downstream. Eventually these pollutants end up in May Creek and/or Lake Washington. This problem is discussed in greater detail in Chapter 8: Water Quality. Fish passage problems are usually caused by 1) incorrect placement of a culvert so as to block fish passage, or 2) high flow velocities resulting from a culvert that is undersized or has been placed at a steep slope. Culverts are incorrectly placed when the bottom of the downstream end is at a higher elevation than the adjacent natural stream channel. Erosion at the downstream end of the culvert can cause this to occur. The ensuing difference in elevation produces a "waterfall" that is difficult or impossible for fish to jump because there is no resting pool at the top of the falls. Culverts should be sized and placed so that their downstream invert remains at or below the natural stream grade. Undersized culverts result in increased flow velocities that exceed the ability of fish to swim upstream against the current. Long culverts are especially a problem because fish are deprived of needed resting pools while swimming the length of the culvert against the high velocities. This issue is addressed in more depth in Chapter 9: Aquatic Habitat and Fisheries. FUTURE CONDITIONS Increased development within the May Creek basin is predicted to result in increased peak flows (see Chapter 5: Hydrology). Increased flows will cause flooding in areas where no problems currently exist. For any given flow threshold at a given point in the stream system, both the frequency and the cumulative duration of that flow will increase as well. This will increase the depth, frequency and duration of overbank flooding, resulting in greater amounts of property damage, a need for more frequent maintenance of drainage systems, and a higher risk to public safety. Predicting the location and severity of drainage problems caused by future land use conditions is difficult, because specific development activities taking place at different locations in the basin cannot be understood with certainty. However, some generalizations can be made. New drainage problems will be most prevalent in areas Chapter 6 Flooding 6-8 where new low -density single-family residential development occurs. These new problems will occur because mitigation in the form of retention/detention facilities is not currently required for this level of development. In addition, land clearing and road building associated with this development will block and/or alter many existing natural drainage pathways, possibly directing runoff onto adjacent properties and producing new drainage problems. In contrast, areas in the basin with existing high levels of development (e.g., upper Honey Creek and Lake Boren) may not experience as large a percentage increase in the number of drainage complaints by local residents. In these areas the major change from natural to artificial drainage networks (that is, storm sewer systems) has already taken place. In some cases, the existing constructed system is adequate to accommodate the current level of development; in some cases, it is not. However, the incremental increase in new development will not affect drainage pathways as much as in the low -density residential development areas. Also, mitigation requirements increase with greater intensity of development and these requirements should help to reduce new flooding and drainage problems in the smaller tributaries (as described below). As is discussed in Chapter 5: Hydrology, mitigation of future land use impacts will be most effective in preventing future problems in the tributaries and small drainage systems that feed them. Proposed mitigation measures will not be successful in reducing future flood flows on the mainstem of May Creek. Mitigation, usually in the form of detention ponds, is effective at delaying and reducing the peak of the runoff from a given development, but is not effective at addressing the increased flow volume that occurs as a result of the conversion of forested areas to grass and impervious surface. As less rainfall is retained in the forest cover, or infiltrated into the ground, the additional runoff is transported to the detention ponds, and then to the stream system, albeit at a slower rate. Thus, detention decreases the tributaries' peak flows by releasing the runoff a few hours after the natural peak has moved downstream. The overall volume of runoff is still delivered to the stream system, though, and eventually makes it way down to May Creek. May Creek peaks much later than the tributaries that feed it. Simulation of the January 1990 flood showed that the mainstem in May Valley peaked some 8 to 15 hours after the tributaries. As a result, delay of runoff from the proposed detention ponds does little to decrease peak flows along May Creek in the valley or downstream in the Lower Basin. Runoff volume affects May Valley flooding more than runoff peak flows. 6.5 CONDITIONS BY SUBAREA The flooding conditions observed in each of the four subareas are discussed below. This discussion is divided into current and future conditions. Predicted future condition results include the effects of mitigation. Chapter 6 Flooding 6-9 The Lower Basin consists of the May Creek canyon and the delta, and several tributaries Gypsy Creek (0284), Newport Hills Creek (0286), the Boren Creek system (Boren Creek, Lake Boren, China Creek)(0287), and Honey Creek (0285). Current conditions In the Lower Basin subarea flooding problems are primarily found in the area around LaKe Boren, in the lower canyon along Jones Ave. NE, and downstream in the delta area near the mouth of May Creek. Drainage problems are found along and in the subcatchments of all the tributaries. Flood flows along Lower May Creek are extremely attenuated by the storage of floodwaters in the May Valley floodplain. Storm runoff from upper basin subareas (Highlands and East Renton Plateau) is delayed, and enters the canyon after the peak flows from the Lower Basin tributaries. Reductions in May Valley flood storage (resulting from channel cleaning, dredging, tightlining, and the like) would concentrate the runoff from the entire basin into the lower May Creek stream channel during a much shorter time period, resulting in larger peak flood flows in the May Creek canyon and at the delta. Flooding May Creek delta. The commercial development at the delta has not experienced flooding in the recent past, but high flows have eroded the constructed channel banks and deposited a large amount of sediment from upstream in the basin. The January 1990 flood crest nearly overtopped the channel adjacent to the lumber holding area of the lumbermill property located at the mouth of May Creek. The recorded January 1990 flow at the mouth is considered less than a 25-year event; modeling suggests that a larger flow event could cause flooding of the mill property and possible loss of stockpiled lumber. The capacity of the constructed channel through the Mill property varies; at a minimum, it is expected that one of the private bridges on the Mill site would overtop from a 25- year flood event. The continuing sediment deposition at the mouth of the stream interferes with commercial operations and requires frequent (currently, biennial) dredging and cleanout. Without this dredging, flooding conditions could worsen here. This sediment accumulation is discussed in more detail in Chapter 7: Sediment Erosion and Deposition. May Creek canyon. May Creek in this area is highly confined within the steep canyon walls, and the narrow floodplain contains mostly undeveloped land, except in a few locations. Below the May Creek park, the flood waters are generally contained on the west and south sides of Jones Ave. NE and NE 31st Street between RM 0.4 and 1.45, Chapter 6 Flooding 6-10 except where the stream crosses to the north side of the road for several hundred yards. The modeled floodplain does not include any homes for all flows up to and including the 100-year event. This dearth of home flooding in the canyon is corroborated by the lack of past complaints of flood problems, and the lack of FEMA insurance claims. In addition to potential flooding of homes, computed elevations were also compared to elevations of major road crossings in the canyon. These results are summarized in Table 6-2. For current conditions, only the second (most upstream) crossing of NE 31 st Street, would be expected to overtop during even a 100-year flow event. This crossing, a 10' x 7' CMP arch culvert, shows signs of erosion and undermining at the upstream face, and a temporary concrete barrier has been placed along the roadway shoulder for stabilization. This situation may require remediation. Lake Boren. Flows into Lake Boren have increased as a result of development and clearing that has occurred on the surrounding hillsides, and in the China Creek drainage. This new development along China Creek has resulted in increased flood flows and sediment buildup in Lake Boren, as well as increased flow out of the lake. Immediately downstream of the lake is a private driveway that serves two homes. The driveway crosses Boren Creek with an undersized bridge. This bridge and accompanying roadway are reported to be under water during periods of high flow out of the lake due to the road surface being too low. Although the channel and bridge were not explicitly modeled, it is estimated that the bridge is probably overtopped when flows exiting Lake Boren exceed 20 to 30 cfs (approximately a 2- to 10-year flood event). Drainage Drainage problems are located in the upland areas above the canyon and in and near the delta. The worst drainage problems are located in the vicinity of the delta, where the land is fairly flat, and near Lake Boren and Honey Creek where extensive land development activities have taken place. A review of the drainage complaints recorded by the County between 1987 and 1992 (the last year for which information was available) shows that the majority of the complaints relate to channel problems and increased runoff from upstream development. Channel problems include storm sewer failures, undersized and blocked culverts, and altered drainage and channel pathways. The most important problems are described below. May Creek, near the delta. Near the delta there is a high percentage of impervious area that produces runoff, and runoff from the hillside to the northeast adds to ponding on the delta prior to runoff reaching May Creek. A drainage problem is found on the delta just north of May Creek. Runoff from the hillside above the delta flows through an 18-inch culvert under 1-405. The runoff then flows in a ditch prior to entering a 12-inch culvert under private property on the north side of May Creek. The 12-inch culvert discharges into a ditch on the east side of Lake Washington Boulevard North and the ditch empties into May Creek. During peak runoff periods the 12-inch culvert is too small to handle the flow from the 18-inch culvert. In addition, water in the 12-inch culvert backs up when the Lake Washington Boulevard N. ditch fills and cannot flow into May Creek because of high water levels in the creek Chapter 6 Flooding 6-11 itself. This results in ponding of the runoff on the private properties on the north side of the creek between 1-405 and Lake Washington Boulevard N. The Washington State Department of Transportation is currently involved in the addition of HOV lanes for 1-405; this work may result in resolution of this drainage problem. Similar inadequacies in the local drainage system exist in the "Gypsy subbasin," a 320- acre drainage located just northeast of the May Creek delta. Although the subbasin normally discharges directly to Lake Washington; during floodflows, overflow into the May Creek basin can occur in the vicinity of NE 43rd Place and Jones Ave. NE. Currently this overflow is uncontrolled, and occurs through overtopping of the roadways. The City of Renton is studying the problem (which also includes some undersized culverts between the May Creek overflow and the outlet into Lake Washington), and will be proposing a comprehensive solution within the next couple of years. One alternative will be to construct a more controlled overflow into May Creek, perhaps through conveyance south along Jones Ave. NE and directly into the May Creek channel. This alternative has not been finalized yet. Total subbasin discharges at the point of overflow range from 18 cfs for the current land use 2-year flow through 115 cfs for the future land use 100-year flow, and it's unclear at this time what percentage of this flow might be diverted into May Creek. More information is available in the City's report, entitled Gypsy Subbasin Analysis: Technical Memorandum No. 2. May Creek Canyon. Another problem of concern in this subarea is erosion of the canyon walls from piped runoff. On the south side of the canyon, runoff from residential areas is collected in storm sewers and piped to the edge of the canyon, where the concentrated flow is then dumped into the canyon. This high velocity flow scours the sandy canyon walls and causes erosion. Properties along the top of the canyon on the north side of NE 28th Street are losing land as it falls into the canyon. The soil that has collapsed into the canyon is transported by the streamflow down to the delta where it is deposited. These sediment deposits fill in the stream channel near the mouth and increase the need for dredging of the channel to protect adjacent properties from flooding. These erosion and sedimentation issues are discussed in more detail in Chapter 7: Sediment Erosion and Deposition. Gypsy Creek. At RM 0.2, Gypsy Creek is crossed by an abandoned access road (possibly once used for logging) that is constructed of loosely compacted fill. If the 48" culvert through the fill became blocked during a large flow event the fill could fail. The resulting flow could cause flooding downstream on the alluvial fan. Newport Hills Creek. At RM 0.18, Newport Hills Creek flows into a pond (inventoried as Class-2 Wetland 12) that is created by a large, abandoned railroad embankment. The pond is drained by a vertical standpipe connected to a clay outlet pipe. At the downstream end of the outlet pipe, outflows have caused lateral erosion, and some pipe has broken away, however, a video inspection of the remainder of the outlet pipe shows that it is in reasonably good condition. Flow also exits the pond via seepage through the embankment. No homes are located in the area between the embankment and the confluence with May Creek: the nearest downstream homes are adjacent to May Creek, slightly more than one mile downstream from the face of the embankment. Chapter 6 Flooding 6-12 A dam -break analysis was conducted for this structure to evaluate the potential hazard to the downstream houses in the event of a failure of this embankment. The results indicate that, if the existing outlet culvert is operating, downstream houses would not be threatened or flooded by a failure of the embankment for all reasonable rainfall and flood events up to and including the design event (an event of much lower probability than a 100-year storm) under the Washington Department of Ecology Dam Safety guidelines. Even if the outlet were to plug during such an unlikely event, potential flooding damage to downstream homes would be minimal —less than one foot in depth. Nevertheless, the potential for plugging of the outlet is an unacceptable condition because it would increase the likelihood of embankment failure, such as through a long -duration filling of the pool from seasonal rainfall. Remedial action should be taken to prevent debris blockage at the outlet. Lake Boren and Boren Creek. Flooding due to increased outflows from Lake Boren is discussed above, and is largely the result of development in the subcatchment and along the tributary streams upstream of the lake. This development has also resulted in a number of more localized drainage concerns, which are observable in and adjacent to the stream system both above and below the lake. Sediment deposits along the lake shore have been noted by residents who live near the China Creek inlet to Lake Boren. Sediment deposits are especially noticeable after major storm events. These sediments are produced by upstream erosion due to increasing runoff and poor erosion controls. There is little or no channel infilling of China Creek because of its steep channel gradient down from the ridge. But some plugging of street catch basins and culverts has been observed in the upper portion of the China Creek subcatchment. Elsewhere in the Lake Boren and Boren Creek catchments, development has produced more runoff than the drainage system can handle. Problems include runoff ponding on private property, clogged culverts, and gully erosion because of excessive runoff. In addition, at RM 0.2 on Boren Creek, a concrete culvert has separated and collapsed along Coal Creek Parkway SE. This partially blocks flow, and has resulted in significant erosion of the streambanks. Honey Creek. The largest number and most severe drainage problems found in the Honey Creek area are due to the high level of residential and commercial development found along the Sunset Boulevard NE (SR-900) corridor. This area is relatively flat, and much of it was developed prior to imposition of legally -mandated drainage requirements. Therefore, existing drainage systems provide little or no detention storage and many conveyance facilities are undersized. As a result of this lack of planning, a variety of drainage problems occur periodically throughout the Honey Creek area. Examples of this type of problem are found in both the City of Renton and in adjacent unincorporated King County. Chapter 6 Flooding 6-13 Future Conditions Flooding May Creek delta. Increased flow peaks resulting from development throughout the basin will increase the likelihood of flooding of the commercial property at the delta. Flows in the 25- to 100-year recurrence interval range are expected to increase approximately 20 to 30% In addition, removal of flood storage in the May Valley through dredging or improved flow conveyance could also lead to increased flood peaks. Similarly to under current conditions, one of the private bridges on the Mill site would be expected to overtop from a 25-year flood event. May Creek canyon. Future development throughout the basin is expected to cause flooding to increase somewhat in the May Creek canyon as well, though not enough to cause any flooding of homes. This is in spite of flow increases of as great as 27% under future -mitigated conditions. The upstream 31 st Street bridge would likely be overtopped more often under future conditions, on the order of once every 25 years (see Table 5-2). Drainage Problems Drainage problems will increase wherever new development occurs. There is already a developed storm sewer system in parts of the Lower Basin. Where there will be limited new development only a relatively small increase in the number of drainage problems is anticipated. However, large new developments will be constructed in the Boren Creek and Honey Creek subcatchments, and these land use changes will result in additional runoff and additional drainage problems. The locations of these future problems are dependent on the exact locations of the future developments, which are unknown at this time. The increased flows into Lake Boren (described above) also result in increased flow out of the lake. As discussed in the current conditions problem section, immediately downstream of the lake is a private driveway that serves four homes. The driveway crosses Boren Creek with an undersized bridge. This bridge and accompanying roadway are reported to be under water during periods of high flow out of the lake due to the road surface being too low. It is estimated that the bridge is probably overtopped when flows exiting Lake Boren exceed 20-30 cfs, which in the future will occur every two years or less. In addition, two culverts in the Lower Basin subarea were analyzed for their capacity, and found to have sufficient capacity to pass expected flows under future land use conditions. Specifically, the upper Boren Creek subcatchment tributary (also known as China Creek) flows through a culvert under 147th Avenue SE. This culvert has a maximum capacity of approximately 40 cfs, which is sufficient for the future 100-year flood (Table 6-1). Upper Honey Creek flows through a culvert under 138th Avenue SE. Chapter 6 Flooding 6-14 This culvert has sufficient capacity for the current 100-year flood, but will be limited to the future 50-year flood without mitigation (100-year flood with mitigation). MAY VALLEY The May Valley subarea is the May Creek floodplain and adjacent lower valley areas upstream of the May Creek canyon. It includes May Creek to the juncture of the three forks, the lower portions of the three forks, and portions of various small tributaries near their confluences with May Creek. Current Conditions Flooding Flooding has long been a concern in the May Valley. This subarea is a natural floodplain, characterized by extremely flat and poorly drained land in the valley itself, much of which is regularly inundated from May Creek overflowing its channel banks and from large flows from the tributaries that collect runoff from the surrounding hillsides. The valley was commonly inundated even before settlement, when the entire basin was largely forested: as development occurred, both in the valley and on the hillsides above it, this natural flooding became problematic for valley residents. The flooding problems in May Valley are concentrated along the mainstem of May Creek and are roughly bounded by SE May Valley Road on the north side of the valley and SR-900 on the southeastern side of the valley. Historically, May Creek has been channelized and sporadically dredged in order to improve flow conveyance. The legacy of these actions is that May Creek is now a straightened ditch within the May Valley, with filled -in overbanks formed from sidecast dredge spoils. Flow paths in the valley have been considerably altered from their natural form. Many sites along the stream channel, including large portions of the original natural wetland, have been filled; those that haven't been filled tend to pond with water during the rainy season, and often drain slowly. Maintenance dredging had the benefit of removing, and thereby compensating for, the large volumes of sediment that are transported from the hillsides adjacent to May Valley and which fill in the stream channel and reduce its capacity. (It also had major negative impacts to the aquatic resources of May Valley, and required an ongoing maintenance expense.) But while the dredging addressed the symptom of flooding, it did not address the root cause of the flooding problem, the filling and development of the natural floodplain. Structures were placed in the path of flooding while simultaneously much of the natural floodplain storage (side channels and wetland complex) was lost through filling and channelizing. Dredging by King County was discontinued in the early 1940s, although some private efforts may have continued as late as the early 1960s. Lacking a program of dredging or restoration of the natural floodplain, the channel has continued to fill in with sediment Chapter 6 Flooding 6-15 and now has a much reduced flood capacity, so that overtopping of the channel banks —flooding —occurs often. Floodwater Storage: Peak vs. Duration. A significant feature of flooding in the May Valley is the extended period of time in which floodwaters remain in various locations in the valley. The valley floodplain provides extensive storage volume for floodwaters, which attenuates (reduces and delays) flood peaks. However, the floodwater correspondingly remains in the floodplain for a long time period, and recedes slowly. This hydrologic functioning is discussed in more detail in Chapter 5: Hydrology. As Chapter 5 also discusses, even small amounts of development in the headwaters of May Creek (especially the Highlands tributaries, but also the East Renton Plateau) can result in significant increases in the volume of floodwater that is delivered to the valley. Because of the valley's shape and large storage capacity, the increased runoff from the tributaries has increased the length of time the valley is above flood stage more than the peak flows or flood depths. The HSP-F model results provide an indication of the degree to which flood durations have been altered by development. For example, at 164th Ave. SE water begins to exceed the capacity of the channel at a flow equivalent to a forested 1.05-year flood event. The number of hours this elevation is expected to be exceeded over a long time period has increased 34% from predevelopment to current land -use conditions. The change in the number of hours that flooding of this portion of the valley occurs has increased dramatically: this increase in duration is much more significant than the increase in peak flows. Floodplain Extent. The extent of the flooding in the May Valley was assessed using the HEC-2 model. The results matched well with those of the 1989 FEMA flood insurance study: in general, the lateral extent of the 100-year floodplain remains largely unchanged from the FEMA study, although some changes in elevations have been computed. The HEC-2 analysis of existing conditions produced flood elevations that average less than two feet higher than the original FEMA flood elevations. Due to the original FEMA map scale (one inch equals 400 feet, 5-foot contours), this difference in elevation will not result in any measurable change to the 100-year floodplain map, but it does suggest that flood depths may be somewhat greater than previously expected. The 25- and 100-year flood elevations and corresponding flood flows are listed in Table 6-2 for important points of interest in the valley. The May Creek 100-year floodplain boundaries in the May Valley are shown on Map 18 in Appendix B. These computed flood elevations and boundaries, along with the records of observations and complaints, are the basis for the following discussion of flooding in May Valley. Road Flooding. At the four major road crossings of May Creek in the valley (148th Avenue SE, 164th Avenue SE, SR-900, and SE May Valley Road) the lowest road surface elevations were compared with the 100- and 25-year flood elevations (Table 6-2). The 100-year flood is the standard benchmark for floodplain management, and is used for this purpose by both the County and the federal government. The 25-year event is commonly used by transportation departments as the design criterion for arterial roadways. Chapter 6 Flooding 6-16 Table 6-2. May Creek Roadway and Flood Elevations Based on HEC-2 Results Road 25-yr. Flood Elevation 100-yr. Flood Elevation Roadway Eleva- Current Future Future Crossings tion Mitigated Change Current Mitigated Change of May Creek (feet) (feet) (feet) (feet) (feet) (feet) (feet) May Creek Canyon and Delta L. Washington 31.7 26.6 27.1 +0.5 27.2 27.9 +0.7 Blvd. N. NE 31 st Street 101.2 97.2 97.6 +0.4 97.7 98.2 +0.5 NE 31st Street 111.4 110.5 111.5 +1.0 111.5 112.9 +1.4 May Valley Coal Cr. Pky. SE >310.0 267.4 267.8 +0.4 267.9 268.3 +0.4 143rd Ave. SE 306.3 303.5 303.9 +0.4 304.1 304.5 +0.4 146th Ave. SE 311.1 309.5 309.8 +0.3 310.0 310.3 +0.3 148th Ave. SE 310.6 310.1 310.6 +0.5 310.8 311.4 +0.6 164th Ave. SE 319.5 319.8 320.1 +0.3 320.3 320.6 +0.3 SR-9001/ 328.4 327.3 328.4 +1.1 328.5 329.4 +0.9 SE May Valley 333.0 331.9 332.1 +0.2 332.1 332.3 +0.1 Road 1/ Modeled elevations at SR-900 were based on a computer routine that has now been superseded. Further analysis suggests the elevations in this table are too high by approximately 2.5 feet due to inaccuracies in the representation of friction losses through the culvert structure. This revised analysis indicates road overtopping at SR-900 is not expected for all modeled events, up to and including the 100-year event. The computed flood elevations overtop the roadway at 148th Avenue SE and 164th Avenue SE. The roadway at 148th Avenue SE is estimated to be overtopped by about 0.2 feet of water during the 100-year flood. The bridge there is estimated to have a maximum flow capacity of 420 cfs, which is in excess of a 25-year flow with current land use conditions. Floodwaters are estimated to overtop 164th Avenue SE by approximately 0.8 feet during the 100-year flood (445 cfs). The 25-year flood (340 cfs) overtops the bridge by 0.3 feet. This bridge has a maximum flow capacity of 280 cfs, which is approximately the 10-year flood. Chapter 6 Flooding 6-17 Observations by valley residents indicate that the 148th Avenue SE roadway may actually flood at a lower flow threshold than the 164th Avenue SE bridge. Flooding of 148th Avenue SE has been observed by valley residents within the last several years, during flood events with lower peak discharges than the computed capacity mentioned above. This indicates that the model may be somewhat overestimating the capacity of that bridge structure. These observations were unavailable at the time of model calibration, and the model has not been rerun to account for this. Neither SR-900 nor SE May Valley Road is predicted to be overtopped by even the 100- year flood. The culvert under SR-900 is estimated to have a capacity of approximately 600 cfs. SE May Valley Road, where it crosses the North Fork, has a capacity of approximately 400 cfs. Roadway flooding problems are not expected at either location. Flooding of Private Structures. Aerial photographs of May Valley were superimposed on the most accurate topographic floodplain maps available (CH2M-Hill, 1986) to identify the locations of homes and other structures within the 100-year floodplain. Surveyed elevations of these structures were not available; thus, it is impossible to determine with certainty whether specific buildings are within the computed floodplain. Because the specific first -floor elevation of each home is unknown, the extent of potential damage from a 100-year flood cannot be fully assessed for individual residences. Based on the topographic data and the HEC-2 model, however, this mapping technique provides a reasonable estimate of the general extent and location of flooding problems (e.g., approximate number of structures in various areas of the floodplain). These modeling results have been compared with observed conditions and reports of complaints, and overall, there is fairly good correlation between the computed floodplain and reports of flooding. The computed 100-year floodplain includes approximately five homes and seven nonresidential structures between Coal Creek Parkway SE and the limit of study at SE 109th Street. The HEC-2 analysis shows that the lateral extent of the floodplain does not vary significantly from the 10-year flow to the 100—year flow, and nearly all structures inundated by a 100-year discharge are in the 10-year floodplain as well. Floodplain Modelling Results by Reach Coal Creek Parkway SE (RM 3.6) to 148th Ave. SE (RM 4.5). For most of this reach at the downstream end of May Valley, floodwaters up to and including the 100-year discharge are largely contained within the stream channel. Relatively few complaints and observations of flooding have been received for this area, and flooding of pastureland is minor. North Side of May Creek: one home in the computed 100-year floodplain South Side: no homes or other buildings 148th Ave. SE (RM 4.51) to 164th Ave. SE (RM 5.93). This reach includes some extensive flooding of pasture, with at least one property with floodwaters typically ponding on the order of months in the winter and spring. One home has had its crawlspace inundated during large floods. Another property has an outbuilding Chapter 6 Flooding 6-18 (stables) that have been flooded, as well as a garage, well, and septic tank that are also occasionally affected. Reed canarygrass growing in the May Creek stream channel may contribute to ponding in the lower section of this reach by increasing resistance to flow in the channel and reducing channel velocities accordingly. Field measurements suggest that such reduced drainage may result in greater flooding depths at small flows, but has little or no effect on depths for flows of the 2- to 100-year range. Removal of the weed from one 200-yard stretch in 1994 did provide some localized reduction in ponding duration. North Side: one home, at least one other building in the computed 100-year floodplain South Side: one home, no other buildings 164th Ave. SE (RM 5.93) to SR-900 (RM 7.02). There is widespread pasture and open -land flooding in this reach, and some long -duration ponding in various places. One residence has complained of difficult access to the home because of deep flooding: this particular residence is located in an obvious low spot, and has reported frequent flooding under the foundation with occasional property damage in the larger events (such as 1990). A feed store is located on fill in the floodplain just upstream of 164th, and has one or two buildings that have been flooded during large events. At least one other residence has complained of septic tank problems related to flooding. In addition, one residence outside of the 100-year floodplain receives floodwater that is actually related to an incoming tributary (Hendrix Creek), possibly with contribution of runoff from SR-900. There is also a residence that has complaints of home flooding and damage on record but maps outside of the floodplain and at the same elevation as nearby houses that do not experience flooding: this may be an error in mapping. North Side: two homes, no other buildings in the computed 100-year floodplain. South Side: no homes, but two commercial buildings on the Keppler Feed Store property in the computed 100-year floodplain SR-900 (RM 7.02) to SE 109th St. (North Fork, RM 0.67). In this area, near the confluences of the three forks of May Creek, it is difficult to differentiate the systemic flooding from the localized drainage problems. The gradient is extremely mild in this area, the overall valley floodplain is very wide, and the drainage divide between the East Fork and McDonald Creek (a tributary to Issaquah Creek) is ill-defined. Residents have suggested that alterations to natural drainage paths in this area have added to the flooding problem. North Fork of May Creek (NFK subcatchment: north of SE May Valley Road). Most properties in this area that are not on fill are within the 100-yr floodplain. A private runoff and drainage system for several short plats is not functioning properly, resulting in annual flooding of this area in recent years, with prolonged ponding of floodwaters. While the immediate cause of the flooding is blockage of the sole outlet of the drainage system by sediment deposition and filling, the root cause is the Chapter 6 Flooding 6-19 placing of these improvements in the floodplain. Furthermore, indications are that the North Fork originally meandered through here, but was channelized and diverted around to the west, so much of this area was historically adjacent to the stream. Flooding analysis for this area is complicated by the malfunctioning drainage system. One home is mapped in the floodplain, but flooding of the actual residence has not been reported to date. Flooding has been reported, however, for an outbuilding, gear stored under a house, two barns, and possibly a well. North of SE May Valley Rd: one home, two other structures in the computed 100-year floodplain East Fork of May Creek (EFK subcatchment: south of SE May Valley Road). The channel is ill-defined in parts of this area. There have been a number of private drainage modifications, including localized berming, channelizing and re-routing. Many of these local efforts have had the effect of raising the flooding probability on adjacent parcels. South of SE May Valley Rd: no homes, but one outbuilding in the computed 100-year floodplain. Tributaries' Contributions to Valley Flooding. In addition to flooding of the mainstem of May Creek, flooding also occurs where major tributaries discharge onto the May Valley floodplain. In particular, flooding has occurred in the vicinity of the confluence of Cabbage and Country creeks, below where they cross under SE May Valley Road. Cabbage Creek has been channelized and diverted 90 degrees to the west to join Country Creek: under higher flows and velocities Cabbage Creek tends to overtop the bank and run directly to May Creek, incidentally sometimes reaching the foundation of a nearby house. As noted above, flows from Hendrix Creek also periodically affect the basement of a house below SR-900, just above the 100-year floodplain of May Creek; runoff from SR-900 may contribute to the flood volume. Drainage Problems In addition to the threat of property damage from a major (100-year) flood, smaller and more frequent runoff problems can occur in this valley. As mentioned above, the valley floor east of SR-900 is very flat. The natural drainage pathways in this portion of May Valley are poorly defined. As a consequence these natural pathways are easily blocked by road building, construction, and filling of low lying properties. Each of these activities forces the flow paths to seek new routes, causing new problems. This portion of May Valley has generated more drainage complaints than nearly any other part of the basin. A review of these drainage complaints shows that the majority of the complaints relate to channel problems and runoff from development in the uplands. Channel problems include undersized bridges, vegetation blocking the stream channel, storm sewer failures, undersized and blocked culverts, and altered drainage and channel pathways. Upland development in the Highlands subarea and East Renton Plateau results in more water in May Valley. These and other important problems are described below. Chapter 6 Flooding 6-20 Land use activities in the valley also result in a variety of flooding, drainage, and water quality problems. Fill, both legal and illegal, alters the movement and storage of water in May Valley. Illegal filling of the floodplain has increased the amount and length of flooding on adjacent lands. Historically, filling in the floodplain has had significant effects on Valley drainage patterns. Additional fills add to the problem, reducing floodplain storage and forcing the water to other locations. It is well recognized that this type of activity is incompatible with good floodplain management practices. Sediment is also washed down the hillsides and dumped on the floodplain by the natural action of the tributaries. This forms alluvial fans at the tributary outlets (see Chapter 7: Sediment Erosion and Deposition). Water quality problems in the valley result from the destruction of the natural valley habitat and washoff of animal manure from land adjacent to the stream channel. Flooding of septic system drain fields also introduces pollutants into the stream. These problems are discussed in Chapter 8: Water Quality. Future Conditions Runoff from new construction and clearing of vegetation on hillsides above May Valley is predicted to result in increased volumes of floodwater into and through the valley. Peak flows will increase somewhat as well. These predicted hydrologic changes are discussed in Chapter 5: Hydrology. Peak flow thresholds in May Creek will also be exceeded more often and the depth and duration of valley flooding will increase. Increased flows and flooding frequency will result in greater and more common property damage, more frequent need for maintenance of drainage systems, and a higher risk to public safety on the roadways that cross or parallel the valley. Future predicted May Valley flood elevations are on average 0.5 feet higher than the existing conditions. As discussed above, the valley is relatively flat with steeply rising side slopes. The current conditions 100-year flood basically fills the valley floodplain, and the anticipated future increase will result in only minor increases in the width of the 100-year floodplain. Additional structures are not expected to be affected, but all those that are currently affected will be impacted more often, and for longer periods of time. The future condition 25- and 100-year flood elevations and corresponding flood flows are listed in Table 6-2 for important points of interest in the valley. As is the case for the current conditions, 164th Avenue SE will be overtopped during a 25-year flood event. In addition, modeling suggests that both 148th Avenue SE would just be overtopped by a future conditions 25-year event: its capacity is very near this flow threshold. As with the model of existing land -use conditions, this capacity may be somewhat overestimated, given recent observations by valley residents. The other two major road crossings in the May Valley, SR-900 and SE May Valley Road, are expected to remain above even the 100-year future flood elevation. More significant than the increase in flood depths or floodplain widths will be the increased volume of floodwaters expected to be delivered by the tributary systems after buildout takes place. Even with hydrologic mitigation measures taken into account, flood Chapter 6 Flooding 6-21 volumes will increase dramatically. In May Valley, this will result in property being inundated more frequently and for longer cumulative durations. For instance, at 164th Ave. SE. water begins to exceed the capacity of the channel at an elevation of approximately 317.5 feet (the flow at this stage is equivalent to a forested 1.05-year flood event). Under future mitigated conditions, this elevation would be exceeded 43% more often than currently, and 77% more often than before any development of the uplands. Thus, the number of hours that flooding of this portion of the valley occurs has increased dramatically, and will increase much further in the future. This increase in duration is much more significant than the increase in peak flows. Similarly, roadway overtopping at 164th occurs at an elevation of 319.5. The cumulative duration of exceedance of this stage has more than doubled from predevelopment to current conditions, and will double again under future mitigated. New drainage problems will be most prevalent in the eastern portion of the valley where new, low density single family residential development is planned. These new problems will occur because no mitigation is required for this level of development. Just as under current conditions, land clearing and road building associated with this type of residential development will block and/or alter many existing natural drainage pathways. This will divert runoff onto adjacent properties and produce new drainage problems. HIGHLANDS Current Conditions Drainage Problems North Fork of May Creek. The number of drainage complaints received for the Highlands Subarea is low compared to the other subareas, in large part because this area has fewer homes and other development. Nevertheless, the majority of the complaints are concerned with problems of drainage and runoff from upland development. In this subarea, any alteration of the shallow soils and steep terrain tends to increase runoff quantity and alter runoff patterns, which can adversely impact downslope and downstream property owners. Observations of residents in the North Fork floodplain is that runoff from Squak Mountain has increased in recent years, in association with new residential development and associated clearing. Recent extensive forest clearing on the upper slopes of Squak Mountain may therefore contribute additional flows to the flood -problem area of the North Fork. Conversions of forest land to low density single family residential lots do not currently require mitigation for the increased runoff from the cleared areas to the floodplain. Drainage problems have been observed along the North Fork of May Creek. This reach parallels SR-900, and much of it has been highly channelized and lined with riprap. There are several culverts of concern along SR-90& the Washington State Department Chapter 6 Flooding 6-22 of Transportation has identified at least one undersized culvert at RM 1.2. Another undersized culvert that is causing flooding and erosion problems is located at RM 1.3, under the driveway for the Issaquah Sand and Gravel stockpile. In the headwaters of the North Fork is the drainage divide with Tibbetts Creek (which flows to Lake Sammamish). Within the Sunset Quarry, quarry operations have resulted in altered drainage paths and, in some places, changed the location of this divide. In several locations, the divide is not very substantial, and is susceptible to breaching. During the January 1990 storm, part of the quarry's R/D system was overwhelmed: there was a large release that breached the divide, and sent natural Tibbetts Creek flow into the North Fork of May Creek. The North Fork bridge opening under SE May Valley Road was evaluated and found to be large enough to handle flows in excess of a 100-year event (Table 6-1). Other Tributary Areas. Analysis shows no capacity problem with May Creek's flow under SR-900. At this location the culvert has a capacity of greater than 500 cfs and is sufficiently large to handle the 100-year flood. The Country Creek and Long Marsh Creek culverts under SE May Valley Road are also sufficiently sized to handle flows in excess of a 100-year event. The Cabbage Creek culvert at SE May Valley Road (RM 0.07) has a maximum capacity of approximately 100 cfs (25-year flood). Cabbage Creek flood flows greater than 100 cfs can potentially damage SE May Valley Road. Below SE May Valley Road, Cabbage Creek has been rerouted into a 90-degree bend, which causes additional conveyance problems at high flows. Sediment and debris accumulates in the outer bank of the bend, and the stream can overflow the channel, and reoccupy its original alluvial fan area. This has caused pasture, and even basement, flooding in the past. The East Fork culvert under SE May Valley Road (RM 0.5) has not been evaluated for capacity; however, the culvert has been identified as being vulnerable to debris blockage. High flows off of Squak Mountain tend to be debris- and sediment -laden and could plug the culvert, possibly leading to road overtopping. Future Conditions Drainage Problems North Fork of May Creek. Although flow values will increase, analysis shows no future capacity problem with May Creek's flow under SR-900. At this location the culvert has a capacity of greater than 500 cfs and is sufficiently large to handle the future 100-year flood. The other culverts along the North Fork which currently have capacity problems will worsen under future land —use conditions. Expansion of SR-900 to four or five lanes will have significant impacts in this area. Runoff would be greatly increased, and due to the constraints of topography there is no way to expand the road without impacting both the North Fork (a Class-2 stream with Chapter 6 Flooding 6-23 salmon), and Class-1 and -2 wetlands. Stream relocation may be difficult, but salmonid use makes culverting the stream inappropriate. At SE May Valley Road, the North Fork bridge opening is sufficiently large to handle flows in excess of a future 100-year event. Other Tributary Areas. Drainage problems are expected to increase with future development in the Country Creek and Cabbage Creek subcatchments on the south slope of Cougar Mountain These areas currently have little or no development, but are zoned for future development at residential single-family low to medium densities. The hillside has steep. shallow soils with a natural tendency for high runoff per unit acre. The runoff generated from this hillside —even under predeveloped conditions —exceeds the developed -conditions values from all other portions of the May Creek Basin (see the discussion on Unit Area Discharge values in Chapter 5: Hydrology). Development activities that result in land clearing and road building will produce additional runoff. This additional runoff, together with alteration of the natural flow paths, is expected to produce new localized drainage and erosion problems downstream of wherever these development activities will take place throughout the Highlands subarea. The most important impact of the additional runoff from this subarea will be to contribute to the flooding problems in the floodplains of the May Valley and the North and East forks (see above). Much of the Long Marsh Creek subcatchment, on the other hand, is located in the Cougar Mountain Regional Park, and is expected to remain in forest cover. Thus, significant future runoff problems are not expected along Long Marsh Creek. The Country Creek and Long Marsh Creek culverts under SE May Valley Road are sufficiently sized to handle flows in excess of a future 100-year event. The Cabbage Creek culvert at SE May Valley Road has a maximum capacity of approximately 100 cfs, which is only equal to a 5-year flow under future land use conditions. EAST RENTON PLATEAU Current Conditions Flooding In the East Renton Plateau subarea, flooding problems are most commonly found in the area around Lake Kathleen, in the drainage of the South Fork of May Creek. Drainage problems occur throughout the subarea. Flooding occurs at the outlet at the north end of Lake Kathleen, and occasionally along the lakeshore. The rate of flow leaving the lake is controlled by two culverts under SE 134th Street: it is estimated that the maximum flow through the culverts is less than 7 cfs because the high downstream water depth controls the flow out of the culverts. When the lake reaches a depth of approximately 3.5 feet above the bottom of the culvert Chapter 6 Flooding 6-24 (an elevation of 522.6 feet), water begins to flow over SE 134th Street. On average this results from a 5-year flow (Table 6-1). The flow velocity is low, but flow over the roadway could create difficult access for residents living on the east side of the lake (although such difficulties have not occurred to date). The restricted outflow from the lake can also result in a rise in the lake level, with flooding of the shoreline areas of adjacent properties. However, the lake elevation usually fluctuates within a narrow 2-foot range. Under current conditions the lake's surface water elevation is usually between 519.2 feet (lowest mean monthly stage) and 520.8 feet (current 2-year flood stage). During periods of high inflows from the surrounding subcatchment area the lake elevation can rise above 521 feet, but rarely overtops the road at the outlet (elevation 522.6 feet). Modelling results suggest that the lake never exceeded 522.6 feet prior to development in the subcatchment, although, as noted above, this elevation currently corresponds to a 5-year flood. Drainage The density of residential development around and uphill of Lake Kathleen has resulted in a number of drainage problems. For example, along West Lake Kathleen Drive SE several residential properties have at times experienced drainage problems due to a combination of excess runoff from uphill development, the filling of wetlands and ponding sites, and the siting of homes in natural drainage paths and ponding sites. Road ditches along W. Lake Kathleen Drive SE have overflowed during rain storms because they could no longer adequately handle the volume of runoff being generated from the upland development. Most of the remainder of the East Renton Plateau has a lower density of development, and correspondingly fewer drainage complaints and problems. Generally, the problems are typical of those found elsewhere in the May Creek basin, resulting from runoff from uphill development and inadequate drainage systems. This problem has been reported in a number of residential neighborhoods. The results of the culvert capacity analysis for this subarea are shown in Table 6-1. The culverts conveying the South Fork under SE 122nd Street have sufficient capacity for the 100-year flood. As discussed above, the Lake Kathleen outlet culverts overtop with a 5-year flood. The culvert along Greene's Creek at SE 100th Place is also somewhat undersized, as it only has capacity for a 10-year flow under current land use conditions. Future Conditions Flooding In the future, flow out of the lake will overtop SE 134th Street more often (future 2-year flood) and eventually cause road stability problems. New development in the subcatchments will be primarily at low density, and mitigation to Design Manual standards will produce no significant reduction in lake stage exceedance durations. As Chapter 5 discusses, the flood storage and low attenuation provided by the lake for the Chapter 6 Flooding 6-25 South Fork and its subcatchments is extremely valuable: any effort to address roadway flooding and outlet capacity should attempt to minimize any decrease in storage capacity. Otherwise, downstream properties may be adversely impacted by greater peak flows Because of the residential development around the IaKe and the elevated level of nutrients entering the lake, the naturally eutrophic Lake Kathleen is aging more rapidly than in the past. The slow filling of the lake with vegetation and sediment (i.e., the natural progression of the lake to a wetland), will occur more rapidly. The flood storage capacity of the lake will correspondingly decrease over time. This process of lake filling will take hundreds of years to occur, even with the acceleration due to development and human activities. The aging of the lake poses no near -future worsening of shoreline flooding. Drainage As is true for the other subareas, drainage problems will tend to occur and increase on the plateau wherever new development occurs. The natural drainage pathways are not well defined and are easily obstructed or destroyed by development activities; many are small, intermittent creeks that flow only during runoff events. Therefore, it is expected that the largest increase in flood problems on the East Renton Plateau will be in areas where little or no mitigation will be required. Results of the analysis of culvert capacity at major road crossings is shown in Table 6-1. The South Fork culverts under SE 122nd Street have sufficient capacity for the 100-year flood, under future land use conditions. The culverts at the outlet to Lake Kathleen (discussed above) will overtop with a 2-year flood. The culvert at the SE 100th Place crossing of Greene's Creek only has sufficient capacity for a 2—year flood with future land -use conditions with no mitigation, or for a 5-year flood under mitigated future land - use conditions. 6.6 KEY FINDINGS • There is a potential drainage safety problem located on Newport Hills Creek. A dam - break analysis for the old railroad embankment indicates that remedial action should be taken to prevent debris blockage at the outlet: if this is done, downstream houses would not be threatened or flooded by a failure of the embankment for all reasonable rainfall and flood events up to and including the WDOE design event (which is well in excess of a 100-year inflow). • The most extensive flooding problems in the May Creek basin are found in the May Valley. This valley is a natural, historic floodplain, which was commonly inundated with floodwaters even before any development took place. Most of the current and predicted future problems are due at least as much to historic development and fill within the May Creek floodplain, as to upland development contributing more runoff to the valley. Chapter 6 Flooding 6-26 • Approximately six homes and a commercial business are located in the 100-year floodplain of May Creek, and two others are affected by tributary flows just above where they enter the floodplain. Flood velocities and depths are low, so that public safety in May Valley is not a significant issue. Much of the flooding that is experienced is of pastureland, and approximately six outbuildings and commercial structures —storage sheds, garages, animal shelters and barns —are also affected. • The width of the 100-year floodplain, and therefore the number of homes in it, is not expected to increase significantly under future land use conditions. Increased flood volumes in the valley will instead result in longer durations of floodwater inundation, greater frequency of flooding, and slightly greater flood depths. • No homes are located in the computed 100-year floodplain for the lower portions of May Creek, in the canyon and at the delta. The altered channel at the delta nearly overflowed during the January 1990 flood (approximately a 25-year event), and a higher discharge could cause flooding of the commercial lumber yard area. Future conditions flows are expected to increase by 27 percent: removal of May Valley storage would increase these flows even further. • There are several culverts and bridges at road crossings in the basin that are inadequate to convey the 25-year flow. These include 164th Avenue SE crossing of May Creek, the SE May Valley Road crossing of Cabbage Creek, the SE 134th Street crossing at the Lake Kathleen outlet, and the SE 100th Place crossing of Greene's Creek. Modeling suggests that the 148th Avenue SE road crossing has sufficient capacity to convey existing but not future 25-year flows without roadway flooding, although recent observations by valley residents suggest that the capacity may be less than modeled. NE 31 st Street would not be overtopped by the 25-year flow under current conditions; however, the expected future -mitigated conditions 25- year flow would likely cause overtopping. • Localized drainage problems throughout the basin are primarily related to alterations to natural stream channels, filling of natural detention areas, undersized conveyance systems, development with inadequate mitigation, or improper installation of drainage measures. These problems are correlated with new development, and most current drainage problems are concentrated in the more urbanized portions of the basin. • The Highlands subarea currently has the lowest number of drainage problems in the basin but is expected to have the largest percentage increase from future development. When disturbed, this subarea's steep slopes will add runoff and sediment to the tributary streams draining the south side of Cougar Mountain. This will cause some local drainage problems on the hillsides and will add significant amounts of water and sediment to the May Valley. Chapter 6 Flooding 6-27 Chapter 7 Sediment Erosion and Deposition Chapter 7 Sediment Erosion and Deposition 7.1 INTRODUCTION Erosion and deposition of sediment occurs on hillslopes and in stream channels as a natural and ongoing process, with rates dependent on climatic and physical conditions of the drainage basin. Development in a basin can drastically modify the response of the basin to rainfall -runoff by modifying the cover vegetation, soil litter, and surface topography. Changes in the way water runs off the surface alters the type and amount of water and sediment that is delivered to basin streams. Changes in channel form, substrate, and channel stability occur in response to the changes in runoff and sediment delivery. Changes to natural drainage and cover conditions have taken place in the May Creek basin over the past 150 years, influencing the channel conditions in the basin. Development of railroad grades, coal mines, roads, farms and logging began in the May Creek basin in the mid 1800s. By 1900 much of the area had been logged and several road systems passed through the basin. By the 1930s most of the basin had been logged one or more times, numerous truck farms in the flat valley bottoms were present, and major portions of the creeks had been dredged and/or moved. In the past 60 years second and third growth forests have grown up throughout much of the basin, the truck farms on the valley bottoms have been replaced by residences, livestock, and noncommercial farms, and increased development of roads and houses has occurred. The response of the hillslope and channel processes to these changes is evident throughout the May Creek basin. 7.2 WATERSHED PROCESSES To create the constantly evolving landforms within a watershed, there is a continuous process of storage, erosion, transport , deposition, and again storage of soils, rock fragments, and organic materials. These processes are generally subdivided into hillslope processes and stream channel processes. Precipitation, wind, flowing water, and gravity drive the erosion and transport of materials from the hillslopes. The power of flowing water controls how the materials delivered from the hillslopes are moved along the stream channels. The forest conditions on the hillslopes and along the stream channels and floodplains controls the aquatic habitat conditions of the basin creeks and lakes. Chapter 7 Sediment Erosion and Deposition 7_1 HILLSLOPE PROCESSES The main hillslope processes in the May Creek basin are surface erosion and mass wasting. Surface erosion encompasses many processes, with the main ones in this region being rilling or gullying, soil creep, treethrow and other forms of bioturbation, and raveling of loose materials. Mass -wasting processes include earth flow, debris flows, rockslides, and landslides. In the May Creek basin the predominate mass -wasting processes are shallow surface slumps and landslides. When eroded from the hillslopes, materials are delivered to upland hollows, to the flat valley floors, to wetlands, or directly into creeks or ditches, where the sediment can be deposited and stored for years or centuries. When eroded sediment is delivered to the creeks, it is transported downstream at rates that depend on the channel slope, quantity and duration of flow, and the form of the stream channel. Hillslope processes remove soil, rock and organic materials and, operating over varying time frames, deliver the materials downslope to stream channels. Processes like mass wasting and rilling can be rapid, delivering large amounts of material to the valley bottom or to creeks in minutes or hours. Processes such as soil creep and bioturbation are generally slower, moving materials downslope at rates of one to ten millimeters per year. Development in the past 150 years in the May Creek basin has increased the frequency and magnitude of hillslope erosion, mass wasting, and channel transport and deposition. Disturbance of surface soils by urban and residential construction, highway construction, logging, and agriculture have increased the runoff and the rate at which eroded sediment is delivered to the wetlands and stream channels. Introduction of additional runoff on hillslopes (or addition of runoff in areas that never previously had any) increases the rate of mass wasting, surface erosion, and raveling of slope materials. Increased water and sediment supply to the basin creeks, combined with creek dredging and loss of large woody debris, have increased the supply and transport of sediment in the basin creeks. The predominate hillslope processes in the May Creek basin that impact wetlands and creeks result from erosion of exposed soils in overgrazed pastures; poorly built and maintained ditches, road cuts, and road fills; poorly managed and regulated quarries; and encroachment of developments onto steep hillsides without proper constraints to prevent erosion. Mass wasting and the resultant delivery of sediment to the creeks has increased in the May Creek basin with construction of roads, structures, and utilities without sufficient engineering controls, encroachment of construction along the edge of steep slopes and creeks, discharge of water over steep slopes, and removal of vegetation from steep slopes without adequate erosion control measures. Landslides in the project region are strongly related to slope, materials, and geologic contacts. Landslides in the May Creek basin generally occur along valley walls where river incision creates steeper slopes and exposes materials above perched water tables. Many of the mass -wasting problems could be prevented or minimized by design, construction, and maintenance controls. However, they are very difficult, costly, and often impossible to control or mitigate once they occur. Chapter 7 Sediment Erosion and Deposition 7-2 STREAM CHANNEL PROCESSES Channel Types Stream channels take on a form based on the geologic materials they are in, the amount and type of sediment delivered from the hillslopes, the climate conditions, and the vegetation cover conditions. The climate conditions result in precipitation at various intensities and durations that influence the amount of hillslope and channel runoff. The geologic materials and vegetation cover influence the amount of runoff and surface erosion. Channel form varies over time in response to weather extremes in the basin and also in response to alterations in the cover and drainage conditions that supply flow and sediment to the creeks and tributaries. The May Creek channel network can be divided into four basic sections based on stream types: the May Creek delta, the canyon section, the May Valley low gradient section, and the high -gradient tributaries (Figure 7-1). The May Creek delta is a depositional area that extends underwater about 3.000 feet into Lake Washington and also extends, above water, for about 3,000 feet upstream from the mouth of May Creek to about RM 0.6. The May Creek canyon section runs from about RM 0.6 to RM 3.5 (Figure 7-1). This is a moderate gradient section where May Creek has eroded into the former 150-meter-elevation glacial base level, forming a canyon. The creek is constrained between steep valley walls, and flows within alluvial terraces of stored sediment that are 30 to 100 feet wide and usually deeper then the channel depth. The creek is often up against the steep valley walls where it erodes valley wall colluvium. In the May Valley section, upstream of RM 3.5 (Figure 7-1), May Creek is an underfit stream in a wide, low -gradient valley. The creek is no longer constrained by the valley walls. It flows through ancient and recent alluvial terraces and fans. The valley section is characterized by low -gradient mainstem and tributary channels that extend upstream to about RM 0.7 of the North Fork of May Creek and to about RM 0.5 up the East Fork of May Creek (Figure 7-1). Most of this portion of the creek has been moved and channelized. Bedload sediment transported from the valley walls is deposited on alluvial fans along the valley bottom. Only the sand, silt, and clays are transported through the low -gradient valley section. The fourth typical type of channel form in the May Creek basin is the section of high - gradient tributaries that drain the uplands to the north of May Valley and the East Renton Plateau to the south. The tributaries are generally located where the ancient subglacial and proglacial streams eroded valleys into the glacial deposits. The tributary creeks are high -gradient to very high -gradient channels and are generally constrained by narrow valley walls of compact sediments or rock. Channel alluvium stored along the tributary creeks varies from zero to 50 feet wide and from zero to about 20 feet deep. The channel alluvium is maintained in terraces by the roots of vegetation in and along the channels, by large logs trapped along the channel, and by rocks that are greater than about two feet in diameter (blocks). Chapter 7 Sediment Erosion and Deposition 7-3 w 1100 1000 900 800 700 600 500 400 300 200 100 0 -100 Lake Washington I I I m May Creek 0282 Boren Creek Honey Creek / 2.00 3.00 4.00 River Mile May Creek Canyon Wilderness Creek S. Fork May Creek f May Creek North Fork May Creek 5.00 6.00 May Creek Valley 7.00 8.00 9.00 Figure 7-1. Profile of May Creek, Selected Tributaries to May Creek and Lake Washington. (Based on the 1983 Topographic Maps of the Area [USGS, 19831). Channel Structure The channel structure of a creek refers to the diversity of physical features that make up a channel, including cascades, falls. point bars, riffles. pools, instream logs referred to as large woody debris (LWD), and channel substrate. The channel structure controls how the water flows down a creek and, in turn, the power of the flowing water forms the channel structure. The varying structure of the channel, including changing width, depth, slope, substrate, and LWD, alters the velocity, depth, width, and turbulence of the flowing water. The physical structure of the channel strongly influences the aquatic habitat conditions. Hydraulic variability of pools, runs, riffles. boulder runs, and cascades are considered an important component of healthy aquatic habitat. Lower diversity of the channel physical conditions is an index of generally lower habitat quality. Channel Substrate Channel substrate ranges from bedrock to silt and clay, with most of the channels being dominated by gravelly sands. The substrate composition is a function of the materials delivered from stream banks, from upstream, and the power of the creek to transport the sediment. The substrate grain size varies from coarse gravel, cobbles, and boulders upstream, grading to sandy gravels and finally sands downstream on the delta. In high - velocity areas like the canyon reach, the silts and sands are transported as suspended load and are rapidly moved through the reach. Gravels, cobbles, and boulders are transported as bedload forming channel bars and channel deposits. Silt- and sand -bedded channels can have active suspended and bedload transport at almost any flow rate. During flood flows the sands and silts are deposited in the overbank areas and at the mouth of the creek. Coarser bedded channels consisting of gravel and cobble beds have significant bedload transport only during flood flows. The substrate of gravel -bed channels consists of an upper pavement layer of much coarser sediment than the underlying material. This pavement layer armors the bed, preventing any significant bedload transport except during higher flows. To avoid significant channel erosion and increased downstream deposition, flows that are large enough to cause significant bedload transport must be limited to their present levels of frequency and duration. Changes in the frequency and duration of the flood flows can change the channel size and substrate conditions. Channel substrate, in turn, is an important aspect of aquatic habitat. If hillslopes and upstream reaches are delivering a lot of fines (clay, silt, and sand), there will be an increase in the percent of fines in the substrate. Sediment Transport and Storage Water flowing at high velocity through high -gradient stream reaches has the power to move and transport larger size substrate; flow in low -velocity and low -gradient reaches generally can transport only the finer materials (gravel, sand, silt, and clay). It is the diversity of channel velocities that segregates the transported sediment into the wide range of sizes found along a stream in channel bars, flood terraces and side channels. Chapter 7 Sediment Erosion and Deposition 7-5 LWD in a channel absorbs stream energy by increasing flow resistance and decreasing velocity that otherwise would be expended in the erosion of channel banks, and as such, adds to the stability of a channel. The presence of LWD and bank vegetation increases the storage of sediment along the channels. The supply of LWD is dependent on the presence of a zone of forest with mature trees (preferably coniferous) along the channel. The May Creek delta and the numerous alluvial fans along May Creek are areas of decreased gradient, decreased flow velocity, and reduced stream power. This results in deposition of the coarser bedload sediment. The fine sediment continues downstream, generally suspended in the water, until the water velocity is low enough for the material to settle out in large pools, ponds, or in Lake Washington. Much of the sediment that is delivered from the tributaries to the low -gradient May Valley section is deposited on alluvial fans and broad floodplain terraces. Eventually, much of the cobbles, gravel, and sand that enter lower May Creek are transported downstream and deposited on the low -gradient May Creek delta. The silt and clay that are transported from the May Creek basin are deposited on the bottom of Lake Washington. Depending on the geologic materials and presence or absence of LWD, channels can handle differing amounts of watershed disturbance without significant downstream impacts: • Channels entirely in bedrock with abundant and relatively large logs can remain stable with moderate flow increases. • Channels with alluvial beds of sand and gravel or confined by erodible valley walls cannot handle any increases in flow, and even under natural flows will transport significant amounts of sediment. • Channels with boulder and block beds and banks can handle some flow increases below the threshold of transport of the armor layer, depending on the condition of the channel bank vegetation. Basinwide loss of stream bank vegetation, LWD, and LWD supply from the banks and channel -migration zone puts channels at additional risk of impacts. Besides the physical changes to the channel and alluvial fans, aquatic habitat downstream is affected (see Chapter 9: Aquatic Habitat and Fish). Channel -Migration Zones Streams naturally migrate within the valley they occupy as a result of continued erosion of banks and deposition of sediment. The channel -migration zone is the area that the creeks and rivers naturally occupy over time. This zone varies in size according to the time span of interest. The relevant time scale of the channel -migration zone depends on the issues and structures of interest. Chapter 7 Sediment Erosion and Deposition 7-6 The width of the channel -migration zone in steep gradient creeks is generally constrained with bedrock or very compact beds and/or banks, leaving a relatively narrow zone. Streams flowing in unconsolidated alluvium, on the other hand, are free to adjust to changes within the basin, and migrate widely. In the May Creek basin many of the channels have eroded down through older alluvium, leaving old flood terraces along the valley edges. The channel -migration zones on the alluvial fans, delta, and low -gradient unconfined creeks are generally bracketed by these older flood terraces. In most cases, the entire delta is the channel -migration zone. On the May Creek delta, the 1-405 and railroad fills have constrained the channel to the south side of the delta. Beyond the fills the area within about 80 degrees either side of the channel is within the potential channel -migration zone. Alluvial Fans Alluvial fans form a special case of a channel -migration zone. Such fans occur in the May Creek basin where high -gradient tributaries join the relatively flat main valley. In these locations a tributary channel is no longer confined by narrow valley walls and is able to shift, allowing the areas of deposition to spread into a roughly fan -shaped deposit. It is common for flood flows to transport sediment and logs from the tributaries. The bedload sediment and debris deposit in the center of the upper part of the alluvial fan. This forces the channel to shift to one side of the fan. Flow is often confined to one of several channels on a fan during most of the year, but during flood flows, multiple and braided channels form. The channel can rapidly shift locations during storm flows. Increases in storm flow in the tributary basins augment sediment transport from channel - bank erosion, valley -wall slumping, and channel -bed transport. This increased sediment load during storms is transported to the low -gradient alluvial fans, which in turn results in increased deposition and channel migration on the alluvial fan. There are 16 main tributaries entering May Creek, eight of which have classic alluvial fans (Map 6). The smaller tributaries have not built up significant fans either because May Creek flow can transport the material away, or because there is not a wide, low - gradient zone for the deposition of a fan. Some of the earliest development in May Creek basin occurred on most of the alluvial fans. The sites were above the main valley floodplain, were near good water supplies, and afforded good views on generally well -drained soils. Some of these houses, farm structures, and road crossings may be at risk of damage during flood flows and some could face an increased risk if upstream stormwater runoff and erosion are not adequately controlled. The shifting nature of the channels presents an additional problem for civil works (such as bridges, culverts, or levees) that are designed to maintain the creek in one location and which are not capable of functioning if the depositional channel shifts. When a road or structure is built on a fan, it should be assumed that maintenance could be needed during and after large flood events. Structures on alluvial fans and those in or near to creeks are at greater risk of flooding impacts as channels become more unstable. Channel incision and bank slumping can put structures that are near to creek banks at greater risk. The downstream increase in Chapter 7 Sediment Erosion and Deposition 7-7 sediment delivered from the eroding channels leads to increased potential for channel migration and aggradation which change flood levels and their location. 7.3 DATA COLLECTION AND ANALYTICAL METHODS HILLSLOPE CONDITIONS Surface -erosion and mass -wasting sites in the May Creek basin were identified on aerial photographs and during ground surveys. The larger landslides are presented on the surficial geology map (Map 6). Numerous slides that exist on the valley side slopes and creek banks are too small to display on the map. Surface erosion areas were delineated using aerial photographs and during field visits; areas of significant erosion are noted in Appendix A. The GIS was used to develop an erosion hazard map and mass -wasting hazard map for use as a management tool in assessing potential surface erosion impacts to public and private resources in the basin. CHANNEL CONDITIONS May Creek and the main tributaries were walked between February and April, 1993, to gather information on aquatic habitat, channel conditions, and basin geology. Collected data included channel morphology (water depth and width, channel width, and bank height); location of pools, riffles, falls, and cascades; identification of substrate materials; and notes on channel -bank and valley -wall conditions. The channel width and bank height are considered close approximations of the bankfull discharge, which defines the maximum flow that can be contained in the channel. A hip -chain, which measures distances in feet, was used to determine the length of tributary sections and the location of tributary features. A global positioning system (GPS) and data logger were used to record the information. The data were post -processed into a spreadsheet for analysis. The data presented here summarize the detailed channel data, which are available only in spreadsheet format. With each channel profile (see Figure 7-1) are graphs presenting the channel dominant and subdominant substrate, channel width, channel depth, the width -to -depth ratio, and a table of estimated channel flow for forested (pre -development), existing (1992 basin conditions), future, and mitigated future conditions, based on the HSP-F rainfall/runoff model (see Chapter 5: Hydrology). The channel data for May Creek is based on a three-point moving average to display trends that were obscured when all the data were plotted. A three-point moving average takes the average of the channel measurement (for example channel width or depth) for the points either side of the station. Then moving to the next station takes the average of the measurement at the station and points either side, giving a smoothed summary of the values. For the tributaries, where less information was gathered, the channel data are presented without averaging. The dominant and subdominant channel -substrate classification divides the bed material into the size class that is the most abundant and the size class that is next most abundant. It provides an index of the roughness of the channel pavement material. This Chapter 7 Sediment Erosion and Deposition 7-8 relates to the aquatic habitat qualities of the stream reach and the discharge needed to mobilize and transport the channel substrate The coarser the substrate class the greater the discharge needed to transport the material for any given channel gradient. 7.4 BASINWIDE CONDITIONS HISTORIC CONDITIONS The first known map of May Creek is the Government Land Survey of 1865, based on field data gathered in December of 1864. May Creek, called "Honey Creek" on this map, is shown as a meandering creek. Two trails are shown, one leaving the south end of Lake Washington to the May Creek delta area and the other leading to the present-day Honey Creek. A wagon road is shown just north of Lake Boren. The Snohomish and Tacoma Quadrangle maps of 1897 (based on surveys of 1894-95, reprinted 1940) show May Creek as a meandering stream and the delta area as wetland. The Columbia and Puget Sound Railroad crossed May Creek at about RM 1.6, where old footings still remain, and crossed Newport Hills Creek at RM 0.2, where the old fill still remains. Forerunners of the SE Renton -Issaquah Road (SR-900), Coal Creek Parkway SE, and SE May Valley Road are present. The February 1900 version of the Tacoma Quadrangle shows about half of the basin as "burnt areas restocking" and half as "marketable forests", with no "virgin timber" classification present. Therefore, at least a portion of the first cutting of the forests and construction of numerous logging grades and several main roads occurred sometime prior to 1900. The 1897 quads show the delta as a wetland. Undisturbed deltas similar to May Creek's are generally a diverse and rich wetland area. Wood debris deposited during floods would have been common. The May Creek channel would have migrated throughout the delta area. The area of the delta has expanded over the years from sediment deposition and from the lowering of Lake Washington in 1916. Approximately 1,100 years ago, the delta may have experienced a 30- to 70-foot wave generated by the slumping of the submerged forest on the opposite shore of Lake Washington. The canyon section of May Creek would have had a lot more channel structure from old - growth tree falls along the channel. The moderate gradient and ample LWD supply from valley wall slumps and streambank treefalls would have created far more channel diversity than currently exists. Channel substrate would have had less sand and fines. Ever since May Creek has been incising into the glacial deposits of the canyon reach (that is, for the past 13,600 years), tributaries like Gypsy Creek and Honey Creek have been trying to keep up. Small old terrace remnants on May Creek and tributary creek valley walls were formed when the creeks were at higher levels. Portions of the original May Creek channel in the May Valley section (above RM 3.6) are apparent on aerial photographs. The channel was a meandering channel with frequent side channels. The original May Creek channel -migration zone prior to channel straightening is along the edges of the older recessional outwash terraces, valley side colluvium, and tributary alluvial fans. Chapter 7 Sediment Erosion and Deposition 7-9 CURRENT CONDITIONS May Creek Stormflow runoff following development in the May Creek basin has increased by 200 to 400 cfs in the canyon section and delta areas compared to the undeveloped (forested) conditions (Figure 7-2). Increased impervious area, increased drainage density, and increased hillslope sediment supply all result in changes to the downstream channels. The increased magnitude and frequency of floods provides greater energy for sediment transport. Above the crossing of May Creek by Coal Creek Parkway SE (RM 3.6), bedload delivered from the tributaries is deposited on the fans and overbank areas; only the sands, silt, and clays are transported downstream. Because of the low gradient, the transport of sediment is limited by the power of the flow and not by the ample supply of sediment from the upland tributaries and stored sediment along the valley bottom. This all changes below Coal Creek Parkway SE (RM 3.6), where the gradient of May Creek increases in the canyon section. The canyon section of May Creek has large amounts of sediment stored in point bars, old flood terraces, and valley wall colluvium. The high channel gradient provides the power to transport large amounts of sediment during storms that are large enough to move the gravel and cobble substrate on the surface of the channel bed. In the canyon section, the amount of sediment transported is not limited by the power of the flowing water but rather by the amount of sediment available in and along the channel. Increased flows in May Creek tend to expand the size of the channel, delivering some of the stored sediment downstream. This results in more sediment delivered to downstream deposition zones for many years to decades, as the stream channel adjusts to the new runoff conditions. Increased channel bank erosion and mass wasting associated with higher flows further increase the sediment supplied to the channel. Channel Stability Index. The condition of a stream channel changes as a result of changes in the magnitude, frequency, and duration of flood flows. Increased bank erosion, channel incision, and loss of channel diversity often results. The channel stability index is the ratio of the estimated existing two-year recurrence interval flood to the estimated forested 10-year recurrence interval flood (Q2e/Qlof). It is an index of potential for changes in a channel resulting from increased flows. An index value of 1 indicates the estimated flood peaks of the subbasin have increased to where the 2-year flood under existing conditions is now as big as the 10-year flood under forested conditions. Because channels form in balance to flows greater than the threshold discharge for moving stream bank and substrate material, any increase in the frequency of large floods is of concern. Based on the analysis in past King County basin plans, a channel stability index of 1 or greater in this region is typically correlated with pervasive channel instability. That pattern is almost precisely affirmed by the data of this basin as well (Figure 7-3). Chapter 7 Sediment Erosion and Deposition 7-10 1200 7 1000 800 0 a) rn t 600 U fn 400 200 0 0-0.43 0.43-1.6 1.6-2.1 2.1-2.6 2.6-3.2 3.2-3.6 3.6-4.5 4.5-5.5 5.5-5.9 5.9-7.0 7.0-8.1 > 8.1 River Mile —• Forested 2 Yr 0 — W Existing 2 Yr 0 —A— Future Mitigated 2 Yr 0 Forested 100 Yr 0 Existing 100 Yr 0 �— Future Mitigated 100 Yr 0 Figure 7-2. Estimated Flood Flows Along May Creek. Shown by River Mile for the 2-Year and 100-Year Recurrence Interval Floods. 7-1 1 Lower May Creek Basin 0282 Gypsy Creek 0284 Lower Honey Creek 0285 Middle Honey Creek 0285 Upper Honey Creek 0285 Newport Hills Creek 0286 Lower Boren Creek 0287 Upper Boren Creek 0287 China Creek 0287 Long Marsh Creek 0289 Greene's Creek 0288 May Valley 0282 Un-Named 0291 A Country Creek 0292 Cabbage Creek 0293 North Fork May Creek 0294 S. Fork May Creek 0282 East Fork May Creek 0297 I I I 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 Channel Stability Index J ] Future Mitigated Conditions Existing Conditions S) Indicates stable channels U) Indicates unstable channels _) Indicates enlarging channels Figure 7-3. Channel Stability Index and Field Observed Channel Conditions for Creeks in the May Creek Basin. 7-12 In Figure 7-3 the channel stability index for May Basin streams is compared to field - observed indicators of channel impacts trom increased flows. Field -observed indicators of channel stability, as noted in Figure 7-3, were based on field interpretation of recent channel incision, extensive active channel bank erosion, channel bar stability, and riparian zone conditions. (U) indicates unstable channels with severe bank erosion and incision, (S) indicates stable channels without significant channel erosion, and (E) indicates enlarging streams displaying locally sever stream bank erosion. Values of Q2 and Q10 were estimated using the HSP-F rainfall -runoff model for May Creek. When floods of greater magnitude and duration have occurred on May Creek basin streams, field indications of these types of impacts are observed (Figure 7-3). The channel stability index for future mitigated conditions shows which streams will have increased flood peaks. Factors such as channel substrate, channel gradient, and the presence of channel structure will control whether the impacts from increased flows occur. The channel width/depth ratio is a measure of channel morphology that relates the form of the channel to the fluvial processes shaping the channel. This ratio can be used to isolate anomalous conditions affecting the stream. A high width/depth ratio often indicates channel sedimentation and the potential for lateral channel migration. Moderate width/depth ratios indicate relatively stable streams, whereas low width/depth ratios may indicate channel bed incision or a constrained channel with greater potential for channel bank erosion and mass wasting due to removal of slope support. High ratio values are related to channel reaches with shallow pool depths. Reaches with high width/depth ratios contain shallow streams actively accumulating sediment and may be flood prone. The variance about the mean channel width, depth, or width/depth ratio gives an indication of the variability of channel conditions along May Creek (Figure 7-4). The variance used here is a measure of the dispersion or extent of differences in the distribution of values of a 5-point moving average along the creek length. The uniform low variance on the delta results from the channelization, riprap, and road fill that constrain the channel form. Tributary reaches that are heavily impacted by loss of channel structure have less variation in channel width, depth, and substrate, and have less temporary storage of delivered sediment. May Creek up to RM 4.5 is highly variable and considered the best aquatic habitat in May Creek. Straightened and dredged reaches in May Creek have reduced channel variability. This is evident in the dredged reaches of May Creek delta, May Valley and North Fork May Creek (Figure 7-4). Removal of LWD has greatly reduced channel diversity in May Creek and in most of the tributaries, and has led to greater potential for downstream impacts. Increased delivery of sediment to the May Creek channel has increased the amount of fines in the channel substrate, which impacts the quality and quantity of the aquatic habitat. Chapter 7 Sediment Erosion and Deposition 7-13 Page 1 of 3 1100 May Creek 0282 1000 900 800 Boren Creek Wilderness Creek fI �a f 0 700 > 600 / S. Fork May Creek w S00 Honey Creek / �a / 400 ~ _ = r =� May Creek �'11 J North Fork 300 Lake � �May Creek r of 200 Washington Ova 100 Ova�� Oyal Longitudinal Profile and Geology 0 Qyal ON -100 1 0 1 2 3 4 5 6 7 8 9 7 • • Boulder ( >256mm) 6 •• •1111110 •Mrs •••• ••••• • Cobble (100-256 mm) a� c° 5 U) Gravel (100-256 mm) in 4 Gravel (<25mm) a? c 3 Sand E 02 • • 000 • Silt/Clay/Organic 1 Dominate Substrate Bedrock 0 -1 0 1 2 3 4 5 6 7 8 9 7 • • • • • Boulder ( >256mm) 6 •• •M6N0 � Cobble (100-256 mm) ,5 •••r • ~ Gravel (25-100mm) in N4 ��• «• • • • • �•• Gravel (<25mm) m c 3 �� •�» • • •••• • • •ate • • • • ••••• Sand E 0 2 • ••• •• •w• • • •• • Silt/Clay/Organic 1 • Subdominate Substrate Compact Clay? 0 -1 0 1 2 3 4 5 6 7 8 9 River Mile Figure 7-4. May Creek Channel Parameters. Width, Depth, Dominant Substrate, Subdominant Substrate, Channel Width/Depth Ratio, and Channel Diversity as Indexed by Variance of the Width/Depth Ratio by River Mile Along the Existing Main Channel. 7-14 Page 2 of 3 50 May Creek 0282 040 Width:Depth Ratio t 30 -B20 � � �•_•� `■ - �■ - ■•�I t�l■ o ■ so j .i �.�■ LL■ ■■■1■ ■ ■ t■ f■ ■■ • I•�`- ■I■r■ ■ ■ . :■--I-r_I\LI■• now I■ ■11� •IIfIf 0 ■ -1.00 0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 6 a) a' 5 r n d 4 N c 3 A L U a) 2 Rf Q 1 0i -1 125 m100 ■ ■ Channel Depth � II■ 1■ L� � , rr■ ■ i ■ ■ i■ ■�i14 i ■ lil■ • I� �i i ■ ■ • r ■■■� ■ . ILA ■ • ■� ■ ■■1■ I�Lf■ • ■�■ I■■ ■•/ A■ ■ ■ ■• f1 .f■.j L■�■ ■ - 4VY►I�i■ ■ I� L on �L 1■ f■ 1■%1j ■ f■ f ■ L. •■ If•L. fl■ 0 1 2 3 4 5 6 7 8 9 Channel Width _ ■ ■ .� ■f�_MIN NO u ,i! ■u 0 1 2 3 4 5 6 7 8 River Mile 9 7-15 Page 3 of 3 1200 1000 N 800 u 600 m C C ♦ 400 200 0 0.00 1.00 2.00 3.00 Variance of Channel Width : Depth Ratio for May Creek .''.•'•-•i•••T•�•�••< •-• •...ice-� 4.00 5.00 6.00 7.00 8.00 9.00 4.5 4 _ 3.5 • . Variance of Channel Depth for May Creek 3 •. LO 2.5 • . •••. 2 191.5 •' •� 0.5 0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 1600 Variance of Channel Width for May Creek 1200 if i 800 C A > 400- 0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 River Mile 7-16 Tributary Creeks Tributaries flowing from the Highlands area north of May Creek are for the most part controlled by bedrock. Channel adjustment to increased runoff is limited to the channel banks. The loose alluvial substrate stored along these channels is held in place by large rocks and large logs, which is now lacking in most of the creeks. The creeks respond to increased magnitude and duration of storm runoff by eroding bank material and by slumping of stream side alluvium and colluvium, which widens the channel. The presence of resistant bed material slows or limits incision of the channels. Gypsy Creek and Newport Hills Creek are exceptions to this general Highlands pattern, because they lie in thick sections of glacial sediment in their lower reaches. Tributaries flowing from the south, from the Renton plateau, and Gypsy and Newport Hills creeks are not constrained by bedrock. They have eroded through compact glacial tills, outwash, and lake beds. Channel incision is slowed by the glacial tills and compact and cohesive lake beds, but stream reaches in the outwash gravels and sands can experience rapid channel incision and bank erosion. Honey Creek serves as an example where very compact silts and clays reduce the incision of the channel bed. The cohesive strength and consolidation of the silts and clays slows their erosion. Honey Creek responds to increased flows and floodway encroachment by eroding the loose bank alluvium and colluvium delivered from the steep valley walls. Tributaries like Greene's Creek have not captured as large a drainage area as Honey Creek and therefore are not eroded as deeply into the glacial deposits. The smaller tributaries are still eroding into the sandy advance and recessional outwash deposits. They are much more sensitive to increased flows because they are not as constrained by compact beds or bedrock. They respond to increased flows by channel bank and channel bed erosion. All of the basin tributaries have cut down through the unconsolidated glacial deposits to establish their present drainage following the end of the last ice age. The substrate of the tributaries display a coarsening of the channel substrate near the advance outwash-till contact. The coarser substrate materials are derived mostly from the till and the top of the advance outwash units. Flood flows are not large enough to transport the bigger rocks eroded from these deposits. They remain behind, accumulating in the valley bottoms of the tributaries. FUTURE CONDITIONS Many tributary channels show evidence of downcutting and accelerated sediment production above natural levels where they drop steeply down the valley sides. Upon reaching the valley floor, channel gradients drop abruptly and the streams deposit sediment prior to reaching May Creek. The sediment clogs drainage ditches and stream channels, damages structures, and adds to existing alluvial fans creating further channel instability on the fan surfaces. Erosion and deposition problems are minimal, however, on the gently sloping plateaus above the May Valley. Chapter 7 Sediment Erosion and Deposition 7-1 7 Long Marsh Creek (0289) is currently stable and will remain so under modeled future conditions if channel and valley wall vegetation are maintained. China Creek (0287) is currently stable, model results indicate that without mitigation, it will become unstable. Several channel reaches are already highly unstable, and modeled flows predict that they will degrade further even with mitigation. Because landscape modification in these areas is so great already, there is relatively little area left to manage for mitigation. These reaches include Gypsy Creek (0284), lower middle, and upper Honey Creek (0285); Greene's Creek (0288); and an unnamed creek (0291A). Based on modeled future flow increases, severe future channel erosion problems are likely in eight subcatchments that currently have stable or nearly stable channels. These subcatchments include lower May Creek (0282), lower and upper Boren (0287), Newport Hills Creek (0286), Cabbage Creek (0293), North Fork May Creek (0294), South Fork May Creek (0282, above RM 7.0), and East Fork May Creek (0297). Impacts to the May Creek basin tributary channels and aquatic habitat will include increased sources of fine and coarse sediment that deliver to the creeks, increased flows that increase the channel erosion and transport rate, and increased deposition rates and channel instability on the alluvial fans and May Creek delta. In combination with the loss of large woody debris, the impacts to the aquatic habitat will be significant. 7.5 CONDITIONS BY SUBAREA May Creek basin contains streams featuring a variety of physical characteristics, ranging from low -gradient, sandy alluvial reaches to high -gradient channels composed of bedrock. These stream and reach types have distinct processes controlling sedimentation and erosion. Each of the basin's four subareas generally reflect these differences in stream characteristics, landscape position, and erosion/sedimentation processes. LOWER BASIN SUBAREA This region extends from the delta at the mouth of May Creek where it enters Lake Washington through the incised canyon section to RM 3.9 of the mainstem. Tributaries that enter the mainstem along this reach are included in this section. May Creek in the Lower Basin is broken into the delta section where it enters Lake Washington (below RM 0.2) and the upper canyon section (between RM 0.2 and RM 3.9) (Figure 7-4). The delta segment has been heavily developed since the lowering of Lake Washington in 1916. Lower Mainstem May Creek (0282) (RM 0.0 to RM 3.9) Current Conditions. The lower May Creek channel can be subdivided into segments based on the general stream geometry: the May Creek delta and the canyon section. The May Creek delta is a depositional area that extends subsurface about 3,000 feet into Lake Washington and also extends, above water, for about 3,000 feet up -valley Chapter 7 Sediment Erosion and Deposition 7-18 from the mouth (RM 0.6). The May Creek canyon section runs from about RM 0.6 to RM 3.5. This is a high -gradient section where May Creek has eroded into the former 150- meter level glacial sediments, forming a canyon. The upstream portions of the canyon section —Honey Creek, lower Newport Hills Creek, Gypsy Creek, and Boren Creek —all contain large amounts of stored sediment that is transported downstream and deposited on the delta during flood flows. Increased flows, loss of LWD supply, and increased surface erosion have increased the amount of sediment that is delivered from these areas. All of these channels have expanded and become less stable, and will experience additional and greater impacts under future conditions. Flooding and sediment deposition on the delta is a natural process that has been increased by greater flood flows, and by the encroachment of development into the floodplain and narrowing of the channel -migration zone. May Creek Delta. The low gradient of lower May Creek is created by the base level of Lake Washington. The May Creek channel slopes are between 0.2 and 1 percent. This causes the bedload sands, gravel, and logs transported from upstream to deposit in the channel. The deposition of sediment and logs would normally in turn lead to channel migration: the historic channel -migration zone covered the full width of the delta. However, the 1-405 and railroad fills force the channel to remain fixed in the upper delta. Beyond these fills the stream is constrained by riprap within a channel that turns 90- degrees to meet the lake at the southern end of the lower delta area. During moderate floods (flows less than 500 cfs), the lower channelized reach can contain the flow and keep the channel in its present location; during large floods, the capacity of this channel could be exceeded. The May Creek delta is a depositional zone that has built out into Lake Washington during the past 13,600 years, and in pre -settlement times extended upstream past the 1-405 crossing. The delta is made up of the gravel, sand, and some of the silt that is transported from the basin as bedload. Bedload transport typically occurs during flows that are large enough to move the channel pavement material (Bathurst, 1987). For the lower May Creek reaches the pavement material is made up of cobbles, gravel, and sand (Figure 7-4) which require flows in the range of a 1-year to a 2-year recurrence interval flood to begin significant amounts of bedload transport (Leopold and Rosgen, 1990, Lepp et al., 1993). In the upper May Valley reaches the slope is lower but the substrate consists of sand and silt with some gravel so transport can occur at much lower discharge rates and results in more suspended sediment transport. The creek also transports a large suspended sediment load of clay, silt, and fine sand that typically makes up 80 to 95 percent of a basin's total sediment yield. The suspended sediment from the May Creek basin is deposited on the bottom of Lake Washington. The May Creek delta has a volume of about 30 million cubic yards. If it is assumed that May Creek basin has a bedload sediment yield of seven percent of the total yield, then the total sediment yield from the basin would be roughly 33,700 cubic yards per year or about 2,400 cubic yards per year per square mile of watershed, for the estimated 13,600 years the delta has been forming. This long-term average sediment yield is on the high side of yields for other high -gradient mountain and foothill basins in the Pacific Northwest region, which typically range from 500 to 2,000 cubic yards per year per square mile of watershed. The extensive incision of the thick glacial deposits in this Chapter 7 Sediment Erosion and Deposition 7-19 basin, particularly downstream of May Valley. may explain this high long-term sediment yield. The channel upstream to about RM 0.6 ranges between 15 and 30 feet wide. The channel width is constrained by rip -rap and fills. Channel substrate ranges from silt to boulders, with sandy gravel and cobbles being the most common (Figure 7-4). Deposition of sand and gravel on the delta occurs when bedload is transported from upstream. This occurs when the discharge is great enough to move the channel bed substrate in the upstream canyon reaches. The threshold for the onset of bedload transport is typically in the range of a 2- to 5-year flood, depending on the amount of large bed elements like large logs, and the composition of the channel substrate. As is described more fully in Chapter 5: Hydrology, the magnitude and duration of flood discharges for the existing conditions have increased considerably from pre - development conditions. Thus, the streams now have more power to move more sediment more often. These changes have greatly increased the erosion occurring in May Creek canyon and in its tributary streams, and this erosion has led to a substantial increase in the rate at which sediment accumulates on the delta. Further aggravating the deposition are the structural changes at the delta (restriction of channel migration, 90-degree turn and slowing of the stream), and the increased delivery of sediment to the channel by increased upstream bank erosion, surface erosion, mass wasting, and loss of functional channel structure on many of the basin tributaries and the mainstem of May Creek. Large quantities of sediment that are deposited at the creek mouth are dredged in order to facilitate commercial activities and prevent channel migration. This deposition, and the necessity for dredging, has had substantial impacts on the operations of the commercial lumber mill located on the delta, as well as on the aquatic habitat of the delta area. Most of the bedload from the upper parts of the basin, such as the East Renton Plateau and Highlands streams, accumulates in the central May Valley, and is not transported downstream to the mouth. Thus, land use changes in the upper parts of the basin have not significantly contributed to increased sedimentation on the delta, as Lower Basin land use changes have. May Creek Canyon. The May Creek canyon section runs from about RM 0.6 to RM 3.9 (Figure 7-1). This is a moderate gradient section where May Creek has eroded into the former 150-meter-elevation glacial outwash channel. The creek channel displays a moderate gradient (1 to 3.5 percent slope) that has incised approximately 250 feet through a variety of Quaternary glacial tills and outwash. Channel width and depth varies far more than in other alluvial reaches in the basin (Figure 7-4). The dominate substrate through the canyon section is gravel and sand, while the subdominant substrate is gravel (Figure 7-4). The valley width, up to about RM 2.2, is enough to contain a 200- to 400-foot-wide alluvial terrace that alternates sides or is bisected by the channel. Upstream of RM 2.2 up to RM 3.9, the channel is more constrained by the steep canyon walls. The gradient and diversity of channel width and depth increases (Figure 7-4). This reach is naturally incising as the channel tries to erode farther up -valley. The channel Chapter 7 Sediment Erosion and Deposition 7-20 encounters the compact advance outwash units and possible bedrock, slowing the up -valley rate of erosion of the canyon. The width/depth ratio varies substantially in the canyon segment of May Creek (Figure 7-4). The ratio is about 10 in the constrained section until RM 0.8, increases to arounc 25 for about one-half mile, falls and fluctuates around 12 until RM 2.2, and again increases toward 25. Upstream of RM 2.6 the ratio slowly falls to about 10 as the channel becomes more constrained at the end of the canyon section. Future Conditions. Sediment deposition is a natural condition for a delta, and will continue to occur on lower May Creek. Future increases in flood flows will promote additional channel -bank erosion and valley -wall slumping in the canyon section, as well as reduce the diversity of aquatic habitat by loss of channel structure. Without mitigation of increased flood flows and sediment delivery (particularly from the May Creek canyon itself and to a lesser extent from its tributaries), as well as recovery of lost channel structure, the delta area will experience a steadily increasing rate of sediment deposition. Gypsy Creek (0284) Current Conditions. Gypsy Creek enters May Creek from the north at RM 1.6 of May Creek. The initial gradient is moderate (one to five percent) as Gypsy Creek crosses its alluvial fan (Figure 7-5). The alluvial fan and channel substrate consists of gravelly sand. As the stream climbs out of the canyon it steepens dramatically (20 to 30 percent) where it incises the sandy advance glacial outwash deposits from RM 0.15 to 0.25. The channel is recently incised from here up to the road crossing at RM 0.45. Here the channel and channel banks would have been stabilized by mature trees and abundant LWD. The channel originally would have been step -pool, meandering within the narrow floodway, rather than incised into the channel alluvium as it is today. The gradient moderates to between three and seven percent above RM 0.25 to RM 0.5. Above RM 0.45 the creek is on top of the plateau, out of the constrained valley, where Wetlands 9, 10 and 11 begin. At about 275 feet elevation the creek encounters the more resistant compact till. Here the valley narrows and the channel substrate changes to sandy gravel, reflecting the change in parent valley wall material. The upland forested wetland that feeds Gypsy Creek and the large extent of recessional outwash sands in the basin have moderated storm flows to the lower reach of Gypsy Creek. From the road crossing downstream, the steep valley walls constrain the creek to a narrow floodway. Sandy colluvium along the valley walls and channel alluvium are being actively incised by the creek, delivering significant amounts of sand to May Creek. Gypsy Creek generally widens upstream from its mouth to RM 0.45, while its depth remains relatively constant between 0.5 to 1.5 feet deep throughout its measured length (Figure 7-5). There are some very narrow, recently incised sections within this reach. Subsequently, the width/depth ratio increases with channel width upstream, which correlates with the incised sections observed in the field. The width/depth ratio is Chapter 7 Sediment Erosion and Deposition 7-21 Page 1 of 2 400 350 a� 300 a� —250 c 0 ,6200 d w 150 100 50 0 0 0.2 0.4 0.6 0.8 1 1.2 16 14 ■ 0 12 Q 10 t ' Q 8 0 O • t 6 ■ • ■ Width:Depth Ratio -B 4-- 2 0 0.00 0.20 0.40 0.60 0.80 1.00 1.20 7 Boulder (>256mm) 6 Cobble (100-256mm) m 5 © O Gravel (25-100mm) ifl 4 ®©©® O O Gravel (c25mm) O 00 O O 00 3 ® Sand 2 © Silt/Organic 1 Channel Substrate O Dominate © Subdominate Bedrock 0 0.00 0.20 0.40 0.60 0.80 1.00 1.20 River Mile Figure 7-5. Gypsy Creek Channel Parameters. Channel Profile, Width/Depth Ratio, Channel Depth, and Width by River Mile Along the Existing Channel. 7-22 Page 2 of 2 9 8 7 a� 6 L 5 a a� 4 c 3 A L 2 U 1 0 0.00 8 7 d 6 m r 5 3: 4 6 c 3 L U 2 1 0 0.00 GvDsv Creek - 0284 0.20 0.40 0.60 0.80 1.00 1.20 River Mile 0.20 0.40 0.60 0.80 1.00 1.20 River Mile Subbasin 0284 Recurrence Natural Interval Forested (( 2 year 6 10 year 10 25 year 13 100 year 16 Existing 02 /Forested Q10 Future 02 /Forested 010 Mitigated Q2 /Forested Q10 Gypsy Creek Existing 1982 (cfs) 16 25 30 38 1.54 2.40 1.73 Future 25 39 47 60 Future ated 18 29 35 44 7-23 between 4 and 9 (Figure 7-5), indicative of a constrained or incised channel. In this case, both apply. Sand is the dominate substrate, while gravel is the next most commonly found particle size; this correlates well with the composition of the eroding advance glacial outwash and valley wall colluvium. Above RM 0.35, this relationship reverses (Figure 7-5), with gravel then sand being the dominant particle size. This change occurs about where the till unit begins. The channel stability index is 1.54 for Gypsy Creek, indicating a strong potential for channel instability. This is verified by the observed actively incising channel. The channel has very little LWD or potential for recruitment in the near future, further aggravating the problem. An unmaintained logging road crosses the channel at RM 0.2. If the culvert were to partially plug, there is a risk that the dammed water could blow out the fill. Because the channel slope is so steep (21 to 33 percent) in this reach, this water could carry all the way downstream to the alluvial fan, where flooding and damage to a home could occur. Future Conditions. Existing and predicted flow increases (Figure 7-3) combined with the high gradient and sandy gravel substrate (Figure 7-5) indicate that impacts to Gypsy Creek will continue. Without mitigation for the past increases in flows and sediment transport, and without any significant LWD, the Gypsy Creek channel will continue to incise and erode, delivering increased sand downstream. Because portions of the channel have already incised into a narrow deep channel form, bank slumps will occur during flood flows leading to a wider channel. An estimated 3,000 cubic yards of sandy material could be delivered from the basin just from bank slumping. Additional material could be expected with continued channel incision. Increased flow and sediment transport will increase channel migration on the alluvial fan and increase sand delivered to May Creek. Honey Creek (0285) Current Conditions. Honey Creek (also called Honey Dew Creek) enters May Creek from the south at RM 2.0. This stream forms a spur to the May Creek canyon, incising through Quaternary alluvium, glacial advance outwash, till, and recessional outwash (Figure 7-6). Most of the Honey Creek basin is already built out. Flood discharges have already been more than doubled. Increased landslides, channel bank erosion, and channel expansion are very apparent from RM 1.0 downstream to the mouth. The lower reach of Honey Creek up to RM 0.3 has a moderate gradient of four to five percent. The lower 0.2 mile of Honey Creek is a deposition zone for bedload sediment transported in Honey Creek during floods. The zone is depositional because of the lower gradient as it crosses the fairly wide and flat May Creek floodplain. This reach is a low, wide alluvial fill where the valley of Honey Creek is wider. Channel substrate is sandy gravel to gravelly sand (Figure 7-6). This is one of the few reaches in the basin that has some functioning LWD. Channel width ranges from 7 to 22 feet (Figure 7-6). The Chapter 7 Sediment Erosion and Deposition 7-24 Page 1 of 2 Honey Creek - 0285 500 400 w 200 100 0 I i i i i I i i i i I i i i i I i i i i F-ri i i l i i 0.00 0.50 1.00 1.50 2.00 2.50 3.00 35 o 30 ■ L 25 ■ ■ a p 20 ' Width:Depth Ratio 15 ■ 10 ' ■■ ■, ■ . • M ' •' :�' ■ ■ 5 r• �� • 0 ■ 0.00 0.25 0.50 0.75 1.00 1.25 1.50 1.75 2.00 2.25 2.50 2.75 3.00 7 00 6 04>Im 5 4 j J> Z>OEEQO O0 db 4Q N 3 ® ® ® ® O 2 © © © Dominate 1 Channel Substrate O Subdominate 0 0.00 0.50 1.00 1.50 2.00 River Mile Boulder (>256mm) Cobble (100-256mm) Gravel (25-100mm) Gravel (<25mm) Sand Silt/Organic Bedrock 2.50 3.00 Figure 7-6. Honey Creek Channel Parameters. Channel Profile, Width/Depth Ratio, Channel Depth, and Width by River Mile Along the Existing Channel. 7-25 Page 2 of 2 Honey Creek - 0285 4 3 a� • y2 � • ■■ ■ L U 0 0.00 0.50 1.00 1.50 45 HMI: �35 a� 230 L 25 d 20 c 15 L U 10 0 0 0.00 Channel Depth 2.00 2.50 3.00 0.50 1.00 1.50 2.00 2.50 3.00 River Mile Subbasin 0285 Recurrence Natural Interval Forested (c 2 year 7 10 year 13 25 year 16 100 year 21 Existing Q2 /Forested Q10 Future 02 /Forested 010 Mitigated 02 /Forested 010 Upper Honey Creek Existing 1992 Future (cfs) Future (cfs) Mitigated 19 34 22 30 53 34 36 63 41 45 81 52 1.52 2.72 1.76 7-26 channel is incised several feet along portions of this reach. During floods a portion of the sediment transported from upstream is deposited in this reach, leading to channel migration and multiple channels. Some of the old side channels form wetland areas. The channel depth in the lower section of Honey Creek is highly variable with an average of 1.75 feet. The maximum channel width occurs near RM 0.25 and 0.75 and creates the higher width/depth ratio there. All morphological parameters are highly variable in the lower reach. The channel is free to respond to changes in hydrology and or sediment supply. Increased upstream runoff and storm flows leading to increased sediment delivery have degraded the aquatic habitat potential of Honey Creek. A service access road crosses Honey Creek at RM 0.3 at a complex culvert structure. Between RM 0.2 and the service road the valley walls close in, leaving only a narrow valley bottom for the channel to migrate in before it bumps into the valley walls. Upstream of the service road the creek is constrained within the valley walls, with only a few sections that have much room for alluvial terraces. The road fill and nearby landslide creates a two percent grade for a short distance. Above here the gradient ranges from three to seven percent. Prior to logging and pipeline construction there would have been numerous steps in the creek over logs and log jams. Large trees and brush along the channel edge would have held the banks together. There would have been landslides along the valley wall, but not as many as there are now. Starting at RM 1.1 the channel bed is riprapped at a one to two percent gradient. Lack of significant accumulations of sand and gravel in the riprapped bed indicates little is delivered from upstream. The upper reach above RM 1.35 is contained in an underground culvert that runs through a heavily developed commercial area. Above the culvert reach the creek is low gradient (0.5 to 1 percent) with numerous wetlands. From RM 0.3 to the riprapped section above RM 1.1, the channel bed consists of a thin layer of alluvium (zero to five feet) that is over compact tills, advance outwash, and clays. The loose sandy gravel alluvium is mobile during floods. The compact subsurface does not erode as easily as the materials along the steep valley walls. The lack of significant amounts of functional LWD further aggravates the bank erosion and valley wall slumping. The pipeline and service road further aggravates bank erosion because it has encroached into the floodway. Hardening of the fill with riprap and logs further affects the opposite bank. The increased bank erosion is also causing surface slumping of the steep valley walls. The channel stability index for the lower, middle, and upper Honey Creek subcatchments are 1.8, 1.9 and 1.5 respectively, indicating a very strong potential for channel instability (Figure 7-2). The incised channel, eroding banks, and numerous valley wall slumps verify the unstable condition of Honey Creek. Former flood magnitudes were only about one-third the size of current peak flows. The increased flows and natural instability of a constrained non -bedrock channel results in a significant increase in delivery of gravelly sand to May Creek. In 1993, the City of Renton began the first phase of improvements to and stabilization of the sewer line access road and Honey Creek channel. Improvements include the Chapter 7 Sediment Erosion and Deposition 7-27 placement of instream habitat enhancements, riparian vegetation, and new rockwork incorporating biological elements. Future Conditions. Increased flows (Figure 7-3) combined with the high gradient, confined channel, and sandy gravel substrate (Figure 7-6) indicate that impacts to Honey Creek will continue Without mitigation, or perhaps even with mitigation, increased sediment transport from Honey Creek may continue. The banks of the riprapped section (above RM 1.35) are stable because of the good growth of alder and brush, without which the banks would erode. Without intervention the riprapped reach will remain barren, but it could be rehabilitated into a spawning area for fish. A large landslide at RM 0.5 has deeply incised and delivers substantial sediment to Honey Creek. This will continue and worsen unless stabilized. Newport Hills Creek (0286) Current Conditions. Newport Hills Creek enters May Creek at RM 2.68 from the north and passes through a high -gradient reach (12 percent) eroded into the valley wall advance outwash. An old railroad fill (dam) at RM 0.18 crosses the full width and height of the valley (Figure 7-7). At RM 0.18, Newport Hills Creek flows into a pond (inventoried as Class-2 Wetland 12) that is created by the large, abandoned railroad embankment. The pond is drained by a clay outlet pipe connected to a vertical standpipe. At the downstream end of the outlet pipe, outflows have caused lateral erosion, and some pipe has broken away; however, a video inspection of the remainder of the outlet pipe shows that it is in reasonably good condition. Flow also exits the pond via seepage through the embankment. A dam -break analysis was conducted for this structure to evaluate the potential hazard to the downstream houses in the event of a failure of this embankment. The results of this analysis are described in Chapter 6: Flooding. Recommended remedial action is to correct the outlet from the pond to prevent debris blockage. Channel incision and sedimentation was observed below the dam and above the pond created by the dam, up to the road crossing at RM 0.4. The low width/depth ratio, typically between 7 and 10, indicates the channel is incised. Channel substrate consists of gravelly sand to sand. The channel stability index for Newport Hills Creek is 1.2 (Figure 7-2), indicating probable channel instability. Field observation verifies this. Channel incision and erosion has probably been moderated by the detention created by the dam. The channel and channel banks would have been stabilized by mature trees and abundant LWD. Future Conditions. Increased flows, reduced bedload sediment supply trapped at the railroad fill, and the confined gravel -bedded channel will lead to continued erosion of the lower channel. Without mitigation for the past increases in flows and sediment transport, and without any significant LWD, the Newport Hills Creek channel will continue to incise Chapter 7 Sediment Erosion and Deposition 7-28 Page 1 of 2 450 Newport Hills Creek - 0286 400 350 >Qv ad Fill Ovt 8 Tt 2 300 OVt 0 250 200 Oyal w 150 100 Longitudinal Profile and Geology 50 0 0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 16 14 12 0 .6 10 r 8 a aD 6 L 4 2 0 0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 7 Boulder (>256mm) 6 Cobble (100-256mm) 5 d Gravel (25-100mm) y 4 ® DO O Gravel (<25mm) a En 3 0W O © ®O ®O Sand 2 © O 0 O© O Dominate Silt/Clay/Organic 1 © Subdominate Bedrock Channel Substrate 0 0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 River Mile Figure 7-7. Newport Hills Creek Channel Parameters. Channel Profile, Width/Depth Ratio, Channel Depth, and Width by River Mile Along the Existing Channel. 7-29 Page 2 of 2 �4 r d 3 0 5 c 2 C m L U 1 0 0.00 90 80 70 m 60 .0 50 40 N c 30 L U 20 10 0 0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.10 020 0.30 0.40 0.50 0.60 0.70 River Mile Subbasin 0286 Recurrence Natural Interval Forested (( 2 year 6 10 year 10 25 year 12 100 year 16 Existing 02 /Forested 010 Future Q2 /Forested 010 Mitigated Q2 /Forested Q10 Newport Hills Creek Existing 1992 (cfs) Future 12 21 20 34 24 41 31 54 1.19 2.08 1.39 Future a� ted 14 22 26 34 7-30 and erode, delivering increased sand downstream. Increased flow and sediment transport will increase sand delivered to May Creek. Boren Creek (0287), Lake Boren, China Creek (0287), and Tributaries (0287A, B, and C) Current Conditions. Boren Creek joins May Creek at RM 3.3 from the north. Lake Boren and Boren Creek follow a south -trending bedrock valley that has been partially infilled by the glacial deposits. During the Vashon glacial recession, Boren valley was infilled to about the 140-meter elevation. Glacial outwash runoff flowing through the valley eroded down through the till and advance outwash layers, leaving old alluvial terraces along the edges of the valley. China Creek (by which name the stream is called above Lake Boren) and its two tributaries (0287B and 0287C) flow off the bedrock uplands to the east. The creek has deposited an alluvial fan where it leaves the steep valley wall, and it enters Lake Boren at RM 1.3. On the eastern side of the lake Tributary 0287A drains a small ravine containing Wetland 47. Boren Creek drops off the bedrock valley bench at RM 0.15. The channel has eroded down through about 40 meters of glacial advance outwash and till, hitting the bedrock in the channel bed between RM 0.3 and RM 0.5. Boren Creek has experienced increased channel and bank erosion from RM 0.5 downstream to the mouth. China Creek has experienced increased flood flows, transport of channel sediment, and deposition on the alluvial fan. The first 400 feet of Boren Creek ascends out of the May Creek canyon (5 to 10 percent gradient) through compact advance outwash that infills the wider, north -trending, glacial carved bedrock valley. The channel is incised into and constrained by steep valley walls up to the RM 0.5 road crossing. The channel substrate is dominated by sand and gravel to about RM 0.8. Beyond Lake Boren the substrate coarsens to gravel; upstream of RM 1.75 the channel substrate is cobbles with sandy gravel (Figure 7-8). Channel depth remains fairly constant along Boren Creek, between one and two feet, while channel width and subsequently the width/depth ratio displays greater variability and declines upstream. In the China Creek section upstream of Lake Boren, the reduced channel width results in a gradual decrease of the width/depth ratio, but because this section is highly constrained by suburban development in the lower portion and by bedrock above RM 1.6, the channel is not free to respond in a meaningful manner. The lower China Creek section has been highly modified by development, with sections of the creek from RM 1.3 to 1.4 straightened and lined with concrete. The upper reaches have a higher gradient (5 to 16 percent) and contain a seven -foot -high waterfall at RM 1.9. The Boren Creek watershed was divided into three subcatchments for hydrologic modeling. The lower watershed includes up to Lake Boren at RM 1.0, the middle section extends to China Creek, and the upper section is the China Creek drainage. All three subcatchments have a channel stability index of less than one, indicating the flow increases are not as large as the other tributaries in the lower May Valley area. The lower Boren subcatchment channel stability index approaches unity, corresponding with field observations of channel instability. Here the narrow channel, constrained by the valley walls and bedrock bed, leads to increased channel bank erosion. Lack of stream Chapter 7 Sediment Erosion and Deposition 7-31 Page 1 of 2 800 700 600 0 500 a>i 400 w 300 200 100 0 0.00 Boren Creek - 0287 0.50 1.00 1.50 2.00 2.50 25 20 • o • • ro ■ ■ ■ ■ � 15 ■ • • r (ai ' • 0 ' 10 L ■ • ■ ■ 5 To ' ri 0 • 0.00 0.50 1.00 ■ ■ Width: Depth Ratio ■ or -on �' ■ ■ 1.50 2.00 2.50 7 Dominate X Subdominate Boulder (>256mm) 6 XX X) (>X X X 4X • Cobble (100-256mm) 5 >XIX XIX:X)X X X X MO)XI •M • • • Gravel (25-100mm) N j 4 X0 XrX X8 wX �>X �XI X)WX9C X»)IX XX Gravel (<25mm) � 3 • NOND WIX X • M X X 4C OQXX aC • Sand 2 • • • XD X • Sift/Clay/Organic 1 Channel Substrate )X X Bedrock 0 0.00 0.50 1.00 1.50 2.00 2.50 River Mile Figure 7-8. Boren Creek Channel Parameters. Channel Profile, Width/Depth Ratio, Channel Depth, and Width by River Mile Along the Existing Channel. 7-32 Page 2 of 2 4.50 4.00 3.50 3.00 L 2.50 a, 0 2.00 a� 1.50 m 01.00 0.50 0.00 0.00 Boren Creek - 0287 0.50 1.00 1.50 2.00 2.50 30 ■ 25 20 ■ I■■ ■ ■ ■ �15' ■ ■ ■ ■■ on ' c 10 i <o ■ ■ L ■ ■ U 5 0 0.00 0.50 ■ �■ ■■ • ■ Channel Width ■ 1.00 River Mile 1.50 2.00 2.50 Subbasin 0287 Recurrence Natural Interval Forested cfs 2 year 21 10 year 36 25 year 45 100 year 60 Existing Q2 /Forested Q10 Future Q2 /Forested 010 Mitigated Q2 /Forested 010 Lower Boren Creek Existing 1992 (cfs) Future 36 51 62 86 72 107 103 144 1.00 1.41 1.16 Future ated 42 76 98 137 7-33 bank forest, channel LWD, and valley wall LWD supply leaves the lower channel sensitive to moderate flow increases. At RM 0.4 a culvert has failed along Coal Creek Parkway SE. Significant erosion and bank slumping into the stream is evident. The Coal Creek Parkway SE sidecast fill encroaches on the channel floodway because it is overly steep and raveling. Retaining structures and intensive vegetation are needed with the present road width. Widening of the road needs to include extensive retaining structures or the creek will be further degraded. Several of these problems are being considered in conjunction with current planning for roadway widening. Future Conditions. Without mitigation for the past increases in flows and without any significant LWD, the lower Boren Creek channel will continue to have eroding banks, with an increasing number of valley wall slumps resulting. Channel incision is limited, however, by bedrock (Figure 7-8). Increased flow and sediment transport will increase sand delivered to May Creek. Without significant upgrades to the Coal Creek Parkway SE fill, the overly steep fill slopes will continue to ravel and slump into the creek. The old jointed concrete culverts should be replaced with culverts that can't separate at the joints. The culvert outlets need to be adequately rocked down the full length of the inner canyon side slope or slumping and increased sediment delivery will continue. MAY VALLEY SUBAREA (MAY CREEK RM 3.9 TO 7.0) The May Valley subarea contains May Creek from RM 3.9 to RM 7.0. May Creek through this area is low gradient (0.2 percent slope), flowing through an agricultural and livestock -raising region. The tributaries to this portion of May Creek are discussed in the Highlands and East Renton Plateau sections. The low -gradient valley section of May Creek leads to deposition of bedload sediment in this reach. Almost the entire channel has been straightened and moved. Channel structure and diversity has been lost in this reach. Exposed soils along the channel, from poorly managed pastures giving animals free access to the creek, leads to surface erosion into the creek during even minor rain storms. Middle Mainstem May Creek (0282) Current Conditions. May Creek from RM 3.9 to RM 7.0 is a classic underfit stream that flows through the wide, low -gradient (0.2 percent) May Valley. This section of May valley is part of the wide "Kennydale Channel" formed as the Vashon ice sheet receded from the Puget Sound region. The stream channel was first straightened sometime between 1910 and 1936. Periodic dredging continued while farms encroached on the stream banks. The area is currently being used for pasture with unrestricted animal access to the creek. Flooding in this low -gradient reach is common and natural. Chapter 7 Sediment Erosion and Deposition 7-34 The Government Land Survey of 1865, based on field data gathered in December of 1864 (GLO, 1865), shows May Creek (but at that time applying the name Honey Creek to the whole system) as a meandering creek. The 1897 Tacoma and Snohomish Quadrangles (both reprinted in 1940) show with much greater detail that the stream had a meandering channel at that time. Portions of the original May Creek channel, in the low -gradient section, are apparent on aerial photographs. The channel was a meandering channel with frequent side channels. Combined, these sources indicate May Creek was formerly a meandering channel in the entire May Valley section (RM 3.9 to RM 8.0). The original May Creek channel -migration zone, prior to channelization, runs up to the edges of the older recessional outwash terraces, valley wall colluvium, and tributary alluvial fans. Cedars, cottonwoods and willows would have been common streambank and bar vegetation. Forested wetlands would be common in the old side channels. Where the May Creek channel cut into the tributary alluvial fans, there would have been more sandy gravel. The valley has terraces of glacial outwash along the edges. Deposited over these terraces, at the toe of the slopes, are valley -wall colluvium and old landslide deposits. Recent channel and overbank alluvium marks the former channel -migration zone. Throughout this subarea the May Creek channel has been moved, dredged deeper, and straightened. In some sections, dredging cuts through the shallow alluvium into the compact till or advance outwash deposits. Historical dredge piles follow along much of the excavated channel. Channel depth ranges between two and three feet, with channel width typically ranging from 20 to 25 feet with wider sections up to 60 feet wide around RM 5.6 (Figure 7-3). The dominate substrate in this reach is silt and organic material, with sand being subdominant. Small patches of gravel occur where the tributaries enter May Creek. Gravel that enters the channel is quickly engulfed in the dominant silt and clay substrate. First intensive farming, and then grazing and livestock access to streams, have left this portion of May Creek almost completely devoid of functional streambank vegetation and channel LWD. Runoff washes fines from the abundant overgrazed pastures and trampled stream banks into the channel, rapidly increasing the turbidity of May Creek after even minor rains. Future Conditions. Downstream water quality and spawning gravels will continue to be degraded by the fine sediment eroding from the pastures, stream banks, and channel bottom. The dredged channel will gradually infill with sediment, decreasing channel capacity and leading, in the long term, to increased meandering of the channel. HIGHLANDS The Highlands subarea includes all the streams that flow into the low -gradient section of May Valley from the north. With the exception of the North Fork of May Creek, most of the tributaries are in relatively steep, undeveloped watersheds. These tributaries drain the steep Tertiary sedimentary and volcanic rocks of Cougar and Squak mountains Chapter 7 Sediment Erosion and Deposition 7-35 before flowing across the May Valley floodplain with associated Quaternary glacial outwash, till, and recent alluvium. The upper reaches of the Highlands area tributaries are relatively undeveloped. The high -gradient stream profiles and steep terrain yields relatively high runoff rates, even under undisturbed conditions. The channels are stable at present, with the exception of the alluvial fans that are naturally unstable Development in these basins will increase delivery of sediment to the channels, increase channel -forming flood flows, and increase transport of channel -sediment downstream to the alluvial fans. Increased flooding, channel migration, and sediment deposition will occur on the alluvial fans. Unnamed Tributary (0287D) and Unnamed Tributary (0287E) This small unnamed forested tributary (0287D) enters May Creek at RM 4.4. It flows off the bedrock bench to the northwest. The bedrock bench has a thin deposit of glacial outwash and tills over it. The first 0.1 mile flows over a sandy alluvial fan with a gradient of four to nine percent. The moderate gradient (about eight percent) of this stream and its narrow width (four to seven feet) create a series of scour pools and falls in the compact till between RM 0.1 and RM 0.4. The result of this can be seen in the variable channel depth and width/depth ratio (Figure 7-9). Stream banks in the upper tributary appears laterally stable, but can be expected to add sediment to the mainstem due to incision. Channel substrate is a sandy gravel. Long Marsh Creek (0289) and Unnamed Tributary (0290) Current Conditions. Long Marsh Creek enters May Creek at RM 4.6. On the May Valley floodplain it flows over an alluvial fan that rests on Quaternary glacial till and recessional outwash. The gradient is moderate (less than five percent) for the first 0.2 river miles, then steepens to about 10 percent to RM 0.25, and then flattens out in Tertiary bedrock for the remainder of the channel distance. The width/depth ratio is less than 10 up to RM 0.2, reflecting the channel incision and dredging on the alluvial fan (Figure 7-10). Upstream the channel width/depth ratio ranges between eight and 45 reflecting the step -pool channel in a constrained bedrock controlled inner canyon. The channel appears stable upstream of the alluvial fan and outwash deposits in the lower section. The upper section of the stream is forested and stable. LWD, rocks, and vegetation along the streambanks store channel alluvium and prevent channel washouts. Culverts and other barriers are found in the lower 0.3 mile of the stream, with a waterfall appearing at RM 0.2 and a dam at RM 0.3. The channel is incised or dredged on the upper alluvial fan and straightened on the lower fan. This section is in a horse pasture where the animals have direct access to the stream. Channel substrate is sandy gravel with cobbles and boulders, reflecting bedload delivery from the bedrock uplands. Chapter 7 Sediment Erosion and Deposition 7-36 Page 1 of 2 500 450 400 350 c 300 ° Ova 16 250 w 200 150 100 50 0 0 0.05 Unnamed Tributary - 0287D Qvt & Qvr Longitudinal Profile and Geology 0.1 0.15 0.2 0.25 0.3 0.35 0.4 20 015 • Width:Depth Ratio r '10 • o • ■ -75 ' ■ ■ 3 5 • ■ 0 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 7 oulder (>256mm) O Dominate © Subdominate 6 obble (100-256mm) 5 ravel (25-I ffnin)O O©O 4 Gravel (<25� © © © O O 3 and fl© O O O O 2"Sift/Clay/Organic O © © O 1'Bedrock Channel S bstrate 0 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 River Mile Figure 7-9. Unnamed Creek (0287D and 0287E) Channel Parameters. Channel Profile, Width/Depth Ratio, Channel Depth, and Width by River Mile Along the Existing Channel. 7-37 Unnamed Tributary - 0287D Page 2 of 2 4.5 4 ■ ■ 3.5 w_ ■ ■ L 3 Channel Depth 2.5 ■ ■ a� 2 c m 1.5 ■ L 1 ■ ■ 0.5 t ■ ■ Q i i i r—i—f i i i i I i i i i 1 i i i i F i r i r I i r r i 1 r-��-rrrT�■i 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 25 1 jz-20 CD 15 C10 V 5 ■ • ■ ■ 0 0.00 0.05 0.10 0.15 0.20 River Mile Channel Width ■ ■i 0.25 0.30 0.35 0.40 Subbasin 0291A Un-Named Recurrence Natural Existing 1992 Future Interval Forested cfs cfs Future cfs Mitigated 2 year 17 33 43 39 10 year 27 51 68 62 25 year 33 59 81 75 100 year 42 76 104 96 Existing Q2 /Forested 010 1.21 Future 02 /Forested Q10 1.58 Mitigated Q2 /Forested 010 1.43 7-38 Page 1 of 2 800 700 ai 600 0 500 .6 a>> 400 w 300 200 100 0 0.00 Long Marsh Creek - 0289 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 50 • 45 • 40 Width:Depth Ratio o35 ¢ 30 ■ L ■ c 25 ■ ■ ■ 20 ■ ■ IN ■ 0 IN 10 In N. .■ ■ ■ IN • i■ 5■II' ■ ■• ■ p 0 0.1 02 0.3 0.4 0.5 0.6 0.7 0.8 0.9 7 3=x . '. 1 Channel � 0 0 0.1 ® © © Boulder (>256mm) ® E30 © Cobble (100-256mm) O 00 © © © ©0 © © ® O © © Gravel (25-100mm) 000®© O©4U ©© *E3 O ® ® 4*121M Gravel (<25mm) Q O® ©00� *0 Sand O O Silt/Clay/Organic 04000© © O FDorninate © Subdominate Bedrock strata 02 0.3 0.4 0.5 0.6 0.7 0.8 0.9 River Mile Figure 7-10. Long Marsh Creek Channel Parameters. Channel Profile, Width/Depth Ratio, Channel Depth, and Width by River Mile Along the Existing Channel. 7-39 Page 2 of 2 3 2.5 CD Z= 2 r a p 1.5 d c ca 1 r U 0.5 0 0 18 16 aD 14 `' 12 r 10 8 c r 6 U 4 2 0 0 Lona Marsh Creek - 02R4 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 River Mile Subbasin 0289 Recurrence Natural Interval Forested (c 2 year 40 10 year 71 25 year 89 100 year 118 Existing Q2 /Forested Q10 Future Q2 /Forested 010 Mitigated Q2 /Forested Q10 Long Marsh Creek Existing 1992 (cts) Future 42 50 75 85 93 105 125 139 0.59 0.70 0.60 Future ated 43 78 97 130 7-40 The channel stability index of 0.59 indicates a potential for a stable channel. Thus observed impacts in the section that flows across the alluvial fan are probably not related to increased flows. Future Conditions. If functional LWD and riparian buffers are maintained, the upland channel will remain stable even with moderate flow increases. Without the large bed elements to hold the steam channel together, increased sediment delivery to the alluvial fan will occur. The alluvial fan will continue to degrade without attention to animal access and channel vegetation. Country Creek (0292) and Cabbage Creek (0293) Current Conditions. Country Creek and Cabbage Creek share a compound alluvial fan. Country Creek enters May Valley at RM 6.5, and Cabbage Creek has been diverted into Country Creek at RM 0.2. Both streams drain similar and adjacent south facing slopes composed of Tertiary sedimentary rocks with deposits of Quaternary glacial till near the mouths and scattered in the uplands. The Country Creek channel gradient is fairly low (one to seven percent) over the fan (Figure 7-11). It is a wide, shallow stream with low banks that have been disturbed by cattle. Above the fan, after passing through four culverts, the stream deepens where it has been rerouted parallel to SE May Valley Road. Where it crosses SE May Valley Road, the stream flows through another culvert where Cabbage Creek joins (RM 0.2). Upstream of the road the channel has been riprapped and has a series of old water diversion weirs. Above RM 0.2 the stream heads steeply upward through a series of waterfalls on steep bedrock slopes (greater than 15 percent). The watershed contains sparse residential housing. The channel width/depth ratios for both tributaries vary between 1 and 12 on the alluvial fans, indicating the channels are incised and or dredged into the fan (Figure 7-11 and Figure 7-12). The channel stability index of 0.59 for Country Creek and 0.61 for Cabbage Creek indicate relatively little watershed disturbance. Potential for channel impacts is low. Bedload sediment discharge is deposited on the alluvial fan, with the cobbles and boulders being deposited between RM 0.15 and RM 0.3. The channel on the fan has been artificially routed to the west. It is unstable and can migrate during floods. The Cabbage Creek channel on the upper alluvial fan has been turned 90 degrees to join Country Creek at RM 0.2. During floods, sediment will deposit on the upper fan and especially in the backwater of the culverts. This will cause the creek to jump to other portions of the alluvial fan. Above RM 0.2 the Cabbage Creek channel is bedrock controlled, with a series of chutes and falls. Streambank instability is due to a lack of bank vegetation. Chapter 7 Sediment Erosion and Deposition 7-41 Page 1 of 2 900 Country Creek - 0292 800 Z 700 2 C 600 Tt R 500 a� w 400 Qvt 300 Ovr Of 200 100 Longitudinal Profile and Geology 0 0.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 1.80 14 T 12 10 . c , r 8 a a� ■ t 6 • ■ 4 2 ; Width:Depth Ratio 0 ■ 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 7 Boulder (>256mm) O Dominate 6 ©O Cobble (100-256mm) ©Subdominate ,5 13 ©®O © Gravel (25 100mm) m 4 © 001 Gravel (<25mm) (n 3 00 O ® Sand 2 13 Silt/Clay/Organic 1 O Channel Substrate Bedrock 0 0.0 0.1 02 0.3 0.4 0.5 0.6 0.7 0.8 0.9 River Mile Figure 7-11. Country Creek Channel Parameters. Channel Profile, Width/Depth Ratio, Channel Depth, and Width by River Mile Along the Existing Channel. 7-42 Page 2 of 2 3 2.5 ■ d s 2 ■ a • m ■ 0 1.5 • a� c ■ ■ c f° 1 r U • 0.5 0 0 0.1 18 16 14 a� L 12 10 c 8 c t 6 U 4 2 0 0 Country Creek - 0292 Channel Depth 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 River Mile Subbasin 0292 Recurrence Natural Interval Forested (c 2 year 24 10 year 42 25 year 53 100 year 70 Existing 02 /Forested 010 Future 02 /Forested 010 Mitigated 02 /Forested 010 Country Creek Existing 1992 Future (cfs) Future (cfs) Mitigated 26 55 35 46 85 63 57 101 80 77 127 108 0.61 1.30 0.83 7-43 Page 1 of 2 1200 1000 a� a� 800 c 0 600 a� w n aoo cx °" I 200 Longitudinal Profile and Geology 0 0.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 Cabbage Creek - 0293 12 ■ 10 0 8 ■ L a 6 ■ 4 Width:Depth Ratio 2 0 0 0.1 7 O Dominate Figure 7-12. Cabbage Creek Channel Parameters. Channel Profile, Width/Depth Ratio, Channel Depth, and Width by River Mile Along the Existing Channel. 7-44 Page 2 of 2 0 0 18 16 14 iu a 12 10 d 8 c 6 cc L U 4 2 0 0 Cabbage Creek - 0293 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 River Mile Subbasin 0293 Cabbage Creek Recurrence Natural Existing 1992 Future Interval Forested cfs cfs Future cfs Mitigated 2 year 43 46 82 78 10 year 77 81 132 124 25 year 96 101 160 150 100 year 126 133 206 193 Existing Q2 /Forested 010 0.60 Future Q2 /Forested Q10 1.07 Mitigated Q2 /Forested Q10 1.01 7-45 Future Conditions. If functional LWD and riparian buffers can be maintained, the upland channel will remain stable even with moderate flow increases. Without the large bed elements to hold the steam channel together, increased sediment delivery to the alluvial fan will occur. The channels on the alluvial fan will infill with sediment and woody debris during floods. plugging the culverts and dredged channel and causing the channel to shift. The channels on the alluvial fan will become less stable without controls on the flows and channel vegetation. North Fork May Creek (0294) Current Conditions. At RM 7.0 May Creek branches to form the North and South forks. The channel flows through a wide valley up to RM 0.6 of the North Fork where the valley walls start to narrow in on the channel, eventually constraining the channel. The creek mouth is forced to enter May Valley on the west side of the North Fork valley because of a recessional outwash terrace at the end of the valley. Up to RM 0.7 the channel has been moved and straightened. This low -gradient lower portion would have been a meandering multiple channel with cedar, cottonwoods, and alder forest. Wetlands would have been common in the area. Pools would have been formed by large logs eroded from the stream banks during floods. Above RM 1.0 the stream is influenced by two rock quarries and SR-900. The creek flows along the highway as a drainage ditch. The stream gradient varies between two and five percent and contains large amounts of fine sediment and sand (Figure 7-13). At one time this reach would have had a step -pool and riffle -pool channel with abundant LWD delivered from bank erosion of the valley walls and stream banks. The steps would be formed by the LWD. The LWD would have stored significant amounts of sediment behind them and created a diversity of runs, riffles, and pools. Channel depths become highly variable above RM 1.0, while channel width declines variably as it flows in a riprapped channel. The width/depth ratios follows this behavior, displaying the impact of the artificial channel up to RM 1.5. Above RM 1.5 the channel is high gradient (10 percent and greater) and bedrock controlled. It drains from a wetland on Squak Mountain and flows at one side of the Sunset Quarry. The stream, by this point, is highly turbid during runoff events from the road and quarry. The width/depth ratio is between 2 and 10, representing the dredged lower reaches and the excavated and constrained upper reaches (Figure 7-13). Channel substrate consists of sandy silt in the low -gradient lower reaches and changes to gravelly sand in the constrained upper reaches. Channel depth increases between RM 0.8 to RM 1.0 where Wilderness Creek enters. This is possibly related to channel incision in the deposition zone where the creek exits the constrained, higher gradient upper reaches. Gradient increases to two percent in this section, related to the constrained narrow valley that is infilled with valley wall colluvium and slide debris. The channel stability index is 0.61, indicating relatively little development per square mile and also indicating that most of the channel impacts are related to the sediment Chapter 7 Sediment Erosion and Deposition 7-46 Page 1 of 2 800 700 600 a� 500 c 0 CU 400 a� w 300 200 100 0 0.00 North Fork May Creek - 0294 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 1.80 2.00 20.00 18.00 ■ 0 16.00 Ir 14.00 Width:Depth Ratio a 12.00 a) O 10.00 • r ■ -B 8.00 ■ 6.00 ■ 4.00 ■ ; ■ ■ 2.00 M. • ■• ■ ■ ■ ■ 0.00 1 1„ 1 r 1 r' ! I i i i I i i i i I I 0.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 1.80 2.00 7 0 13 Boulder (>256mm) 6 © Cobble (100-256mm) m 5 CQ O O O Gravel (25-100mm) U 4 Gravel (<25mm) U) 311O O® © © *OM MMDO0M 00 O© Sand 2 DI fl 000 O O 0 0000 O Q 0 02 QJ Silt/Clay/Organic 1 O Dominate © Subdominate Channel Substrate Bedrock 0 0.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 1.80 2.00 River Mile Figure 7-13. North Fork May Creek Channel Parameters. Channel Profile, Width/Depth Ratio, Channel Depth, and Width by River Mile Along the Existing Channel. 7-47 North Fork May Creek - 0294 4 '' • 3.5 ' ■ ■ a) 3 2_ • 4:-2.5 •■ ■ ■ ■ ■ CI m '■ ■ '■ ' ■ ■ ■ 0 m ■ O2 ■ .■ ■ a c 1.5 m ■ m ■ m L ■ ■ ■ U 1 ■ ■ Channel Depth 0.5 0 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 20 ■■ 18 16 = 14 ■ 12 - ■ ■ ■ on ■ �10■ 1■ ■■■■ ■ ■■ ■ on ■ ■ ■ .. ■ Milo ■■ ■ ■ CU L 6 ■ • I■ ■ 4 Channel Width ■ 2 0 0.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 1.80 2.00 River Mile Subbasin 0294 Recurrence Natural Interval Forested (( 2 year 105 10 year 175 25 year 211 100 year 268 Existing 02 /Forested 010 Future 02 /Forested 010 Mitigated 02 /Forested 010 North Fork May Creek Existing 1992 Future (cfs) Future (cfs) Mitigated 123 176 169 199 248 242 211 282 277 296 332 328 0.70 1.01 0.97 Page 2 of 2 7-48 runoff from the quarries, encroachment by SR-900, channel realignment, and loss of LWD and LWD supply. Future Conditions. Predicted increased flows (Figure 7-3) combined with the silt, sand, and gravel channel substrate and banks could lead to channel -bank erosion. Without extensive mitigation of the runoff from the quarries, encroachment by SR-900, the loss of channel form caused by realignment, and loss of LWD and LWD supply, the channel will continue to be silted up and lack hydraulic diversity. Wilderness Creek (0295) Current Conditions. Wilderness Creek enters at RM 1.0 of the North Fork of May Creek, draining a steep basin of Tertiary bedrock. The basin is undeveloped and mostly forested. The lower 0.15 mile of channel flows through glacial recessional outwash. The lower section is a low -gradient, fast -water gravel and cobble bed channel. Above RM 0.2 the channel becomes steep (20 to 30 percent) and bedrock controlled. LWD, rocks, and vegetation along the streambanks stores alluvium along the creek channel and helps prevent channel washouts. Future Conditions. If functional LWD and riparian buffers are maintained, the upland channel will remain stable even with moderate flow increases. Without the large bed elements to hold the stream channel together, increased sediment delivery to the alluvial fan will occur. The alluvial fan could degrade without controls on the flows and channel vegetation. East Fork May Creek (0297) Current Conditions. The East Fork of May Creek intersects the South Fork within a flooded wetland and is made up of a collection of artificial ponds and dredged channels that intermittently disappear within the wetlands. The low channel gradient combined with a lack of a distinctive channel precluded meaningful morphology measurements. Based on the landforms and old growth stumps, the lower East Fork May Creek area was once a forested wetland surrounded by forest on the drier valley areas and valley walls. The channel above the wetland is degraded by grazing livestock. The channel and wetlands have been modified by horse paddocks, gravel berms, and chicken wire barriers that constrain the channel. The channel is then routed through riprap and culverts along SE May Valley Road. Above the wetland the gradient increases upstream across the alluvial fan. During floods the channel could shift to a new location on the fan. The channel steepens (greater than 10 percent) as it drains a steep hillside partially developed with residential homes. Chapter 7 Sediment Erosion and Deposition 7-49 The channel stability index is 0.64, indicating a relatively undisturbed basin and potential for a stable channel except on the alluvial fan (between RM 0.45 and RM 0.6). On the alluvial fan the channel flows through a culvert under SE May Valley Road and is forced to turn 90 degrees just downstream of the culvert. Deposition of bedload on the fan, aggravated by the culvert backwater and plugging, creates a need for continual road and channel maintenance on the alluvial fan. Future Conditions. If functional LWD and riparian buffers are maintained, the upland channel will remain stable even with moderate flow increases. Without the large bed elements to hold the stream channel together, increased sediment delivery to the alluvial fan will occur. The alluvial fan will continue to cause maintenance problems at the May Valley culvert, and will worsen without controls on the flows from upstream development and enhancement of the channel inner canyon vegetation. EAST RENTON PLATEAU SUBAREA The East Renton Plateau subarea is south of May Valley. It includes four small creeks draining off the East Renton Plateau, the South Fork of May Creek draining out of Lake Kathleen, and two small creeks/wetlands draining into Lake Kathleen. Tributaries flowing off the East Renton Plateau have relatively little channel erosion in their upper, low -gradient reaches. Channel expansion and erosion is occurring where the creeks flow over the steep valley walls to May Creek. Channel -forming flood flows have more then doubled with current development and will double again with proposed future development. Future development will cause greater channel expansion, erosion, and deposition on the tributary alluvial fans and in May Creek. Greene's Creek 0288 Current Conditions. Greene's Creek joins May Creek at RM 4.5. The alluvial fan and low gradient (between one and three percent) extends upstream to about RM 0.3 (Figure 7-14). The channel is expanding in some reaches as it erodes through compact silty advance outwash. The upper reaches have been straightened. The channel stability index for this subbasin is 1.4, which correlates well with field -observed channel instability. The channel and channel banks would have been stabilized by mature trees and abundant LWD. Future Conditions. Even greater increases in flows are predicted for Greene's Creek (Figure 7-3). This combined with the sandy alluvial substrate will lead to further channel erosion. Without mitigation for the past increases in flows and sediment transport, and without any significant LWD, the channel will continue to degrade, delivering increased sand downstream. Increased flow and sediment transport will increase sand delivered to May Creek. Chapter 7 Sediment Erosion and Deposition 7-50 450 400 350 300 Of Q7 Ova 250 0 co 200 w 150 100 - 50 0 --- — — 0 0.1 0.2 Greene's Creek - 0288 Subbasin 0288 Recurrence Natural Interval Forested 6 Ova 0.3 River Mile 2 year 10 10 year 18 25 year 23 100 year 31 Existing Q2 /Forested Q10 Future 02 /Forested Q10 Mitigated Q2 /Forested 010 Qvt Longitudinal Profile and Geology 0.4 0.5 0.6 0.7 Greene's Creek Existing 1992 (cts) 26 42 52 68 1.41 2.23 1.74 Future 41 66 81 106 Future ag ted 32 51 62 82 Figure 7-14. Greene's Creek Channel Profile Along the Existing Channel. 0.8 7-51 Unnamed Tributary 0291A Current Conditions. This unnamed tributary to May Creek enters the mainstem at RM 5.5 from the south. This low -gradient stream (one to three percent slope) cuts through young alluvial fan and stream terrace sands and gravels near its mouth. The channel varies from indistinct at the mouth to well defined and incised from RM 0.1 to 0.3 at the SR-900 road culvert. The SR-900 culvert acts as a hydraulic control, preventing channel incision from migrating further upstream and creating an aggradation area just upstream. Upstream the tributary flows through compacted Quaternary glacial till, resulting in well defined channel banks and meanders before returning to a braided form at RM 0.3. By RM 0.4 the channel is a single thread that enters a residential area, where it is constrained by culverts and ditches. Horses have direct access to the stream until RM 0.4. Stormwater flows directly into the stream from many homes in the area. Channel depth decreases slowly upstream, while channel width is more variable . Width/depth ratio for the channel mimics channel width and points to the section between RM 0.3 and 0.4 as aggrading, potentially unstable, and flood prone. The channel stability index is 1.17, which correlates well with field observation of channel instability below the SR-900 culvert. The channel and channel banks would have been stabilized by mature trees and abundant LWD. Future Conditions. Without mitigation for the past increases in flows and sediment transport and without any significant stream bank vegetation and LWD, the channel will continue to incise and erode, delivering increased sand downstream. Increased flow and sediment transport will increase sand delivered to May Creek. South Fork May Creek (0282, above RM 7.0), Lake Kathleen, Unnamed Tributary (0282A), and Unnamed Tributary (028213) Current Conditions. The confluence of the South and North forks of May Creek at RM 7.0 (just above the SR-900 crossing) form the mainstem of May Creek. The low - gradient (less than one percent) region of the May Valley where the South Fork enters from the south consists of alluvial fan and terrace deposits over glacial till. The South Fork drains Lake Kathleen and several wetland areas on the East Renton Plateau. The South Fork was misclassified by the WDF stream survey as the headwaters (primary fork) of May Creek. In this report the WRIA number, 0282, is retained for this fork, but the stream is labelled as the South Fork upstream of RM 7.0 on the maps. Channel depth decreases dramatically upstream of the confluence while channel width declines slowly (Figure 7-4, upstream of RM 7.0). This results in the width/depth ratio increasing initially, reflecting a depositional environment with associated wetlands. Upstream of RM 7.3 the gradient increases to 10 to 15 percent. Substrate consists of gravel and sand substrate. This section is in an area of recent residential development. Above RM 7.4 to RM 7.7 the stream passes through an incised ravine (five to nine percent gradient) that is transporting coarse bedload. Channel depth increases while Chapter 7 Sediment Erosion and Deposition 7-52 width and width/depth ratio decreases, supporting field observations of a constrained channel in this reach. This stream reach is relatively undeveloped. Above RM 7.7 the channel gradient reduces to one to three percent, passing through a former wetland that has been developed for residential use. The channel has been modified by dredging and straightening Silt blocks the channel, which is dry during the summer. A culvert connects this modified reach to Lake Kathleen at RM 8.1. Bedload and a portion of suspended sediment load from the upper watershed is trapped in Lake Kathleen and the surrounding wetlands. The channel stability index of 0.65 reflects the runoff buffering of the lake and wetlands. Future Conditions. The channel and channel banks have been stabilized by mature trees and abundant LWD. If this good riparian vegetation along the channel and valley walls continues to be maintained, the channel should not experience significant future degradation. 7.6 KEY FINDINGS Two sediment -related conditions are particularly problematic in the May Creek basin: 1) degradation of aquatic habitat in the canyons of May Creek and the lower tributaries as a result of sediment deposition; and 2) loss of flood -flow capacity of May Creek across the delta. The major sources of sediment to the May Creek delta are in the Lower Basin subarea: the canyon of May Creek, and to a lesser extent the eroding channels of tributaries that enter the mainstem downstream of May Valley. The most prominent of these sources are probably Honey Creek (0285), Gypsy Creek (0284), and Newport Hills Creek (0286). Several channel reaches are already highly unstable, and modeled flows predict that they will degrade further even with mitigation. Furthermore, landscape modification in these areas is already so extensive that there is relatively little area left to manage for mitigation. These subbasins include Gypsy Creek (0284); lower, middle, and upper Honey Creek (0285); Greene's Creek (0288); and an unnamed tributary (0291A). Based on modeled future flow increases, severe future channel erosion problems are possible in eight subcatchments that currently have stable or nearly stable channels. These include lower May Creek (0282), lower and upper Boren/China Creek (0287), Newport Hills Creek (0286), Cabbage Creek (0293), North Fork May Creek (0294), South Fork May Creek (0282, above RM 7.0), and East Fork May Creek (0297). The frequency, duration, and magnitude of flood greater than the critical discharge threshold of significant bedload transport must be maintained to avoid channel impacts. Chapter 7 Sediment Erosion and Deposition 7-53 Chapter 8 Water Quality Chapter 8 Water Quality 8.1 INTRODUCTION The water quality of May Creek is closely linked to the activities occurring on the land surface throughout the basin. Each type of land use contributes a variety of pollutants that can affect the beneficial uses of the water. The water quality in May Creek and most of its tributaries has been affected, to some degree, by human activity such as urbanization, resource mining or agricultural practices. Concentrations of contaminants during storm events can be significant, often exceeding established aquatic life toxicity standards. Water temperature in the May Valley is of concern for fish survival during summer months, and nutrients, particularly phosphorus, entering the creek during storms are at concentrations that often exceed recommended levels. The following sections discuss land uses and their potential contribution to water quality degradation, current pollutant concentrations in stormwater and baseflow, and the impact of future land -use changes on water quality. 8.2 WATER QUALITY CONCEPTS AND REGULATIONS This section summarizes general concepts related to surface water, sediment, and groundwater. Beneficial uses of May Creek are discussed, as well as applicable water quality standards, criteria, and threshold values. WATER AND SEDIMENT QUALITY CONCEPTS Surface Water Water quality can be defined as the chemical, physical and biological integrity of the water. Water quality degradation can include changes in temperature, taste, color, turbidity, or odor, or the discharge of any substance into a water body that is likely to create a nuisance or render waters harmful to public health, safety, or welfare, or to domestic, commercial, industrial, agricultural, recreational, or other legitimate uses, or to livestock, wildlife, fish or other aquatic life (WAC 173-201A-020). Distinguishing water quality degradation from natural cycles and influences can be difficult, and often requires an evaluation of the system as a whole. Common water quality parameter definitions, significance, and typical ranges used in evaluating the health of a water body are given in Table 8-1. Degradation of a stream can occur through natural or human -caused sources of pollution; these sources can be further classified as either point or diffuse (i.e. Chapter 8 Water Quality 8-1 Table 8-1 Definitions, Significance and Possible Sources of some Water Quality Parameters that are used in Evaluating the Health of a Water Body. Page 1 of 2 Possible Parameter Definition Significance Sources Carbon. Total Concentration of Metals adsorb to and are Vegetation, organic (TOC) carbon associated transported by carbon and soil, animal with organic particulates. TOC is used for wastes, oils material determining relative risk of and greases three organics. Coliforms, Bacteria present in Fecal coliform bacteria are not Failing septic Fecal (FC) the gut and feces pathogenic but are possible tanks, waste of warm-blooded indicators for pathogenci from wild and animals bacteria. domestic animals and livestock Nitrite (NO,-) Concentration of A measure of the bioavailable Failing septic and nitrate oxidized forms of forms of oxidized nitrogen tanks, animal (NOA nitrogen (principal- (principally NO,). Nitrogen is waste, farm ly NO,). an essential micronutrient, and and lawn can be a limiting nutrient for fertilizers, biological productivity. combustion >10 mg/L in drinking water is processes toxic. Oil and Any material that High concentrations are Petroleum pro - Grease, Total can be extracted indicative of water ducts, crank- (O/G) from water by the contamination by large case oil, oils of organic solvent anthropogenic organic animal or veg- trichlorotrifluoro- compounds. etable origin ethane Phosphorus, Total concentration Indicates the trophic state of Fertilizers, Total (TP) of all forms of lakes. Phosphorus is an human and phosphorus essential micronutrient, and is animal waste, most often the limiting nutrient phos. laundry in aquatic systems. Excess products, soil, phosphorus may result in gasoline nuisance algal blooms and aquatic plant growth. Orthophos- Concentration of phate inorganic phosphorus Phosphorus is an essential Fertilizers, micronutrient, and is most human and often the limiting nutrient in animal waste, aquatic systems. Ortho-P is phos. laundry the biologically available form, products, soil, and is used by phytoplankton. gasoline, human and animal wastes Chapter 8 Water Quality 8-2 Table 8-1. Definitions, Significance and Possible Sources of some Water Quality Parameters that are used in Evaluating the Health of a Water Body. Page 2 of 2 Possible Parameter Definition Significance Sources Solids, Total Suspended Indicative of stream clarity Runoff and Suspended particulate matter and suspended bedload. erosion from (TSS) > 0.45 pm Interferes with recreational construction (micrometers) uses and aesthetic enjoyment sites, lawns, of water. Detrimental effects overgrazed to aquatic life and habitat. pastures; quarries Lead (Pb) Concentration of Acute and chronic toxicity to Leaded gaso- inorganic heavy aquatic life. line, paint, car metal batteries, lead pipes, soils Copper (Cu) Concentration of Micronutrient; acute and Vehicle brake inorganic heavy chronic toxicity to aquatic life. linings, metal metal corrosion, paint, wood preservatives, petroleum pro- ducts, soil Zinc (Zn) Concentration of Micronutrient; acute and Corrosion, inorganic heavy chronic toxicity to aquatic life. paint, wood metal preservatives, petroleum pro- ducts, soil Chapter 8 Water Quality 8-3 "nonpoint") pollution. Point source pollution originates from a definite source (such as a pipe, channel, or container), is easily identifiable, and can be traced to a particular individual, residence, business, or activity. Point sources regulated by the Clean Water Act and require a National Pollutant Discharge Elimination System (NPDES) Permit, which establishes limits for specific parameters. No regulated point sources exist in the May Creek basin. Nonpoint pollution from human sources is the primary source of pollutants into May Creek. Nonpoint pollution originates from diverse sources, often over wide areas and is difficult to monitor. Some forms of nonpoint pollution originate from routine daily activities that most people do not identify as sources of water quality degradation, such as driving, gardening, or home maintenance. Other potential sources of nonpoint pollution include agriculture (commercial and small farms), urbanization (construction and stormwater runoff), failing septic systems, improper pesticide/fertilizer applications, hazardous waste disposal, leaking underground storage tanks, landfills, resource extraction (quarries), and forestry operations. These potential sources are discussed in Section 8.4. Sediment Sediments are the loose (unconsolidated) materials at the bottom of water bodies such as lakes, rivers, estuaries, and oceans. Sediments consist of mineral particles (clay, sand, silt, gravel), organic material (plant debris, living and decaying tissue, animal wastes), and water. They are significant because they provide habitat to a variety of benthic or bottom -dwelling aquatic life that provide key links in the food web, leading from nutrients in the water and sediment to fish and wildlife. Sediments can serve as a "reservoir" from which fish and benthic organisms take up contaminants that can be passed along the food chain to larger fish, birds, and mammals until they accumulate to levels that may be toxic to themselves or humans. In addition, people can be exposed to contaminants directly through contact with sediments during recreational activities such as fishing, hunting, wading, and swimming. Contaminants can be introduced into sediments through many routes, including runoff from cropland, farms, lawns, construction, roads, and urbanized areas; spills of chemicals, solvents, fuels, and oils; municipal and industrial plant discharges; and airborne pollutants. Common contaminants that accumulate in sediments include pesticides, herbicides, polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), and metals such as lead, arsenic, and zinc. Once these pollutants are in the water, they tend to accumulate in sediments and provide an indication of the historic and recent contamination entering the stream. Groundwater The term groundwater generally refers to the subsurface water that occurs at and below the water table, in saturated soils and geologic formations. Nearer to ground surface, an unsaturated or soil -moisture regime (vadose zone) is generally present and important in the water cycle because it transports precipitation to the water table to replenish (or Chapter 8 Water Quality 8-4 recharge) the saturated groundwater system. Groundwater usually discharges to surface water systems and in that way creates base flow, the stream flow that occurs during periods of little or no precipitation. In some places surface water systems infiltrate some portion of their flow directly to groundwater. During flood events this kind of recharge is more common because high surface water levels reverse the usual gradient (which is normally from groundwater to surface water). However. most of this extra recharge (called bank storage) is soon released back to the stream when the flood levels recede. Groundwater often has different water quality characteristics from surface water mainly due to its slow travel time and limited contact with air. The long contact period with soil particles allows mineralization to occur from a process of slow dissolution. Groundwater can readily be contaminated. either directly by releases from leaking underground storage tanks or septic systems, or indirectly by infiltration of contaminated surface water. Sources of groundwater contamination are agricultural areas (nitrates, salts, other nutrients, and pesticides), landfills (organic and inorganic contaminants), and highway ditches and drywells (petroleum products and metals). Contaminated groundwater, as the source of base flow, can also adversely affect surface water through discharge into streams, springs, and wetlands. BENEFICIAL USES May Creek and its tributaries are designated by the Washington State Department of Ecology as "Class AA" (superior) because May Creek is a feeder stream to Lake Washington and has not been designated otherwise ( WAC 173-201A-130). Class AA waters can be used for water supply (domestic, industrial, and agricultural), stock watering, fish and shellfish rearing, spawning, and harvesting, wildlife habitat, recreation (primary contact recreation, sport fishing, boating, and aesthetic enjoyment), and commerce and navigation. Fish habitat is discussed in more detail in Chapter 9: Aquatic Habitat and Fish. Water Supply While most residents within the western and southern portions of the May Creek basin are served by the Renton Water District and by Water and Sewer Districts 107 and 90, many residents in the northeastern portion of the basin in the valley rely on shallow wells recharged by precipitation falling on shallow aquifer recharge areas. Livestock, which are plentiful in the upper creek valley, rely on the stream for a continuous supply of water. Aesthetics and Recreation The May Creek basin provides numerous opportunities for recreational and aesthetic enjoyment. The basin contains two lakes used for fishing and boating (secondary contact), a canyon park utilized for swimming and wading (primary contact), hiking, and relaxation, and portions of state/regional parks (Cougar Mountain and Squak Mountain) Chapter 8 Water Quality 8-5 in the northern and eastern part of the basin which are heavily utilized for hiking and biking. The aesthetic and recreational uses of May Creek depend on the integrity of the water quality, which in turn depends on the overall health of the basin's land uses. STANDARDS The State of Washington and the federal government have established water quality standards to protect the use and quality of water resources. Surface waters are defined by class depending upon the existing water quality and the designated uses of the water body, known as "beneficial uses". These standards are consistent with public health goals and the protection and propagation of fish, shellfish, and wildlife. Surface Water Standards Several freshwater standards apply to May Creek and its tributaries to protect beneficial uses. Table 8-2 summarizes the WAC 173-201A-030 freshwater water quality standards for Class AA streams such as May Creek. These standards regulate water quality parameters such as fecal coliform, dissolved gases, temperature, pH, turbidity, and general aesthetic values. Table 8-2. Summary of Standards and Recommended Threshold Valuesi/ for Common Water Quality Parameters for Class AA Freshwater Streams such as May Creek. Water Quality Parameter Class AA Freshwater Standard Fecal Coliform shall not exceed a geometric mean of 50 colonies/100 mL, with less than 10 percent of samples exceeding 100 colonies/100 mL. Dissolved oxygen shall exceed 9.5 mg/L. Total dissolved gas shall not exceed 110 percent of saturation. Temperature shall not exceed 16°C due to human activities. If natural conditions exceed 16°C, no temperature increases greater than 0.3°C. pH shall be within the range of 6.5 - 8.5; human -caused variation within a range of less than 0.2 units. Turbidity shall not exceed 5 NTU over background with a background of less than 50 NTU. If background is greater than 50 NTU, shall not exceed a 10 percent increase. Aesthetic values shall not be impaired (including senses of sight, smell, touch, or taste). 1 / WAC 173-201 A-030. Several important water quality parameters, such as nutrients and total suspended solids, do not have Washington State numeric criteria. Instead, recommended threshold Chapter 8 Water Quality 8-6 values from U.S. EPA or previous basin plans are given in Table 8-3 to serve as guidance values for May Creek. The threshold values for nitrate -nitrogen are based on other study results, water quality monitoring data, and the professional judgment of King County SWM Division staff. The total suspended solids threshold was based on a study of the effects of suspended solids on macroinvertebrate and benthic invertebrate populations (Gammon, 1970). To prevent the development of biological nuisances and to control accelerated or cultural eutrophication, total phosphorus as (P) should not exceed 0.05 mg/L in any stream at the point where it enters a lake. This threshold is important to May Creek, because it flows into Lake Washington. For the health of streams themselves and to prevent nuisance plant in streams, a desired phosphorus goal is 0.10 mg/L total phosphorus (U.S. EPA, 1986). It is important to point out that the current average phosphorus concentration in Lake Washington is below both EPA guidelines; exceeding the current concentration of 0.02 mg/L could result in water quality degradation. Toxic substances, such as metals, are regulated in all surface waters in the state of Washington under WAC 173-201A-040. These criteria regulate substances that have the potential to either singularly or cumulatively adversely affect the most sensitive species dependent upon those waters, or adversely affect public health. Table 8-3. Guidelines for May Creek Basin Planning for Water Quality Thresholds for several Parameters that do not have Established Numeric Criteria. Water Quality Parameter Recommended Threshold Values Total phosphorus 0.05 mg/L" Total suspended solids 50 mg/L2/ Nitrate + Nitrite (N) 1.25 mg/L21 1/ Total phosphates as phosphorus (P) should not exceed 0.05 mg/L in any stream at the point where it enters any lake or reservoir. USEPA (1986). 2/ Guidance values developed for the East Lake Sammamish Conditions Report (King County, 1992). In terms of metals criteria, all surface waters are required to meet both acute (short- term, high levels) and chronic (long-term, lower levels) toxic criteria for the protection of aquatic life. Acute toxicity often causes death. Chronic toxicity can result in disease, reproductive failures, growth inhibition, and behavioral changes. Metal toxicity is dependent on the water hardness; in general, the softer the water, the more bioavailable, and hence the more toxic the metal. Acute and chronic criteria are calculated as a function of water hardness (see Table E-11 in Appendix E). Table 8-4 gives approximate criteria values based on hardness that would apply to May Creek. Chapter 8 Water Quality 8-7 Table 8-4. Calculated Values for Metal Toxicity for May Creek based on WAC Criterial/ and Measured Water Hardness 21 Metal Toxicity Values at 15 mq CaC033/ 41 at 35 mg CaC033 at 64 mg CaC033/ Acute Chronic4/ Acute Chronic Acute Chronic Metal (mg/L) (mg/L) (mg/L) (mg/L) (mg/L) (mg/L) Coppery 0.0026 0.00201 0.0057 0.0042 0.0021 0.00696 Lead5/ 0.005 0.0002 0.015 0.00057 0.032 0.0012 Zinc5/ 0.021 0.019 0.043 0.039 0.071 0.065 1/ Per WAC 173-201A-040. 2/ Metal toxicity depends on the water hardness: the "softer" the water, the more bioavailable and therefore more toxic the metal. Hardness is expressed as mg of calcium carbonate per liter of water. 3/ Acute and chronic toxicity criteria have been calculated for water hardness of 15 and 64 mg CaCO3/liter (the measured range during baseflow and stormflow) and for 35 mg CaCO3/liter (the geometric mean of measurements for May Creek). 4/ Chronic toxicity is long-term low-level exposure that often results in sickness, behavioral changes, cancer. Acute toxicity is short-term high-level exposure that often results in death. 5/ These criteria apply to dissolved metal concentrations. State Water Quality Listings The Washington Department of Ecology is required by EPA to identify waterbodies that do not meet water quality standards and where technical controls are not likely to bring the waterbody into compliance. This list of impaired waterbodies is known as the "305B List." After assessing 97 percent of May Creek, the creek was classified on the 305E List in 1992 as Freshwater Class AA, although two of the beneficial uses were designated as impaired. Primary and secondary contact recreation are reported as impaired due to elevated metals and fecal coliform. Potential sources included in the listing for metals and fecal coliforms in May Creek were pasture land, animal holding/management areas, land development, urban runoff/storm sewers, streambank modification/destabilization, in -place contaminants, and sources unknown. Lake Boren was also listed in the 1992 305B report. Of the 34 percent of the lake that was assessed, Lake Boren was classified as eutrophic (rich in dissolved nutrients), but with no beneficial use impairment. May Creek is also included on the Washington State Department of Ecology's 1994 list of "troubled waters" (water -quality -limited bodies), referred to as the "303D List," because of high fecal coliform counts and elevated metals concentrations. This listing Chapter 8 Water Quality g-g reflects monitoring results that show water quality standards are not being met for these parameters. The Department of Ecology has indicated that those water bodies on the 303D list may be subject to further regulatory action. Sediment Standards Although Washington State has promulgated sediment criteria for marine sediments (WAC 173-204), freshwater sediment standards are only in the preliminary stages of development. The state has, however, summarized existing criteria and guidelines for contaminated freshwater sediment (WDOE, 1991). Excerpts of this summary, including a table providing a compilation of contaminant -specific guidelines, are provided in Appendix E (Table E-1). These guidelines provide the best guidance for assessing the condition of sediment in the May Creek basin. Groundwater Standards Groundwater quality standards for the state of Washington are contained in WAC 173- 200. The intent of the standards is to maintain the highest quality of the state's ground waters and to protect existing and future beneficial uses (a non -degradation policy). A summary of these standards is included in Appendix E (Table E-2). 8.3 POLLUTANT SOURCES This section summarizes the relative potential sources of pollutants in the May Creek basin, and gives relevant background information needed to evaluate current and future conditions for probable sources of pollution. NONPOINT SOURCES Nonpoint source pollution is a principal water quality problem in May Creek. The land uses in the basin that are likely to contribute the majority of nonpoint pollution include urbanization, land conversion, forestry, resource extraction, septic systems, localized agricultural practices, roads and highways. The quantity and quality of runoff varies as a function of the rate and frequency of rainfall, soil type, season, land condition, slope, vegetative cover, and use. Not only is the timing and extent of nonpoint source pollution highly variable, but the effects of nonpoint source pollutants, either singly or in combination, are also variable. Therefore, the effect of a given pollutant on water quality depends upon local site -specific environmental conditions and can require extensive sampling and analysis to determine its specific source and significance. Forest Practices In general, tree removal associated with forest conversion to residential and commercial uses can significantly increase water runoff and erosion through land development and Chapter 8 Water Quality 8-9 associated construction activities. Increased site disturbance, including road construction, stump removal, grading, and attendant soil compaction, creates potential for serious erosion and sediment loads long before a site is stabilized. Natural erosion rates from forests or well -sodded prairies vary from 0.01 to 1.0 tons per acre per year, while construction sites lacking effective erosion and sedimentation control measures erode soil at the rate of 50 to 500 tons per acre per year (WDOE, 1988). During storm events, the eroded soil deposits in streams, lakes, and wetlands where it can have adverse impacts, including: smothering of fish eggs and other organisms; filling of pools and reduction in salmonid habitat; irritation of gills and an increase in the incidence of disease and mortality; increased vulnerability to predation; and alteration of behavior and feeding efficiency (Hicks et al., 1991). In order to assess forest use and conversions of forest land, the King County Resource Planning Section prepared an assessment of forestry in the May Creek basin (King County, 1993b). In this report, forest practice applications (FPAs), current -use taxation for forestry, development applications and pre -applications, and aerial photographs from 1985 and 1990 were reviewed. The report concluded that in general the May Creek basin appears to be in transition from forested and agricultural use to residential development, although many of the largest forested areas are targeted for acquisition by the King County Parks Department. The largest contiguous areas in forest land are in the northern and eastern part of the basin; most of these are in state or regional parks (Cougar Mountain and Squak Mountain). Commercial forestry in the May Creek basin is very limited; only a total of 108.5 acres are taxed for forestry use. Because current use taxation for forestry may represent a discount of more than 99 percent from the property's otherwise assessed value, it is probable that these parcels represent all the parcels in the basin for which owners have chosen long-term forestry. Future land -use pressures for development will probably decrease this acreage. The large forestry -oriented landowners who once owned forest land in May Creek basin (e.g. Weyerhaeuser, Palmer Coking Coal Company, Plum Creek) have essentially given up practicing commercial forestry in the basin. Therefore, commercial forestry operations impacts are not likely to be a significant source on nonpoint pollution. Land Conversion Although land conversion is temporary, the impact of erosion and siltation from disturbed sites is a significant source of sediment and phosphorus. Many studies confirm that the suspended sediment loads of rivers may have increased by a factor of 10 or more as a result of land conversion in a watershed (Novotny and Olem, 1994). Sediment yields from developing urban areas can be extremely high, sometimes reaching values in excess of 100,000 tons per square mile (Novotny, 1980). Almost half of the basin is currently not forested, representing a significant impact from past clearing. An additional 2879 acres of forest (63 percent of the currently forested acres) is anticipated for future conversion. Chapter 8 Water Quality 8-10 Residential subdivisions are the most common large development type in the basin, especially in the western half of the basin. Clearing in the eastern half of the basin tends to be for single-family residences, which is probably due to the larger lot sizes in the eastern part of the basin (almost all are five acres or larger). Between 1987 and March 1993, two projects —both development of new subdivisions —comprised more than 75 percent of the acreage converted (214 acres out of a basin total of 278 acres). Future developments in the basin will be subject to the sensitive areas codes and drainage regulations of King County or the City of Renton (and of the City of Newcastle as they are prepared), which should decrease the potential for adverse impacts on basin hydrology, water quality, and loss or degradation of wildlife habitat. For King County unincorporated areas, the Surface Water Design Manual requirements apply to selected types of development including multifamily, commercial and single family high residential. Single-family development at low densities are not subjected to the Design Manual requirements. The Sensitive Areas Code applies to all development applications submitted since November 27, 1990. Projects permitted prior to the Sensitive Areas Ordinance and Code (e.g. Licorice Fern Phase 2) can be constructed without meeting these requirements because permits were issued prior to the implementation of the ordinance. Urbanization Current land uses in May Creek basin are predominantly suburban residential and undeveloped. The basin's population is approximately 16,000, with the highest density of single- and multi -family homes in the City of Renton in the southwestern portion of the basin. Higher densities also follow sewer extensions south of May Creek, and are developing in the new City of Newcastle. Several commercial districts have developed in the basin: two in the Honey Creek area and one northeast of Lake Boren are located in the urban area, and one small commercial area is located in the rural area along the SE Renton -Issaquah Road. Surface water runoff represents both a quantity and quality problem in urban areas where land use has been converted from primarily forested and open space into large impervious surfaces in residential, commercial, and industrial areas. High stream flows associated with urbanization result in stream bed scouring, erosion, and harm to salrnonids and degradation of habitat, and these effects are seen in the lower May Creek reaches, adding to the natural erosion in the canyon and side ravines. Typical pollutants found in surface water runoff in urbanized watersheds include bacteria, heavy metals, and organic compounds (primarily PAHs and petroleum products). Significant pollutant sources in urban areas can include vehicular traffic, street litter accumulation, failing septic systems or leaking sanitary sewers, fertilizers, construction activities, domestic pets, metal corrosion and pesticides. Urbanization can increase pollutant input to streams by at least an order of magnitude over pre - development levels (Schueler, 1987), and urban area water quality is often degraded to the point that beneficial uses are compromised. Chapter 8 Water Quality 8-1 1 Motor vehicle traffic is directly responsible for the deposition of substantial amounts of pollutants, including toxic hydrocarbons (gasoline and oil), asbestos (brake and clutch linings) and toxic metals (copper, lead and zinc) (Kirkpatrick, 1990, Novotny and Olem, 1994). Sediment and a variety of contaminants tend to accumulate on impervious surfaces like roads and parking lots between rainfall and storm events, then are washed off into storm drains or directly into streams during heavy rainfall. Large sources of vehicular runoff in the basin are SE May Valley Road and the SE Renton -Issaquah Road, each of which runs the length of the basin, and the 1-405 crossing and Coal Creek Parkway SE. Coliform bacteria are also present in high levels in urban runoff and can be expected to exceed EPA water qualitv criteria during and immediately after storm events in many surface waters (EPA, 1983), especially in areas where failing septic systems are present or livestock have uncontrolled access to the streams, and this is observed in the May Creek basin. In heavily urbanized areas, it is observed that pets usually replace farm animals as the major nonhuman source of fecal pathogens. In urban areas where streamside vegetation is removed, mean summer water temperatures generally increase and mean winter water temperatures generally decrease. In the mainstem of May Creek this pattern is reversed, with the forested canyon and ravines urban areas provide cooling, while the open and unshaded May Valley reach in the rural area exhibits temperature problems. As urbanization continues and densities increase, the quantity of pollutants will also increase (see Section 8.5). Onsite Sewage Disposal Systems Recent and historic storm water quality data collected by Metro and other King County departments show elevated levels of fecal coliform bacteria and nutrients throughout the basin. Fecal coliform bacteria, found in the intestines of warm blooded animals, are an indicator of the presence of other pathogens. The two principal sources of fecal coliforms in the basin are livestock waste and failing septic systems; both of which are potential health concerns. It is often difficult to distinguish between the two sources of coliforms in water samples; an attempt to distinguish the two sources by subarea is discussed in Section 8.4 below. Portions of the May Creek basin are currently served by two sewer districts. The City of Renton provides sewer service to areas within the city limits. Much of the northwestern area of the basin is serviced by Sewer District 107. The areas currently connected (or in construction planning) to public sewer systems are shown in Map 9 in Appendix B; the remainder of the basin uses onsite sewage disposal systems. A typical onsite septic system consists of a septic tank and drainfield. The septic tank provides initial treatment of liquid -borne wastes and settling of solids. The drainfield dis- perses wastewater into the surrounding soil and must be sized adequately to allow con- stant flow from the septic tank into the soil. Purification of the wastewater occurs in the soil surrounding the drainfield, removing nutrients, bacteria, metals, organics, and toxins. Chapter 8 Water Quality 8-12 The efficiency of removal depends on the soil type and depth of soil to a saturated or impermeable layer. The average life expectancy of an onsite sewage disposal system is 20 to 40 years, if adequately maintained. Typically, systems over 20 years old are more likely to fail. The average age of systems in the May Creek basin is 21 years. Onsite sewage disposal systems become a nonpoint pollution source to ground and surface waters when they begin to fail. A failure occurs when the volume of effluent exceeds the absorbent or treatment capacity of the soils and results in a backup of the plumbing or the release of partially treated effluent onto the ground surface. This type of failure constitutes the most obvious system malfunction and does not address potential contamination of groundwater through inadequate treatment of effluent by surrounding soils. Cause of system failure is usually due to siting in marginal or unsuitable soils, inadequate design, improper construction, lack of maintenance, or abuse of the system. Systems that have not yet backed up, but release partially treated effluent onto the ground surface, are in a prefailing condition. Prefailing systems may exhibit one or more of the following characteristics: 1) lush vegetation growth over the drainfield, indicating sewerage may be rising near the ground surface; 2) wet or swampy areas adjacent to or in the drainfield area; or, 3) profuse growth of wetland plants over the drainfield. The ability to treat and absorb sewage effluent is dependent on the receiving depth, structure and texture of the soils. Soils such as clays or clay foams (e.g., Kitsap series) are efficient in filtering and attenuating contaminants but are limited in their ability to carry effluent flows. Coarse soils (e.g., Everett series) have a substantial capacity to accept effluent, but the high permeability of the soil and consequent low retention time in the vadose zone is ineffective in removing contaminants. Septic systems installed on these highly infiltrative soils (rocky or sandy) or on steep slopes may fail due to the inadequate soil absorption of the effluent. The majority of the soils in the May Creek basin are Alderwood gravely sandy loam (49 percent) and Ovall gravely loam (24 percent). These soils are moderately well drained with a shallow hardpan layer at a depth of 20 to 40 inches. In 1993, the Seattle -King County Department of Public Health (SKCDPH) reviewed the status of onsite sewage disposal system failure in May Creek basin (SKCDPH, 1993c). The review included a file review of 995 onsite sewage disposal records throughout the basin, followed by field surveys in fourteen target areas. Target areas were selected based on the clustering of septic system problems (repairs, failures) or proximity to sensitive areas, such as May Creek, and encompassed 89 percent of the unsewered homes in the basin. Approximately 37 percent (322) of the systems in the target areas were field inspected. Map 10 shows the target areas and those systems in a failing or pre -failing condition at the time of inspection. Within the target areas, prefailure or failure rates determined during inspection ranged from 0 to 31 percent, depending on the target area. Target areas located at SE 89th Place, Lake Boren, 156th Avenue SE and Evergreen Terrace had the highest failing and prefailing rates at 31, 17, 17, and 15 percent, respectively. The average failure rate for the basin was six percent (of those inspected). These results likely represent the current condition of onsite sewage systems throughout the basin. This rate is higher than the three -to -five percent failure rate for the entire Puget Lowland (PSWQA, 1989), lower Chapter 8 Water Quality 8-13 than the 8.8 percent failure rate of the adjacent Cedar River basin, and similar to the rate observed in the Issaquah basin (5.5 percent). Table E-3 in Appendix E compares repair rates and ages by target area (neighborhoods) for systems reviewed. Of the 995 systems reviewed, the average repair rate for which any system was repaired at least once is 16 percent. This average is higher than the approximate nine percent average repair rate for a similar study in the neighboring Cedar River Basin. Some septic systems with records of repairs also have had multiple repairs to the same system. When considering multiple repairs to the same system, the average repair rate basinwide is 18 percent. Locations with the highest repair rates, including multiple repairs, are SE 122nd Street (51 percent), 156th Avenue SE (33 percent), and 151 st Avenue SE (35 percent). The survey also revealed that eight of the 20 failing or pre -failing systems had either marginal or inadequate reserve area in which to make repairs. The inability to repair such systems results in repeated overflows and health and environmental risk. As a standard practice, the Health Department does not take action for prefailure conditions, although owners are required to repair failing systems. If a failed system has inadequate reserve area, construction of an alternate system (such as a mound system) will be required to properly treat the wastes. Additionally, present standards for minimum lot size for residences with on -site septic systems is generally 12,500 square feet. In some cases this threshold may vary depending on septic system characteristics. Within the target areas of May Creek, 53 percent have lot sizes smaller than the current minimum required. There are several significant points which should be considered when evaluating these results. Onsite sewage disposal systems installed prior to 1970 were generally designed for disposal, not treatment, of wastewater. These systems account for approximately 44 percent of the systems reviewed, and may be a source of nonpoint pollution of groundwater if located in excessively permeable soils or within high recharge areas above groundwater. The Washington State Department of Health has determined that a minimum of three feet of unsaturated soil is needed to assure adequate treatment of effluent and to protect potable groundwater aquifers (WAC 248-96-100). This required soil depth is most often limited by seasonal high water tables. Most soils in the basin (73 percent) are moderately drained (Alderwood and Ovall series) underlain by shallow, slowly permeable glacial till with seasonal water table depths of 24 to 40 inches. Prior to 1987, the Seattle -King County Department of Public Health allowed conventional gravity -type onsite disposal systems to be placed on sites with 30 inches of suitable soil. A minimum of 18 inches of native permeable soil between the drainfield and groundwater, or other restrictive layer, was required. In July 1987, the minimum separation between drainfield and restrictive layers was increased to 36 inches for gravity systems and 24 inches for pressure distribution systems. The average depth for systems with recorded soil types in the SKCDPH files is 37.5 inches. Fourteen percent of systems reviewed had soil depths recorded. Of those systems with soil types, 39 percent had soil depths less than the minimum required. Chapter 8 Water Quality 8-14 To summarize, many of the septic systems within target areas of the May Creek basin were designed under older standards, requiring less reserve area and less soil depth. Repair rates and the percentage of systems in a prefailing or failing condition are lower than the Cedar River basin but higher than Puget Sound averages. Several target areas had significantly higher prefailure and failure rates than the basin average. Evidence of existing systems in failure and prefailure conditions indicate that inadequately treated wastewater is potentially entering groundwater and surface waters. Without proper maintenance, these systems will continue to contribute pollutants to the May Creek system. Livestock and Other Animal Wastes Livestock The primary source of agricultural nonpoint pollution in the May Creek basin is livestock on small commercial and non-commercial operations. Without landowner awareness and proper management practices, livestock ownership on small parcels is expected to remain a significant source of nonpoint pollution in the future. Throughout the county, the land use trends are toward smaller parcels of land, usually under ten acres, with numerous non-commercial farms or "small hobby farms" (KCD, 1992). Often, the land used for livestock is "non -buildable" such as in wet areas, along streams, on slopes or in areas with poor soil. Additionally, these small farms frequently have higher densities of animals than the land can support without good management practices. The cumulative impact of inadequate livestock and pasture management of many small livestock operations can have a significant impact on water quality, aquatic habitat and riparian zone buffers. Though streams and wetlands provide convenient and inexpensive pasture and water sources, unrestricted animal access to waterways contributes pollution both from animal wastes and eroded banks trampled by livestock. Streambank destruction eliminates riparian vegetation that filters pollutants and stream canopy cover which results in increased water temperatures, less protective area, and decreased woody debris input. In addition to direct access, overgrazing of pastures combined with compacted soils produce increased runoff, washing nutrients and bacteria into the water system. Several studies have isolated animal -associated enteric viruses and bacteria that can be transmitted to humans in stormwater or surface waters in urban, rural and agricultural watersheds, indicating that the disease -causing potential of these sources cannot be ignored (O'Shea and Fields, 1992). Animal wastes are potential sources of 150 diseases including cholera, tuberculosis, polio, and respiratory diseases. A recent study was conducted by the King Conservation District and King County SWM to locate and characterize livestock keeping practices of small non-commercial farms in relation to water quality in May Creek basin (KCD, 1992). Farms were located by aerial photographs and by windshield surveys of the basin. The study located 126 animal keeping sites. The highest concentration of small farms is in the east of Honey Creek and along the May Valley (see Map 11 in Appendix B). Most of the small farms contained a few animals, mostly horses, on no more than five acres of land. Livestock seen during the survey included 345 horses, 46 beef cattle and 175 other animals (llamas, sheep, goats, and pigs). Actual livestock numbers in the basin are assumed to be higher because more animals may have been present than were actually observed. Chapter 8 Water Quality 8-15 Table 8-5 shows pasture size in relationship to livestock density (animals per acre of utilized pasture). Many of the farms (74 percent) are small (five acres or less) and animal densities exceed the capacity of the pasture to support them. The density of livestock alone does not in itself pose a nonpoint pollution problem if animal -keeping best management practices (BMPs) are employed. However, the absence of BMPs combined with an animal density exceeding the carrying capacity of the land dramatically increase the potential for chronic nonpoint pollution. From the observed farms, it appears that approximately one-third to one-half of the farms were implementing various BMPs. Table 8-5. Livestock Densities by Farm Size in the May Creek Basin.1/ Average Livestock Density Farms Pasture Size (animal units/pasture acre) (number) N Less than 1.5 acres 3 15 12 From 1.5 to 5 acres 1.2 76 62 From 5 to 10 acres 1.4 20 16 From 10 to 20 acres 0.5 10 8 More than 20 acres 0.25 1 1 Average Density2l 1.4 1/ Source: Small Farm Nonpoint Pollution Project, King Conservation District (1992). 2/ Calculated using the average livestock density multiplied by the number of farms in each size category and divided by the total number of farms. Livestock density can be used as a measure of pollution potential for livestock operations. Daily waste production from the animals observed in the survey is estimated at 21,000 pounds, or the equivalent amount of waste generated by a human population of 4,350. This waste must be properly contained and utilized to prevent water pollution. When properly utilized, the amount of nutrients in the animal waste applied or spread on the land equals the amount of nutrients used by the pasture vegetation. Over -fertilization with manure can result in excess nutrients, organic matter and bacteria washing into May Creek. The amount of nutrients utilized by a pasture varies with the species of grasses and soil type. A well managed acre of pasture on Alderwood soils, the predominate soil type in the basin, can produce up to three tons of bluegrass per acre per year (PSCRBT, 1992). This grass production will fully utilize the nitrogen in the waste produced annually by one full-grown steer or horse (one animal unit). One third of the farms surveyed had poor pasture conditions resulting from high livestock densities or livestock use of pastures with saturated soils. In poor condition, it is estimated that three acres of pasture is required to utilize the waste of one animal unit (PSCRBT, 1992). Approximately half of the farms surveyed produce more livestock manure than could be utilized by the pasture size. Combined with the poor manure management observed in some form at 90 percent of the farms surveyed, excessive nutrient and bacteria concentrations in runoff is likely. Excessive nutrients can result in eutrophication, which can cause algal blooms, excessive plant growth in lakes, aesthetic problems (taste and odor), and low dissolved oxygen conditions in deep waters. Chapter 8 Water Quality 8-16 When available pasture cannot utilize all the manure produced, due to either a lack of acreage or a lack of grass production, excess manure must be collected, properly stored, and applied elsewhere. Waste storage is especially needed in winter months to prevent wastes from being applied during the non -growing season or especially wet periods. During these periods, the ground is saturated and infiltration rates are low, resulting in excess runoff. Waste storage areas can include lagoons, bunkers, paddocks and barns, which can also serve as animal confinement areas. Animal waste storage areas should be located away from flowing surface water, ditches, swales, and areas with shallow groundwater tables, and they should be covered. Given some of the manure storage practices observed in the basin, excessive nutrients, bacteria and organic matter from animal wastes contribute to the current degradation of May Creek's water quality. Management of roof water from barns and sheds is critical to reducing nonpoint pollution from animal waste on many small farms. Using an approximate annual precipitation of 45 inches per year, a ten -by -ten foot roof in May Valley would collect over 2,800 gallons of relatively clean water per year. If this volume were to flow through a manure collection area and flow through an overgrazed pasture to a creek, contaminants would enter the creek. Of the farms observed in the survey, 59 percent of the farms do not have roof runoff systems. Of the 22 percent that do, downspouts at the base of the buildings were common. The preferred option is a buried pipe to carry water from downspouts away from areas where runoff could carry pollutants to nearby waterways. This practice could significantly reduce the contribution of nonpoint pollution and improve barnyard conditions for livestock. Livestock grazing in the May Valley wetland is of particular concern. Unrestricted animal access results in wastes deposited close to or directly in the stream channel, stream bank and fish habitat destruction, and elimination of riparian vegetation and buffers. Overgrazing in the wetland adjacent to the stream channel impairs the wetland function and filtering capacity, and contributes to soil compaction, reduced grass production, and increased runoff into May Creek. A comparison of pasture conditions for nine King County watersheds is shown in Table 8-6 (King Conservation District, 1992). In general, pasture conditions in King County are evenly distributed among poor, fair, and good. This table shows that May Creek has an average number of farms under five acres yet has a high percentage of poor pasture conditions. The King Conservation District concluded that out of 126 farms sun/eyed, 32 farms had a stream or creek running through it, and 17 of those could benefit by stream fencing. An estimated 17,900 feet (3.4 miles) of fencing would be needed to protect May Creek and its tributaries from livestock damage. Given the survey method, these numbers are most likely an underestimate. Domestic Animal Keeping and Wildlife As rural or agricultural lands shift toward urban uses, the animal keeping practices shift from livestock (e.g., horses) to domestic pets (cats and dogs). Wastes from domestic pets can be a significant nonpoint pollution source, contributing nutrients and coliforms. Wastes are washed from impervious surfaces and yards into streams. A recent bacteriological investigation conducted in Seattle suggested increased coliform levels in urbanizing areas could also be from pigeons and raccoons (Seattle Engineering Department, 1993). Chapter 8 Water Quality 8-17 Table 8-6. Pasture Conditions on Farms in Nine King County Watersheds.1/ Roof Runoff Small Farms Systemy Pasture Conditionti (< 5 acres) With Without Good Fair3/ Poor Watershed % % % % % 1% May Creek 74 22 59 16 37 38 Cedar River 48 3 75 22 37 41 Issaquah Creek 72 32 50 31 41 27 Newaukum Creek 42 22 36 26 49 25 Lower Green River 72 23 58 30 38 32 Bear -Evans- 80 n.d.4/ n.d. 28 40 32 Sammamish East Lake Sammamish 80 30 38 25 39 36 Jenkins Creek 89 23 60 25 35 36 Average 70 22 54 25 39 32 1/ Source: Small Farm Nonpoint Pollution Project. King Conservation District (1992). 2/ Windshield surveys: presence of roofing systems or pasture condition could not be determined for some small percentage of farms. 3/ Good: lush grass, well -covered with vegetation (no bare spots or soil showing), not overgrazed, working swales/ditches, manure distributed and being utilized by vegetation. Poor: lacking vegetation or with very short grass, bare spots and soil showing, compacted and often saturated soils, too much manure for vegetation to utilize. Fair is intermediate between these conditions. 4/ No data. In the May Creek basin, wildlife wastes can also be a source of fecal contamination in open spaces, wildlife corridors, and parks. High levels of coliforms in some lakes can be attributed to ducks and geese. However, the total contribution from wildlife is insignificant compared to livestock in the basin. Pesticides/Herbicides The use of pesticides and herbicides in agriculture, roadside maintenance, forestry, and household products presents a potential water quality threat to the May Creek basin. Persistent pesticides with the potential to migrate from application sites have the highest Chapter 8 Water Quality 8-18 potential to be nonpoint source pollution problems. In particular, herbicides tend to be water soluble and therefore more easily transported. In general, pesticide effects on aquatic organisms vary with the relative toxicity of the pesticide, its persistence in the environment, and its tendency to accumulate in the food chain. The amount, method, and timing of application, and the intensity of the first storm event following application, affect pesticide exposure. The application of pesticides within the basin is governed by state regulation (WAC 16- 228 General Pesticide Rules) and applies to labeling, ingredients, distribution, transportation, application, use restrictions, and disposal. Users of pesticides in the May Creek basin, in addition to private residential users and farms, are the WSDOT, school districts, and commercial applicators. The Washington State Department of Agriculture (WSDOA) may use contract applicators of pesticides for occasional applications of a specialized nature, such as the Gypsy Moth Program. King County Department of Public Works, Roads and Engineering Division, uses herbicides but not pesticides in its roadside maintenance activities. At the present time there are no pesticide manufacturers in the basin. The Seattle -King County Board of Health recognized that WSDOA is primarily concerned with the agricultural applications of pesticides, and that the WSDOA's did not adequately address urban pesticide problems. To address this regulatory gap, King County adopted a pesticide ordinance in 1993 that establishes a Pesticide Advisory Council, requires registration of businesses and master applicators, and applies to all commercial pesticide applicators. All registered master applicators must pass an examination concerning topics such as pesticide applications in environmentally sensitive areas, integrated pest management, and pesticide storage. Pesticides are sprayed along railroads and highways (but not county roads), and are of concern because these transportation corridors are often located directly adjacent to main waterways, are routinely sprayed, and the pesticides are generally applied in porous soils. Diuron®, Oust®, and a small amount of Roundupe are used for roadside and ditch maintenance by the WSDOT Diuron is a State -restricted pesticide in order to protect groundwater (WAC 16-228-164); Oust and Roundup are not restricted -use pesticides. The Washington Department of Transportation applies more Roundup than Oust in its pesticide application program. In 1992, WSDOT sprayed 3.6 oz. of Oust and 1 lb. of Roundup per acre along the shoulder strips of SR-900 within the May Creek basin. The total mixture sprayed between mile post (MP) 13.00 to MP 21.42 was 210 gallons. In the same year, 3 lbs. of Garlon® 3a, and 2.9 lbs. of 700 Banuel® was applied per acre for noxious weed and brush control along SR-900, for a total of 150 gallons of mixture. Thirty-five gallons of the same mixture of Oust and Roundup was sprayed along 1-405 between 112th Avenue SE and Coal Creek Parkway SE, as was 10 gallons of the same mixture of Garlon and Banuel for brush control. No change in the present spraying program is anticipated. To monitor the concentration of Diuron, Oust, and Roundup in the spray areas, the Seattle -King County Department of Public Health has a pesticide monitoring program in Chapter 8 Water Quality 8-19 which roadside soils and water are routinely tested. Samples were taken immediately before and after spraying. During the pesticide monitoring program, no herbicides were detected in the water samples. Diuron and Oust were present in the roadside soils for less than one week. Roundup was not tested because it is only applied by hand sprayers to the most resistant weeds and was therefore applied in much smaller quantities than Diuron and Oust. The King County Roads and Engineering Division operates a roadside herbicide spraying program in the May Creek basin. The herbicides are not sprayed in ditches or near streams. In 1992, approximately 250 lbs. of Diuron, 250 lbs. of Oust, and 64 ozs. of Roundup were used. The Oust was applied at 4.8 ozs. per acre, Diuron at five lbs. per acre, and Roundup at 32 ozs. per acre. Testing of spray sites showed no residual seven days after application; thus, long-term exposure should be minimal. The WSDOT and the King County Roads and Engineering Division have on -going programs in which information is kept regarding the total amounts, application rates, and types of pesticides/herbicides used in the May Creek basin over given periods of time. Other commercial users must obtain permits from the WSDOA, the lead regulating agency for pesticides, and as a condition of those permits must keep records on the amounts, locations, and types of pesticides they use. To reduce the amount of herbicides sprayed within King County, the Department of Public Works has developed an "Owners Will Maintain Program" which allows property owners to mechanically remove weeds from their ditches. The action, through contracts with the Roads and Engineering Division, allows for the elimination of herbicide spraying in these areas. In addition, a review board is being formed to review the King County Road Department's use and control of pesticides. With respect to small quantity pesticide users (e.g., homeowners and renters), a public education program may be required to promote and market the conservative use of pesticides. In addition, groundwater can be contaminated by the use of pesticides and fertilizers. To date, there have not been any reported incidents of groundwater contamination related to pesticide or fertilizer use in King County. However, groundwater quality in King County has not been closely examined. The proximity of agricultural or other pesticide/fertilizer use areas to aquifer recharge areas is addressed in Section 8.4 below along with the discussion of the aquifer recharge areas. Home use accounts for approximately 20 percent of pesticide use in the Puget Sound area. Although the proper application of pesticides by home users should not pose a significant threat to surrounding water quality, home users often apply pesticides improperly. The use of fertilizers and pesticides by agricultural and non-agricultural users will likely increase by two -to -three percent per year as King County population continues to grow and expand into traditionally agricultural and non-agricultural lands (King County, 1991). Chapter 8 Water Quality 8-20 A golf course is proposed for most of the land presently occupied by the former Newcastle Landfill (see below). Golf courses routinely apply a variety of pesticides and herbicides for the maintenance of greens and fairways. Proper turf management and BMPs can minimize the use and impact of pesticides and herbicides. Solid Waste Management Collected wastes can contribute to nonpoint pollution at all stages from generation to ultimate disposal. Liquids can leak out of dumpsters and collection trucks and wash into the storm drains. Although no large transfer stations are located in the May Creek basin, there is high potential for contaminated runoff to leave the site where wastes are stored or transferred if proper containment is not provided. Landfills are potential sources of nonpoint pollution due to inadequate erosion and stormwater control, and improper management of landfill leachate. May Creek basin contains only one landfill, the now closed Newcastle Landfill, which occupies approximately 70 acres. The landfill was operated from the early 1970s to January 1990 first by the Palmer Coke and Coal and then by Rebanco, and was the only major construction, demolition, and land -clearing waste landfill in King, Snohomish, and Pierce counties. Construction materials dumped at the site included wood, concrete, drywall, masonry, roofing, siding, wire, fiberglass insulation, plastics, styrofoam, twine, cans, buckets, packaging materials, and containers as well as rubble from demolished buildings, floor slabs, parking lot debris, piers, utility buildings, bricks, corrugated metal, creosote -treated timbers, pilings, and wood treated with preservatives. The closed facility is now governed by a 20-year maintenance and monitoring permit from the SKCDPH, because leachate from this type of landfill may result in surface and groundwater contamination if it is not managed properly. A system of groundwater monitoring wells was completed in 1988 with the installation of an up -gradient well east of the landfill and three down -gradient wells on the west. Initially, a priority pollutant analysis was run on samples from all of the wells. Quarterly samples were analyzed for conventional parameters, volatile organic compounds, and pesticides. Several stormwater sedimentation ponds in the southwest corner of the landfill received intermittent contamination from leachate weeps from the landfill, but since that time, better control of the leachate has been initiated onsite by the operator. This includes more effectively covering weeps when they are observed, and installation of a leachate collection and detention facility. Current closure plans include extending sewer lines to pick up the leachate, and installation of proper gas -monitoring wells. Landfills closed after 1989, including the Newcastle Landfill, are subject to standards such as liner placement and leachate management. At this point, however, compliance with these new standards would be exceedingly difficult. Other standards, such as the installation of a non -permeable cover and/or remediation of impacts, must be met, and the site must be maintained by the owner for 20 years or longer to control, minimize, or eliminate the threat to groundwater from leachate. Chapter 8 Water Quality 8-21 Resource Extraction Resource extraction within the May Creek basin includes both logging and quarry activity. At present, logging is occurring only in localized areas for quarry activity and housing construction. Impacts from these activities are discussed in the forestry section (see above). Sediment is the most common pollutant associated with quarries. During the process of gravel mining, large areas of rock and soil are mined and sorted according to size. Fine silts and sands that result from this separation process are often washed into streams or into the drainage systems during storm events, producing significant amounts of sediment in surface water runoff. Downstream, these silts and sands are deposited into the large pores found in stream beds, in essence "cementing" salmon spawning gravels and other aquatic habitat. In a study downstream from the discharge of a rock quarry where inert suspended solids were increased to 80 mg/L, the density of macro - invertebrates decreased by 60 percent, while in areas of sediment accumulation, benthic invertebrate populations also decreased by 60 percent, regardless of the suspended solid concentrations (Gammon, 1970). There were three active quarries within the basin in 1993: Sunset Materials/May Valley Sand and Gravel, Hazen/Palmer Quarry, and Sunset Quarry. Sunset and Hazen quarries are located adjacent to May Creek where it flows along SR-900, and Sunset Materials is located just south of May Creek on the SE Renton -Issaquah Road (SR-900). Runoff from all three sites has been observed on various occasions to be turbid and high in suspended solids, indicating that additional erosion and sedimentation controls are necessary. The turbidity of the runoff water greatly exceeds May Creek background turbidity, and downstream May Creek turbidity was elevated as a result. Missing, inadequate, nonfunctional, or improperly maintained controls have been observed at all three locations. Sunset Quarry, located on Squak Mountain along the North Fork of May Creek, has previously been cited as a major source of silt, sand, and sediment to Tibbetts Creek. In the spring of 1991, the former King County Building and Land Development (BALD) Division (now, Department of Development and Environmental Services) issued an enforcement action against the owner of the quarry. This action required the owner to prepare drainage, erosion, and sediment control plans and to provide enhancement and stream restoration to both Tibbets and May creeks. According to WDOE (Zinner, personal communication, 8/24/93), Sunset Quarry had a State Waste Discharge Permit (applicable to groundwater), which was issued on September 5, 1980 and technically expired on September 5, 1985. However, this permit was "administratively extended" pending the development by WDOE of a class NPDES industrial stormwater permit for quarries and sand and gravel operations to cover surface and groundwater discharges. As of 1995, WDOE has developed NPDES permits for quarries and sand and gravel operations and it is the responsibility of the individual quarries to obtain the permits. Washington State law requires dischargers to apply all known, available, and reasonable methods of treatment (AKART) to prevent and control the pollution of waters in the state of Washington. Discharge includes both infiltration and discharge to surface water. All facilities will be required to manage, treat, and discharge their water in a manner Chapter 8 Water Quality 8.22 consistent with Chapters 173-200 and 173-201 WAC. Otherwise, high suspended sediment loads will continue to degrade the water quality within May Creek. Hazardous Waste Small Quantity Hazardous Waste Generators Businesses that produce moderate risk waste are commonly referred to as small -quantity hazardous waste generators (SQGs). A small -quantity generator is defined by the State of Washington as any business that generates hazardous waste in quantities less than 220 pound per month or extremely hazardous waste in quantities less than 2.2 pounds per month. Household hazardous waste is also included in the definition. SQGs must dispose of wastes properly but are exempt from many of the record keeping and reporting requirements of larger generators. SQGs were investigated by the Seattle -King County Department of Public Health as a potential source of nonpoint source pollution (SKCDPH, 1993a). The increased use of chemicals in the home and in businesses has resulted in increased volumes of hazardous wastes. The basin's population is approximately 9,000, which translates to about 3,000 households. Each of these households may represent a nonpoint source of household hazardous waste (HHW). Leftover cleaners, paints, paint removers, pesticides, solvents, coolants, waste oils, polishes, epoxy resins, wood preservatives, gasoline, and other products containing hazardous chemicals are typically generated from households. In addition, over 100,000 pounds of banned pesticides such as DDT and 2, 4, 5-T have been found stored in King County households. Also, because most of the households in the basin are not sewered, individual septic systems represent another potential source of nonpoint pollution from improper hazardous waste disposal. Those chemicals disposed of in a septic system can percolate through soil and contaminate groundwater, which can be used for drinking water or discharge to surface waters. Hazardous waste also enters surface water through stormdrains via street and parking lot runoff. Direct dumping on the ground or in roadside ditches contributes contaminants to the surface water. King County Solid Waste Division and Department of Metropolitan Services (Metro), and Renton Solid Waste Utility currently have household waste collection and recycling programs to address residential sources. Despite these efforts, it has been estimated that in 1989 King County households improperly disposed of over 6,000 tons of hazardous waste down drains, in trash, and on the ground (SKCDPH, 1993a). Hazardous materials are commonly used in a variety of commercial and industrial businesses in King County. The actual number of businesses that produce small quantities of hazardous waste within the May Creek basin is not known because SQHWGs do not have regulatory reporting requirements, nor were onsite audits conducted. Based on an analysis of all the local businesses in the basin, the Seattle - King County Department of Public Health estimated that at least 101 businesses in the basin have the potential to be small quantity generators. Of these, 84 generators are located in the western portion of the basin, with 70 of these concentrated near Honey Creek. The remaining 17 businesses are located in the southeastern portion of the basin (see Map 12 in Appendix B). Small business generators include motor vehicle service Chapter 8 Water Quality 8-23 shops, which use oil -based products and solvents containing volatile organic compounds (VOCs)(e.g., benzene, toluene, phenols); dry-cleaning establishments, which use such solvents as perchloroethylene and other chlorinated ethanes and ethylenes, commercial printers that use a variety of solvents, and wood treatment facilities that use preservatives that contain heavy metals and polyaromatic hydrocarbons. Within the basin, there are five cleaners, 16 gas/car service stations, five photography/magazine centers, two lumber/timber related services, four lawn/excavating services, two paving/construction companies, one septic tank service, one kennel, and one leather/firearms facility. The rest of the SQGs are restaurants, shops, barbers/beauty salons, medical and veterinary offices, schools, and child care centers. Improper storage, use, or disposal of their wastes can pollute surface water or infiltrate to the groundwater. The proximity of these reported SQGs to aquifer recharge areas is addressed in Section 8.4 below, together with the discussion of the aquifer recharge areas. About 19,000 tons of unregulated hazardous wastes passed through King County's municipal wastestreams in 1988: 16,000 tons in solid waste and 3,000 tons in the sewers. In both, SQG waste accounted for about two-thirds of the tonnage and household waste one-third. It is estimated that by the year 2000, HHW and SQG wastes will increase to 33,000 tons. Jurisdictions in King County developed and adopted in 1991 the Local Hazardous Waste Management Plan for Seattle -King County. This plan focuses on an initial five-year period and a long-term 20-year period, with the goal of 100 percent diversion of hazardous wastes from the municipal wastestreams. Hazardous Waste Generators Five hazardous waste generators have been identified in May Creek basin (WDOE, RCRA Notifiers Listing, February 8, 1993). The locations are scattered through the basin (see Map 12 in Appendix B). Generators are regulated under the federal Resource Conservation and Recovery Act (RCRA), which governs the entire hazardous waste cycle from generation, transportation, treatment, recycling, and storage to ultimate disposal. The stringent requirements of RCRA include comprehensive record keeping, contingency plans, containment designs, waste reduction requirements and many other controls to ensure the safe treatment, transportation and disposal of hazardous waste. Because the number of generators in the May Creek basin is small, and they are extensively regulated, their potential as major sources of nonpoint pollution, unless a large spill occurs, is less significant over the long term than widespread, continual sources such as household hazardous waste or septic systems. Listed Waste Sites Technically, there are no listed hazardous waste sites in the May Creek basin as it is currently delineated. However, the Quendall Terminals site is located in Renton on the shore of Lake Washington, on a portion of the former deltaic fan of May Creek. From 1917 to 1970, the property was owned by Reilly Tar and Chemical Company, which produced creosote and other chemicals at the site. This facility closed in 1970. In 1971, the property was sold to Quendall Terminals, which first used it for oil Chapter 8 Water Quality 8-24 stcrage and now leases it to a log sorting yard. The storage tanks and related equipment for the original manufacturing processes were removed in the early 1980's. A '1973 Environmental Impact Study of the Quendall site revealed widespread contamination by polynuclear aromatic hydrocarbons (PAHs) and volatile organics (benzene, toluene, and xylene compounds (BTX)) on the 25-acre site. Since that time, several site investigations have been conducted, including sampling of Lake Washington sediments offshore from the Quendall Terminals site (April 1990), and well water and soil samples on the site (Spring 1991). Contamination of onsite soils and offsite Lake Washington sediments has been confirmed, with some testing showing PAH concentrations greater than one percent of soil content (WDOE, 1988b). Historical accounts refer to numerous spills and land applications of waste products, which are believed to be responsible for this contamination. Currently, most of the onsite contamination is believed to be sub -surface. No evidence of direct impacts on May Creek was found in a search of WDOE's files, although former creek beds did pass through locations near the south border of the site. According to WDOE personnel, WDOE dredged part of May Creek and the sediments tested clean. Under the proposed Consent Decree, Quendall Terminals will identify the type and extent of groundwater contamination beneath the site as well as impacts to Lake Washington from groundwater migration. Future actions under a Phase-ll Remedial Investigation/Feasibility Study will include defining sources and evaluating cleanup options. According to the present project manager at the Department of Ecology (Sato, personal communication, 8/94), cleanup should begin in approximately five to six years after completion of the final Remedial Investigation, Risk Assessment, and Feasibility Study. The schedule is indefinite at this point. Underground Storage Tanks Commercial and Industrial Tanks Underground storage tanks (USTs) were investigated by the Seattle -King County Department of Public Health (SKCDPH, 1993b) as a potential source of nonpoint pollution in the May Creek basin. USTs are used for the storage of petroleum products and other regulated substances. Leakage of USTs through deteriorated walls and pipes, improper installation and/or spills and overfills poses a potential threat to groundwater and possibly to surface water, depending on the location, type of contaminant leaked, and migration patterns of the groundwater. Single walled, bare steel tanks without corrosion protection, particularly those that have been in the ground over 15 years, are the most vulnerable to leakage. Even relatively small arriounts of certain compounds can have a serious adverse impact on groundwater quality. A one -quarter -inch hole in an underground storage tank can release up to 930 gallons of gasoline in a single day. In addition, USTs can contaminate the environment through fires, explosions, and spills. Twenty-six underground storage tanks have been reported in the May Creek basin since January 1989 (WDOE, 1993). This number includes all known commercial and industrial registered tanks currently in operation or properly closed, but does not include the hundreds of home heating oil tanks exempt from the WDOE UST regulations. Although Chapter 8 Water Quality 8-25 the WDOE has identified 26 tanks in the May Creek basin, this number may underestimate the total because the original registration of these tanks was voluntary. The registration of USTs is now mandatory, so the results may include a higher representation of newer tanks. Fifty-four percent of the 26 total tanks are 21 to 30 years of age and 46 percent fall within the size range of 10,000 to 20,000 gallons. Leaded and unleaded gasoline and diesel fuel account for 85 percent of the compounds stored in the known USTs. The age, contents, size, and frequency of detection devices for these tanks are listed in Table 8-7. Map 12 (Appendix B) shows the location for five USTs. Most of the tanks are associated with fuel service stations in the commercial areas of the basin and are not adjacent to a major tributary or the mainstem except for those near Honey Creek along SR-900. The location of these known USTs in relation to aquifer recharge areas is addressed in Section 8A below, together with the discussion of the aquifer recharge areas. Based on the combined impact of the number of large, old, unsecured tanks, the USTs containing leaded fuel pose the highest risk of leakage, followed by tanks containing diesel fuel, unleaded fuel, waste oil, and the other substances. Table 8-7. Underground Storage Tank Inventory in the May Creek Basin % with number % between % between unknown or no Tank of 10,000 - 21 and 30 detection Contents tanks 20,000 gallons years old devices leaded fuel 10 50 50 60 unleaded fuel 8 50 63 12 diesel fuel 4 251/ 50 50 waste oil 3 331/ 67 33 other 1 100 n.a.ti 100 1/ 50 percent of diesel fuel tanks and 67 percent of waste oil tanks are between 1,000 - 5,000 gallons. 2/ This tank is older than 30 years. The EPA has estimated that nationwide, on average, 25 percent of all USTs are leaking (EPA, 1988). Under this assumption, six to seven tanks within the basin are leaking. While 57 percent of the 26 USTs in the May Creek basin have been reviewed for leak detection systems, 42 percent still need to be evaluated and either removed from the ground or provided with approved leak detection systems. Without these systems, leakage may be occurring without the knowledge of the tank owners or regulators. The WDOE has an active program to identify and register USTs. Detection methods are being phased in depending on the age of tanks. Methods include, but are not limited to, Chapter 8 Water Quality 8-26 tank tightness testing, automatic monitoring control of product level, vapor monitoring, groundwater monitoring, barrier interception monitoring or interstitial monitoring. Of the 26 tanks known in the basin, 15 have some method of leak detection. Eight tanks do not have any leak detection but are required to comply with the regulations. The WDOE assesses a fee to fund the UST program (WAC 173-360). The WDOE can transfer the responsibility for UST enforcement to a local jurisdiction upon request. The annual fees would then be appropriated equitably between WDOE and the local jurisdiction. When delegated responsibility, the local jurisdiction can develop stricter requirements for USTs in designated "Environmentally Sensitive Areas" and can levy higher tank fees. In addition to the UST program, there are federal and state programs to assure cleanup of releases of contaminants from leaking tanks. All known leaking tanks-27 in total —in the May Creek basin have been removed (WDOE, 1993). Remediation efforts such as soil removal, groundwater treatment, and monitoring have been completed at all known sites. Home Heating Oil Tanks The number of home heating oil tanks in King County is not known. These tanks are likely to be found in older residential areas because new homes tend to utilize sources of energy other than oil. Most home heating oil tanks are single walled, without detection systems, and are susceptible to deterioration and leakage. In addition, as other sources of energy replace oil, many home oil tanks have been abandoned and not removed. Because these tanks have not been properly closed, their contents pose a growing threat to groundwater as the tank walls deteriorate. The King County Fire Marshall's Office regulates the removal of abandoned home heating oil tanks and requires that tanks that have remained unused for one year be properly abandoned. Because there is no system to identify residential home heating oil tanks, it seems likely that many abandoned tanks do not comply with the code. The Seattle -King County Department of Public Health is not aware of any incidents of groundwater contamination that have been attributed to home heating oil tanks in King County. However, there has been no attempt to determine whether groundwater is being contaminated from this source. Other Sources Boating Recreational boating and associated facilities such as marinas and launching/access sites can contribute pollutants to lakes. Nonpoint pollutants from recreational boating activities include untreated and partially treated human waste, oils and grease (including petroleum hydrocarbons), detergents, solvents, paints, toxic antifouling agents such as tributyltin (TBT), and litter (particularly plastics and styrofoam). No marinas exist in the May Creek basin, although a there is a public access ramp at Lake Boren. Boating activity at Lake Boren is moderate to heavy, with some usage of power boats. Boating on Lake Kathleen appears to be light to moderate. The levels of boating reported at these two lakes are not expected to pose serious threats to the water quality relative to other land use practices and activities in the basin. Chapter 8 Water Quality 8-27 Utility Rights -of -Way Several local power utilities operate substations and high voltage powerlines that traverse the watershed. Unpaved access roads to tower sites have become popular areas for off -road vehicle and bike use. This usage on steep grades exposes soil and causes water channelization on road surfaces and failures of cross ditch water structures, all of which can contribute to sediment problems. Many of the roads are gated, but uncontrolled access continues in many areas. Trash dumping is also occurring in some powerline areas. Utility roads and rights -of -way can be significant sources of erosion where road construction and maintenance practices are poor. Such roads are usually not paved, and become permanent sediment sources in the basin. Summary of Nonpoint Source Pollution Nonpoint source pollution is occurring in the May Creek basin, attributed primarily to general urbanization (vehicles, human activity, construction, and the like), older failing septic systems, livestock management practices, and resource extraction. Each source contributes a variety of pollutants, and for some sources, the quantity and type of pollutant is directly dependent on operating or maintenance practices such as resource extraction and livestock management. Though the water quality data is limited, it is apparent that nonpoint sources are the primary source of pollution in the basin. POINT SOURCES Point source pollution in May Creek appears to be insignificant because there are no permitted point -source discharges (i.e., NPDES permits) in the May Creek basin (Carriveau, EPA, personal communication, 3/24/94). During stream surveys conducted in the winter and spring of 1993 (see Chapter 9: Aquatic Habitat and Fish), approximately seven small pipes (i.e., less than six inches diameter) were located discharging into May Creek. The source and content of these pipes are not known, but will be investigated by King County. With the exception of Sunset Quarry, the state does not have any record of issuing waste discharge permits within the basin, which are generally issued for temporary (less than one year) discharges (Purell, WDOE, personal communication, 3/25/93). No new permits of this kind are being issued in the Lake Washington drainage area. The City of Renton and King County Department of Metropolitan Services (Metro) are currently considering a new sanitary sewer interceptor line for the Honey Creek area, to connect to the Metro trunk line near Lake Washington Boulevard via a connecting Metro interceptor line (see also Chapters 3 and 11). One of two principal groups of alternatives would construct a gravity -line interceptor in the May Creek canyon downstream from Honey Creek. Unstable soils are found in several locations along the gravity sewer alignments, and there would be the potential for line leakage or breakage due to slope rotation or failure to release sewage directly to May Creek and the LSRA. Such failures have occurred in ravine —located sewer lines in the Seattle -King County area, and one failure occurred in this locale along the City of Renton's former line from the Honey Creek pump station. Chapter 8 Water Quality 8-28 8.4 WATER QUALITY DATA COLLECTION AND ANALYSIS This section contains a brief description of the methods used to collect and analyze water and sediment samples collected in May Creek, and also provides parameter - specific discussions of water and sediment quality issues. Data are compared to standards to determine the locations of sites containing degraded water quality in order to evaluate possible pollutant sources. DATA COLLECTION AND METHODS Surface Water—Stormwater In anticipation of this basin planning process, King County Surface Water Management collected grab water samples at 17 stations during four storm events in 1992 and 1993 (Tables E-4 and E-5 in Appendix E); locations of King County sampling stations are shown on Map 13 in Appendix B. Stormwater quality is difficult to characterize because there is no "typical sample." Samples are influenced tremendously by the intensity and duration of the storm; furthermore, the quality of the stormwater is tremendously influenced by the frequency and intensity of the storm, the timing and location of the sample collection relative to the onset of the storm, and the number of dry days between storms (i.e., antecedent weather conditions). Ideally, the "first flush" runoff, which generally occurs within the first 30 minutes to several hours of a storm event, and which typically contains the poorest quality water, is the preferred sample. However, due to resource constraints and logistics, it is more likely that wet weather samples are collected as soon as possible after the storm begins and during the rising limb of the hydrograph. Surface Water—Baseflow Metro has been routinely monitoring one station (0440) near the mouth of May Creek (corresponding to King County Station 1) at approximately monthly intervals since 1978. In addition, Metro collected samples at five other creek stations and in the two lakes for a limited period. While the Metro data appear to be collected at approximately mid - month or end -of -month, without regard to flow conditions, the conditions tend to characterize baseflow rather than storm conditions. In addition, King County Surface Water Management grab -sampled the mouth of May Creek and at the 148th Avenue SE crossing during summer baseflow conditions. While both ambient (baseline) and storm flow conditions have been monitored, it is important to note that water hydrograph (flow) conditions sampled represent a continuum rather than simply baseflow or stormflow conditions . Temperature Water and air temperature monitoring was conducted during 1993 and 1994 by King County Surface Water Management. Thermometers that record maximum and minimum Chapter 8 Water Quality 8-29 temperatures were installed in four locations throughout May Creek. Readings were conducted on a periodic basis, depending on the season with more frequent readings during the summer months (weekly) and less frequently during the winter. Groundwater The primary interest in groundwater is to understand the connection between the May Creek basin and Renton's groundwater drinking supply; however, available groundwater data for the May Creek basin are limited. Most of the data are out-of-date, unrepresentative of groundwater quality conditions, or not specific as to location within the basin. Sources of groundwater data reviewed include a series of Water Supply Bulletins put out by the state in cooperation with the US Geological Survey (Luzier, 1969, Liesch, et al., 1963-see Chapter 4: Geology and Groundwater); about 150 well logs obtained from the Department of Ecology for the Township, Range, and Sections included in the basin; a database of some 25 community water supply wells obtained from the SKCDPH; and a printout obtained from the Department of Ecology for the water rights permits in the vicinity, again by Township, Range, and Section. The data were examined and taken into consideration in effort to generate a rough map of potential aquifer recharge areas within the basin (see Map 7 in Appendix B). The primary interest is the adjacent watershed groundwater supplies associated with the City of Renton water supply. Potential aquifer recharge areas are those portions of the basin where contaminant releases to the ground have a greater likelihood for reaching an aquifer. Mapping of these areas is required in the Growth Management Act (RCW 36.70A) as regulated by WAC 365-190-080. The possibility that contamination can reach the aquifer is referred to as "hydrogeologic susceptibility." To evaluate the likelihood that the aquifer actually may become contaminated (referred to as the "vulnerability" of an aquifer) requires that this susceptibility be combined with the "contaminant loading potential" (i.e., the possibility that release near the surface could occur). The contaminant loading potential, for each type of land use which could release contamination, is described in the various subsections of Section 8.2 above, particularly with regard to onsite sewage disposal systems, agricultural practices, pesticides, solid waste management, hazardous waste, and underground storage tanks. The methodology used to evaluate potential recharge areas is consistent with that used by the Seattle -King County Department of Public Health for one of the five Groundwater Management Area programs in King County (SKCDPH, 1992; SKCDPH, no date), including one in the Issaquah Creek Valley, adjacent to the May Creek basin. The same methodology has also been used for one other basin plan (Cedar River), but is slightly different than that used by the City of Renton (GeoEngineers, 1992). The procedure to derive the potential aquifer recharge areas combines four factors: surface soils; surficial geology; depth to ground water; and topographic slope. At each location in the basin, each of these four factors was estimated and assigned high, medium, or low values. The four factors were then combined additively, and with equal weight, to get a total score for aquifer recharge potential. Chapter 8 Water Quality 8-30 The surface soil factor was determined by the soil series at each location, as defined by the US Soil Conservation Service [now the Natural Resources Conservation Service](SCS, Terrell and Perfetti, 1973). The soils map was input into the GIS and the different soil series present in the basin were assigned high, medium, or low recharge potential consistently with previous usage or, where a previous estimate for the series had not been made, according to the SCS reported drainage class and permeability. The soil series listed as being present in the basin, and their recharge potentials, are presented in Table E-6 in Appendix E. By this categorization, most of the southern half of the basin is medium in recharge factor, while the much of the uplands in the northern half of the basin are high in recharge factor (see Figure E-1 in Appendix E). There are only limited areas of low recharge factor, mainly in the wetlands in the valley bottom in the middle basin. The surficial geology was determined from a combination of previous mapping and field classification, as described in Chapter 4: Geology and Groundwater. The recharge classifications were evaluated from this data consistently with analyses for previous studies, or (for units not previously classified) by analogy with those classifications. The surficial geologic units, and their recharge potentials are presented in Table E-7 in Appendix E. According to this classification, most of the basin outside the immediate valley is low in recharge potential, while the immediate valley is mainly high in recharge potential with some areas of medium recharge potential (see Figure E-2 in Appendix E). Slopes were estimated consistent with Seattle -King County Department of Public Health recharge potential evaluation procedures which call for classification divisions at 40 percent (22-degree slope angle) and 80 percent (39-degree slope angle) slopes. Slopes in the May Creek basin were estimated by the GIS from a digital representation of the elevations across the basin, in which areas with slopes less than 40 percent were assigned a recharge potential factor of High, slopes 40 to 80 percent were assigned a recharge potential factor of Medium, and slopes greater than 80 percent were assigned a recharge potential factor of Low. According to this classification, virtually all the basin is high in recharge potential, with only small areas of the valley walls and some rugged topography in the most easterly portion of the basin having moderate recharge potential (greater than 40 percent slopes) (see Figure E-3 in Appendix E). Areas with low recharge (extremely steep slopes, greater than 80 percent) were considered to be extremely small in extent. Depth to groundwater was estimated using the "triangulated irregular network" (TINT"^) interpolation system in the ARC/INFOO Geographic Information System (GIS)(ESRIO, 1991). The system is designed to produce a smooth terrain -like surface from a set of scattered data points where elevations are known. The points of assumed known groundwater elevations were specified to be the surface water system of the basin, including streams, lakes, ponds, and wetlands. A map of the resulting estimate of groundwater elevations is included in Figure E-4 in Appendix E. The depth to groundwater was then estimated by subtracting this derived groundwater elevation from the ground surface elevation. This method may overestimating depth to groundwater because the groundwater is higher in between its points of discharge to surface water rather than simply linearly interpolated between the surface water elevations. On the other hand, there are also locations where surface water discharges to groundwater, and here (and between these locations) the depth to groundwater is slightly Chapter 8 Water Quality 8-31 underestimated. The main advantage of this method is that the depth to groundwater is accurately estimated to be zero at locations of wetlands and ponds, a result which is not guaranteed using other methods unless they are carefully checked. Depth to groundwater is greatest (i.e., contributing to low recharge potential) in the highlands between stream segments, mainly in the northern half of the basin but also in the plateau between Honey Creek and the main stem (see Figure E-5 in Appendix E). Areas of shallow depths to groundwater (high recharge potential) are found near the streams and wetlands. Recharge potential factors of High, Medium, and Low were assigned to depth to groundwater categories of less than 25 feet, 25 to 75 feet, and greater than 75 feet, respectively. The four recharge potential factors discussed above (soil, geology, slope, depth to groundwater) were combined to obtain an overall estimate of aquifer recharge potential, based on Seattle -King County Department of Public Health procedures (SKCHD, n.d.). This methodology is equivalent to assigning a numerical value to each of the four recharge potential factors, using High=3, Medium=2, and Low=1, and adding these numerical factors up to give a composite total recharge potential factor which can range between 4 (if all factors were Low) to 12 (if all were High). Composite factors of 4 to 5 are rated as Low total recharge potential, composite factors of 6 to 9 are rated as Medium, and composite factors of 10 to 12 are rated as High total recharge potential. This total recharge potential is indicated in Map 7. This method is only appropriate for a screening -level analysis of aquifer susceptibility. It is important to understand when interpreting Map 7 that "high" is where potential is high, not where recharge is high. Recharge potential concerns only inflow, because the method is designed to screen for areas which may have problems with contaminant sources; it does not deal with outflow from aquifers such as is the issue for wetlands and for groundwater contributions to streamflow and quantity. Sediment Sediment quality data are limited in May Creek basin: the key data come from a recent sampling effort conducted September 15,1992. Sediment samples were collected at 11 locations corresponding to a subset of surface water quality stations, representing sites on May Creek and its tributaries (see Map 13 in Appendix B). All samples were analyzed for the following selected indicator parameters: physical condition: % solids, % volatile solids, grain size nutrients: total phosphorus hydrocarbons: total petroleum hydrocarbons, oil and grease trace metals: aluminum, cadmium, chromium, copper, lead, and zinc. In addition, extensive testing for organic contaminants was performed on the two replicate samples located at station 1 (at the mouth of May Creek). These tests included a scan for semivolatiles (66 compounds by EPA method 8270, GC/MS), chlorinated pesticides/PCBs (27 compounds by EPA method 8080, GC/ECD), and herbicides (nine compounds by EPA method 8150, GC/ECD). The organic analyses were not performed Chapter 8 Water Quality 8-32 on all samples because it is very expensive; data are therefore limited to the two replicate stations. A review of the supporting analytical quality control results indicate that the precision, accuracy, and completeness of these data, as defined by the specified EPA methods, are within acceptable ranges and that significant sample contamination did not occur. The QA/QC data for the comprehensive organic screens of the sediments from Analytical Resources Inc. may be found in their original data reports. WATER AND SEDIMENT QUALITY DATA ANALYSIS Surface Water Quality Assessment Water quality assessments were made by examining existing water quality data from monitoring points throughout the basin and comparing historical data, baseline (non - storm flow) and storm flow data with water quality criteria, standards, and threshold values. Elevated levels of water quality parameters were noted when measured values exceeded applicable criteria, standards, or threshold values. The potential impacts on beneficial uses were then evaluated within the basin based on the data comparison and observations from field surveys. Organic Compounds Concentrations of fats, oils, and grease (FOG) were monitored in stormflow. FOG was below the detection limit (less than 0.25 mg/L) at all stations, except in Honey Creek near the commercial area at 132nd Ave SE where values of 1.3 and 2 mg/L were reported. Total organic carbon (TOC) was monitored in the baseflow and ranged from 2.3 to 5.26 mg/L at the mouth of May Creek and in May Valley at 164th Avenue SE. These FOG and TOC values are not unreasonably high for urban/suburban freshwater systems. Further analysis could potentially identify the type (petroleum or natural) source of the FOG. Metals Analyses for metals were performed in both the baseflow and the stormflow. A full summary of the results and a comparison of measured concentrations to standards are presented in Appendix E (Tables E-8 and E-9). High metals concentrations can contribute to acute and chronic toxic responses in aquatic organisms. The State metal standards are based on dissolved metal concentrations because dissolved metals are believed to be more bioavailable to aquatic organisms, and thus are considered to be a more direct measure of the metal's potential toxicity. Federal metal criteria are based on total metal concentrations. Assumptions reclarding the dissolved metal concentration were required to compare measured concentrations (which are total metals in most cases) to state dissolved metal standards. These assumptions were based on samples collected January 19, 1993 from stormflow samples throughout the basin in which both total and dissolved metals were analyzed in order to determine a metal -specific geometric mean fraction of dissolved metal relative Chapter 8 Water Quality 8-33 to total metal (see Table E-10 in Appendix E). This factor was then applied to all other stations on a metal -specific basis. This provides a rough comparison because the dissolved to total fraction can significantly change with changing hardness, alkalinity, temperature and pH. Because the toxicity generally increases with decreasing hardness, in soft waters some of the numerical criteria can yield very low concentrations that can be hard to measure in some cases. Due to the low criteria values in soft water (such as May Creek), exceedances in urban runoff are very common. In fact, the acute toxicity concentrations for copper are very close to the concentrations reported for pristine waters, and chronic lead toxicity criteria are actually exceeded in pristine waters. Table 8-8 summarizes the number of samples in which metals concentrations exceeded state or federal standards or federal total criteria. The number of exceedances were found by comparing calculated dissolved concentrations to state standards and by comparing measured total metal concentrations to federal criteria. As shown in Table 8- 8, exceedance of criteria for total metals was much more frequent than exceedance of dissolved standards, using assumed dissolved concentrations. Furthermore, when measured dissolved concentrations are compared to site -specific criteria, fewer exceedances occur. This indicates that the use of a geometric mean ratio may overestimate the number of actual exceedances of state standards. In general, measured lead concentrations exceeded the acute standard (denoted lead acute) most often, followed by zinc acute, zinc chronic, copper acute, copper chronic, and lead chronic. Aluminum concentrations were relatively low, ranging from 0.1 to 9.3 mg/L. There are no criteria for aluminum toxicity. Based on the total percentage of metal exceedances, the overall exceedance rank for a site can be calculated. Using this approach, Station 6 (located in a swale in Honey Creek at 132nd Avenue SE; see Map 13 in Appendix B) contains the worst water quality with respect to exceedance of metal toxicity values. The stations ranked as follows, better water quality to the most degraded: Chapter 8 Water Quality 8-34 Station # Location [Least Degraded] 7 Lake Boren outlet (Boren Creek) 10 Long Marsh Creek 13 Country Creek 14 Cabbage Creek 9 May Creek at upstream canyon end 15 May Creek at SR-900 culvert crossing 12 May Creek at 164th Ave. SE bridge 8 China Creek 2 Gypsy Creek 5 May Creek, upstream of Honey Creek 11 Tributary 0291 A 17 South Fork of May Creek 16 North Fork of May Creek 1 May Creek Mouth at Lake Washington 3 Stormline at NE 27th Street 4 Honey Creek, above confluence with May Creek 6 Honey Creek at 132nd Ave. SE [Most Degraded] It appears that the more -urbanized tributaries such as Honey Creek have more metal exceedances and higher concentrations than the less -developed tributaries such as Cabbage and County creeks. It also appears that the number of metal exceedances increase along the mainstem, with the mouth of May Creek containing the highest number of mainstem exceedances. Lead exceeded at least one criteria/standard at all stations, copper exceeded criteria at all stations except Long Marsh Creek, and zinc exceeded at least one criteria/standard at more than half the stations. On a metal -specific basis, the extent of exceedance was determined to evaluate the significance of the exceedance. Table 8-8 indicates a total of 236 exceedances of federal and state chronic and acute standards for all three reported metals combined. In general, about 80 percent of the exceedances were within a factor of three of the lowest criteria (federal, chronic criteria), which means that water quality degradation in these areas is not severe. However certain stations exhibited high exceedances, with lead concentrations being of most concern. In Honey Creek (at both 132nd Avenue SE and at the mouth), measured lead concentrations exceeded the federal, chronic criteria up to 193 and 156 times, respectively. Concentrations greater than 20 times the federal, chronic criteria for lead were observed at the mouth of May Creek, Tributary 0291 A, and the North and South forks of May Creek. Zinc and copper exceedances were not as severe as those of lead. No exceedances were measured greater than 11 times the federal, chronic criteria for these metals. The highest zinc and copper concentrations were found in Honey Creek and the North Fork for copper, and in the stormline at NE 27th Street for zinc. Chapter 8 Water Quality 8-35 Table 8-8. Number of Samples with Metals Concentrations that Exceed Dissolved (State) or Total (Federal) Criteria n Station Number Total Number of Copper Lead Zinc and Location Samples Acute Chronic2/ Acute Chronic Acute Chronic CD D T� D T D T D T D T D T co May Creek mainstem locations 1—Mouth at Lake Washington, 44i 0 3 1 3 0 1 3 4 2 2 2 2 i6 `D 5—Upstream of Honey Creek 4 0 3 1 3 0 1 3 3 1 1 1 1 9—Upstream canyon end 4 0 0 0 1 0 0 2 3 0 1 0 1 12-164th Ave. NE bridge 4 0 2 0 2 0 0 2 3 0 0 0 1 15—SR-900 culvert crossing 4 0 2 1 2 0 0 2 2 0 0 0 0 Tributary locations 2—Gypsy Creek 3 0 1 0 1 0 0 3 3 1 1 1 1 3—Stormline at NE 27th St. 1 0 0 0 1 0 0 0 1 1 1 1 1 4—Honey Creek near May Creek 4 1 3 1 4 1 1 3 3 2 2 2 3 6—Honey Creek at 132nd Ave. NE 4 1 4 1 4 1 3 4 4 3 4 3 4 7—Lake Boren outlet (Boren Creek) 4 0 1 0 1 0 0 0 3 0 0 0 0 Cj rn 8—China Creek 4 0 2 0 3 0 0 2 4 0 1 0 1 10—Long Marsh Creek 3 0 0 0 0 0 0 2 2 0 0 0 0 11—Tributary 0291A 24i 0 2 0 2 0 1 2 4 0 3 1 3 13—Country Creek 3 0 0 0 1 0 0 2 2 0 0 0 0 14—Cabbage Creek 3 0 1 0 1 0 0 2 2 0 0 0 0 16—North Fork of May Creek 4 1 3 1 4 0 0 2 4 1 2 1 2 17—South Fork of May Creek 44i 0 3 0 4 0 0 3 4 1 1 1 1 TOTALS 61 3 30 6 37 2 7 37 49 12 19 13 21 1/ See Map 13 in Appendix B for station locations. 2/ Chronic toxicity is long-term low-level exposure that often results in sickness, behavioral changes, cancer. Acute toxicity is short-term high-level exposure that often results in death. 3/ D = calculated dissolved concentration, T = total concentration. 41 Excluding field replicate. According to these results, water quality within Honey Creek and at its confluence with May Creek is the worst in the basin with respect to metals. Monitoring showed high metals concentrations in the mainstem along SE May Valley Road (approximately 500 feet east of the SE Renton -Issaquah Road), South Fork of May Creek below Lake Kathleen and Tributary 0219A. High metals concentrations were also observed within May Creek just upstream of the Honey Creek confluence. Sources of metals are runoff from heavily traveled road surfaces and general urbanization. Based upon the spatial distribution of high metals exceedances, Honey Creek appears to be a major source of metals contamination. Considering the locations of other stations with high concentrations, road runoff and urbanized conditions appear to contribute significantly to high metals concentrations. Other potential sources include small quantity waste generators (SQGs), such as welding operations and automobile maintenance shops. An illicit hookup survey has not been conducted to determine illegal connections to the stormwater system, thus, such connections might be contributing to the pollutant loading. Storm events wash pollutants that have accumulated on surfaces such as roads, roof tops, and parking lots into stream flow. As is shown in Table 8-9, copper, lead, and zinc concentrations are somewhat higher during stormflow than during baseflow conditions at the mouth of May Creek and at the 164th Avenue SE bridge, the only stations sampled under baseflow conditions. Even larger stormflow-baseflow differences might be occurring at some stations that have especially high metals concentrations during stormflow conditions. Because baseflow has a greater hardness than the storm flow and the metal concentrations are lower, fewer water quality criteria exceedances occur during baseflow conditions. In general, even though water quality criteria exceedances occur, the concentrations of metals measured within May Creek basin are in the low end of the range measured in the nationwide Urban Runoff Program (NURP) study (EPA NPDES Guidance for Modeling) (Table 8-10). Nutrients and TSS Nutrient and total suspended solids concentrations within the basin are of interest for the integrity of May Creek itself and for the health of Lake Washington, which is phosphorus limited. Most of the nitrate/nitrite concentrations did not exceed the suggested threshold level, and those that did were not correlated with high total phosphorus values. Nitrate/nitrite exceedances (Table 8-11) were found at four locations during wet weather and one station during baseflow. In ascending order of nitrate/nitrite exceedances of guideline thresholds these were: Tributary 0219A, Cabbage Creek, May Creek mouth at Lake Washington, Long Marsh Creek, and Country Creek. Nitrate concentrations were relatively similar during both base and storm flow. None of the stations within the basin exceeded the federal criterion of ten mg/L. This criterion is primarily for protection of human health for domestic supply waters, and would not Chapter 8 Water Quality 8-37 Table 8-9. Total Metals Concentrations in May Creek Baseflow and Stormflow May Cr. mouth at L. Washington May Cr. at 164th Ave. SE Metal baseflow stormflow baseflow stormflow (mg/L) (mg/L)" (mg/L) (mg/L)" Copper Acute Toxicity 0.010 0.006 0.009 0.008 Chronic Toxicity 0.007 0.004 0.006 0.005 Measured < 0.01 0.013 < 0.01 0.006 Values Lead Acute Toxicity 0.032 0.015 0.026 0.022 Chronic Toxicity 0.0012 0.0006 0.0010 0.0009 Measured < 0.003 0.013 < 0.003 0.002 Values Zinc Acute Toxicity 0.071 0.043 0.062 0.056 Chronic Toxicity 0.065 0.038 0.056 0.051 Measured < 0.01 0.051 < 0.005 0.03 Values Hardness 2/ 64 35 54 48 1/ Stormflow concentrations are geometric means. 2/ Metal toxicity depends on the water hardness: the "softer" the water, the more bioavailable and therefore more toxic the metal. Hardness is expressed as milligrams of calcium carbonate per liter of water. Table 8-10. Metals Concentrations in May Creek Stormflow Compared to Median Urban Site Values. Median Urban Sitel/ May Creek Stormflow Storm Mean Concentration2/ Range of detected concentration Parameter (mg/L) (mg/L) copper 0.001 - 0.100 0.002 - 0.016 lead 0.004 - 23.0 0.002 - 0.017 zinc 0.010-2.40 0.010-0.342 1/ Nationwide Urban Runoff Program Study, U.S. EPA (1983). 2/ Flow -weighted averages of samples collected over the course of storms. Chapter 8 Water Quality 8-38 Table 8-11. Baseflow and Stormflow Concentrations of Total Suspended Solids (TSS), Nutrients, and Fecal Coliforms in May Creek Basin. Fecal Total Sus- Coliform pended Total Nitrate + (number Station Solids Phosphorus Nitrite per Number -Location (mg/L) (mg/L) (mg/L) 100 mL) Threshold values' 50 0.05 1.25 < 50 May Creek Baseflow Values 1-Mouth at Lake Washington < 10 < 0.10 2.2 n.d.2/ 1-Mouth at Lake Washington 3 0.033 1.12 n.d. 12-164th Avenue SE bridge 10 < 0.10 n.a n.d. 12-164th Avenue SE bridge 4.9 0.035 0.839 n.d. May Creek Stormflow Values3/ 1-Mouth at Lake Washington 104.7 0.267 0.413 1,292 5-Upstream of Honey Creek 48.4 0.139 0.381 353 9-Upstream canyon end 21.7 0.105 0.934 937 12-164th Avenue SE bridge 58.1 0.146 0.984 660 15-SR-900 culvert crossing 29.2 0.084 0.558 137 Tributaries Stormflow Values3/ 2-Gypsy Creek 10.0 0.097 0.409 185 3-Stormline at NE 27th Street 26 0.064 0.918 660 4-Honey Creek near May Creek 95.2 0.182 0.634 3,016 6-Honey Creek, 132nd Ave. SE 43.7 0.123 0.26 705 7-Lake Boren outlet (Boren Cr.) 20.0 0.089 0.545 813 8-China Creek 137.0 0.28 0.526 2,468 10-Long Marsh Creek 10.6 0.055 2.501 212 11 --Tributary 0291 A 53.0 0.145 1.277 1,471 13-Country Creek 13.9 0.047 2.739 46 14-Cabbage Creek 19.1 0.039 2.071 167 16-North Fork of May Creek 122.2 0.174 0.707 678 17-South Fork of May Creek 37.3 0.107 1.169 794 1/ See Tables 8-2 and 8-3. 2/ No data. 3/ Stormflow values are geometric means (n = 1-4). Chapter 8 Water Quality 8-39 necessarily prevent eutrophic conditions. However, none of the lakes moniored in the basin appear to be nitrogen limited. Total suspended solids (TSS) exceeded the guideline threshold value at four locations for stormwater. In ascending order of TSS exceedances, these were: Honey Creek above the confluence with May Creek, May Creek mouth at Lake Washington, North Fork of May Creek. and China Creek. Several of these locations also contain the highest total phosphorus values, indicating a possible correlation between suspended solids and total phosphorus. This correlation could occur due to high phosphorus in the surrounding eroding soils: these are the stations expected to be most influenced by urbanization, quarries, and roads, and high turbidity from construction or quarry runoff. For example, on January 19, 1993, in a stormwater sample taken in the drainage ditch from Sunset Materials (which discharges into May Creek at the SE Renton -Issaquah Road), the TSS concentration (243 mg/L) and turbidity level (348 NTU) were more than 6.5 and 23 times higher, respectively, than the mean value for all of the 17 other stations sampled, correspondingly, the TP concentration of 0.442 mg/L, was almost five times higher than the mean value for all of the other 17 stations sampled. Phosphorus levels (geometric means) during storms in the May Creek mainstem were high, exceeding both the EPA criterion for protection of lakes (0.05 mg/L) and the criterion for the protection of the stream itself (0.10 mg/L). During storms, most monitoring stations (tributaries and May Creek mainstem) exceeded the stream protection criterion of 0.1 mg/L, and all exceeded the lake protection criterion of 0.05 mg/L (Table 8-11). Stations with the highest total phosphorus values are listed in ascending order: North Fork of May Creek, Honey Creek above the confluence with May Creek, May Creek mouth at Lake Washington, China Creek, and Long Marsh Creek. Lake Washington is the receiving water for May Creek, and as such it is important to understand the impact of May Creek on the quality of the lake. A comprehensive study is beyond the scope of this report; however, many studies are being conducted regionally, and information presented on May Creek's phosphorus loading may be useful to these studies. At present, Lake Washington is in good condition for an urban lake. This is principally because it receives about half of its water from the Cedar River, which has very good water quality (King County, 1994). It is a mesotrophic (i.e., moderately biologically productive) lake, with low levels of phosphorus and chlorophyll a throughout the year except during the spring algal bloom. Loadings from six tributaries to Lake Washington were compared (Table 8-12, and Appendix E, Table E-14) to determine the significance of total phosphorus loadings from May Creek. These six tributaries were selected because they are the major sources of flow (Cedar and Sammamish rivers) or represent basins with a range of land -use conditions. Flows and measured total phosphorus concentrations from October 1990 to October 1992 were used to calculate total phosphorus loadings. Chapter 8 Water Quality 8-40 May Creek has a higher average concentration of total phosphorus-2.5 times greater —than the Cedar River. but the loading from May Creek is only six percent of the Cedar loading, or approximately two percent of the total loading to Lake Washington from these six streams (Figure 8-1). Because phosphorus loadings are dependent on land uses and land area, the amount of phosphorus per acre (pounds/acre/year) is compared in Table 8-12. The amounts of phosphorus per acre for the Cedar River and May Creek are comparable, and this result is consistent with the similar land uses in the two basins. The more urban basins such as Coal Creek and Sammamish River have higher unit loadings. In terms of the dissolved phosphorus loading to Lake Washington (encompassing all possible sources of phosphorus, including the six above tributaries), approximately two- thirds comes from sources other than the Cedar River, although the Cedar River is the major water source for the lake (King County, 1994). When comparing all the sources, the largest single source of dissolved phosphorus is the Sammamish River, which contributes 34 percent. Smaller tributaries (including May Creek) and direct urban runoff contribute 16 percent of the dissolved phosphorus. The phosphorus concentration in the Cedar River greatly influences the concentration in the southern end of the lake. The average total phosphorus concentration is currently about 0.02 mg/L. It is believed that a majority of the river's flow passes by the west side of Mercer Island. The water quality on the eastern side of Mercer Island is influenced partly by the Cedar but primarily by the three tributaries (Coal, Kelsey, and May creeks) that discharge on the eastern side of the island, all of which have higher phosphorus concentrations than does the Cedar River. Though the average annual flows for all three basins (Coal, Kelsey, and May) are relatively close, May Creek has the lowest phosphorus concentration and a substantially lower loading than the other two creeks, and thus acts as a diluting force to help maintain the water quality and clarity as good as it currently is. Increases in phosphorus loadings from May Creek could affect the water quality on the eastern side of Mercer Island as well as at the southern end of Lake Washington. Bacteria Fecal coliform (FC) values in the May Creek basin are very high (up to 3,016 colonies/100 ml) during storms relative to the recommended threshold level of less than 50 colonies/100 ml (Table 8-13). Concentrations at all stations during storms exceeded the threshold, except at the confluence of Cabbage and Country creeks (Station 13). Widespread exceedances of coliform standards are common in urban streams. The sampling points on Honey Creek above the May Creek confluence, China Creek, and Tributary 0291A contained the highest concentrations of fecal coliforms, whereas the highest fecal streptococci measurement was in the mainstem of May Creek upstream of Honey Creek. This pattern indicates a possible urban source of fecal coliform because all these areas primarily drain urbanized areas. Pet wastes in these areas may be important contributors, as may be some residual concentrations of septic tank use. High fecal strep was detected on the mainstem of May Creek just upstream of the Honey Creek confluence. Because fecal strep was measured only at two locations (stations 5 and 12), the relatively high value at station 5 (May Creek mainstem upstream of Honey Creek) may reflect the combined contribution of the stream area in between Chapter 8 Water Quality 8-41 Figure 8-1. Flows and Phosphorus Loads Supplied to Lake Washington by Six Stream Systems. Chapter 8 Water Quality 8-42 Table 8-12. Annual Total Phosphorus Loadings to Lake Washington from Six Selected Basins.1 Ave. Total Ave. Annual Phosphorus Basin Phosphorus Phosphorus per Unit Concentration Load Area Basin Ave. Size Flow (acres) Land Uses (cfs) (mg/L) (Ibs./yr.) %Z (Ibs/acre/yr.) May Creek 8,990 43% dev.3 21 0.046 1,697 2 0.19 51 % for. Lower and 42,240 32% dev. 689 0.018 27,247 36 0.22 Middle 56% for. Cedar River4 Kelsey 5,291 30% res. 22 0.100 4,317 6 0.82 Creek Coal Creek 4,194 26% dev. 24 0.071 3,860 5 0.92 70% for. Sammamish 16,873 36% dev. 399 0.051 37,095 48 2.2 River 52% for. Thornton Cr. 7,232 90% dev. 12 0.082 2,455 3 0.34 1/ Calculated using long-term water quality records from the Washington Dept. of Ecology and Metro, and flow records from King County, the USGS, Bellevue and Metro. See Appendix E. 2/ Percentages are based on these six basins only, and do not represent percentages from a comprehensive phosphorus budget. 3/ dev. = developed; for. = forested; res. = residential 4/ The area from Landsburg Dam to Renton. Does not include City of Seattle Cedar River Watershed, which is above the Landsburg Dam and is within the forest resource area. Chapter 8 Water Quality 8-43 the Honey Creek confluence and the 164th Avenue SE bridge crossing. The 164th Avenue SE station is located in the major livestock grazing area. As a source indicator for bacteria, fecal coliform to fecal streptococci ratios are frequently calculated: high FC/FS ratios imply a human source (e.g., leaking septic tank) and low FC/FS ratios indicate a livestock or domestic animal source (e.g., uncontrolled access of livestock to stream water). Fecal coliform and fecal streptococci ratios were calculated from samples taken at three May Creek mainstem sites (Stations 5, 9, and 12) on January 5, 1991 and January 28, 1992. Both samples from Station 5 (May Creek upstream of Honey Creek) imply possible contamination from livestock or other animals (Table 8-13). Although the 1992 samples from Station 9 (May Creek upstream of the Table 8-13. Fecal Coliform/Fecal Streptococci Ratios Determined from Storm Samplings in May Creek. Date of Station Storm Number —Location FC/FS Ratio Categoryti L ML G MH H 12/5/91 5—Upstream of Honey Cr. 0.16 9—Upstream canyon end 1.4 12-164th Ave. SE bridge 1.1 1 /28/92 5—Upstream of Honey Cr. 0.31 9—Upstream canyon end 0.57 12-164th Ave. SE bridge 0.56 1/ One sample was collected from each station. 2/ FC/FS ratios were categorized as follows: L = possible pollution from livestock (ratio s 0.7); ML = mixed pollution, predominately livestock (0.7 < ratio < 1). MH = mixed pollution, predominately human (2 < ratio < 4); H = possible pollution from human waste (ratio z 4). G = uncertain interpretation (1 < ratio s 2). head of the canyon) and Station 12 (May Creek at the 164th Avenue SE crossing) indicated a livestock source (i.e., low ratios), the interpretation of the 1991 samples taken from the same locations was uncertain (mid -range ratios) and may indicate transient human waste contamination in combination with contamination from livestock. Temperature, Dissolved Oxygen, and pH In addition to other parameters, temperature, dissolved oxygen, and pH were monitored intermittently from January 1972 through January 1992. These historic data revealed water temperatures which varied from 0.5 to 18.7°C in May Creek at the mouth to the station at the SR-900 crossing. During this same time period, dissolved oxygen ranged from 5.2 to 18.6 mg/L (mean 11.2 mg/L at the mouth of May Creek). Saturated conditions were generally around 7-10 mg/L (temperature dependent), so these extremes represent periods of occasional undersaturation and supersaturation, respectively. However, because these periods did Chapter 8 Water Quality 8-44 not appear to be persistent and did not occur in the Spring during critical spawning times (the supersaturation extreme was in December and the undersaturation extreme was in September), they do not appear to be a key concern. The pH in May Creek was relatively neutral, ranging from 6.0 to 8.5. The pH decreased slightly moving upstream, with an average of 7.6 at the mouth to 6.97 at the North Fork. Water temperatures influence fish behavior and physiology including food digestion, growth, disease incidence, aging, weight, size, swimming speed and energy requirements. Generally, all coldwater fish cease growing at temperatures above 200C and it is recommended that 20°C- 21 °C should not be exceeded (Welch, 1992). Extreme thermal conditions can stress the fish to the point of death, but temperatures above the preferred range can create a severe thermal block preventing fish movement through an area. During 1993 and 1994, King County Surface Water Management conducted a study to identify water temperature trends in the May Creek system to evaluate impacts on aquatic life, particularly fish. Temperature monitoring in May Creek began in June 1993 and continued through September 1994. Maximum/minimum thermometers were placed in the North Fork of May Creek at SE May Valley Road between SR-900 and 186th Avenue SE, and in May Creek at the 164th Avenue SE bridge, the 148th Avenue SE bridge, and NE 31 st Street south of Jones Avenue NE. Readings were made once per week during the summer months (June -September) and twice per month during the winter months (October -May). Water temperatures typically followed air temperatures, which is expected unless factors such as groundwater or tributary discharges or shading intervene. In general, the highest readings occurred during the Summer months, at the 164th Avenue SE and 148th Avenue SE locations in the open May Valley reach. Lower temperature ranges were recorded both upstream and downstream of the open reach in the May Valley. Temperatures were the highest at 164th Avenue SE road crossing, and tended to be slightly lower at 148th Avenue SE. They were again at relatively lower ranges in the densely shaded reaches at NE 31 st Street. The ranges and average weekly minimum and maximum water temperatures for June 1993 through September 1994 are summarized in Table 8-14 and in Appendix E, Table E-15. Increases in temperature are mostly due to the lack of canopy cover in the May Valley reach. The water temperature in the stream attempts to reach an equilibrium with air temperature: with direct solar radiation and no shade, air temperatures increase and correspondingly drive up the water temperatures. Under these circumstances, it might be expected that the water temperatures at 148th Avenue SE would be higher than those at 164th Avenue SE because it is further downstream in the open valley. However, water temperatures at 148th Avenue SE were lower, likely due to the cooling influence of groundwater discharge (see Figure 8-2). The temperature decrease observed further downstream at NE 31 st Street is likely due to the return of canopy cover, cooler tributary waters and groundwater. In the upper May Creek basin, coldwater fish are represented by coho salmon (Oncorhynchus kisutch), rainbow trout (O. gairdnen) and cutthroat trout (O. clarki). The Chapter 8 Water Quality 8-45 Table 8-14. May Creek Water Temperature Ranges Preferred Rearing Temperatures' Species Lower Lethal Preferred Upper Lethal Limit (°C) Range (°C) Limit (°C) Coho Salmon 0.0 12.0 - 14.0 25.6 Rainbow Trout 0.0 12.2 - 18.9 29.4 Cutthroat Trout 0.6 9.4 - 12.8 22.8 Measured Weekly Temperature Ranges Location Minimum (C) Maximum (C) N. Fork at SE May Valley 1.0 - 13.5 8.0 - 21.0 Rd. bridge May Cr. at 164th Ave. 1.0 - 15.0 8.0 - 26.5 SE bridge May Cr. at 148th Ave. 1.5 - 18.0 6.0 - 25.0 SE bridge May Cr. at Jones Ave.NE 1.0 - 12.5 8.0 - 21.0 /NE 31 st St. 1 Bell, 1986. preferred year-round rearing temperatures for these species are shown in Table 8-14. Maximum temperatures in the open May Valley are above the preferred range for these fish and are at or approaching the upper lethal limits. Temperatures in the reaches above and below the May Valley are generally much more tolerable, rarely exceeding 20°C. During 1993, maximum weekly temperatures at 164th Avenue SE exceeded 21 °C eight out of sixteen weeks (50 percent). Twenty degrees was exceeded 75 percent of the time. Figure E-6 in Appendix E shows the temperature results compared to the 21 °C level. Temperature is clearly a limiting factor for fish passage and survival in the open May Valley reach in the Summer months. A lack of riparian vegetation, direct sunlight on the stream, and slower movement of water in the Valley are responsible for the critically warm temperatures in the May Valley. Lake Quality Assessment Water quality was measured through Metro's Minor Lakes Monitoring Program in Lake Kathleen from 1971 through 1980 on a semi -regular basis (twice monthly in 1975 and 1976 and every other month in 1979 and 1980), and in Lake Boren from 1988 through Chapter 8 Water Quality 8-46 Figure 8-2. Water Temperatures are Cooler both Upstream and Downstream of the May Valley. Chapter 8 Water Quality 8-47 1992 (once a month except in November, December, and January, when no samples were taken). Table 8-15 contains a summary of the results. The full table of results is presented in Appendix E (Table E-12). Measurements were taken from a one- to seven - meter depth in Lake Kathleen and one- to eight -meter depth in Lake Boren. Although the Lake Kathleen measurements are rather old, and therefore should not be directly compared to those in Lake Boren, they are included in this discussion because more recent data are not available. Lakes are often described in terms of a trophic level (oligotrophic—less productive; mesotrophic, and eutrophic—very productive), which is determined by a number of chemical, biological, and physical characteristics and dynamics of the lake system. Evidence for eutrophication includes high nutrient levels, low dissolved oxygen, and high turbidity levels during Spring and possibly Fall blooms of algae. Based on the water quality data presented in Table 8-15, Lakes Kathleen and Boren appear to be meso- eutrophic, which could result in periodic taste and odor problems for the water. Lake Kathleen appears to be stable and is relatively isolated. Lake Boren, however, is within a rapidly urbanizing area and receives water from China Creek that is high in total phosphorus, total suspended solids, and fecal coliforms. While the water quality in Lake Boren appears to be relatively good now (based on limited data), it has the potential for degradation in the future if urban runoff (especially via China Creek) is not controlled. Groundwater Assessment Due to the lack of groundwater data available, assessment of groundwater quality must be based on potential contamination rather than actual monitoring data. This section discusses areas of concern. Implications of Total Recharge Potential Estimates The implications of the relative Total Recharge Potential estimate are discussed in the following paragraphs in relation to the potential sources of groundwater contamination discussed in Section 8.3 above. On -site sewage disposal systems On -site sewage disposal systems are a major possible source of groundwater contamination. Map 10 (see Appendix B) shows target areas where septic systems were found to have a history of repairs or be in a failing or prefailing condition. Of these fourteen target areas, five are wholly or partially in areas of high recharge potential: Area H (SE May Valley Road); Area I (Evergreen Terrace); Area J (Lake Boren / Coal Creek Parkway SE); Area K (SE 89th Street); and Area L (Newport Glen/Hills). In addition, the observation of "failing septic systems" usually implies seepage to the surface, which is a danger due to surface exposure associated with public health rather than its possible impacts to groundwater. Most of the areas with high recharge potential have septic systems that are not currently reported to be failing or prefailing, although they may have histories of repair. Only in the area around and downstream of Lake Boren (Areas I and J) are reported failing (or Chapter 8 Water Quality 8-48 Table 8-15. Ranges of Water Quality Measurements in Lake Kathleen and Lake Boren. 1 Parameter Comments Lake Kathleen Lake Boren Temperature (°C) high temperatures 2.0 - 25.2 3.0 - 23.0 may be a problem for trout Transmissivity (M) The lakes are relatively clear Dissolved oxygen Low values show (mg/L) evidence of a summer thermocline pH Slightly more acidic and smaller range than expected Conductivity extremes probably (/umhos/cm) represent storms or dry spells Turbidity (NTU at High value in April 1 meter depth) shows early blooms Alkalinity (mg Lakes are not well CaCO3/L) buffered Total suspended Lakes are generally solids (mg/L) <5 NTU. High value may reflect runoff. NH3 (mg/L) Orthophosphate > 0.01 is generally (mg/L) considered eutrophic; 0.30 is very high NO2-NO3 (mg/L) 0.2 - 0.4 is meso- eutrophic range Total phosphate 0.010 - 0.030 is (mg/L) meso-eutrophic4 Fecal Coliform (no. of mean 5 50 colonies/ colonies/100 ml-) 100 mL; not more than 10% exceeding 100/100 ml-5 1.0 - 3.5 0.7 - 4.6 0.1 - 13.0 5.2 - 12.6 5.6 - 7.3 6.8 - 7.4 34 - 150 49 - 156 0.4 - 21.0 n.m.3 5 - 15 n.m.3 0.1 - 14.6 n.m.3 0.002 - 0.212 n.m.3 0.001 - 0.30; ave. = n.m.3 0.006 (n = 111) 0.001 - 2.590; ave. = n.m.3 0.283 (n = 130) 0.010 - 0.120; ave. _ 0.038(n=111) 10 - 250; ave. = 29 (n= 61) 0.008 - 0.060; ave. _ 0.023 (n = 40) n. m.3 1/ Measurements gathered by Metro's Minor Lakes Monitoring Program: in 1971-80 for Lake Kathleen, and in 1988-92 for Lake Boren. 2/ Reported values of 0 were not reported in the range, were not included in the average, or were labeled "not measured" due to lack of information related to detection limits and reporting format. 3/ Not measured. 4/ Cf. Wetzel, 1975. 5/ Criteria in WAC 173-201A-030. Chapter 8 Water Quality 8-49 prefailing) septic systems located. This kind of nonpoint source contamination can contribute nitrate and other nutrients to groundwater. Hypothetically, if these contaminants are entering the groundwater system, impacts are likely to occur in Lake Boren, its outlet, and the mainstem just south of Lake Boren, at points where groundwater from these potential source areas would discharge to surface water. Livestock Possible impacts from agricultural practices have been noted, including poor animal -keeping practices. From a groundwater point of view, the impacts are similar to those from failing septic systems, including nitrate and other nutrients. The impact to surface water from storing manure is almost certainly greater from overland flow than from groundwater. Septic systems may have a greater impact on groundwater quality than manure handling, despite the smaller quantities of waste disposed, because they are more directly in contact with groundwater. Overland flow impacts on surface water quality, on the other hand, are more likely from manure handling and are probably the greater problem to surface water. Map 11 (Appendix B) shows that most of the small farms likely to overgraze livestock are located in two areas of the basin: east of Honey Creek and along the May Valley. Comparing these areas to areas of high total recharge potential indicates that the farms east of Honey Creek are less likely to impact groundwater (generally in areas of medium recharge potential) while those farms along May Valley are generally in areas of high recharge potential. The impacts from the May Valley farms may degrade water quality in the adjacent portions of the main stem of May Creek. Pesticides/Herbicides The most likely source of contaminants from pesticide overuse is the same small farms discussed in the previous paragraph, as well as roadways within the basin that lie in areas of high recharge potential. Solid Waste Management The main solid waste site in the area is the Newcastle Landfill. Its location (Map 12, Appendix B) is noted to be mainly in an area of high recharge potential. This landfill has apparently been monitored for groundwater quality. Other potential solid waste management areas are dispersed around the basin, and cannot be singled out as potential sources of groundwater contamination. Resource Extraction The quarries in the May Creek basin are possible sources of groundwater contamination, but are generally of more concern for their impacts to surface water (e.g., in suspended solids discharge). The quarry areas (Map 12) appear to be in possible areas of high recharge potential. This conclusion should be viewed with some caution, however, because the quarry generally removes all of the soils over the mineral resource as well as some portion of the surficial geology. This situation results in these quarry areas having high recharge potential simply by definition. Small Quantity Hazardous Waste Generators Checking the locations reported for SQGs (Map 12) indicates that many of them are located in the Honey Creek subcatchment area of the basin, which is outside the areas of highest recharge potential. However, a few are located along May Valley, which does have high recharge potential. Underground Storage Tanks The few USTs reported in the basin (Map 12) are again mainly located in the portion of the basin east of Honey Creek, which is outside the high Chapter 8 Water Quality 8-50 recharge potential area. There is one UST location on 132nd Avenue SE which is in an area estimated to have high recharge potential. The sections above discuss the combination of recharge potential ("hydrogeologic susceptibility") and possible sources of contaminants to groundwater ("contaminant loading potential"). This combination is in turn referred to as the "vulnerability" of the aquifer. It would appear that while much, although not a majority, of the May Creek basin has high susceptibility (high recharge potential), there are few well-defined sources of contaminants to estimate locations where serious groundwater contamination may be occurring. Given the lack of data regarding groundwater in the basin, an intensive survey of both possible sources of contamination as well as well locations is indicated. Next, a map of groundwater levels would be prepared using these existing wells along with improved measurements of their static water levels (as possible), production pumpages, and elevations. Estimates of aquifer recharge areas could then be improved using more sophisticated (but still simple) models of recharge mechanisms. Aquifer Protection Areas Aquifer vulnerability studies address groundwater contamination by restricting potential sources in areas of high recharge potential. Regulations are also being developed to address the issue in terms of protecting the aquifer at critical locations, such as water supply wells. The objective of such regulation is to determine the area around a well where contamination in the aquifer could contaminate the well water. Such an area is referred to as an Aquifer Protection Area (APA), and some estimate of its extent will be required of most public water supply systems in the next few years. There are several methodologies of varying complexity which have been proposed for this determination, and the regulations will probably allow some flexibility in the process. The following presents an application of APA methodology for the May Creek basin. There is one major water supply well, the City of Renton Well 5A, which is just outside the May Creek basin but is potentially affected by groundwater conditions within the basin. The APA for Well 5A was estimated previously (CH2M Hill, 1988) by assuming a simple constant and uniform regional groundwater flow regime from which the well produces at a constant rate. Using measured, or conservatively estimated, parameters for the groundwater flow, the study estimated a zone of capture for the well which extends indefinitely upgradient (east) of the well, as far as 1,900 feet downgradient (west, almost to Lake Washington), and laterally (north and south) along a parabolic boundary which could reach 12,000 feet in width at its ultimate extent upgradient (to the east). For the purposes of the City of Renton's application, this boundary was cut off at the City limits. In its full extent, the zone of capture would include virtually all (except some northwesterly corners) of the May Creek basin. There are two caveats to applying this previously -estimated aquifer protection area to the May Creek Basin Plan. First, the assumptions of infinite extent and constant uniform regional flow break down when extrapolated this far, especially when extended into the bedrock areas of the northern part of the basin. The parameters for the flow system are based on data obtained from studies very local to the well and may not apply at this Chapter 8 Water Quality 8-51 distance. Second, the well is screened in a confined aquifer, and the groundwater flow system used in the estimate is based on confined flow. This assumption was conservative in predicting a wider zone of capture. The confinement would also limit interaction with near -surface groundwater and prevent (by definition) much of the potential for contamination. Nevertheless, given the lack of data available on groundwater regimes in the May Creek basin, this estimate is reasonable. Sediment Quality Assessment To evaluate the existing condition of the sediments in May Creek and its tributaries, the existing sediment data were compared to the guidelines found in WDOE (1991) (Table 8-16). The table contains only contaminants for which these guidelines are available for comparison, because guideline development for freshwater sediment is not complete. Compounds detected in the sediments but lacking sediment quality guidelines are TPH, 4-methylphenol, di-n-butylphthalate, butyl benzylphthalate, benzofluoranthenes, indeno(1,2,3-c,d) pyrene, chrysene, benzo(g,h,i)perylene, aluminum, and total P. Only TPH, FOG, TP, and metals were measured at stations other than #1(the mouth of May Creek). All other organic compounds were measured only at the mouth of May Creek. Table E-13 in Appendix E presents a complete list of the sediment results. The guidelines listed in Table 8-16 are included only as indicators of freshwater sediment quality. According to the guidelines, the lowest -effect level indicates a level of sediment contamination that can be tolerated by most benthic organisms. The severe - effect level indicates a concentration at which pronounced disturbance of sediment - dwelling organisms can be expected (i.e., detrimental to the majority of benthic species). The EPA Region V guidelines, which include the moderately contaminated range cited below, were originally released to classify Great Lakes harbor sediments, and are considered adequate only for determining the suitability of dredged material for open water disposal. In general, organic compounds did not exceed the guidelines found in WDOE (1991), which contains guidelines for phenanthrene, fluoranthene, pyrene, benzo(a)anthracene, and benzo(a)pyrene. All measurements were several orders of magnitude less than the EPA interim criteria for nonpolar organic compounds (EPA, 1988b). Measured concentrations of PCB-1260 (0.03—estimated—and 0.1 mg/kg) exceeded the lowest -effects level of 0.005 mg/kg (carbon normalized) (Persaud et al., 1991). Although these measurements may very well indicate an exceedance, it should be noted that detection limits for sediment matrices are generally higher than 0.005 mg/kg, and the QA/QC data that accompanied these measurements should be reviewed. Although none of the oils and grease measurements exceeded the lowest -effect levels, Station 6 (Honey Creek at 132nd Avenue SE, near the commercial area) contained levels which exceeded background (1,000 mg/kg) as defined by the Wisconsin Department of Natural Resources (WDNR, 1985, 1990) and would be classified as moderately polluted by EPA Region V Based on this information, the levels at Honey Creek at 132nd Avenue SE are elevated, and indicate moderate historical or recent pollutant influx of organic compounds. Chapter 8 Water Quality 8-52 Table 8-16. Locations where Contaminant Concentrations exceeded WDOE Freshwater Sediment Guidelines./ Range Signifying Range Moderate Observed in Stations Exceedinq Guidelines Contam- Effects levels ai,si Contaminant Sediments2/ Location Concentration ination Lowest Severe (mg/kg) (mg/kg) (mg/kg)3/.a/ (mg/kg) (mg/kg) copper 16.7 - 106.0 1. May Cr. at L. WA 22.7 & 25 - 50 16 110 36.5 9. May Cr. head of canyon 16.7 12. May Cr. at 164th 79.4 4. Honey Cr. near May Cr. 18.7 6. Honey Cr. at 132nd 106.0 7. L. Boren outlet 19.1 13. Country Cr. 23.3 16. N. Fork 40.1 17. S. Fork 21.3 18. N. Fork 39.5 lead 4.0 - 255.0 12. May Cr. at 164th 42.9 40 - 60 31 250 6. Honey Cr. at 132nd 255.0 17. S. Fork 51.0 zinc 39.5 - 551.0 6. Honey Cr. at 132nd 551.0 90 - 200 120 820 oil & greases/ 23.6 - 1474.0 [no stations exceeded] 1,000 - 1,500 2,000 1 / WDOE, 1991. 2/ Stations 1, 4, 6, 7, 9, 12, 13, 14, 16, 17, 18 were sampled. 3/ EPA Region V Guidelines for the Pollutional Classification of Harbor Sediments (EPA, 1977). 4/ mg/kg dry weight (metals); mg/kg organic carbon normalized (organics). 5/ Provincial Sediment Quality Guidelines (Persaud et a/., 1991). 6/ Guidelines are for oil & grease; measurements were fuels, oil, and grease. G:\WP\4248\MAYCREEK\08256A ♦ 8-31-95 Chapter 8 Water Quality 8-53 Metal concentrations are undoubtedly elevated at Honey Creek at 132nd Avenue SE, near the commercial area (Station 6). Concentrations of copper, lead, and zinc all exceeded the lowest -effects levels at Station 6, and lead exceeded the severe -effects level as well. The mouth of May Creek (Station 1) and the North Fork (Station 16) also contained elevated concentrations of copper. The 164th Avenue SE bridge location on May Creek and the South Fork (Stations 12 and 17) contained elevated concentrations of copper and lead, too. The North Fork along SR-900 (Station 18) contained elevated copper. In part, these results confirm the presence of elevated metals levels observed in the stream water. As is discussed in section 8.5 below, the highest aqueous metals concentrations were found at Honey Creek at 132nd Ave. SE, Honey Creek, above confluence with May Creek, Stormline at NE 27th Street, mouth of May Creek, North Fork, and South Fork. Although high sediment levels of metals were found at Honey Creek at 132nd Avenue SE, mouth of May Creek, North Fork, and South Fork stations, elevated sediment concentrations were not found at Station 4 (Honey Creek, above confluence with May Creek), and elevated water concentrations were not found at Station 12 (164th Avenue SE bridge location on May Creek). Road runoff appears to be responsible for the elevated metals concentrations at these locations, although SQGs could also contribute. 8.5 NONPOINT MODELING APPROACH This section presents the approach used for, and results of, modeling pollutant inputs from nonpoint sources. The modeling provides an understanding of how land uses affect water quality, and allows a comparison to be made between current and future water quality conditions. The results of the modeling are meant as a guide to indicate the location and potential importance of contamination problems within the basin resulting from a variety of existing and predicted future land use changes. The loadings generated by the model are estimates, and are to be used for comparison on a relative basis to determine the relative difference between current conditions and future conditions. Modeling is a useful tool for predictive analysis or planning purposes, but the inherent uncertainty associated with simulated numbers must be recognized if the loadings are used for any purpose requiring more precision and accuracy. MODELING APPROACH Many of the water quality parameters identified in the historic description are still problematic today. In particular, levels of total phosphorus (TIP), fecal coliform (FC), and metals (especially lead) are elevated throughout the basin. In addition, total suspended solids (TSS), nitrate -nitrite (NO3), and temperature are elevated at numerous locations. Organic compounds were not sufficiently monitored to determine if they are of concern within the basin. In summary, stormwater quality within May Creek and many of its tributaries does not meet Class AA standards and other recommended threshold values at this time. Chapter 8 Water Quality 8-54 Water and sediment samples are useful indicators of water quality at the exact location and time of sampling. However, because measured concentrations vary on a daily basis with flow and other conditions, pollutant loadings provide another perspective to water quality analysis. Pollutant loadings are a measure of the total amount (mass weight) of a pollutant delivered to a waterbody over a period of time (for example, a year). Total loading (L) equals flow (Q) multiplied by concentration (C). Interpreting loading and concentration information is somewhat different. High concentrations are generally problematic because they can result in short or long-term issues of toxicity and eutrophication at a given location or downstream. In contrast, high loadings do not always signal a cause for concern because high loadings can result from high flow, high concentration, or a combination of both. High flow conditions can actually lower the concentration of a toxic compound (such as a metal), and thus lower the exposure of aquatic life to a given compound to a level below the aquatic life criteria. Therefore, high loads which are due to high flows only are not problematic in the short- term, but may be significant over time due to cumulative effects. However, if high loadings are due to high concentrations, then toxic or eutrophic responses can occur, and there is justifiable cause for concern. A simple yet reliable loading model (Horner, 1990) was used to analyze the current and anticipated future loadings of key water quality parameters. Modeling loadings allows a comparison of relative loadings between subcatchments and between current and future water quality conditions. Annual contaminant -yield coefficients for total suspended solids (TSS), total phosphorus (TP), zinc (Zn), and fecal coliforms (FC) were applied by land -use to each subcatchment. By multiplying these factors by areas of specific land -use, an annual pollutant loading was calculated. Neither calibration nor monitoring data were used, reducing the ultimate accuracy of these results but allowing the modeling process to be efficiently and rapidly completed, providing a relative understanding of pollutant increases due to land -use changes. Yield coefficients were compiled from a wide variety of references (Horner, 1990; Reinholt and Homer, 1994; Novotny and Olem, 1994) to simulate pollutant loadings. The coefficients, summarized in Table E-16 in Appendix E, were based primarily on locally derived data where available and chosen for their particular applicability to the basin. Current loadings were based on existing land uses. In calculating the future pollutant loadings, two basic scenarios were modeled in conjunction with the future land use/cover map (see Map 5, Appendix B). The first scenario assumed that all new development would take place without water quality treatment of runoff. The second scenario assumed that all areas of new impervious, commercial, multi -family residential, and single-family high -density residential development would be required to implement those best management practices (BMPs) as will be required by the pending update of the King County Surface Water Design Manual (King County, 1990). Following the hydrologic modelling assumptions of past basin plans, 20 percent of the runoff (and associated pollutants) was assumed to bypass treatment facilities. Chapter 8 Water Quality 8-55 The fraction of pollutant removal was taken from proposed requirements in the pending update to the Design Manual, which has a menu of alternative BMPs with which to achieve the desired pollutant removal. In areas that must provide any water quality treatment at all, TSS must achieve 80 percent reduction. In addition, zinc has a 40 percent reduction goal if the runoff is discharging to a "sensitive waterbody" as defined by the Design Manual, or significant resource area. Phosphorus removal would not be required by the Design Manual, but 40 percent removal was assumed in this modeling as a result of the removed TSS (Minton, 1992). Treatment was not assumed to reduce the FC loading. In terms of current loadings, Honey Creek, Boren Creek and the North Fork had the highest loadings of TSS, Zn and TP due to current land uses. This is consistent with measured stormwater quality data. Lower May Creek mainstem, Honey Creek and Canyon 2 subcatchments had the largest unit area loading of all three parameters. Figures 8-3, 8-4, and 8-5 show the total loadings. With unmitigated future development, water quality will degrade in all of the subcatchments but most dramatically in those with the greatest increase in projected urbanized areas (see Tables 8-17 and 8-18). The Highlands tributaries —particularly Country Creek —and Newport Hills Creek show the overall largest increases, particularly in zinc (one- to four —fold increases) and total phosphorus (one- to two fold -increases). The increase in zinc is predicted to be great basinwide, except for Honey Creek and Canyon 2: these two subcatchments are already developed and have poorer water quality so the percent increase is not as large as the Country Creek (almost four -fold increase) where the land uses shifts from primarily forested and single-family low -density to primarily single-family low- and medium -density. Because zinc is an easily detectable pollutant and an indicator of other toxic and harmful metals, a variety of toxic -related water quality problems associated with other metals can be expected where zinc is present. With maximum buildout the likelihood of such problems becomes will increase in a number of subcatchments, particularly Country, Newport Hills, and Cabbage creeks. In contrast, total suspended solids and fecal coliforms show less than a one -fold increase in every subcatchment. The approximate order in which the subcatchments will suffer from future unmitigated water quality degradation, from least to greatest change, is shown below: Least Change: Long Marsh Creek Tributary 0219A South Fork Honey Creek Greene's Creek Boren Creek Gypsy Creek East Fork North Fork Cabbage Creek Newport Hills Creek Greatest Change: Country Creek Chapter 8 Water Quality 8-56 Figure 8-3. Total Suspended Solid Loads by Subcatchment. May Valley/Coalfield May Valley Middle I May Valley Lower Coal Cr Pkwy. to 148th Canyon at Boren Cr. confluence Canyon upstream of Newport Hills Cr _. Canyon, upstream ® Current M Future from Honey Cr ❑ 50% Mitigation M 100% Mitigation Canyon. upstream from Gypsy Cr Canyon, upstream from 1-405 Lower May Creek East Fork North Fork Cabbage Creek Country Creek Long Marsh Creek South Fork subcatchments Tributary 0291A Greene's Creek Boren Creek subcatchments Newport Hills Creek Gypsy Creek Honey Creek subcatchments E w Y N U m 0 5,000 10,000 15,000 20,000 25,000 30,000 35,000 40,000 Total Suspended Solids (kg/yr) Chapter 8 Water Quality 8-57 Figure 8-4. Total Phosphorus Loads by Subcatchment. East Fork North Fork Cabbage Creek Country Creek Long Marsh Creek South Fork subcatchments Tributary 0291A Greene's Creek Boren Creek subcatchments Newport Hills Creek Gypsy Creek Honey Creek subcatchments 0.0 ® Current g Future 050% Mitigation a 100% Mitigation E Y N N U m m 1- v c m t rn ■m N � N N N m :3 a c a m• m m `m d 3 o J 20.0 40.0 60.0 80.0 100.0 120.0 140.0 160.0 180.0 200.0 Total Phosphorus (kglyr) Chapter 8 Water Quality 8_58 Figure 8-5. Zinc Loads by Subcatchment. May Valley/Coalfield May Valley Middle May Valley Lower Cr. Pkwy Canyon at Boren Cr a� confluence Canyon upstream of Newport Hills Cr Canyon. upstream \\\\ from Honey Cr Canyon, upstream from Gypsy Cr Canyon, upstream from 1 Lower May Creek East Fork North Fork Cabbage Creek Country Creek A\ Long Marsh Creek South Fork Q\\\\\\\\\\\\\\\\\\\ subcatchments Tributary 0291A Boren Creek subcatchments Newport Hills Creek Gyosy Creek Honey Creek viiiiii............................ subcatchnnents ®Current 0 Future p 50% Mitigation M 100% Mitigation E as C o T C = l9 � w 0.0 20.0 40.0 60.0 80.0 100.0 120.0 140.0 160.0 Zinc (kglyr) Chapter 8 Water Quality 8-59 0 cu 13 co 00 m c m q Table 8-17. Percent Increase in Water Quality Parameter Loadings from Current Conditions. Page 1 of 2 Total Suspended Solids Total Phosphorus Zinc Fecal Coliforms Future Future Future Future Mitigated Future Future Mitigated Future Future Mitigated Mitigated Unmit. 50% 100% Unmit. 50% 100% Unmit. 50% 100% Unmit. 50% 100% May Creek Mainstem Subcatchments May Valley/ 19 14 10 67 64 62 58 53 47 11 11 11 Coalfield May Valley Middle 35 26 18 111 107 103 89 79 69 6 6 6 May Valley Lower 39 36 34 106 104 102 94 90 85 26 26 26 148th to Coal 62 61 60 93 92 92 155 154 153 61 61 61 Cr. Pkwy. Canyon at Boren 49 36 23 89 81 72 102 92 82 51 51 51 Cr. confluence Canyon, upstream 50 40 30 113 106 99 168 155 142 42 42 42 from Newport Hills Cr. Canyon, upstream 22 15 7 65 59 54 73 65 58 16 16 16 from Honey Cr. Canyon,upstream 7 3 -2 4 2 0 13 11 8 6 6 6 from Gypsy Cr. Canyon, upstream 44 27 9 56 46 37 85 72 59 41 41 41 from 1-405 Lower May Creek 35 16 -2 36 28 20 47 37 27 -11 -11 -11 Highlands Subcatchments East Fork 30 30 29 84 84 84 84 82 81 21 21 21 North Fork 28 25 22 83 81 79 123 115 107 18 18 18 Cabbage Creek 41 41 41 106 106 106 99 99 99 44 44 44 Country Creek 83 83 83 176 176 176 356 356 356 82 82 82 Long Marsh Creek 17 17 17 29 29 29 96 96 96 16 16 16 Table 8-17. Percent Increase in Water Quality Parameter Loadings from Current Conditions. Page 2 of 2 0 ? w East Renton Plateau Subcatchments m South Fork 22 22 22 59 59 59 36 36 36 15 15 15 00 subcatchments Tributary 0291A 17 16 14 57 56 55 37 35 34 10 10 10 m Greene's Creek 26 23 19 51 50 48 62 59 56 20 20 20 jo c =' Lower Basin Tributaries Boren Creek 30 22 14 55 50 45 59 54 48 27 27 27 subcatchments Newport Hills Cr. 54 38 22 107 96 85 135 121 108 46 46 46 Gypsy Creek 39 22 5 55 45 36 65 54 44 38 38 38 Honey Creek 28 17 7 37 31 26 46 39 33 22 22 22 subcatchments .MI c� m 1 00 N m C m `c 00 6) tV Table 8-18. Parameter Loadings from May Creek Water Quality Modelinq. Panel of 2 Total Suspended Solids Total Phosphorus Zinc Fecal Coliforms Future Future Mitigated2 Future Future Mitigated3 Future Future Mitigated4 Future Future Mitigated5 Curr. Unmit.1 50%6 100%7 Curr. Unmitl 50%6 100%, Curr. Unmitl 50%6 100%7 Curr. Unmiti 50%6 100%7 (#'E+ (#'E+ (#"E+ (#'E+ (kg/yr) (kg/yr) (kg/yr) (kg/yr) (kg/yr) (kgtyr) (kg/yr) (kg/yr) (kg/yr) (kg/yr) (kg/yr) (kg/yr) 11tyr) 11/yr) 11/yr) 111yr) May Valley/ 13,095 15,580 14,977 14,374 Coalfield May Valley 2,658 3,588 3,360 3,132 Middle May Valley 5,656 7,862 7,710 7,559 Lower 148th to Coal 8,551 13,884 13,802 13,720 Cr. Pkwy. Canyon at 1,540 2,298 2,096 1,894 Boren Cr. confluence Canyon, 1,413 2,123 1,981 1,839 upstream from Newport Hills Cr. Canyon, 2,637 3,222 3,021 2,821 upstream from Honey Cr. Canyon, 6,960 7,444 7,144 6,844 upstream from Gypsy Cr. Canyon, 4,068 5,874 5,150 4,425 upstream from 1-405 Lower May 3,429 4,615 3,988 3,361 Creek May Creek Mainstem Subcal 50.1 83.6 82.3 80.9 8.10 17.1 16.7 16.4 20.7 42.6 42.3 42.0 39.8 76.8 76.6 76.4 6.5 12.3 11.7 11.2 4.7 10.1 9.8 9.5 9.6 15.7 15.2 14.7 38.8 40.4 39.6 38.8 19.4 30.1 28.3 26.5 12.6 17.1 16.1 15.0 chments 24.8 39.3 37.9 36.5 4.6 8.7 8.2 7.8 8.5 16.4 16.0 15.7 17.7 45.3 45.1 45.0 4.1 8.3 7.9 7.4 2.6 7.0 6.6 6.3 6.0 10.3 9.9 9.4 25.8 29.2 286 27.9 12.1 22.3 20.8 19.2 12.6 18.6 17.3 16.0 6.07 6.72 6.72 6.72 1.26 1.34 1.34 1.34 2.74 3.46 3.46 3.46 3.91 6.29 6.29 6.29 0.70 1.06 1.06 1.06 0.70 0.99 0.99 0.99 1.30 1.51 1.51 1.51 3.20 3.38 3.38 3.38 1.90 2.69 2.69 2.69 1.15 1.02 1.02 1.02 Highlands Subcatchments East Fork 5,655 7,363 7,326 7,290 22.7 42.0 41.9 41.8 6.9 12.6 12.5 12.4 2.60 3.15 3.15 3.15 North Fork 15,411 19,719 19,255 18,792 51.1 93.3 92.3 91.3 13.8 30.8 29.7 28.6 7.52 8.89 8.89 8.89 Cabbage Creek 5,591 7,883 7,883 7,883 20.3 41.7 41.7 41.7 6.5 13.0 13.0 13.0 2.39 3.44 3.44 144 C) zr n� m OD m Q c v w w Table 8-18. Parameter Loadings from May Creek Water Quality Modeling. Page2 of 2 Total Suspended Solids Total Phosphorus Zinc Fecal Coliforms Future Future Mitigated Future Future Mitigated3 Future Future Mitigated4 Future Future Mitigated5 Curr. Unmit.1 50%6 100%, Curr. Unmiti 50%6 100%7 Curr. Unmiti 50%6 100%7 Curr. Unmitl 50%6 100%7 (#*E+ (#*E+ (#•E+ (#'E+ (kg/yr) (kg/yr) (kg/yr) (kg/yr) (kg/yr) (kg/yr) (kglyr) (kg/yr) (kg/yr) (kg/yr) (kg/yr) (kg/yr) 11/yr) 11/yr) 11/yr) 11/yr) Country Creek 3,591 6,585 6,585 6,585 12.9 35.5 35.5 35.5 3.4 15.6 15.6 15.6 1.60 2.92 2.92 2.92 Long Marsh 4,975 5,826 5,826 5,826 19.1 24.7 24.7 24.6 4.3 1 8.5 8.5 8.5 2.30 2.67 2.67 2.67 Creek East Renton Plateau Subcatchments South Fork 9,360 11,424 11,424 11,424 41.4 66.0 66.0 66.0 21.5 29.4 29.4 29.4 4.34 5.00 5.00 5.00 subcatchments Tributary 0291A 8,538 10,026 9,897 9,767 35.6 55.9 55.6 55.4 20.9 28.5 28.2 27.9 4.05 4.45 4.45 4.45 Greene's Creek 9,734 12,274 11,943 11,611 45.3 68.6 67.9 67.2 25.0 40.5 39.7 38.9 4.59 5.52 552 5.52 Boren Creek subcatchments Newport Hills Creek Gypsy Creek Honey Creek subcatchments 23,957 31,120 29,249 27,377 3,463 5,349 4,794 4,240 4,904 6,812 5,987 5,163 31,248 39,887 36,592 33,297 Lower Basin Tributar 104.1 161.1 156.1 151.1 14.1 29.2 27.6 26.1 24.3 37.6 35.3 33.0 137.4 187.8 180.5 173.3 es 71.3 113.5 109.5 8.5 19.9 18.7 15.8 26.1 24.4 109.2 159.0 152.0 1/ The "Future" scenario assumes no water quality mitigation. 2/ Assumes 80% removal from treated area. 3/ Assumes 60% removal from treated area. 4/ Assumes 40% removal from treated area. 5/ No removal required or assumed. 6/ Assumes treatment for 50% of new development as required by proposed Surface Water Design Manual revisions. 7/ Assumes treatment for 100% of new development as required by proposed Surface Water Design Manual revisions. 105.5 17.6 22.7 145.0 1087 13.79 13.79 13.79 1.69 2A6 2A6 2A6 2.28 3.14 3.14 3.14 11.93 14.55 14.55 14.55 Although the zinc loading in Country Creek shows the largest increase from current to future conditions (356 percent), the predicted future loading (13.0 kg/yr) is still less than the current loading from Honey Creek (109.2 kg/yr), a developed subcatchment. To generalize, the future loading of many of the currently undeveloped subcatchments will approach the current loadings of Greene's Creek or Tributary 0219A which is a mix of land uses. Several of the May Creek mainstem subcatchments show significant increases in loadings of phosphorus and zinc. The greatest increases (one- to two -fold increases) are from May Creek at Coal Creek Parkway SE downstream to the mouth of Newport Hills Creek. Again, this is due to the shift in more urbanized land uses from single-family low density and forest. The runoff from the CCP subcatchment into May Creek will experience the largest increases in zinc, phosphorus and suspended solids of the mainstem subcatchments due to the land -use shift from primarily forested to single- family medium density. This increase is greater than the increases in many of the tributaries. Although unmitigated development would substantially degrade water quality in most parts of the basin, required treatment substantially limits water quality changes in those areas where treatment is required. Land uses requiring treatment are commercial/ institutional, multi -family and single-family high -density residential. All the tributaries in the Highlands and East Renton Plateau subareas will experience an increase in loadings from development; however the type of development, primarily single-family low- and medium -density residential, will not be required to treat runoff as part of the pending Design Manual requirements. Only the Lower Basin tributaries and some of the May Creek mainstem drainages will experience a reduced loading due to treatment because the type of future development will require treatment. In a few drainages, such as May Creek in the Lower May Valley, future mitigated total suspended solids loadings are actually equal or lower than current loadings. This means that with mitigated development, in some instances, the water quality is the same or better than current conditions. Treated development in some instances can result in cleaner runoff than current conditions, depending on the type of existing and proposed land uses. For future developed conditions to yield "cleaner" runoff may seem counter -intuitive, but the area of the watershed that will develop with TSS treatment required by the pending Design Manual update is enough to equal or improve on the current, untreated condition (as reflected by the recommended loading coefficients which do not include instream erosion). The approximate order of water quality degradation under fully mitigated future conditions is somewhat different than for the unmitigated future scenario, although the subcatchments with the highest resource values experience degradation under either scenario: Least Change: Honey Creek Gypsy Creek Chapter 8 Water Quality 8-64 Tributary 0219A Boren Creek Greene's Creek Long Marsh Creek South Fork East Fork North Fork Newport Hills Creek Cabbage Creek Greatest Change: Country Creek In reality, not all of the future development in the basin will fall into the Design Manual categories. Increased storm flow (1-22 percent) is predicted basinwide, with the highest increase in Lake Kathleen, MVL (lower May Valley), and COP (Coal Creek Parkway) subcatchments. As a basin, total acreage designated as wetland, forest, quarry, grass, and clearcuts is predicted to decrease, while single-family low -density, single-family high -density, multi -family, commercial, and single-family low -density cover types/uses are predicted to increase. In other words, the basin is predicted to experience increased flow due to the conversion of undeveloped forested lands and open lands to developed, residential and urban lands. At future development levels, both instream flows and pollutant concentrations would increase, with concentrations likely to exceed chronic and acute water quality metals standards during storms in most subcatchments. The frequency and duration of exc:eedances would depend directly upon the size and duration of the storm and intensity of the land uses. However, to achieve these loads, the concentrations must be significantly higher than under current conditions. In contrast to nutrients and metals, fecal coliforms are not assumed to be reduced by Design Manual regulations, so no treatment factor was applied in the modeling. Future fecal coliform loadings are forecast to increase as much as 81 percent in Country Creek and 61 percent in the COP subcatchment. These future fecal coliform loadings for buildout conditions may be high because eventually the area to the west of the Urban Growth Boundary will be sewered. However, infrastructure investments may lag behind many of the land -use changes. Also, before the sewer lines are installed, the loadings of fecal coliforms and other contaminants may be higher due to contributions from both failing septic systems on small lots and increased numbers of small farming/livestock keeping, impairing both baseflow and stormflow water quality. From this analysis, significant increases are predicted for total suspended solids, phosphorus, zinc and fecal coliforms loadings throughout the basin. These increases could affect beneficial uses in the basin. For example, total phosphorus loadings into Lake Boren are predicted to increase more than 56 percent. Because Lake Boren has already been classified as meso-eutrophic (nutrient rich) by the WDOE, the possibility of future problems associated with increasingly eutrophic conditions (e.g., odor, algal blooms, weed growth) is significant. In summary, projected future unmitigated loadings suggest significant adverse water quality impacts would occur throughout the basin under the projected land use Chapter 8 Water Quality 8-65 scenarios. Those areas predicted to undergo the greatest land -use changes (e.g., from forest and grass areas to single-family high -density) will likely experience the largest increase in water quality degradation. Those areas that currently are already urbanized, such as parts of Honey Creek, will experience less of an increase. Although the increase may be small, the current water quality in Honey Creek is already affected significantly by urbanization and exceeds some toxics criteria. 8.6 CONDITIONS BY SUBAREA The Lower Basin and May Valley subareas have conditions of degraded water quality due to a variety of sources but primarily to urbanization (Lower Basin) and livestock management practices (May Valley). The Highlands and Renton Plateau currently have relatively good water quality, but it is predicted that these subareas will have significant land -use changes in the future that will affect the clarity, toxicity and habitability of the water for aquatic life. LOWER BASIN The Lower Basin subarea contains the mainstem May Creek (0282) mouth and canyon area from river mile (RM) 0.0 to 3.9, and all of the tributaries that flow into the mainstem in this reach, including Gypsy (0284), Honey (0285), Newport Hills (0286), and Boren (0287—including Lake Boren and China Creek) creeks. Potential nonpoint sources within this area include 14 small -quantity and two large -quantity generators of hazardous waste, five underground storage tanks, a segment of 1-405, most of the commercial and multi -family and high -density housing areas within the basin, and several areas with pre —failing or failing septic systems. As a result, it is not surprising that within this area, current and future stormwater concentrations for total phosphorus, total suspended solids and fecal coliforms are of concern. Currently, metals in stormwater exceeded toxicity criteria at the mouth of May Creek and upstream of the confluence with Honey Creek, as well as in several of the tributaries. Table 8-19 gives a summary of water quality concerns and possible sources within this subarea. Within the Lower Basin subarea, urbanization and its attendant activities appears to be the dominant source of contamination. In particular, elevated metals concentrations are probably due to runoff from large areas of impervious surfaces. The Honey Creek drainage contributes high metals loadings from road and parking -lot runoff in the nearby commercial center. It is possible that the small quantity generators in this commercial area contribute metals to runoff as well: copper, lead, and zinc concentrations were elevated in sediments collected in Honey Creek near the commercial area. The lead concentrations were high enough to categorize the sediments as heavily polluted (EPA, 1977). Similarly, commercial activities are also contributing to the degradation of the water quality north of Lake Boren. At the station just upstream from Lake Boren, the highest suspended solids and the second highest total phosphorus and fecal coliform Chapter 8 Water Quality 8-66 Table 8-19. Lower Basin Subarea Water Quality Issues. Page 1 of 2 Station and Location Water Quality Issues Possible Sources 1. May Creek mouth at Lake Washington 2. Gypsy Creek Metals: exceedances, 4th highest; also high in sediments TP: Both baseflow and stormflow exceed threshold NO3: Baseflow > threshold TSS: Stormflow exceeds threshold; 3rd highest FC: Stormflow 25x > standard; 4th highest Metals: some exceedances TP: Exceeds threshold FC: 3x > standard 3. Stormline at NE 27th Metals: exceedances, 3rd Street highest TP: Exceeds threshold FC: 13x > standard 4. Honey Creek 5. May Creek upstream from Honey Creek 6. Honey Creek at 132nd Ave. SE 7. Boren Creek Metals: exceedances, 2nd highest TP: Exceeds threshold; 4th highest TSS: Exceeds threshold; 4th highest FC: 60x > standard: highest exceedance Metals: exceedances TP: Exceeds threshold FC: 7x > standard Metals: highest %age of exceedances, also high in sediments TP: Exceeds threshold FC: 16x > standard O/G: High in water and sediment Metals: Some exceedances TP: Exceeds threshold FC: 16x > standard Metals: runoff from 1-405 TP: phosphorus in suspended sediment TSS: erosion in May Cr. canyon, Honey and Gypsy creeks TP: phosporus in eroded sediment Significant number of septic system repairs Metals: runoff from urban area FC: urban area runoff (pet waste) Metals: urban runoff, SQGs Phosphorus - correlated with TSS TSS - Significant erosion in Honey Creek FC - Urban runoff (pet waste), known septic system problem in Sierra Hts. Metals: urban runoff TP: erosion in May Cr. canyon FC: 4% failure rate of septic systems within subcatchment, 31 % failure just upstream Metals - Urban runoff, SQGs FC - relatively high septic tank repair rate at head of Honey Creek; urban runoff (pet waste) O/G - urban runoff, SQGs Metals - urban runoff Phosphorus - possibly outflow from Lake Boren FC - 17% failure rate of septic systems within subcatchment. Chapter 8 Water Quality 8-67 Table 8-19. Lower Basin Subarea Water Quality Issues. Page 2 of 2 Station and Location Water Quality Issues Possible Sources 8. China Creek Metals: Some exceedances TP: Exceeds threshold; 2nd highest TSS: Highest exceedance of threshold FC: 49x > standard; 2nd highest 9. May Creek, Metals: Some exceedances upstream canyon TP: Exceeds threshold end (—RM 3.4) TP: Appears to be associated with high TSS TSS: Nearby development FC: unknown; septic systems were not surveyed, livestock and pet wastes could contribute Chapter 8 Water Quality g_gg measurements in the basin were recorded. Elevated suspended solids concentrations are probably the result of development within these subcatchments, and may eventually decline as construction within these areas decreases. In urbanized areas, elevated levels of fecal coliforms are often caused by leaking sewer lines, septic tank leakage, pumping station malfunctions, and/or pet/animal waste. Domestic animal waste is likely to be a dominant source of fecal coliforms in the Honey Creek subcatchment. (The Honey Creek confluence with May Creek contained the highest FC values in the basin.) This subarea also contains many major road crossings, including 1-405 and Coal Creek Parkway SE, which typically contribute metals, suspended solids, and petroleum hydrocarbons. While it is difficult to quantify each source of pollution, it appears that the lead and copper concentrations are significantly higher at the mouth than upstream of the 1-405 crossing. MAY VALLEY The May Valley subarea includes the mainstem of May Creek (0282) from RM 3.9 to RM 7.0, and extends from just below the beginning of the agricultural area of May Valley to the region of the SE Issaquah -Renton Road (SR-900) where the three forks of May Creek merge to form the main channel, including also the immediately adjacent reaches of the North, East, and South forks (0294, 0297, and 0282). Water quality issues within this; subarea are summarized in Table 8-20; the mouths of the three forks and all other tributaries entering this subarea will be discussed below as part of the Highlands and East Renton Plateau subareas. Within the agricultural valley, water quality is seriously degraded primarily through poor animal -keeping practices, which contribute to high suspended solids, fecal coliforms, nitrate nitrogen and total phosphorus. In addition, historic logging and dredging together with flooding and unrestricted animal access in this area have virtually eliminated riparian vegetation and shade, and thus water temperatures throughout this valley, particularly near 164th Ave. SE, reach critically high levels during summertime, low -flow periods. These temperatures may be causing significant stress or even acute toxicity to certain fish populations. It is evident that most beneficial uses of the mainstem have already been reduced or virtually eliminated in this subarea. Present water quality in this area does not appear to even satisfy Class C, "fair," state standards. Additional water quality samples should be taken near RM 4 to verify these water quality conditions. Quarries within the area also contribute elevated loads of total suspended solids and associated phosphorus. Sampling within a runoff ditch from Sunset Materials revealed suspended solids and total phosphorus concentrations which are significantly higher than the recommended threshold levels. In addition, flow from tributary 0291A contributes metals and high fecal coliform levels to the mainstem May Creek at about RM 4.9. The source of this contamination could be the, urbanized area at the headwaters (which is near an area with a 17 percent rate of failing septic systems) and also from livestock near the mainstem. High fecal coliform Chapter 8 Water Quality 8-69 Table 8-20. May Valley Subarea Water Quality Issues. Station and Location Water Quality Issues Possible sources 11. Tributary 0291A Metals: exceedances TP: Exceeds threshold NO3/NO2: Exceeds threshold FC: 29x > standard, 3rd highest 12. May Creek at 164th Metals: Some Ave. SE bridge exceedances, high in sediments TP: Exceeds threshold FC: 13x > standard Metals - urban runoff from commercial area at headwaters of tributary, SQGs TP - erosion in lower reach FC, NO3, TP - septic tanks: one area has a failure rate of 17%, all the areas have high repair percentages, livestock -keeping in the catchment and lower reach above confluence TP, FC - livestock -keeping in the May Valley (no septic failures were observed in nearby area). 15. May Creek at SR-900 Metals: Some exceedances TP, TSS - quarry releases, runoff crossing TSS: high values at times from dirt roads and driveways, of storm runoff livestock access to creeks TP: Exceeds threshold FC - livestock FC: 2x > standard concentrations during storms in May Creek at the 164th Avenue SE bridge pose a potential health risk to anyone coming in contact with the water. HIGHLANDS The Highlands subarea includes an unnamed tributary (0287D), Long Marsh Creek (0289), Country Creek (0292), Cabbage Creek (0293), the North Fork May Creek (0294), Wilderness Creek (0295), and the East Fork of May Creek (0297). These tributaries flow into May Creek from the north side of May Valley: most originate in steep, undeveloped land underlain by bedrock on Cougar and Squak mountains. Water quality issues in this area are summarized in Table 8-21. Water quality within these northern tributaries (Long Marsh Creek, Country Creek, and Cabbage Creek) is relatively good except for nitrate (the three tributaries have three of the highest four nitrate levels within the basin). While nitrate levels do not exceed the federal criteria for nitrate, they are higher than the recommended threshold value for protection of aquatic life, and indicate a significant source of nitrate is present in these highlands. Typically, forested runoff is generally much lower in nitrate than observed in this area. Because septic failure rates in the area are reportedly low, development is sparse, and SQGs are not known to exist in these subcatchments, the source of the Chapter 8 Water Quality 8-70 Table 8-21. Highlands Subarea Water Quality Issues. Station and Location Water Quality Issues Possible sources 10. Long Marsh Creek 13. Country Creek 14. Cabbage Creek Metals: Some exceedances TP: 64x > threshold NO3/NO2: exceeds threshold FC: 4x > standard Metals: Some exceedances TP: Exceeds threshold NO3/NO2: 2x > threshold Metals: Some exceedances TP: Exceeds threshold NO3/NO2: Exceeds threshold FC: 3x > standard TP, NO3: Possibly due to fertilizer use in lower reach. [no noted recent septic failures, no SQG, no USTs. Low density housing.] NO3: Source unknown. NO3 - Source unknown. 16. North Fork May Cr. Metals: some exceedances, Metals - SR-900 runoff high in sediments TP - correlation with TSS. TP: Exceeds threshold TSS - runoff from quarries. TSS: Exceeds threshold FC: 13x > standard nitrate is not known. It may be from localized fertilizer applications or an undetected failing septic system close to a tributary. Another water quality issue within this subarea concerns the North Fork, where stormwater quality is poor. Excessive suspended solids and metals concentrations have been measured. The high metals concentrations probably result from road runoff because May Creek is essentially a roadside culvert in this area, whereas the suspended solids loadings probably originate in the quarries located alongside the road, supplemented by road runoff. High suspended solids in this reach could adversely affect the spawning grounds for anadromous fish observed in portions of the creek. Future loading predictions are excessive for some subcatchments located within the Highlands subarea due to dramatic changes in land use from primarily forested lands to single-family residential. For example, phosphorus loadings are projected to increase in the North Fork catchment by 82 percent and zinc is predicted to increase by 121 percent. The other drainages in this subarea , particularly Country and Cabbage creeks, are predicted to experience increased urbanization, resulting in future water quality degradation. Chapter 6 Water Quality 8-71 EAST RENTON PLATEAU The East Renton Plateau Subarea drainage consists of the South Fork of May Creek (0282, including Lake Kathleen), Greene's Creek (0288), and several small unnamed tributaries (0291 A, 0291 B, 0291 C, and 0291 D). Water quality issues in this subarea are summarized in Table 8-22. Table 8-22. East Renton Plateau Subarea Water Quality Issues Station and Location Water Quality Issues Possible sources 17. South Fork May Metals: exceedances, high Metals - road runoff (from SE 128th Creek concentration in sediment St.) TP: Exceeds threshold FC - 2% septic failure observed in FC: 15x > standard upstream area, livestock -keeping Lake Kathleen meso-eutrophic High TSS possibly from runoff. In general - WQ is reasonable. Relative to other parts of the basin, the East Renton Plateau subarea appears to have satisfactory water quality. Water quality in the Lake Kathleen area has fecal coliform levels which exceed the standard, and which may be moderately affected by road runoff from SE 128th Street. Lake Kathleen is naturally meso-eutrophic, and does not appear to be in immediate danger of increased eutrophication due in part to the lack of significant drainage into the lake. However, residents near the lake and livestock raisers should follow best management practices with respect to sewage and animal wastes to minimize the introduction of additional phosphorus into the lake, and any construction in the area should take precautions to prevent increasing the supply of suspended solids to the lake. In the long term, without human intervention, it appears the lake will follow a natural transformation process to a typical bog system, with gradual changes in water quality, especially increased nutrients and dissolved organic compounds. 8.7 KEY FINDINGS • Nonpoint pollution is the major source of pollution in May Creek, and conditions are expected to worsen in the future. The most pronounced increases will be seen in streams associated with projected newly developing and urbanizing areas: the Highlands tributaries (particularly Country Creek) and Newport Hills Creek. • Current fecal coliform levels during and following storm events pose a significant health threat to water users within the basin. Levels suggest that direct contact activities (swimming and wading) should be discouraged in most of the streams in the basin and that untreated surface waters throughout the basin are unfit for human consumption. Chapter 8 Water Quality 8-72 High water temperature, due to a lack of riparian vegetation and its shading, is clearly a limiting factor for salmonid survival in the upper May Valley reach in the late summer months. In the lower, urbanized portion of the basin, stormwater in both the tributaries and the mainstem of May Creek has higher instream concentrations of toxic metals than it has in the upper, largely rural basin. Honey Creek, and May Creek at its outlet to Lake Washington, have the highest concentrations, exceeding both acute and chronic total metal criteria for copper, lead, and zinc for nearly all monitored storm events. Sediment quality has been degraded at many sites due to elevated metals concentrations (primarily lead and copper). Honey Creek contained especially high lead concentrations. Storm event phosphorus concentrations for May Creek, expected to increase in the future, already well exceed EPA guidelines. However, the relative phosphorus loading contribution from May Creek to Lake Washington is relatively low when compared to the load from other tributaries to the lake. Chapter 8 Water Quality 8-73 Chapter 9 Aquatic Habitat and Fish Chapter 9 Aquatic Habitat and Fish 9.1 INTRODUCTION The May Creek basin exhibits a variety of habitat conditions from moderately disturbed areas of the lower mainstem to heavily altered regions such as the central May Valley. The system contains numerous wetlands in various states of disturbance, two major lakes, and a variety of low- to high -gradient, perennial and intermittent streams. The best stream habitat in the system exists in the lower four miles of May Creek. Most of the tributaries on the south side of the valley, particularly around Honey Creek, have been affected by recent and historical rural and urban development. Streams on the north side of the basin have been less altered by development although some areas, such as the upper Lake Boren tributary and portions of the North Fork (0294), have been markedly modified in the past decade. The following sections discuss how the stream, lake, and wetland habitats and surrounding landscape elements interact in the basin area, and how these interactions affect important aquatic resources, including resident, adfluvial, and anadromous salmon and trout. 9.2 LANDSCAPE AND HABITAT CONCEPTS Aquatic habitats form as a result of complex interactions among water, soil, and vegetation. The nature of these interactions is determined by physical features such as valley morphology, stream substrates, and vegetation, which create local variations in hydraulic complexity, and by landscape processes that affect the storage and transport of water and sediment. The biological condition of aquatic habitats, such as the presence of diverse plant communities and fish populations, is determined in large part by many of these physical processes (Schlosser, 1991). Land use throughout much of the Pacific Northwest has reduced the quality and abundance of aquatic habitats through channelization, dredging, filling, and increases in storm runoff and flow velocities. These impacts eliminate such resources and their associated functions, or transform aquatic habitats from diverse and complex systems to more uniform systems of lesser complexity. For example, these changes tend to transform stream systems from complex mosaics of pools with varying depths combined with riffles to streams uniformly dominated by shallow pools and riffles (Hicks et al., 1991; Ralph et al. 1992). LANDSCAPE AGE The aquatic habitats of the basin are susceptible to damage by many land uses, in part because they are situated in a geologically "young" landscape. The basin is characterized by large areas of highly erodible soils and is dissected by numerous high Chapter 9 Aquatic Habitat 9-1 and moderate gradient stream systems that flow through moderately and deeply incised ravines. As a result, much of the landscape is susceptible to considerable erosion until a relatively stable geologic base is achieved. This natural process is aided by seasonally intense storms common to the west slope of the Cascade Mountains. These events result in periodic large storm runoff and stream environments that are naturally prone to frequent localized disturbance due to erosion. BUFFERING ELEMENTS The May Creek basin landscape is composed of moderately diverse aquatic and terrestrial ecosystems including forested uplands, riparian areas, stream channels, wetlands, and lakes. Each of these systems is differentially affected by the frequency and magnitude of disturbances such as landslides and floods. Buffering in a landscape is provided by elements that reduce the rate and magnitude of disturbance. The type and condition of buffering mechanisms surrounding or adjacent to aquatic habitats largely determines the nature and intensity of these disturbances. Land development often affects habitat by reducing or eliminating buffers and thereby changing the rate and magnitude of disturbances and the quantity and quality of aquatic habitat. Dramatic destruction of stream fish habitat and degradation of wetlands or lakes is often the most obvious effect of human development (Booth, 1991). In many instances, these changes parallel, or occur prior to, other problems such as erosion of roads and utilities and damage to flood control structures. Soil, vegetation, and topographic features such as lakes, wetlands, and floodplains are the principal buffering agents for aquatic habitats in the May Creek basin. Buffers modify the effect of disturbances and thereby create and maintain the hydraulic condition and aquatic habitats of the basin. Loss or reduction of these buffering elements increases the rate and amplifies the magnitude of disturbances and this alters the rate and direction of change in aquatic habitats and contributes to the physical damage of those habitats and artificial structures. Soil as a Buffering Element Soil acts as a buffer by absorbing and storing much of the precipitation in our region, thus dampening the energy of stormwater runoff. When soils lose their permeability as a result of paving or soil compaction on lawns and pastures, stormflow and subsequent erosional and flooding damage to habitat and public and private property often increases dramatically. Reduced infiltration of stormwater also results in less groundwater recharge and less available water for discharge during summer low -flow conditions. This may threaten the recharge of aquifers that provide baseflow to many aquatic systems, and further reduce fish and wildlife habitat. Chapter 9 Aquatic Habitat 9-2 Vegetation as a Buffering Element Vegetation is an important buffering agent because it profoundly affects the interaction between soil and water. The distribution, type, and quantity of vegetation are important in determining its buffering value and functions. Historically, the lowland valleys west of the Cascades were blanketed with extensive and abundant vegetation, much of it arranged in great structural complexity as a result of both standing and dead -and -down trees. Dominated by ancient coniferous forests with deep duff layers, this vegetation dampened the impact of storms by storing and slowing water movement through the landscape. In addition, vegetation was critical in stabilizing soils and creating much of the hydraulic diversity of stream environments. The roots of riparian vegetation stabilize streambanks, retard erosion, and create overhanging cover for fish. The above -ground portions of plants dissipate the energy of stormflows, obstruct the movement of sediment and detritus, and provide large woody debris to streams. For many Pacific Northwest streams west of the Cascades, over 50 percent of the complex pool environment important for fish production is directly created by large woody debris recruited from forests along stream channels (Franklin, 1992). Stream channel stability is maintained and enhanced by this material, often seen in complex debris jams that form deep pools. Topographic Features as Buffers Lakes, wetlands, and floodplains are topographic and hydrographic features that are important aquatic habitats on their own. They also buffer downstream aquatic habitat by temporarily storing floodwater so that the flow is spread out over a longer period of time. Sediment and other pollutants settle -out in the lakes, wetlands, and floodplains, cleansing the water before it flows downstream. Their value as habitat and buffer elements is affected by changes in surrounding soil and vegetation that can lead to dramatic changes in water level fluctuation, as well as large increases in water inflow or inputs of sediments and other pollutants. Human development often leads to filling in these areas, which directly reduces their water storage and cleansing capabilities. Effects of Reduced Buffering Buffering capacity is lost when elements such as vegetation, permeable soils, stream channel roughness, or volume of topographic depressions are reduced. Consequently, water energy is redirected and often increased as a result of reduced storage and/or diffusion of water in the landscape. The net effect of reduced buffering is to overwhelm downstream aquatic habitats with excessive quantities of water and/or sediment. These flows can scour stream channels or dislodge and smooth stream channel and riparian roughness elements such as largely woody debris, which are important in forming pool habitat and storing sediments. Throughout the basin, the isolated and cumulative effects of development have reduced buffering, increased the rate and magnitude of disturbances, and transformed affected areas to a geologically and biologically less mature condition. For example, affected streams become structurally simple and some wetlands become dominated by earlier Chapter 9 Aquatic Habitat 9-3 successional states: forested swamps revert to less structurally complex scrub/shrub wetlands and scrub/shrub wetlands revert to emergent systems. RIPARIAN VEGETATION Importance of Riparian Vegetation Productive fish habitats and good water quality depend on well -developed plant communities that exist along streams. This area of interaction between plant communities and streams is known as the riparian zone. A healthy, functioning riparian zone contributes directly to the health of the stream by providing streambank stability, shade, overhanging cover, leaf litter and other organic matter for invertebrate production, recruitment of large woody debris, reduction of water velocity, and storage of flood flows. The extent to which riparian vegetation contributes to stream structure depends on the type, amount, and health of the vegetation. Riparian ecosystems in western Washington were typically made up of a complex matrix of living, dead, and fallen conifers. Logging in the Pacific Northwest usually included removal of streamside timber until the early 1980s. As a result, the amount of large woody debris and the composition and structure of the riparian vegetation have been greatly altered in many streams, including May Creek. May Creek is currently dominated by deciduous riparian zones in the lower canyon, and shrub or grass -dominated wetlands and denuded pastureland in the May Valley area. Riparian areas of the East Renton Plateau are a mixture of grassy fields, immature deciduous forests, and immature coniferous forests. Most other tributaries in the Lower Basin and Highlands subareas have primarily immature mixed and deciduous riparian areas. The rapidly decomposing fine organic material (small woody debris) produced by deciduous trees and shrubs is less effective at influencing channel structure than that from decay -resistant coniferous trees. In an old -growth forest, deciduous large woody debris typically constitutes only five percent of the pieces in the system (Bilby, 1991). Thus, replacement of conifers by deciduous trees substantially and directly affects the complexity and diversity of fish habitat within the basin (Bilby and Ward, 1991). The health of small streams closely depends on the well-being of their riparian zones, and is highly responsive to alterations in riparian vegetation and the adjacent watershed area. Removal of the forest canopy adjacent to and within the riparian area can produce higher summer and lower winter water temperatures, reduce bank stability, and remove the buffering effect of the riparian zone. It also reduces or eliminates the recruitment of large woody debris, which in tum results in less structural complexity of the stream (Brown, 1985). Role of Large Woody Debris In intact and unlogged stream systems in westem Washington, large woody debris (LWD) is the product of an old -growth riparian forest ecosystem and is important in the Chapter 9 Aquatic Habitat 9-4 creation of channel diversity. LWD is a direct source of instream and overhead cover and functions as an instream scouring agent to produce and maintain high quality pools, provide surface turbulence, sort substrate materials. and form undercut banks. Large woody debris also provides stability to stream channels, retards the rate of downstream flow, and accumulates fine sediment. During flooding. woody debris can form a complex network of channels that act as dissipators of stream energy and tend to mitigate the height of downstream flood peaks by slowing stream flow. Salmonids make substantial use of wood -associated cover during high flows when the low -velocity areas created by the debris may offer the only suitable low -flow refuge. In low flow periods, large woody debris can provide cover and a complex array of depths, velocities, and substrates suitable for a variety of salmonid and other fish species. Large woody debris directly contributes to habitat complexity and overall productivity of streams for salmonids. Good fish habitat is directly associated with large woody debris, which is dependent on the health and diversity of the riparian zone in maintaining the habitat complexity within the stream channel (Bilby and Ward, 1989; Sedell, 1991, Brown, 1985). LWD also provides a food and cover source for macro invertebrates and amphibians, which in turn can be prey for salmonids. In general, large woody debris creates greater habitat diversity, including pools, riffles, cover, off -channel habitat, and flood -channel habitat, which creates greater rearing potential for salmonids. Abundance of juvenile cutthroat and steelhead in second and third order streams has been closely correlated with cover. Coho and other pool -dwelling salmonids in small streams also depend on pools and cover created by large woody debris (Brown, 1985). In high flows juvenile fish may physically be flushed down the river if there is no velocity cover in which to take refuge. For coho salmon, cutthroat, and steelhead, the deficiency of woody debris in varying degrees throughout the basin is a serious problem. SALMONIDS AND THE HYDRAULIC ENVIRONMENT Natural Effects of Hydraulics There are eleven distinct species, and numerous unique populations, of naturally occurring salmonids in the Pacific Northwest, comprising the most diverse salmonid-based ecosystem in the world. Five of these species occur in the May Creek basin. The evolution of stream fish communities is the result of adaptation to the hydraulic, chemical, and biological attributes of the aquatic systems and surrounding landscape. Under pristine conditions, the hydraulic condition of streams in the Pacific Northwest is typically highly diverse, with conditions ranging from complex patterns of small step pools and pocket -water common in headwater and peripheral stream channels to deep, expansive pools and backwaters of larger, lower gradient rivers. Wetlands, lakes, and side channels naturally form along many streams, providing additional habitat complexity for many species and life history stages of salmonids. Wetlands and small lakes are often highly productive environments for coho salmon and Chapter 9 Aquatic Habitat 9-5 cutthroat trout when water temperature and oxygen levels are adequate. Side channels provide additional habitat complexity along low gradient areas of larger streams and are utilized by all species of salmonids for spawning or rearing, or both, depending on timing and availability of water and channel size. Theoretically, as a landscape ages following a disturbance, vegetation interactions will play a greater role in buffering and shaping the landscape, and stream habitat patches will become increasingly stable, larger, and more complex. This successional process provides the habitat complexity to accommodate diverse biological communities and individual species. One example is chinook salmon, which spends varying periods of time in fresh water rearing, migrating, and spawning, and has a large adult body size. As a result, it requires a diverse array of water flows and stream depths to complete its fresh water life stages. At the other end of the spectrum, younger, more dynamic landscapes are generally dominated by biological communities that don't require the hydraulic diversity found in a more complex stream. Pink salmon and cutthroat trout, both small -bodied species, are two examples of fish that do not have expansive habitat requirements. The ecological implications are that some fish species can do well in a stream channel that lacks habitat diversity while other species will fail to thrive. Invariably, the consequences of human development are to reduce buffering and increase the effects of disturbance. As a result, the landscape and its biota adjust themselves accordingly, with the most dramatic and permanent changes in stream hydraulic environments and fish species compositions predicted in the urban environment. This relationship appears to be consistent with observed changes in stream fish populations in the Lake Washington drainage basin (Lucchetti and Fuerstenberg, 1993). Effects of Human -Induced Change on Habitat Changes to runoff patterns due to land use changes have been substantial in the May Creek basin and could be permanent. Urbanization, overgrazing, and forest practices have all changed the hydrologic patterns that directly impact stream channels and their habitat in the May Creek basin. Discharges that would naturally occur several times in a decade will instead occur several times every year following urbanization (WDF, 1992). Vegetation removal has greatly increased natural flow variations, resulting in higher maximum flows and lower minimum flows. Salmonid life cycles have evolved in freshwater stream systems to match the temporal variations in flow conditions. Life cycle phases are timed to take advantage of seasonal and daily flow characteristics. During different stages of the life cycle, flow requirements vary. In May Creek, the primary limiting factor for chinook and sockeye is probably spawning area and incubation success. Shortly after the fry emerge, they will leave the basin and enter Lake Washington to rear. For coho salmon, steelhead, and cutthroat trout, the primary limiting factor is probably availability of high quality rearing and overwintering habitat. These fish do not leave the basin for one to two years after they emerge from the gravel. Chapter 9 Aquatic Habitat 9-6 With increased flows in the basin, the likelihood increases for more flows with high enough velocities to move substrate. The lower mainstem is used by spawning salmonids for seven months of the year. Young salmonids at the egg and alevin stage are highly sensitive to any alterations to the incubation environment. Though high flows are important in flushing fine sediments from spawning gravels, too much flow can destabilize the stream substrate and force egg or alevin into the stream before incubation is complete. The historical removal of the forest from the May Creek basin has decreased slope stability, increasing sand and silt levels in streams, wetlands and lakes. This is particularly evident in the Lower Basin subarea (see Chapter 7: Sediment Deposition and Erosion). Increased sediment input from roads due to higher flows and more storm runoff is also evident throughout the basin. Elevated sediment input to May Creek has been added to by poor grazing practices in May Valley, poor gravel quarry sediment control practices in the upper basin (upper tributaries of the East Renton Plateau and Highlands subareas), and channelization. Cumulatively, these increased sediment inputs are directly affecting fish and invertebrate habitat in the basin. Incubation habitat suitability depends on how much, what size, and when sediment is transported. Accumulation of sediment, particularly sand, in gravel reduces permeability and decreases intergravel flow velocity. This results in a lack of egg oxygenation and also can block fry emergence. Many studies show a measurable decrease in intragravel survival of eggs as sediment increases. Generally, as road density increases the amount of suspended and intragravel fines in adjacent streams also increases (Cederholm and Salo, 1979.) Not only does sedimentation affect spawning quality, but aggradation reduces summer rearing capacity in pools and reduces winter carrying capacity when deposition occurs in interstitial spaces of stream substrates (Bjornn, 1977). The loss of riparian habitat, as well as the lack of woody debris, exacerbate the impact of the hydrologic change and increased sediment on the May Creek ecosystem. Turbidity and suspended sediment is also a concern for fisheries resources in the system. Excessive turbidities can stop or delay upstream migrating salmonids (cf. Lloyd, 1987). Some studies have found that growth can be reduced or gill tissue damaged after 5 to 10 days of exposure to water with a turbidity of 25 NTU (McDonald et al., 1991). Because salmonids feed by sight, increased turbidity in a stream reduces the effectiveness of their feeding. A study working with cutthroat trout found that fish ceased feeding in turbidities of 35 parts per million (Bachman, 1958; as cited in WDF, 1992). Salmonid Populations and Disturbance Stress Ecological systems typically respond to stresses caused by significant disturbance by reducing their physical and/or biological complexity. When these stresses are sustained beyond the natural adaptive capabilities of the species or community, the system is replaced. Salmon populations throughout the Pacific Northwest have been subjected to high levels of sustained stress caused by human disturbances. Many of these stresses are different in magnitude and behavior from those to which local fish populations Chapter 9 Aquatic Habitat 9-7 adapted. These stresses include the physical modification of habitat and landscapes described above, as well as overfishing, interaction with hatchery stocks, and acute and chronic pollution. While it is not possible at this time to sort out which of these factors has had the greatest influence, it is likely that land -use driven habitat degradation is a primary contributor (Hicks et al., 1991, Bisson et al., 1992). The cumulative response of salmonids to these stresses is manifested in the loss or near extermination of many specialized populations, and a concomitant reduction in the overall diversity of the aquatic community. Thus, a major concern with fish populations is that continued sustained stress, from habitat modification or other pressures, will ultimately lead to further declines in fish species diversity, and possibly the complete loss of unique salmon stocks. MAY CREEK FISHERIES The May Creek basin supports five species of salmonids: sockeye (Oncorhynchus nerka), coho (O. kisutch), and chinook (O. tshawytscha) salmon, and steelhead (O. mykiss) and cutthroat (O. clarki) trout. Historically, chinook, coho, and sockeye salmon used May Creek extensively. Cutthroat and steelhead trout also spawn and rear in the stream. The current known distribution of anadromous and adfluvial salmonid species within the basin is shown in Table 9-1. Chinook and sockeye salmon, steelhead, and cutthroat trout in the basin are maintained solely by natural reproduction. Coho and rainbow trout are sustained by stocking. Currently, the Washington Department of Wildlife annually stocks catchable rainbow trout in Lake Kathleen (1,000 to 2,000 fish) and Lake Boren (500 to 3,000 fish) to supply a local sport fishery. Stocking of May Creek with rainbow trout ended in 1983 (Washington Department of Wildlife Stocking records). The Washington Department of Fisheries annually releases 40,000 to 120,000 coho fry into May Creek from the Issaquah hatchery. On May 4, 1993, for example, 40,000 coho fry were released in the middle mainstem between 148th Street and 164th Street, with more released later in the upper North Fork (personal communication, Chuck Baranski, Washington Department of Fisheries, Olympia Washington, May 18, 1993). Warm -water fish such as bass, perch, crappie, and catfish can also be found in Lake Boren and Lake Kathleen (King County, 1980). The Renton School District annually releases about 2,600 to 3,000 coho fry into Honey Creek; annecdotal reports are that 2-5 fish have returned during each of the last three years (personal communication, Susanna Epler, Renton School District, May 25, 1995). To the extent possible, the May Creek basin stream fisheries are co -managed by the Washington Department of Fish and Wildlife and the Muckleshoot Indian Tribe (a result of the decision in U.S. vs. Washington) for the natural production of salmonids. In order to keep salmon harvest rates relatively low in an effort to re -build the salmonid runs, the south end of Lake Washington is closed to commercial fishing except when sockeye salmon are targeted. For its part, the Muckleshoot Tribe has voluntarily restricted its commercial fishing in Lake Washington since 1988. Directed harvests of May Creek sockeye runs occur only as the fish enter the lake. Chapter 9 Aquatic Habitat 9-8 n� Table 9-1. Distribution of Anadromous and Adfluvial Salmonid Species and Habitat." Page 1 of 2 Currently Total Accessible Stream or WRIA Length Length" Lake Name Number (miles) (miles) Species","' Comments May Creek 0282 0.0-9.1 7.7 CO/SE/CH/CT/SH Locally Significant Resource Area from RM 0.2 to 3.9. RM 0.0-3.9 All CO/SE/CH/CT/SH Heaviest utilization by fish of any reach in the basin. RM 3.9-7.0 All CO/CT Heavily impacted by grazing in riparian areas. RM 7.0-9.1 0.72 CO/CT 128-ft.- long culvert at SE 128th St. blocks anadromous fish (South Fork) passage at RM 7.7. Portions of the creek go intermittent in Summer. Lake Kathleen 0282 8.2-8.4 0.0 RB WDW stocks rainbow trout in the lake. Gypsy Creek 0284 0.9 0.18 Unknown Accessible to anadromous fish to culvert barrier at RM 0.18, but no documentation of any use. Entire channel largely barren of habitat (much incising, no pools or LWD). Honey Creek 0285 2.9 0.35 or 1.08 CO/CT First culvert barrier may be at RM 0.35, could be flow - related. Cutthroat use to RM 1.08. Schools plant coho fry in reach RM 0.4-1.0. Entire streambed is armoured in RM 1.0-1.38. Long culvert from RM 1.35-1.95. Newport Hills 0286 0.8 0.18 CT Outlet of railroad fill dam at RM 0.2 is a fish barrier. Creek Boren/China 0287 2.45 0.75 CO/CT Creek Lake Boren 0287 0.9-1.3 0.0 RB/CT [Unnamed] 0287D 0.4 0.08 CO/CT Long Marsh 0289 1.20 0.06 or 0.18 CT Creek [Unnamed] 0291A 1.4 0.50 CO/CT Potential culvert barrier at RM 0.48; definite culvert barrier at RM 0.75. Natural fish barrier (waterfall) at RM 1.89. WDW stocks rainbow trout in the lake. Culvert at RM 0.08 and pond spillway at RM 0.11 block fish passage; natural step -falls barriers above RM 0.13. Culverts and gradient probably limit access and/or use to first 300 feet; natural barrier (waterfall) at RM 0.18. Culvert at SE 116th St. (RM 0.5) is a fish passage barrier. Most upstream area is culverted and ditched. n� cD 0 Table 9-1. Distribution of Anadromous and Adfluvial Salmonid Species and Habitat." Page 2 of 2 Currently Total Accessible Stream or WRIA Length Length" Lake Name Number (miles) (miles) Species"" Comments Country Creek 0292 1.7 0.11 CO/CT A concrete block is halting anadromous fish passage above RM 0.11. Riprap and ponds to natural waterfall barrier at RM 0.24' stream doesn't flow above RM 0.11 in Summer. Historical observations indicate fish passage and use above RM 0.1. Cabbage 0293 1.3 0.00 none No current access because of downstream concrete Creek blockage on Cabbage Creek. Historical observations indicate anadromous fish use in creek. At RM 0.22 is a natural fish barrier. North Fork of 0294 2.46 1.45 CO/CT Heavily impacted by SR-900 and sediment from three May Creek quarries, but spawning was observed. Stream above RM 1.45 enters Sunset Quarry. WDF plants coho in the upper reach between RM 1.0 and RM 1.45. Wilderness 0295 0.7 Unknown Unknown Above RM 0.19 the gradient increases to more than 20 Creek percent. Typically there is no flow during dry periods. East Fork of 0297 1.0 Unknown CT? Highly manipulated stream, with berms, ponds, and May Creek culverts. No flow for much of the year. Some cutthroat use reported for lowest pools. Lower berms or culverts from RM 0.4 to RM 0.7, are probably passage barrier. 1/ Fish observations were made during stream habitat surveys in February through April 1993, and seasonal spawning surveys conducted during Fall -Winter of 1992-1993 (for salmon) and Winter -Spring 1993 (for steelhead and cutthroat trout). Streams 0284, 0286, 0287D, 0289, 0295, and 0282 (above RM 7.0) were not included in seasonal spawning surveys. See Table 9-2 for spawning survey data. 2/ Accessible by anadromous and adfluvial fish to this mile; 0.00 means inaccessible to anadromous fish. Resident fish may utilize stream above the barrier. 3/ CO=Coho, SE=Sockeye, CH=Chinook, CT=Cutthroat, SH=Steelhead, RB=Rainbow 4/ Most of the cutthroat trout observed were adfluvial (migrating from Lake Washington). Coho Salmon Naturally produced coho salmon from the Lake Washington drainage are harvested at relatively high rates when associated with hatchery fish in mixed -stock fisheries of south Puget Sound. However, once coho salmon enter the Shilshole Bay area, they are harvested at considerably lower rates, more compatible with sustained natural production. Once coho destined for streams in Lake Washington enter south Lake Washington, they are not targeted for harvest. Some coho may be caught incidentally when sockeye are targeted. Spawning escapement of anadromous fish in the Lake Washington system has declined in recent years. The most dramatic decline appears to be that of wild coho salmon, whose spawning escapement in 1991 and 1992 was only 800 and 1,300 fish, respectively, for all of Lake Washington. By comparison, escapement levels averaged 13,700 in the 1970s and 7,700 in the 1980s. The escapement goal for Lake Washington wild coho salmon is 15,000 fish. While no formal escapement goal is available for May Creek, an older, rough estimate included in the 1980 May Creek Basin Plan indicated that May Creek has the potential to support 250 to 500 coho spawners. At such spawning densities, the May Creek system would support only a small portion, less than three percent, of the total potential coho production of the Lake Washington system. Spawning survey information from the May Creek basin has been sparse, with coho surveys conducted sporadically in 1976, 1977, and 1985. Peak coho densities in lower May Creek (below RM 4.0) during these three years was 23, 5, and 55 coho per mile for the segments surveyed within this reach. During our 1992-93 survey, peak density of coho was only two fish per mite (Table 9-2) in this region, suggesting this system is following the regional trend of low escapement. Limited escapement data from the WDF spawning survey data base indicate that at least Honey Creek (0285), Boren Creek (0287), Country Creek (0292), and the mainstem May Valley area have been used to a limited degree by coho for spawning. The 1992-93 data indicate that in addition to the streams mentioned above, the upper North Fork (0294) and tributary 0291A are also usec by spawning coho (Table 9-2). Chinook Salmon While wild chinook salmon have maintained steady escapement levels to the Lake Washington system for the 20 years period prior to 1991 (averaging 5,500 to 6,000 spawners per year), their numbers have diminished in the last two years. Escapement was 1,900 and 1,800 fish in 1991 and 1992, respectively. It is likely that May Creek contributes less than one percent of the wild chinook to the Lake Washington system, because chinook typically spawn in larger streams and rivers. In 1976 and 1977, partial surveys in the lower canyon area of May Creek found peak densities of one and seven fish per mile, respectively, During the 1992-93 surveys, peak density was one fish per mile for the whole lower four -mile segment, which appears to be similar to limited historical information. Chinook were not observed upstream of the lower canyon area in 1992-93 (i.e., above about RM 3.0). Chapter 9 Aquatic Habitat 9-11 CD Table 9-2. Summary of May Creek 1992-1993 Spawning Surveys." SOCKEYE COHO CUTTHROAT' Peak Peak Total Redds/ Peak Peak Total Redds/ Peak Peak Total Redds/ Stream Total Fish/ Redds Mile Total Fish/ Redds Mile Total Fish/ Redds Mile Fish Mile Fish Mile Fish Mile May Creek 0282 RM 0.0-4.5 305 67.8 248.031 55.1 " 9 2.0 0 v 0 3' 47 10.4 119 26.4 4.4-7.0 " -- -- -- — -- -- -- -- 0 0 8 3.1 5.7-6.9 5' 0 0 0 0 0 0 3 2.5 -- -- -- -- South Fork 0282 7.0-8.1 " -- -- — -- -- -- -- -- 0 0 0 0 Honey Creek 0285 0.0-0.3 0 0 0 0 0 0 0 0 -- -- -- -- 0.0-1.1 -- -- — -- — -- -- -- 7 6.4 26 23.6 Boren/China Creek 0287 0.0-0.9 0 0 0 0 0 0 0 0 2 2.2 18 20.0 0.9-1.7 u -- -- -- -- -- -- -- -- 0 0 2 2.2 Tributary 0291A 0.0-0.2 0 0 0 0 3 7.5 6 15.0 0 0 19 47.5 Country Creek 0292 0.0-0.2 0 0 0 0 2 10.0 4 20.0 3 15.0 16 80.0 Cabbage Creek 0293 0 0 0 0 0 0 0 0 0 0 0 0 0.0-0.2 North Fork 0294 0.0-0.4 5' 0 0 0 0 0 0 0 0 -- -- -- -- 0.0-0.8 " -- -- -- -- -- -- -- -- 11 13.8 7 8.8 0.8-1.4 0 0 0 0 5 8.3 6 10.0 24 40.0 49 81.7 East Fork 0297 0.4-0.6 0 0 0 0 0 0 0 0 0 0 0 0 1/ Seasonal spawning surveys were conducted during Fall -Winter of 1992-1993 (for salmon) and Winter -Spring 1993 (for steelhead and cutthroat trout). 2/ No steelhead were observed during any spring spawning survey. 3/ A few sockeye redds may have been coho redds. 4/ One sample date in spring for trout. 5/ One sample date in fall -winter for salmon. Sockeye Salmon Cedar River sockeye salmon spawning escapement represents as much as 90 percent of the Lake Washington system escapement. The Cedar River sockeye salmon escapement has dropped from an average of 261,000 fish per year throughout the 1980s to 93.000 and 87,000 in 1990 and 1991, respectively. In 1992, total escapement to the Lake Washington system was also low at 155,000 sockeye (personal communication, Chuck Baranski, WDF, Olympia). The decline in Cedar River sockeye escapement is indicative of a trend occurring in the Lake Washington system as a whole, which includes the May Creek basin. These numbers are far below the escapement goal for the Cedar River, which is 350,000 sockeye (personal communication, Jim Ames, WDF, Olympia). The original May Creek Basin Plan Appendices (King County, 1980) indicate the potential for an escapement of 300 to 500 sockeye to the May Creek system, less than one percent of the Cedar River escapement goal. Major tributary escapement was high relative to the Cedar in 1992, however, with an estimated peak count of over 300 sockeye salmon in May Creek. Limited spawning survey data from 1976, 1977, and 1984 found peak densities of 2, 29, and 35 fish per mile in the lower canyon area, compared to a peak count of 101 fish per mile in 1992-93 (Table 9-2), suggesting that 1992 may have been an exceptionally high escapement to the May Creek system. Sockeye were observed only below RM 4.5 in the mainstem. The primary spawning area for sockeye in the system appears to be below RM 3.0, where the most suitable spawning gravel occurs (Figure 9-1). As a result of the recent decline in Lake Washington sockeye production, the 1993 Washington State Salmon and Steelhead Stock Inventory (SASSI Report; WDF et al., 1993) has listed the Cedar River and all tributary stocks of sockeye as "Depressed." Although there were record high numbers of sockeye salmon entering many of the small Lake Washington tributaries in 1992, including May Creek, the overall Lake Washington spawning escapement numbers were low. The current cause is unknown but appears to be related to changing conditions in Lake Washington, including changes in zooplankton composition and abundance, increased competition for food or predation from longfin smelt, possibly increased incidence of disease (e.g.., IHNV, the Infectious Hematopoietic Necrosis virus), and parasites such as the parasitic copepod (Salmincola sp.). Steelhead The steelhead population in May Creek has also declined in recent years, as it has been in other streams to Lake Washington (WDF et al., 1993) (Table 9-3). No steelhead were observed in the lower mainstem or in any other area of the May Creek basin surveyed during the spring of 1993 (Table 9-2). The escapement goal for wild winter steelhead into May Creek is 46 adults (personal communication, Bob Pfeiffer, Washington Department of Wildlife). While escapement has usually exceeded 10 steelhead to the system, the latest (1993) escapement estimate indicated no steelhead escaped to this system for the first time since surveys began in 1984 (Table 9-3). One of the primary reasons for this reduction is thought to be the predation by California sea lions at the Chapter 9 Aquatic Habitat 9-13 3 Steelhead 2 1 0 Vy r� O� M W, r� 0�1 M r r� O� M r O O O O O ^ ^ N N N N N M M M M M 4 � River Mile 8 7 Cutthroat 6 5 'n 4 a� 3 2I 1 p ^ M O O O O O —^ -^ N N N N N M M M M M tt tt 'IT River Mile 25 20 15 10 5 . . . . . . . . . . . . . . . . . . . . . . . N N N N N M M M M M tt et 'e River Mile Figure 9-1. May Creek sockeye (1992), cutthroat (1993), and steelhead (total 1984 through 1987) redds (steelhead surveyed from RM 0.3-3.9). Chapter 9 Aquatic Habitat 9-14 Table 9-3. Steelhead and Cutthroat Escapement Data for Lower May Creek (RM 0.0 to 4.0 or 4.5). i'/ WINTER WILD STEELHEAD WILD CUTTHROAT Estimated Fish Fish Fish Year Redds Escapementti Observed Redds Observed 1993 0 0 0 119 4731 1992 3 2 0 41 3 1991 -- -- -- -- -- 1990 13 22 0 30 7 1989 11 12 0 9 2 1988 14 22 1 0 0 1987 18 30 2 10 0 1986 7 26 1 1 2 1985 4 6 3 7 2 1984 -- 12 — -- -- 1/ 1984-1992 data from Bob Pfeiffer (Washington Department of Wildlife). Numbers of fish observed are approximate. Cutthroat count was made after major spawning period, and therefore is not comparable to 1993 data. 2/ WDW goal of fish escapement to May Creek is 46 wild winter steelhead. 3/ 1993 fish count is the total from the first two weeks of the March survey periods. Chapter 9 Aquatic Habitat 9-15 Ballard Locks. While SASSI lists native steelhead stocks of the Lake Washington system as "depressed", Bob Pfeiffer of the Washington Department of Wildlife considers the latest escapement counts (spring 1993) to be so low that the native runs should be categorized as "critical". Despite the low escapement of steelhead to May Creek, spawning gravel area below RM 4.0 is well supplied and distributed (Figure 9-1). No surveys have been made above this area. Cutthroat Trout The cutthroat trout population in May Creek appears to be increasing (Table 9-3). This population originates from adults that rear for much of their lives in Lake Washington and spawn as adults in creeks. The apparent trend may be less dramatic than indicated on Table 9-3 because the spring 1993 surveys are not directly comparable to past years. The life history and characteristics of the cutthroat stolcks in this system are not well known, but the apparent increase suggests at least one important salmonid population may be on the increase in the Lake Washington system. Similar trends noted in other stream systems in the Lake Washington drainage suggest the trend may be drainage -wide (personal communication, Bob Pfeiffer, Washington Department of Wildlife). Whether the increase is indicative of changes in the May Creek system is not clear at this time. It has been noted in other Lake Washington basins that cutthroat tend to dominate streams whose catchments have relatively large areas of impervious area development (Lucchetti and Fuerstenberg, 1993). The peak areas for spawning cutthroat appear to be below RM 3.0 (Figure 9-1). Substantial use of several tributary areas also occurs, with peak spawning occurring in the region above RM 0.8 on the North Fork, 0294), lower Honey Creek (0285, primarily below RM 0.4), lower Boren Creek (0286, primarily below RM 0.4), below RM 0.2 of Tributary 0291A, and below RM 0.2 of Country Creek (0292). Other Aquatic Species Freshwater mussels, which are thought to indicate good water quality conditions, have been observed in upper portions of May Creek in the North Fork (0294). Crayfish have also been observed in May Creek at the SR-900 road crossing (RM 7.0). LAKES AND WETLANDS The May Creek basin's two major lakes and more than 60 individually identified freshwater wetlands are critical elements of the basin's aquatic habitat (see Map 1). At 208 acres, Wetland 5 is among the largest known freshwater wetlands in King County. In total, there are more than 410 acres of wetlands and more than 65 acres of lakes in the basin, making up approximately five percent of the basin's total acreage. Actual wetland acreage is greater if all riparian wetland acreage is included; further, there are additional wetlands not included in the inventory. Chapter 9 Aquatic Habitat 9-16 Wetland areas provide habitat for a wide variety of flora and fauna, and they also perform other valuable ecological functions such as flood storage and biofiltration of storm runoff. Many of the basin's wetlands have been altered by past development, although a number of the larger systems remain in surprisingly good condition. We°lands are defined as transitional areas between land and water that are typically saturated or inundated by surface or shallow groundwater for a significant part of the year in years with normal rainfall. Prolonged saturation of these areas results in the formation of soils with distinctive characteristics and communities of plants adapted to life in wet growing conditions. The wetlands of the May Creek basin include marshes, forested swamps, and riparian areas, as well as shallow water areas in or near lakes and ponds. No bog or fen communities are currently known in the basin. Wetlands store water in rainy periods and release it slowly during periods of dry weather. By acting as storage areas during rainstorms, wetlands help protect the May Creek mainstem and its tributaries from excessive peak flows, erosion, and scouring. They also provide a source of sustained stream flow during hot, dry periods during summer and early fall. By filtering silt and pollutants, wetlands also help protect water quality throughout the basin and in its downstream receiving waters, including Lakes Washington and Union, and Puget Sound. These wetland functions are vital in maintaining productive fish and wildlife habitat throughout the basin. Wetland Flora and Fauna A great diversity of plants and animals utilize wetland habitats within the basin. Common marsh plants include cattail (Typha latifolia), yellow pond lily (Nuphar polysepalum), bulrushes (Scirpus spp.), sedges (Carex spp.), and rushes (Juncus spp.). Scrub -scrub wetlands are dominated by species such as hardhack (Spiraea douglash), willows (Salix spp.), and red -osier dogwood (Comus stolonifera). The forested swamps are typically composed of dense stands of western red cedar, red alder, and Oregon ash (Fraxinus latifolia), and have shrub understories consisting of salmonberry (Rubus spectabilis), and forest floors with skunk cabbage (Lysichitum americanum) and lady -fern (Athyrium filix-femina). Among the mammals of these wetlands are the beaver (Castor canadensis) and river otter (Lutra canadensis); both are denizens of ponds, marshes, and riparian areas. Beavers have probably been historical agents of wetland formation on the May Valley floor. At the present time, the basin contains only one active beaver lodge in the May Valley at RM 5.6. Beavers subsist mainly on deciduous plants, including the bark of the trees and shrubs they use to construct their dams and lodges. Beaver dams —formed by sticks, mud, and brush —impound water, trap sediment and nutrients, and help moderate stream flows during storms and periods of low flow. Because of this, beaver ponds are among the most productive rearing environments for juvenile salmonids. The basin's wetlands and buffer areas also support other small mammals such as porcupine (Erethizon dorsatum), raccoon (Procyon lotor), mountain beaver (Aplodontia rufa), hares and rabbits (Leporidae), as well as several species of mice, voles, and rats. Predators such as black bear (Euarctos amercianus) and coyote (Canis latrans) use Chapter 9 Aquatic Habitat 9-1 7 wetlands and other habitats in the less developed parts of the basin, as do black -tailed deer (Odocoileus hemionus). Dozens of species of birds nest and feed in the wetlands of the basin. Among these are the great blue heron (Ardea herodias), osprey (Pandion haliaetus), red -winged blackbird (Ageliaus phoeniceus), yellow warbler (Dendroica petechia), wood duck (Aix sponsa), bufflehead (Bucephala albelola), and hooded merganser (Lophodytes cucullatus). Value of Wetlands Wetlands are a critically valuable resource in the May Creek basin. Protection of wetlands is essential in order to maintain, and where possible restore, valuable resource functions, including flood storage and stormflow attenuation, water quality purification, groundwater exchange, streamflow maintenance, and fish and wildlife habitat. As elsewhere in King County, many wetlands in the May Creek basin have been damaged by a variety of human activities, including clearing, drainage, filling, and conversion to stormwater detention facilities. In the process, wetlands are often subjected to increased water level fluctuation, water quality degradation, and sedimentation, all of which can damage wetland plant communities and thereby decrease overall habitat quality. Wetlands not directly affected may become increasingly isolated from adjacent aquatic and upland habitats. Such isolation within the landscape almost invariably leads to loss of plant and animal species richness and/or replacement with other weedy, invasive, or exotic species such as reed canarygrass (Phalaris arundinacea), the Norwegian rat (Rattus norvegicus), the bullfrog (Rana catesbeiana), and the brown -headed cowbird (Molothrus ater) (Terborgh, 1989; Richter et al., 1991; Askins, 1995; Robinson et al., 1995). Some wetlands such as Wetlands 4, 9, and 11 remain in relatively good condition because until recently they have been relatively remote from intense development pressures. Such wetlands typically retain largely forested catchment areas and broad forested buffers that help preserve their hydrologic regime and provide habitat for species that depend on wetlands. Upland buffers also help protect these wetlands from noise, light, pollutants, and predation on their inhabitants by domestic animals. Although buffer protection is essential, it is important to recognize that wetlands cannot be protected by focusing solely on wetlands and their immediate buffer areas. Protected wetlands can still be degraded by levees, stream channelization, groundwater withdrawal, urbanization of upper catchment areas, water pollution, and other landscape changes. Therefore, as development continues, efforts must be made to preserve adjacent upland habitat corridors and wetland hydrologic source areas, which often extend far beyond standard -sized buffers. Wetland Classification, Inventory, and Regulation The King County Wetlands Inventory (King County, 1990b) contains information about the presence, extent, and characteristics of some of the wetlands within unincorporated King County. Additional wetlands in the May Creek basin were identified through field Chapter 9 Aquatic Habitat 9.18 work. Wetlands are normally rated as Class 1, 2, or 3 according to a set of criteria. For this Conditions Report, newly identified wetlands were rated using definitions in the 1990 King County Sensitive Areas Ordinance (SAO, King County Ordinance 9614) as follows: "Class-1 wetlands" are those assigned the Class-1 rating in the 1983 King County Wetlands Inventory, or those that meet any of the following four criteria: a. The presence of species listed by the federal government or the State of Washington as endangered or threatened, or the presence of critical or outstanding actual habitat for those species; b. Wetlands having 40 to 60 percent permanent open water in dispersed patches with two or more classes of vegetation; C. Wetlands equal to or greater than ten acres in size and having three or more wetlands classes, one of which is open water; or d. The presence of plant associations of infrequent occurrence. 2. "Class-2 wetlands" are those wetlands assigned the Class-2 rating in the 1983 King County Wetlands Inventory, or those that meet any of the following criteria: a. Wetlands greater than one acre in size; b. Wetlands equal to or less than one acre in size and having three or more wetlands classes; C. Wetlands equal to or less than one acre that have a forested wetland class; or d. The presence of heron rookeries or raptor nesting trees. 3. "Class-3 wetlands" are those wetlands assigned the Class-3 rating in the 1983 King County Wetlands Inventory; or any wetlands that are equal to or less than one acre in size and have two or fewer wetland classes. In the past, many wetlands within the May Creek basin were drained, cleared, and filled for conversion to agricultural land or other development. Many wetland acres have been disturbed by past road construction and extractive or renewable industries such as mining and logging. The King County Sensitive Areas Code currently restricts development in and near wetlands, and requires mitigation for unavoidable impacts of public and private development projects. In spite of this regulation, wetland encroachment continues due to permitted and unpermitted activities. No estimate of the rate of absolute wetland loss is available at this time, but based on analysis of wetland impacts in other basins in King County (King County, 1990c) and in other parts of Washington (Puget Sound Water Quality Authority, 1986), it is possible that up to half the wetlands in the basin have been lost or severely altered by development. Other studies indicate that even when required as a development permit condition, wetland mitigation projects are not always successful (Cooper, 1987; Kunz et al., 1988; Rylko Chapter 9 Aquatic Habitat 9-19 and Storm, 1991). During field data collection for this report, staff noted that a high percentage of wetlands had undergone some degree of buffer removal, clearing, drainage, or filling since the 1983 inventory. Several wetlands were in the process of being altered at the time of the field visits conducted for this report. 9.3 DATA COLLECTION AND ANALYTICAL METHODS STREAM HABITAT Data Collection Data collected in the field specifically for this basin planning effort included a habitat inventory and a spawning survey. Field work to assess stream habitat condition in the May Creek basin was conducted from February 1993 through April 1993. The Forest Service's Fish Habitat Relationship (FHR) methodology (Marcus et al., 1990) was used to quantify stream channel characteristics at a watershed scale. The habitat units inventoried were equal to or greater than one channel width of the stream. A hip chain (a string attached to a metered counter) was used to determine the length of each habitat unit, as well as the cumulative length of May Creek and all its tributaries. Characteristics of the existing stream corridor and riparian zone were noted; vegetation types and condition were noted at the same time to establish an aquatic ecosystem condition on a basin -wide scale. All data were collected using a Global Positioning System (GPS) to identify exact locations of the stream channel and key features such as road crossings, culvert locations, erosion, large woody debris, fish spawning nests (redds), and associated wetlands. The data were saved to be accessible in a spreadsheet format for further analysis. The file was also saved so that all data can be identified according to the GPS location. Spawning surveys were conducted during the fall and winter of 1992-93 for coho, chinook, and sockeye salmon, and in the late winter and spring of 1993 for steelhead and cutthroat trout. These surveys were generally conducted weekly from mid -November to mid -December in the lower mainstem of May Creek (below RM 4.5) and bi-weekly through mid -January. Major tributaries were surveyed during this period biweekly. During the spring, the mainstem was surveyed approximately every one to two weeks from early March through mid -May, with major tributaries also surveyed bi-weekly. Additional spawning information was gathered during the spring on all streams during habitat surveys. During all surveys, a photo record of various conditions was kept. The record includes time and location, and identifies features such as culverts, substrate, bridges, riparian area, and spawning fish. Chapter 9 Aquatic Habitat 9-20 Analytical Methods As part of the aquatic habitat analysis, the type. size. and abundance of LWD was summarized. Because the frequency distribution of diameter and length of pieces of debris were lognormal, a geometric mean was used to calculate average diameter and length of debris for summary analysis. The types and quantity of major habitat features, including riparian composition and the relative composition of "fast" and "slow" water conditions, were noted by appropriate regions of May Creek and its tributaries. Locations Of upstream fish blocks, both natural and artificial, were indicated. The relative frequency of occurrence and relative percent of finer habitat type delineations were summarized for the May Creek mainstem. WETLAND HABITATS Data Collection Wetlands in the May Creek basin were evaluated to assess past and present land -use effects on wetland habitats and their associated functions. Initially, existing information on known wetlands was assembled from a variety of sources. These sources included the King County Wetland Inventory (King County, 1990b), the City of Renton wetland inventory (unpublished), and the National Wetland Inventory (U.S. Fish and Wildlife Service, 1985). Because of the scant or dated information contained in these sources, the previously inventoried wetlands in the basin were revisited to update and supplement this information. The basin was also investigated for additional, previously uninventoried wetlands. The inventory for additional wetlands began with the analysis of U.S. Geological Survey topographic maps and low altitude color aerial photography (February 1992; 1 inch = 600 feet), in which potential wetland areas were identified. Peripheral portions of the basin lacked photographic coverage, and thus were not examined intensively for additional wetlands. Field verification for all such suspected wetlands was conducted during February and March 1993. All known, previously inventoried wetlands were visited at that time as well. In addition, field notes and photographs were made of most of the wetlands to document current conditions and impacts. Wetland functions and values were evaluated for all previously inventoried wetlands using a modified version of the Reppert et al. (1979) wetland evaluation method. This information will be used to develop restoration projects and wetland management plans for selected wetlands that can benefit from protection, restoration, and enhancement measures beyond those provided in the King County Sensitive Areas Code. Historical Analysis Low -elevation black and white aerial photographs from July 1936 (1 inch = 800 feet) were examined in order to understand the nature and magnitude of historical land use changes in the basin, particularly with respect to impacts on vegetation, stream, and Chapter 9 Aquatic Habitat 9-21 wetland resources. The photographs were especially useful in providing insights on the intensity of timber harvest practices in upland, wetland, and riparian habitats. They also assisted in developing a rough estimate of wetland habitat loss due to filling since 1936. Generalized Wetland Conditions A total of 60 wetlands —more than four times as many wetlands as were described in the inventory —are located in the basin. All identified wetlands (including Lake Kathleen, which has many wetland characteristics) occupy a total of about 461 acres, or about five percent of the basin. The basin also contains other wetlands that have not yet been inventoried. All classes of freshwater wetlands exist in the basin: open water ponds, aquatic bed habitats, deep and shallow marshes, scrub -shrub wetlands, forested swamps, and riparian systems. Table 9-4 summarizes characteristics of the identified wetlands in the May Creek basin. In terms of area, the basin has a high percentage (291 out of a total of 461 acres, or 63 percent) of Class-1 wetlands. The majority of the Class-1 and large Class-2 wetlands are a mosaic of freshwater wetland habitat types, including open water, emergent marshes, scrub -shrub systems and forested swamps. Many of the Class-2 wetlands are located in riparian areas (i.e., along May Creek and its tributaries), reflecting a high degree of interconnectedness among streams and wetlands in the basin. A few of the Class-2 wetlands are considered to be Locally Significant Resource Areas (LSRAs) because of their outstanding functions and values. Many of the remaining Class-2 and Class-3 wetlands are relatively small, and typically consist of constructed ponds or relatively homogenous patches of scrub -shrub and/or emergent vegetation. A number of these systems are hydrologically isolated from other wetlands and streams. Nonetheless, these isolated wetlands may carry out important functions in spite of their small size, isolation, and/or apparent lack of habitat diversity. Results of the Puget Sound Wetlands and Stormwater Management Research Program indicate that multiple vegetation classes are not predictable indicators of high animal species diversity. Moreover, while wetland size is a factor in attracting breeding bird species, amphibian and bird diversity is determined more by the presence of plant species preferred for habitat and food. The research program has also found that wetlands that are low in amphibian and mammal richness tend to have poorer water quality, as evidenced by high conductivity and bacteria counts (Richter et al., 1991). 9.4 SIGNIFICANT RESOURCE AREAS One function of this Conditions Report is to designate certain habitats —particularly stream and wetland habitats —as Significant Resource Areas (SRAs). This designation is used by the County and City to identify habitats that possess characteristic features and functions that are of overriding importance to fish, wildlife, water quality, or aesthetic appreciation in the basin. The County Comprehensive Plan and County Code provide for consideration of SRAs, particularly RSRAs (see below), and recommended management actions will be described in the draft Basin Plan. Systems not designated as SRAs will Chapter 9 Aquatic Habitat 9-22 Table 9-4. Wetland Summary.l� Page 1 of 2 Regionally Locally Wetland Previously King County Significant Significant Number2l Acreage Inventoried Classification Resource Area Resource Area 1 61.29 X 1 X 2 11.77 X 1 X 3 11.70 X 2 4 4.01 X 2 X 53i 207.63 X 1 X 6 3.13 X 2 7 9.59 X 2 8 22.66 X 1 X 9 8.40 X 2 X 11 7.05 X 2 X 12 0.91 X 2 13 5.66 X 1 X 24 3.47 X 2 28b 7.97 X 2 304/ 41.85 2 31 0.68 3 32 0.25 3 33 0.26 3 34 2.385/ 2 35 1.18 2 36 2.14 2 37 2.18 2 38 3.17 2 X 39 1.77 2 X 40 3.67 2 X 41 4.47 2 42 0.67 2 43 2.20 2 44 0.56 2 45 0.48 2 46 1.06 2 47 3.69 2 48 1.00 2 49 1.67 2 50 2.58 2 51 0.41 2 52 1.04 2 53 0.51 2 54 0.43 3 55 4.00 2 Chapter 9 Aquatic Habitat 9-23 Table 9-4. Wetland Summary.i/ Page 2 of 2 Regionally Locally Wetland Previously King County Significant Significant Number2/ Acreage Inventoried Classification Resource Area Resource Area 56 1.11 2 58 1.33 2 59 2.36 2 60 0.39 3 61 1.06 2 62 1.13 2 63 1.39 2 64 4.03 2 65 0.24 3 66 1.20 2 67 0.92 3 68 2.13 2 69 0.91 3 70 0.3 3 72 0.47 3 73 1.04 2 74 1.63 2 756/ 35.14 Unclassified 76 6.25 Unclassified 77 3.51 Unclassified 78 4.92 Unclassified 1/ Wetland field surveys were conducted during 1993. 2/ Newly inventoried wetlands were tentatively assigned numbers beginning at 30. 3/ Wetland 5 includes the portion upstream of the SR-900 crossing, shown in the inventory as both part of Wetland 5 and as a separate Wetland 15. 4/ Wetland 30 is outside of the current May Creek basin boundary. 5/ Acreage figure represents the portion of Wetland 34 that is within the basin. 6/ Wetland 75 includes includes previously inventoried Wetlands 14, 26b, and 27b, as well as newly inventoried areas. Chapter 9 Aquatic Habitat 9-24 still receive protection through existing regulations, including those provided by the Sensitive Areas Code. Regionally Significant Resource Areas (RSRAs) contribute to the resource base of the entire southern Puget Sound region by virtue of exceptional species and habitat diversity and abundance. compared to aquatic and terrestrial systems of similar size and structure elsewhere in the region. RSRAs may also support rare or endangered species or communities. Although typically found together, any of the following criteria are sufficient to recognize RSRAs in the watersheds of King County: 1. Watershed functions are not appreciably altered from predevelopment conditions. as measured by corridor integrity, hydrologic regime, sediment movement, and water quality, or 2. The diversity and abundance of aquatic or terrestrial habitats are of consistently high quality and are well dispersed throughout the system, or 3. Aquatic and terrestrial life, particularly salmonids, exhibit abundance and diversity consistent with undisturbed habitats and make a significant contribution to the regional resources of Puget Sound. The following wetland within the basin is considered to have characteristics that fit the RSRA definition. None of the stream segments in the basin so qualify. Long Marsh Creek (0289): Wetland 11. This Class-2 wetland meets criteria 1 and 2 of the RSRA definition. Locally Significant Resource Areas (LSRAs) also contribute to the resource base of the region, but at a lesser level of both abundance and diversity compared to RSRAs. LSRAs are, however, significant within a particular basin, providing habitat that is important for plants and animals. Because aquatic systems require adequate functioning of all elements to contribute significantly to system productivity, all of the following criteria are necessary to recognize LSRAs in the watersheds of King County: 1. Watershed functions have been altered by clearing and filling, but corridor integrity, hydrologic regime, sediment movement, and water quality are adequate for spawning and rearing of salmonids or for maintenance of other plant and animal species, and 2. The diversity and abundance of aquatic and riparian habitats are good but not exceptional; instability, damage, and stream alterations are evident but confined to localized sites, and Chapter 9 Aquatic Habitat 9.25 3. Aquatic and terrestrial life, particularly salmonids, are supported at one or more species and life stages at population levels that may be low but are sustainable. All Class-1 wetlands in the basin (with the exception of most of Wetland 5) are categorized as LSRAs due to their large size, association with important stream or lake habitats, and their vital role in protecting downstream aquatic resources, but fail to meet the standards for RSRA designation because of the impacts of past land uses. In addition, several Class-2 wetlands are within stream corridor LSRAs (that is, they actually are contiguous with the streams). As such, they are assigned that same SRA designation as the adjoining streams, which is consistent with past basin plans. The protection of these wetlands is critical in maintaining fish and wildlife habitat, water quality, and stormflow attenuation in these stream systems. The following list of stream segments and wetlands within the May Creek basin have been identified as LSRAs: Stream Segments May Creek Mainstem (0282): RM 0.2 to 3.9 Honey Creek (0285): RM 0.0 to 0.4 Boren Creek (0287): RM 0.0 to 0.48 Unnamed Tributary (0291A): RM 0.06 to 0.3 Country Creek (0292): RM 0.09 to 0.14 North Fork (0294): RM 0.4 to 1.0 Wetlands May Creek Mainstem and South Fork May Creek (0282): Class-1 Wetland 5 (a 20- to 30-acre conifer forest remnant east of SR-900 and south of SE May Valley Road only) Honey Creek (0285) and May Creek Mainstem (0282), Wetlands 38, 39, and 40 Lake Kathleen: Class-1 Wetland 1 Gypsy Creek (0284): Wetland 9 China/Boren Creek (0287): Wetland 4 and Class-1 Wetland 8 Unnamed Tributary (0291A): Class-1 Wetland 2 North Fork May Creek (0294): Class-1 Wetland 13 9.5 BASINWIDE CONDITIONS HISTORIC CONDITIONS: BASIN VEGETATION Pre -settlement Conditions (pre-1850s) Vegetation of the May Creek basin has changed dramatically in both character and quality over the last 140 years. The main change has been a conversion of the forest vegetation from predominantly coniferous to predominantly deciduous, with extensive clearing for agriculture and urbanization. These changes have had significant impacts to wetland and stream resources in the basin. Chapter 9 Aquatic Habitat 9-26 The May Creek basin is located in the Western Hemlock Zone of the Pacific Northwest (Franklin and Dyrness, 1973). In presettlement times, the entire basin was probably vegetated with a mosaic of coniferous forest types, with western hemlock (Tsuga heterophylla) and western red cedar (Thuya plicata) being the dominant species. A large percentage of this evergreen forest likely included "ancient forest" habitat, stands characterized by extremely high structural and spatial diversity as well as numerous trees older than 200 years. Deciduous forest communities were probably restricted to riparian environments and recently burned upland areas, and likely composed of black cottonwood (Populus trichocarpa), red alder (Alnus rubra), bigleaf maple (Acer macrophyllum), and Douglas -fir (Pseudotsuga menziesh). Most wetland communities —including the May Valley Wetland 5—were also probably dominated by conifers. Such wetland habitats would have contained Sitka spruce (Picea sitchensis), western red cedar, and western hemlock. A 20 to 30-acre remnant of such spruce/cedar forested habitat is still present at the east end of Wetland 5. Post -settlement Conditions (1850s-1936) With the arrival of settlers of European descent in the basin, forest communities were logged. This logging proceeded rapidly and on a surprisingly large scale. Photographs from 1936 show strikingly massive clearcuts, and also document that most of the forest vegetation in wetlands not already converted to agricultural uses had also been logged, as well as forests along streams. For example, most of the forested riparian system associated with the mainstem of May Creek had been removed, exposing more than two-thirds of the streambed and riparian zone to the sun and elements. Nearly all of the western half of the basin had been deforested by 1936; much of the eastern half had also been logged by then. Vegetation in clearcut areas at that time appears to have been grass or scrub/shrub communities. In addition, much of the basin had been converted to agricultural uses such as pasture, hayfields, hopfields, and orchards by 1936. Portions or all of Wetlands 2, 3, 5, 7, 8, 13, 28b, 36, 37, 45, 49, 50, 65, 66, 68, 73, and 75 had been converted to agricultural uses (mostly pasture, hay, and/or truck crops) by that time. Many of these wetlands were ditched and/or drained in conjunction with their conversion to farm lands, most notably Wetlands 5, 7, 28b, and 75. Because there was relatively little construction -related development at the time, there appears to have been no loss or only a small amount of wetland loss due to filling prior to 1936. However, spoils from ditching, dredging, and stream realignments were sidecast and deposited in Wetland 5, and it is possible (but unconfirmed) that such spoils were also used to fill wetland habitats, particularly in Wetlands 5 and 75. HISTORIC CONDITIONS: STREAM HABITAT Instream and riparian conditions were initially altered by logging, coal mining, and railroad construction in the basin. During high flow periods, sediment accumulated at the delta, which was known for its natural, sandy beaches. Before development of the delta, May Creek migrated over the delta, typically switching locations during large floods. The Chapter 9 Aquatic Habitat 9-27 flat delta was expanded when Lake Washington was lowered. Subsequent development and filling of the delta led to the progressive confinement and channelizing of May Creek to an outlet at the extreme southwestern corner of the delta. A lumber mill and sorting yard now straddle May Creek. Development of roads and buildings and the placement of riprap has further restricted the natural migration of the river. The creek has since been dredged periodically, most recently after the 1990 flood. Above the delta, the creek was realigned from approximately RM 0.3 to 0.6, possibly when 1-405 was built. Aerial photographs from 1936 indicate multiple channels downstream from where the creek emerges from the canyon in the lower subbarea near NE 31 st Street. Currently most of the Lower Basin mainstem corridor has been designated a City of Renton/King County park. Land clearing associated with agriculture dramatically altered the May Valley region of the mainstem. The flat valley floor of this area and some of the uplands to the south of May Creek were cleared and heavily farmed. Originally, May Creek in May Valley probably flowed in a braided, partially defined channel and through well -developed spruce -cedar wetlands. A 1909 USGS map of the area shows considerable stream meandering. USGS Maps of the 1920s indicate that some channel straightening had occurred. The earliest aerial photographs from 1936 show stream channelization to be almost as it is today, indicating that the channel was most likely straightened and dredged between 1910 and 1936. In the 1940s, due to extensive flooding and increased sediment loads, the County dredged the creek and deposited dredge material on surrounding properties. By the 1960s, sediment had again accumulated in much of May Creek. CURRENT CONDITIONS (1936-1993): BASIN VEGETATION Comparison of aerial photographs from 1936 and 1992 reveals startling changes in the basin in a 56-year period, the most notable difference being the return of much of the basin to a forested —albeit deciduous —condition. The 1936 aerial photographs offer no evidence that the massive, contiguous clearcuts of the preceeding years were replanted or were naturally regenerating back to conifers at that time. It is unlikely these areas would have been replanted to conifers, as this was not a requisite or recognized practice at that time. Nor is it likely that natural restocking of conifers could have happened on a large scale, because this requires relatively nearby seed sources, which were greatly diminished by the widespread clearcutting. These circumstances resulted in the prevalence of deciduous forest vegetation observed in the basin today, which remains a persistent reminder of the grand scale of the forest practices of that earlier time and the substantial changes they precipitated in the basin. Though portions of the basin have returned to a coniferous forest condition —particularly at higher elevations —most present-day coniferous stands appear to be only 60 to 80 years old, still too young to provide significant structural and spatial habitat diversity and recruitment of large woody debris to the forest floor or stream channels. Nonetheless, from vegetation and habitat perspectives the present-day condition of much of the basin has improved compared to conditions earlier in this century. In Chapter 9 Aquatic Habitat 9-28 contrast with the scrub/shrub nature of the vegetation in the 1936 basin, the relative abundance of forest habitats —whether coniferous or deciduous —represents a suite of improved functions, including more valuable and diverse wildlife habitat, potentially increased soil/slope stability, more effective buffering of stream and wetland resources, and more valuable riparian conditions. Mature coniferous forests however, are most effective at providing high levels of these functions. Approximately 61 percent of the basin is currently either forest or forest mixed with low density single-family housing. Aside from deciduous and coniferous forest lands, the May Creek basin today supports a diverse mixture of land uses, including suburban residential areas, livestock -raising and low -intensity agriculture in the central valley and floodplain, park lands in the Lower Basin subarea and on Cougar Mountain, rock quarries in the upper basin, and industrial development on the delta. Thus, another importance difference between conditions in 1936 and the present is a dramatically heightened urbanization/commercialization of the basin, particularly in the Renton, Lake Kathleen, Lake Boren, and central valley areas. Such development has had and continues to have conspicuous impacts on the character of the basin and its aquatic resources. Notable in this regard is the filling of wetlands to accommodate development. A rough but conservative analysis of wetland loss due to filling after 1936 suggests that more than 180 acres of wetland (28 percent of estimated pre -settlement wetland acreage) have been filled or used for commercial properties, agricultural and residential purposes in the basin. These losses have historically occurred mostly within the present-day boundaries of the City of Renton, where most of the urbanization in the basin has occurred. The largest and most significant historic wetland fills and disturbances are located on the delta of May Creek, in a formerly large but now completely filled wetland near the intersection of Lake Washington Boulevard North and Interstate 405, in Wetland 8 on the north side of Lake Boren, and in Wetland 1 (associated with Lake Kathleen). A large number of smaller fills in the central valley Wetland 5 represent a substantial cumulative impact. In addition, large portions of Wetlands 2, 3, 6, and 34 have been filled. At least three moderately sized wetlands (each between one and ten acres) have also been completely converted to upland within the present-day City of Renton, and now are occupied by residential developments. CURRENT CONDITIONS: STREAM HABITAT Natural waterfalls and cascades on some tributaries are natural barriers to fish migration and have historically limited anadromous fish use of the upper stream reaches. Other passage barriers have been created by construction of the railroad and roads throughout the drainage. The placement of culverts during these projects rarely considered the requirements of migratory fishes. A fish ladder installed in the Lower Basin subarea after the gas pipeline was installed at RM 2.9 can be a fish barrier if not maintained properly. The riparian conditions in most of the streams are poor. Without active intervention, prospects for future inputs of large woody debris to the streams are fairly bleak. This is especially true in May Valley and the lower portions of most tributaries. The substrate is moderately sedimented in much of the basin, reducing spawning success of salmonids. Chapter 9 Aquatic Habitat 9-29 High turbidity occurs in many reaches of basin, particularly May Valley and the upper North Fork. While development has affected some streams in the Highlands area, causing increased high flows, increased sediment and turbidity, and loss of riparian cover, development there has been less pronounced than in tributaries in the Lower Basin. Intensive livestock use in the May Valley continues to reduce the habitat quality of the stream. This section of May Creek is used primarily as a passage for salmon and trout headed upstream, and for outmigrating fry. FUTURE CONDITIONS Future conditions of aquatic resources will depend in part on what actions are taken to improve current conditions and manage future development. Stands of second -growth Douglas -fir and red alder continue to be harvested, with subsequent conversion of forested areas to urban and suburban uses. As conversion occurs and forested lands are permanently lost, the landscape assumes a fragmented function and appearance. Large blocks of forest critical to the survival of many wildlife species are reduced in size and isolated from each other, reducing the volume and complexity of the habitat. Ultimately, the diversity and abundance of wildlife species decreases as well, or species are replaced with opportunistic (and often less desirable) species that become dominant in the remaining patchwork of habitats. Considering the current rates of development and forest conversion, loss of habitats and the species specific to those habitats will continue unabated in the basin. Further, the paucity of coniferous forest vegetation, the near -total lack of forest regeneration in riparian and upland areas, and the abundance of weedy shrubs in understory environments present an alarming ecological situation. These circumstances suggest that natural habitats in the basin —particularly at lower elevations and in riparian zones —will slowly be converted to non-native shrub habitats in the long term as existing deciduous trees die, thus further exacerbating the habitat and wildlife effects described above. Continued development of the basin will increase high -flow frequency, particularly in the Lower Basin tributaries, and reduce overall fish habitat quality. The May Valley area is not likely to change substantially from its degraded condition of a wide, sedimented, poorly buffered stream habitat, unless changes in management in the valley and upstream, and active habitat restoration actions occur. The future SR-900 road widening along the North Fork May Creek is also likely to increase flows downstream and reduce the quantity and quality of habitat in this region. Continued sediment input from the three major quarries in the upper basin will continue to add moderate levels of suspended sediment into the system during storm events. Important large -pool habitat in the Lower Basin mainstem—where most of the usable stream habitat currently exists —will probably decrease as the remaining trees along the stream die and are not replaced by new conifers. Conifers are needed to maintain an input of large woody debris, a major source of pool formation and habitat diversity in streams. Chapter 9 Aquatic Habitat 9-30 9.6 CONDITIONS BY SUBAREA LOWER BASIN This subarea contains the mainstem May Creek canyon area, from the creek's confluence with Lake Washington at RM 0.0 to RM 3.92. It includes all the tributaries that flow into the mainstem in this reach, including Honey (0285) and Boren (0287) creeks (Map 2). Current Conditions: Stream Habitat Lower May Creek Mainstem (0282). This portion of May Creek can be broken into twc reaches: the delta, which extends from the mouth at RM 0.0 where May Creek enters Lake Washington to RM 0.2; and the Canyon, where the creek flows through a steep -banked, moderate gradient (one to two percent) valley beginning at RM 0.2 and extending to RM 3.9. The first two -tenths of a mile, which makes up the delta, is heavily developed and lacks any riparian vegetation or LWD. A lumber mill occupies both sides of the stream corridor and is primarily made up of lawn and parking lots. The instream channel is largely dominated by fast -flowing water and riffle habitat, and functions primarily as a migration corridor for anadromous fish entering and leaving the basin. However, a few midchannel and lateral scour pools have formed from bridge deposition and riprapped edges. Despite the lack of habitat diversity, the substrate is made up of cobbles and gravels that are used by low numbers of spawning steelhead and cutthroat trout, and chinook, coho and sockeye salmon (Figure 9-1). Herons, mallards, coots and other waterfowl have been observed using this reach, as well as deer. The Canyon reach (RM 0.2 to 3.9) has a moderate gradient (one to two percent) and is probably the most important basin reach from a fisheries standpoint. This reach is heavily used by sockeye salmon and adfluvial cutthroat trout, but is currently used less by coho and chinook salmon and steelhead trout (Table 9-2, Table 9-3, Figure 9-1). Its few large pools nevertheless provide the most habitat diversity in the system, and probably the best rearing habitat available for all overwintering salmonids in the entire mainstem (Table 9-5). This region contains a wide range of fast- and slow -moving water habitat types. The slow —water habitat types are primarily lateral scour pools and mid - channel pools; fast —water habitat types are primarily low gradient riffles and runs (Tables 9-6, 9-7, and 9-8). Although the riparian area has been greatly modified by historic timber harvesting and negatively affected by increased sedimentation and high flows caused by upstream development, the canyon reach contains relatively good fish habitat of value to the Lake Washington system and is therefore designated an LSRA. This reach is made up of 53 percent slow -water habitat (Table 9-7). This is expected because of the canyon's moderate gradient and steep canyon walls. However, the slow water is made up of 25 percent glides and 30 percent lateral scour pools (Table 9-6). There is a lack of deep, complex pools within the system. Plunge pools and dammed pools are heavily used by juvenile coho salmon, age 1 steelhead, and all age -classes of cutthroat trout. Lateral scour pools, with their higher current velocities, are used by older Chapter 9 Aquatic Habitat 9-31 C Table 9-5. Large Pool Habitats in the Mainstem of May Creek (0282). m POOL TYPE1/ to a LSP BWP PLP DPL MCP CCP CRP TOTAL #/RM Subarea Reach Mile #Z/ %3/ # % # % # % # % # % # % # % Lower Basin 0.00-3.94 62 15 13 3 8 1 11 2 46 12 3 0 16 4 159 38 40.4 m Sr n� May Valley 3.94-7.02 2 1 1 0 0 0 0 0 7 3 1 1 1 0 12 5 3.9 �. BOTH 0.00-7.02 68 9 14 2 8 1 11 1 53 8 4 1 17 2 171 24 242 1 / Pool Type LSP = lateral scour pool MCP = mid channel pool BWP = back water pool CCP = channel confluence pool PLP = plunge pool CRP = corner pool DPL = dammed pool CO 2/ Frequency of occurrence eWv 3/ % = Percent of stream length n zr 70 m Cp c n� 2 Q v Table 9-6. Slow Water Habitat Types in the May Creek Mainstem Channel. Primary BWPIr CCP CRP DPL GLD LSP MCP PLP SCP SLW Subarea River Mile #2/ %11 # % # % # % # % # % # % # % # % # % Lower Basin 0.00-0.50 2 4.1 0 0.0 0 0.0 1 2.0 5 10.2 16 32.7 3 6.1 0 0.0 1 2.0 0 0.0 Lower Basin 0.50-1.00 3 5.8 0 0.0 3 5.8 3 5.8 0 0.0 7 13.5 7 13.5 3 5.8 0 0.0 0 0.0 Lower Basin 1.00-1.50 0 0.0 0 0.0 4 8.9 2 4.4 3 6.7 4 8.9 9 20.0 1 2.2 0 0.0 0 0.0 Lower Basin 1.50-2.00 1 2.3 1 2.3 3 6.8 0 0.0 4 9.1 10 22.7 6 13.6 1 2.3 0 0.0 0 0.0 Lower Basin 2.00-2.50 5 10.4 1 2.1 2 4.2 0 0.0 7 14.6 8 16.7 7 14.6 0 0.0 0 0.0 1 2.1 Lower Basin 2.50-3.00 2 4.8 0 0.0 1 2.4 4 9.5 6 14.3 8 19.0 5 11.9 2 4.8 0 0.0 1 2.4 Lower Basin 3.00-3.50 2 5.1 1 2.6 1 2.6 1 2.6 6 15.4 5 12.8 7 17.9 1 2.6 0 0.0 1 2.6 Lower Basin 3.50-4.00 2 6.7 0 0.0 2 6.7 0 0.0 7 20.0 4 13.3 3 10.0 0 0.0 0 0.0 1 3.3 May Valley 4.00-4.50 1 4.5 0 0.0 1 4.5 0 0.0 9 40.9 1 4.5 3 13.6 0 0.0 0 0.0 0 0.0 May Valley 4.50-5.00 0 0.0 0 0.0 0 0.0 0 0.0 4 44.4 0 0.0 3 33.3 0 0.0 0 0.0 0 0.0 May Valley 5.00-5.50 0 0.0 0 0.0 0 0.0 0 0.0 5 100 0 0.0 0 0.0 0 0.0 0 0.0 0 0.0 May Valley 5.50-6.00 0 0.0 2 20.0 0 0.0 0 0.0 6 60.0 1 10.0 0 0.0 0 0.0 0 0.0 0 0.0 May Valley 6.00-6.50 0 0.0 0 0.0 0 0.0 0 0.0 4 80.0 0 0.0 0 0.0 0 0.0 0 0.0 0 0.0 May Valley 6.50-7.00 0 0.0 0 0.0 0 0.0 0 0.0 8 88.0 0 0.0 1 11.1 0 0.0 0 0.0 0 0.0 1/ BWP = back water pool LSP = lateral scour pool CCP = channel confluence pool MCP = mid channel pool CRP = corner pool PLP = plunge pool DPL = dammed pool SCP = secondary channel pool GLD = glide SLW = slow water 2/ Count of occurrence in 0.5-mile intervals. 3/ % = Percent frequency of occurrence in 0.5-mile intervals. n zr W Table 9-7. Relative Habitat Composition and Large Woody Debris (LWD) per Mile for the Mainstem of May Creek and Selected Tributary Reaches./ CD Stream Primary Subarea Reach Mile % Fast Water2/ % Slow Water21 LWD/Mi co May Creek 0282 Lower Basin 0.00-3.92 47 53 153/mi May Valley 3.92-7.02 7 93 7/mi n Gypsy Creek 0284 Lower Basin 0.00-0.48 95 5 70/mi Honey Creek 0285 Lower Basin 0.00-1.08 86 14 176/mi 1.08-1.39 88 12 115/mi m Newport Hills Creek Lower Basin 0.00-0.36 70 30 174/mi 0286 Boren/China Creek Lower Basin 0.00-0.48 75 25 318/mi 0287 0.48-0.91 58 42 14/mi 1.29-1.88 94 6 114/mi South Fork 0282 East Renton Plateau 7.02-8.11 49 51 63/mi Tributary 0291A East Renton Plateau 0.00-0.78 97 3 26/mi co A North Fork 0294 Highlands 0.00-0.82 8 92 6/mi 0.82-1.00 61 39 141 /mi 1.00-1.64 84 16 50/mi Country Creek Highlands 0.00-0.25 87 13 16/mi 0292 Cabbage Creek Highlands 0.00-0.26 99 1 121/mi 0293 Long Marsh Creek Highlands 0.00-0.78 87 13 97/mi 0289 Tributary 0287D Highlands 0.00-0.39 76 24 72/mi East Fork 0297 Highlands 0.00-0.38 39 61 O/mi 1/ The short reaches of tributary streams within the May Valley Subarea have been combined with the rest of their respective streams in the East Renton Plateau and Highlands subareas. 2/ % = Percent of stream length Table 9-8. Fast Water Habitat Types in the May Creek Mainstem Channel. m Primary CAS11 FNT LGR POW RUN SRN CD Subarea River Mile #ti %3/ # % # % # % # % # % Lower Basin 0.00-0.50 0 0.0 0 0.0 16 32.7 0 0.0 5 10.2 0 0.0 Lower Basin 0.50-1.00 0 0.0 0 0.0 15 28.8 4 7.7 7 13.5 0 0.0 Lower Basin 1.00-1.50 0 0.0 0 0.0 17 37.8 1 2.2 4 8.9 0 0.0 Lower Basin 1.50-2.00 0 0.0 0 0.0 10 22.7 0 0.0 8 18.2 0 0.0 Lower Basin 2.00-2.50 0 0.0 0 0.0 8 16.7 0 0.0 9 18.8 0 0.0 Lower Basin 2.50-3.00 0 0.0 1 2.4 7 16.7 0 0.0 5 11.9 0 0.0 Lower Basin 3.00-3.50 1 2.6 0 0.0 4 10.3 0 0.0 6 15.4 3 7.7 Lower Basin 3.50-4.00 0 0.0 0 0.0 4 13.3 1 3.3 5 16.7 2 6.7 co May Valley 4.00-4.50 0 0.0 0 0.0 0 0.0 1 4.5 6 27.3 0 0.0 W "' May Valley 4.50-5.00 0 0.0 0 0.0 0 0.0 0 0.0 2 22.2 0 0.0 May Valley 5.00-5.50 0 0.0 0 0.0 0 0.0 0 0.0 0 0.0 0 0.0 May Valley 5.50-6.00 0 0.0 0 0.0 0 0.0 0 0.0 1 10.0 0 0.0 May Valley 6.00-6.50 0 0.0 0 0.0 0 0.0 0 0.0 1 20.0 0 0.0 May Valley 6.50-7.00 0 0.0 0 0.0 0 0.0 0 0.0 0 0.0 0 0.0 1 / CAS = cascade POW = pocket water FNT = fast non -turbulent RUN = run LGR= low -gradient riffle SRN = step run 2/ Count of occurrence in 0.5-mile intervals. 3/ % = Percent frequency of occurrence in 0.5-mile intervals. salmonids but not by young -of -the -year. Thus, the dominance of lateral scour pools and glides may influence the species composition and age structure of the salmonid populations and limit the rearing potential of the whole basin (Bilby, 1989). The habitat diversity that does exist within this reach is heavily dependent on the LWD in the system. A few houses border the stream in the lower 1.5 miles from RM 0.5 to RM 1.7 and in the upper 0.3 miles (RM 3.6 to 3.9) of the canyon. However, most of the canyon riparian area is protected as park land. The park land has grown back primarily as deciduous trees that are nearing their climax stage (Table 9-9). The composition and structure of the riparian vegetation is characterized by a conspicuous lack of conifers. The canyon lacks coniferous tree recruitment potential, and instead has a high proportion of deciduous trees and herbaceous vegetation. These species decompose rapidly and do not supply durable LWD to influence channel structure (Bilby, 1991). Within the May Creek channel, 62 percent of theLWD was deciduous, while only 15 percent was made up of coniferous trees. Twenty-two percent of the LWD could not be identified as either deciduous or coniferous. Even if this unidentified portion were grouped with the coniferous woody debris, it is still evident that coniferous trees needed to produce large quantities of LWD are missing. The canyon has approximately 153 pieces of in -channel LWD per mile (Table 9-7). This estimate includes pieces of wood at least four inches in diameter and six feet in length. In a study conducted by Bilby (1989), approximately 354 pieces of LWD per mile were found on old growth streams of comparable size located in western Washington. In Bilby's study, woody debris had to be at least four inches in diameter and 6.5 feet long to be counted. The lower May Creek mainstem does not appear to have the potential to supply even half of the LWD typically produced by an old -growth forest. The size of woody debris determines its long-term stability. Small pieces of woody debris may have a short-term effect on channel morphology, but tend not to stay anchored in high flows (Bisson, 1987). In a study by Bilby in 1985, a relationship was observed between the length and diameter of stable woody debris and channel width. For a stream of May Creek's width in the canyon, the average diameter and length of a stable piece of woody debris that will remain anchored for long periods of time is approximately 1.5 feet and 23 feet respectively (Bilby, 1989). In May Creek, the average diameter was 1.0 foot and average length was 19.8 feet. When placing coniferous and deciduous LWD into separate categories, it becomes more obvious that there is a decline in the average size of LWD. The average diameter of coniferous LWD was 2.3 feet and the average length was 11.5 feet . The deciduous LWD averaged 0.8 foot in diameter and 22 feet in length. Most of the large -sized pieces of LWD are coniferous and are declining in number within the system due to the lack of conifer recruitment. Fish habitat is also threatened by chronic lateral bank sliding and accelerated input of sediment into the channel. There is some indication that sediment deposition and sloughing is not being flushed from the channel and is filling pools and silting spawning gravels. This could greatly affect salmonid spawning success, as well as overwintering habitat. With the potential decline of LWD, this problem could escalate. Houses recently constructed on the bank in the upper 0.4 of a mile also threaten bank stability. At RM Chapter 9 Aquatic Habitat 9-36 Table 9-9. Riparian Conditions for May Creek and Its Tributaries. v (o Mature Immature Immature Immature to Complex Deciduous Coniferou Mixed Shrub Grasslan Wetland No Riparian Primary LB/RB1l LB/RB s LB/RB LB/RB d LB/RB LB/RB 1. AC)Tributary # Subarea Reach Mile M) M) LB/RB (%) (%) LB/RB (%) (%) n� M M n May Creek 0282 Lower Basin 0.00-3.94 0/0 66/67 1/2 13/8 11/7 112 1/2 6/12 May Valley 3.94-7.02 0/0 12/11 0/0 2/0 36/27 2/8 18/24 30/31 tS Gypsy Creek 0284 Lower Basin 0.00-0.48 0/0 0/0 0/0 79/79 21/21 0/0 0/0 010 Honey Creek 0285 Lower Basin 0.00-1.08 0/0 42/52 3110 6/0 18/25 0/0 0/0 31/13 1.08-1.39 0/0 0/0 75l75 0/0 0/0 0/0 0/0 25/25 Newport Hills Creek Lower Basin 0.00-0.36 0/0 50/52 010 27/14 14/34 6/0 0/0 2/0 0286 Boren/China Creek Lower Basin 0.00-0.48 0/0 19/21 17/37 60/50 0/0 0/0 0/0 410 0287 0.48-0.91 0/0 41174 0/4 2/2 0/0 0/0 16/16 41/4 1.29-1.88 0/0 28/38 5/0 27/33 10/5 6/6 0/0 23122 South Fork 0282 East Renton 7.02-8.11 0/0 4/7 27/29 28/29 0/0 10/10 16/15 16/9 (p Plateau v Tributary 0291A East Renton 0.00-0.78 0/0 53/43 0/0 24/34 0/5 14/8 0/0 10110 Plateau North Fork 0294 Highlands 0.00-0.82 0/0 30/32 0/0 4/0 30/39 34126 0/0 3/3 0.82-1.00 0/0 0/0 010 96/75 0/18 0/0 0/0 4/7 1.00-1.84 0/0 36/12 0/0 21/9 34124 0/0 010 10/56 Country Creek Highlands 0.00-0.26 0/0 0/6 8/0 30/38 616 23/0 6/0 27/50 0292 Cabbage Creek Highlands 0.00-0.26 0/0 2/0 0/0 98/98 0/0 0/0 0/0 0/2 0293 Long Marsh Creek Highlands 0.00-0.78 0/0 13/25 18/14 53/51 0/0 0/0 0/0 16/9 0289 Tributary 0287D Highlands 0.00-0.39 7/0 0/28 11/0 64/56 5/0 0/0 0/0 14/16 East Fork 0297 Highlands 0.00-0.38 0/0 3112 0/0 010 615 0/0 31/47 31/47 1/ LB = Left Bank RB = Right Bank (facing downstream) % = Percent of stream length 3.7, for example, residential construction combined with lateral bank scouring is causing sediment to slough into the stream. The natural gas line crossing at RM 2.5 is a highly erosive area due to unrestricted access by all -terrain vehicles (ATVs). This stream segment lacks riparian cover and the area has exposed gravel dirt banks. A fish ladder has been placed in this segment to control channel downcutting that could expose the gas line, which was not installed deeply enough. This ladder is the key access for fish passage to the upper basin for seven months of the year. It has the potential to become a fish barrier because sedimentation in the weirs and water velocity changes are altering its accessibility and usability for migrating fish. Gypsy Creek (0284). This tributary enters May Creek at RM 1.6. It runs through a moderately wooded canyon with a high percentage of immature mixed (primarily coniferous) riparian forest for one-half mile, ending in wetlands just across from SE 88th Place. The entire channel is largely barren of habitat because it lacks pools or LWD (Table 9-7), and exhibits severe sediment loading due to its incision through extensive and highly erodible recessional outwash sands. Increased runoff from urbanization has incised the channel up to five feet in depth; large quantities of sand are being added to May Creek. Despite the habitat degradation in this stream, resident trout could possibly reside in the tributary and even anadromous fish might be able to enter the stream during high flow periods. At RM 0.2 Gypsy Creek flows through an old corrugated metal culvert covered by approximately 15 feet of loose logging road fill. The culvert outlet is suspended three feet above the water surface, and effectively blocks fish passage. Wmtlanri Q Current Conditions: Wetland 9 is an 8.4-acre inventoried Class-2 system located between RM 0.5 and RM 0.8 in the headwaters of Gypsy Creek north of SE 88th Place. Aerial photographs from 1936 indicate this wetland is similar to its original post - settlement or even presettlement condition. The wetland comprises deciduous forested plant communities. Water enters the wetland from Gypsy Creek, surface flows, and possibly groundwater discharges. Two small areas of this wetland along the channel of Gypsy Creek have been cleared for pasture. The uppermost portions of Gypsy Creek have been developed and the stream in these areas is tightlined and ditched through single family residential lots and streets which are sources of fertilizer and road runoff. The wetland is bordered by deciduous and coniferous forests along nearly its entire perimeter. This wetland provides a high level of groundwater discharge, some moderate or high levels of floodflow alteration, sediment and toxicant retention, nutrient removal and transformation, and high -quality aquatic and wildlife habitat. For these reasons, this wetland is considered an LSRA. Future Conditions: Increasing development within the Gypsy Creek subcatchment suggests that future increases in nonpoint loading, runoff volumes, human and pet intrusion, and buffer violations are likely. Effects of these changes on vegetation and fauna within the wetland depends on the exact nature of such changes and the resiliance of the biota that inhabit the wetland. Chapter 9 Aquatic Habitat 9-38 Wetland 37 Current Conditions: Wetland 37 is approximately 2.2-acre uninventoried Class-2 wetland located above the confluence of Gypsy Creek and May Creek (May Creek RM 1.6) north of NE 31 st Street in the City of Renton. The wetland comprises emergent and scrub/shrub plant communities. Water is received from Gypsy Creek, and probably from groundwater discharges from the bottom of adjacent steep slopes. This wetland provides groundwater discharge, some moderate or low levels of floodflow alteration, sediment and toxicant retention, and wildlife habitat. Future Conditions: The wetland is located in the backyard of a single-family residence, and should not experience major changes in the future. Platting or future development of parcels affecting this wetland will require stream, wetland, and buffer protection, in accordance with the Sensitive Areas Code. Honey Creek (0285). Entering the canyon at RM 2.0, Honey Creek is the largest tributary in the basin. The stream can be separated into four reaches. The lower reach starts at the confluence with May Creek at RM 0.0 and ends at the power lines at RM 1.1 This reach has a moderate gradient (approximately four percent). The second reach, from RM 1.1 to RM 1.4, has been armored with riprap. The third reach, beginning at RM 1.4 at the Union Road crossing, is culverted under a heavily developed commercial area to RM 2.0. The last reach, from RM 2.0 to 2.8, was not surveyed. The lower reach is vegetatively well buffered by park land, but poorly buffered hydrologically because of the extensive urbanization of the upper catchments. The reach is dominated by deciduous forest, with some admixture with conifers in the upper part of the segment (Table 9-9). The reach is dominated by fast water, made up mostly of runs and low gradient riffles (Table 9-8). This section contains some the highest density of LWD in the May Creek basin (Table 9-7), although it is still not comparable to streams with coniferous vegetation. This abundance of LWD acts as an effective sediment trap for large amounts of sand and silt, and also creates a diversity of plunge pools and dammed pools. This entire segment is heavily used by adfluvial cutthroat trout for spawning (Table 9-2), and has been designated an LSRA. Although no coho were actually seen spawning in the channel during the 1992 survey, in the spring of 1993 a small number of coho fry were sighted below the gage station culvert (RM 0.35). The Renton School District releases approximately 2,600-3,000 coho fry in the Spring in Honey Creek (personal communications, David Christensen and Susanna Epler, City of Renton), and it is likely that the observed coho were derived from this planting; however, WDF has previously documented that some coho salmon spawning does occur in the lower half mile of stream. It was not immediately apparent whether the 35-foot-long road culvert and a 95-foot-long culvert at the pumping station block upstream fish migration: the presence of coho fry in the small (ten -foot) space between the two culverts could have been a result of fry release upstream, although adfluvial cutthroat spawning was observed above the culverts. Annecdotal reports are that 2-5 coho have returned to the stream upstream of the culverts during each of the last three years (personal communication, Susanna Epler). Chapter 9 Aquatic Habitat 9-39 The greatest threat to this reach is increased flows and water quality degradation from the highly developed upper catchments, combined with chronic sediment loading from slumping of the over -steepened roadsides, hillslope landslides, constriction of the stream channel by a sewer line access road, and erosion from steep, unmaintained ATV trails along the ridge. The resulting sedimentation is filling pools and infiltrating gravels. This sediment also feeds into lower May Creek, threatening the spawning and rearing habitat in the canyon. In the second reach of Honey Creek, from RM 1.1 to RM 1.4 above the power lines, the stream flows through a moderately steep wooded ravine. Apartment developments and SR-900 are beginning to encroach on the steep stream banks. Angular rubble has been used to armor the entire channel from the gas/power line crossing to 132nd Avenue SE, turning it into an artificial low -gradient riffle and eliminating any fish habitat that previously existed in this reach. Cutthroat trout were seen spawning in the creek up to the power line crossing at RM 1.0, but trout cannot utilize the substrate above this point. The channel in this reach also lacks woody debris of any size, though the riparian area is made up of a mixture of deciduous and coniferous trees; there is no refuge for fish from flood flows in this reach. The upper reach of Honey Creek begins at 132nd Avenue SE (RM 1.4) and extends to the stream's uppermost headwater wetland. From just above the crossing of 132nd Avenue SE, until just east of 142nd Avenue SE, the creek is conveyed within a 0.6-mile- long culvert that passes under SR-900 and adjacent commercial developments. Upstream of 142nd Avenue SE the creek was not surveyed for fish habitat. However, the creek flows through Wetland 6 after emerging from a predominantly coniferous - forested corridor. The creek originates in Wetland 24b, a well -forested headwater wetland. Wetlands 38, 39, and 40 Current Conditions: These uninventoried Class-2 wetlands are located at the base of steep slopes in the vicinity of the confluence of Honey and May creeks (May Creek RM 2.1) within May Creek Park in the City of Renton. The 6.3 acres of wetlands and the surrounding slopes appear to not have been disturbed by clearcutting as of 1936. Vegetation consists of emergent, scrub/shrub, and deciduous forested communities. These wetlands receive water from groundwater discharges from the adjacent steep slopes and from localized surface flows. Primary wetland functions include groundwater discharge, wildlife habitat, and good riparian support to May and Honey creeks. Because of these characteristics and the wetlands' association with segments of May and Honey creeks, that have been designated as LSRAs, these wetlands are also considered LSRAs. Future Conditions: These wetlands are fully contained in the May Creek Park and are thus unlikely to experience major changes in the future. However, it is possible that Wetlands 38 and 40, which are situated on a low terrace above May Creek, may eventually be undercut by the meandering of the creek. WPtlanri FR Current Conditions: This inventoried Class-2 wetland is 3.1 acres in size, situated south of SR-900 and east of 138th Avenue SE in the City of Renton. The wetland is Chapter 9 Aquatic Habitat 9-40 predominantly forested, but also contains scrub/shrub and emergent habitats. The wetland lies in the floodplain of Honey Creek (RM 1.7 to RM 2.1), from which it receives water. The creek channel disappears in several places in this wetland, and creek waters appear to flow underground at several other points. Most of the wetland's boundaries have intact forested buffers. The wetland has been reduced in size by filling associated with commercial development of the surrounding area, particularly west of 138th Avenue SE, and has also been segmented by two road crossings and their associated fills. Portions of the wetland have been affected by trash dumping, minor fills, and buffer reductions. The wetland is affected by noise from SR-900. Because of its association with Honey Creek, the wetland supports aquatic and wildlife diversity and provides moderate levels of floodflow alteration, sediment and toxicant retention, and food web support. Future Conditions: Any future development adjacent to the wetland will be required to provide stream and wetland protection, as required by the Sensitive Areas Code. However, considering the intense level of development in this locality, this wetland will likely continue to be disturbed by buffer violations and trash dumping, and will also experience higher levels of human and pet intrusion. Because of the anticipated future development in the Honey Creek basin, this wetland may be adversely affected by increased runoff volumes and flows in Honey Creek, summer drying, and nonpoint pollution that could result from such development. Wetland 24b Current Conditions: This 3.5-acre inventoried Class-2 forested wetland is situated at the headwaters (RM 2.8 to RM 3.0) of Honey Creek west of 148th Avenue SE, north of SE 128th Street. Water derives from localized surface flow and groundwater discharges. The wetland retains a mature forested buffer along most of its perimeter. A dirt road and associated fill cross the middle the wetland in an east -west direction. A nursery business just uphill of the wetland may be a source of nutrients and/or pollutants. The wetland provides wildlife habitat and groundwater discharge, and possibly nutrient and toxicant removal and transformation. Future Conditions: Additional build -out in the vicinity of this wetland may cause increased runoff volumes, summer drying, pet and human intrusion, and pollutant loadings. Newport Hills Creek (0286). This stream enters May Creek at RM 2.7 and can be separated into three reaches: the lower reach (RM 0.0 to 0.18), which ends at an old railroad fill dam; the middle section (RM 0.18 to 0.24), which is the pond behind the fill; and the upper headwaters (RM 0.24 to 0.4), which flow from Wetland 41. The high -gradient (about 12 percent) lower reach of Newport Hills Creek has limited quantities of LWD and largely immature deciduous riparian vegetation. Sedimentation and some channel incision is evident from upstream erosion and increased runoff. Overall, the stream channel lacks any habitat complexity. Despite these problems, cutthroat trout redds were located in this reach during the 1992-93 survey. Chapter 9 Aquatic Habitat 9-41 The fill was placed when the railroad was first constructed, and is a barrier to any upstream fish migration. The pond (Wetland 12) behind the fill is approximately 275 feet long and five to twenty feet deep. A Seattle City Light transmission line crosses the upper end of the pond. The pond is used by trout and various introduced fish species. The reach of Newport Hills Creek upstream of the pond is very similar to the lower segment, except that the riparian system has a greater admixture of conifers, and there is a greater quantity of LWD (Table 9-7). Also, there is habitat encroachment from housing developments bordering the upper banks of the stream, as well as increased stormwater runoff from upper catchment areas. It is very likely that this stream channel dries up during parts of the summer, further lowering its fish habitat value. Watlanri 17 Current Conditions: This 0.9-acre inventoried Class-2 wetland is located at the bottom of the deep ravine at RM 0.2 of Newport Hills Creek, between 124th Avenue SE and 89th Place SE. The wetland is almost all open water (a pond) formed by a massive embankment constructed for a railroad. Slopes above this wetland appear to have been selectively cut by 1936. The wetland receives water from the creek, from upslope stormwater runoff, and from seeps and other groundwater discharges associated with the steep slopes of the ravine. This pond and its well -established deciduous forest buffers appear to have been relatively undisturbed due to steep topography and difficult access. The pond currently provides habitat for a high diversity of waterfowl and other birds, small mammals, amphibians, and other aquatic organisms. Future Conditions: The wetland is privately owned, but contributes to the value of the property and its surround, and it is probable that the existing character of the pond and its springs and wetlands will be retained. However, intensive residential development of the headwaters of Newport Hills Creek and upslope is evidently causing increased sedimentation into the creek, higher flow velocities, and greater nonpoint pollutant loadings, all of which probably could have significant adverse impacts on the wetland. Wetlands 41 and 42 Current Conditions: Intermittent Newport Hills Creek flows through a steep -sided ravine north of the junction of 124th Avenue SE and 89th Place SE. Much of this ravine and its valley bottom appear to have been clearcut by 1936, although some moderately sized patches of mixed deciduous/coniferous forest were present at that time. The bottom of the ravine currently contains 0.7-acre Class-2 Wetland 42 at RM 0.4, and 4.5-acre Class-2 Wetland 41. The wetlands are bordered by a riparian area of forest and scrub/shrub plant communities. Water is delivered to the wetlands and riparian areas by the creek, localized surface flows, and groundwater discharges from neighboring steep slopes. These wetlands provide moderate to high levels of wildlife habitat, floodflow attenuation, groundwater discharge, and sediment and toxicant retention. A sewer or stormwater line has been constructed across the upper part of the ravine through the creek, and stormwater flows have been tightlined into the creek from developments above the ravine. An equestrian and pedestrian trail follows the ravine along the west slope. Future Conditions: Development in the immediate vicinity of the wetlands is unlikely because of the steep slopes bordering them. However, high -density residential Chapter 9 Aquatic Habitat 9-42 developments both upstream and on top of the bluffs are already contributing to increased sedimentation into the creek and its wetlands, higher flow velocities, greater nonpoint pollutant loadings, and increased human and pet visitation, all of which have major adverse implications for these wetlands. Boren Creek (0287). The main tributary from Lake Boren begins in the canyon at May Creek RM 3.3. The first reach, from RM 0.0 to 0.5, is a moderately steep banked channel. The lower 400 feet of this channel has the highest gradient (10 to 30 percent), while the upper portion is more moderate (averaging about four percent). The riparian system in this stretch is generally well vegetated with a mixture of immature coniferous and deciduous trees (Table 9-9). However, Coal Creek Parkway SE has encroached on the left bank of the stream, on top of the ridge, and is affecting the riparian area's stability, causing bank failures and erosion. Of particular note is a culvert at RM 0.4 that has fallen into the stream channel, causing excessive erosion and slumping into the stream channel. Where slumping has occurred, the stream channel is eroding road fill along Coal Creek Parkway SE. Habitat throughout this lower reach has suffered from the accelerated input of sediment and high flows caused by urban development upstream. The stream system is dominated by fast -water habitat lacking in fish habitat diversity (Table 9-7). This section of stream has the highest density of LWD of any stream in the basin, but most of the LWD is relatively small and deciduous, reducing its value in providing good quality, long-term habitat. However, there are a few small pockets of stable LWD that add to the channel complexity. Thus, this segment has been designated an LSRA. Fish utilization in this reach appears to be dominated by cutthroat trout, with a high density of adfluvial cutthroat spawning (Table 9-2). While no coho were observed spawning in this reach in 1992, WDF records indicate this region has been used by coho in the past. From RM 0.48 where SE 89th Place crosses the tributary to RM 0.9, the stream channel gradient drops to less than two percent and is no longer constrained by steep banks. In this reach, Boren Creek passes through Wetlands 7 and 8, pastures, and backyards to Lake Boren. Cow pastures and development along the stream channel are affecting fish habitat in this segment of the creek. Instream habitat is also highly sedimented and devoid of LWD (Table 9-7). The overriding impact to fish in this reach is provided by road and driveway crossings with culverts that impede or block upstream anadromous fish migration upstream and potentially trap resident fish that move downstream. The culvert under SE 89th Place is a potential fish barrier during high flows and when garbage collects at its intake. A private driveway culvert off Coal Creek Parkway SE at RM 0.8 is a definite fish barrier. The long and complex street culvert under SE 84th Way and Coal Creek Parkway SE is also a potential fish barrier. During the 1992-93 survey, resident cutthroat were observed at the outlet of Lake Boren. watInnrl 7 Current Conditions: This 9.6-acre inventoried Class-2 wetland is located west of Coal Creek Parkway SE and north of SE 89th Place, at RM 0.6 to RM 0.7 of Boren Creek. The wetland currently contains emergent, scrub/shrub, and deciduous forested habitats, but was completely cleared and possibly drained for hay production in 1936. Forested buffer vegetation is minimal except for substantial blocks on the west and north sides. A Chapter 9 Aquatic Habitat 9-43 gas pipeline right-of-way, roads, residences, and mown turf border the other wetland boundaries. The wetland has a long history of agricultural disturbance that continues today with low- level grazing from cows. Some trash accumulation is also evident. Boren Creek passes through the middle of the wetland in a straightened channel (evident in 1936 aerial photographs). Water enters the wetland from Boren Creek and local surface flow. The wetland provides wildlife habitat, floodflow attenuation, sediment and toxicant retention, and nutrient removal and transformation. Future Conditions: Because the wetland is bounded on three sides by a gas pipeline and roads (including Coal Creek Parkway SE, which is scheduled to be widened to four lanes), there appears to be minimal room for more intensive residential or commercial development. Thus, future impacts will likely be associated with changes caused by upstream development, including increased runoff velocities and higher flows, summer drying, and increased nonpoint pollutant loadings. The nature of the effects these changes will have on Wetland 7 depend on the intensity of future development and the resiliency of the wetland's vegetation and soils: these and existing impacts of Coal Creek Parkway SE should be addressed as part of the road widening project. Lake Boren is a shallow, 15.3-acre lake extending from RM 0.9 to RM 1.3 on Boren Creek. This stream is stocked annually with rainbow trout by the WDW and has public access for boating and fishing on the east side. Wetland 8—South End Current Conditions: The 1.7-acre Class-1 wetland at the south end of Lake Boren has had a long history of disturbance, which has become less intensive in modern time. Aerial photographs from 1936 illustrate a wetland that was completely cleared and probably drained for hay or crop production. Currently, the wetland consists of forest and scrub/shrub vegetation with a small amount of emergent habitat. Coal Creek Parkway SE, a residence, and a new King County park adjoin the wetland. May Creek passes through the middle of the wetland in a constructed channel (visible in the 1936 photograph). This wetland provides wildlife habitat, minor levels of floodflow alteration, and sediment and toxicant retention. A portion of the wetland was probably filled by a now -vanished railroad grade that paralleled Coal Creek Parkway SE. In addition, County Parks developed a portion of the wetland's northwest boundary during the construction of the park, and altered the last remaining natural and undeveloped segment of shoreline on Lake Boren. The alterations included buffer removal and filling of part of the wetland and its associated springs to create a wetland mitigation feature, a dock, and sidewalks. In addition, a non-native weed species (creeping buttercup) was planted as part of the wetland mitigation project. Future Conditions: Limited developable space surrounds the wetland, so few opportunities exist for intensive adjacent development. However, the wetland and its buffer may be disturbed by the future widening of Coal Creek Parkway SE. Use of the park facilities by visitors will likely increase human and pet intrusion. As with other wetlands in this rapidly urbanizing subarea, future impacts will occur due to changes Chapter 9 Aquatic Habitat 9-44 caused by development in the upstream basin, including increased runoff velocities and higher flows, summer drying, and increased nonpoint pollutant loadings. The nature and extent of these impacts will depend on the intensity of the actual changes and the resiliency of the wetland's vegetation and soils. Wetland 8—North End Current Conditions: In 1936, the wetland at the north end of 17.1-acre Lake Boren was mostly deciduous forest with a lesser scrub/shrub element, and was much larger than its present size of 3.8 acres. Currently, this Class-1 wetland is a scrub/shrub and emergent habitat complex, with a limited forested component. Water enters the wetland from a small inlet tributary to Lake Boren, probably some groundwater discharge, and localized surface flows. The 1936 aerial photos suggest the main inlet tributary to Lake Boren was associated with this wetland, but the creek has since been realigned away from the wetland to discharge directly to Lake Boren. Portions of the emergent habitats of the wetland are currently grazed by horses. Also stormwater flows from the apartment complex to the north are discharged to the wetland. The wetland nonetheless provides important wildlife habitat, minor levels of floodflow attenuation, nutrient removal/transformation, and sediment and toxicant retention. For these reasons, the Lake Boren wetland system is considered an LSRA. The wetland appears to have been severely reduced in size by filling activities since 1936. An estimated five acres (55 percent) of this wetland area has been lost, much of it by a large apartment development and a currently vacant flat fill area. Future Conditions: It is likely that the farming activity along the east boundary of the wetland will be replaced by residential or commercial development, resulting in increased runoff volumes and velocities and a different type of nonpoint pollution loading. A small amount of development is also possible on the west boundary as well. Increased human and pet intrusion, trash dumping, and summer drying can also be expected as development increases at the north end of Lake Boren and catchment areas upstream. The name China Creek is applied to the stream beginning at RM 1.3 above Lake Boren. It is highly fragmented and degraded by development activities, including apartment complexes, housing developments, and an extensive network of roads and culverts. The first 630 feet of China Creek, from RM 1.3 to 1.4, is channelized, straightened, and lined with cement. Upstream from that point the stream flows under Coal Creek Parkway SE, and above that, through an apartment complex. Salmonids were observed in the reach above the Parkway to RM 1.9, 0.6 mile above Lake Boren, where there is a seven -foot -high waterfall that is an absolute natural fish barrier to both resident and anadromous fish. There are a few segments of relatively complex fish habitat above the falls, characterized by woody debris and a mixed riparian zone of immature coniferous and deciduous trees (Tables 9-7 and 9-9). Fish habitat utilization above the falls is limited by the lack of access and the fact that the stream dries up in the summer, making it impossible for resident fish to re—enter this reach when flows resume. Chapter 9 Aquatic Habitat 9-45 Wetland 4 Current Conditions: This 4.0-acre inventoried Class-2 wetland forms the headwaters of China and Boren creeks, and is located at RM 2.4 in the China Creek residential development east of Lake Boren and east of the 147th Avenue SE crossing of China Creek. Currently among the least disturbed systems in the May Creek basin, the wetland is a complex of deciduous forest and scrub/shrub habitats mostly surrounded by a substantial acreage of intact deciduous/coniferous buffer. The wetland vegetation appears to be similar to pre -settlement conditions. Water enters the wetland from groundwater discharges and local surface flow. The wetland provides unique, important aquatic and wildlife habitat, groundwater discharge, and floodflow attenuation, and is thus considered an LSRA. Future Conditions: The character of the wetland is changing rapidly due to development along the wetland's west, south, and north boundaries. Clearing has already occurred within the minimum required buffer (50 feet) and led to small-scale human intrusion, vegetation removal, and trash accumulation. Greater levels of development will likely increase the level of these disturbances as well as cause higher runoff volumes, nonpoint pollution loadings, and sedimentation that will adversely affect this wetland. Future Conditions: Stream Habitat The reach of May Creek that flows through the canyon in the Lower Basin subarea is heavily dependent on woody debris for the dissipation of high flows, sediment storage, and maintenance of complex fish habitat within the channel. As old coniferous LWD continues to disappear and is replaced by less stable deciduous woody debris, the stream will be at risk of much more dramatic degradation, leading to the decline in habitat complexity. Loss of debris within this reach will lead to fewer and smaller pools, and less overwintering and low -flow habitat. These limitations, plus the increased flows and sediment loads from upstream development will reduce fish habitat diversity and stability. Similar changes will occur on Honey Creek from loss of coniferous LWD in the channel, which will reduce rearing habitat. Increasing high flows from increased stormwater runoff, resulting from upstream developmental activities, will increase erosion of the sandy banks, increasing fine sediment composition and filling pools in Honey Creek and the lower mainstem. Habitat enhancement of Honey Creek is planned as part of the mitigation for the access road redevelopment, and should contribute to improve rearing conditions in this upper area. The planned widening of Coal Creek Parkway SE to four lanes, with associated encroachment on Boren Creek, has the potential to accelerate erosion of the already unstable riparian area and cause increased sediment loading and more storm water runoff (see also Chapter 7: Sediment Erosion and Deposition). The road project should include mitigation measures to address current and future road impacts. Chapter 9 Aquatic Habitat 9-46 Current and Future Conditions: Wetlands Habitat Lower May Creek Mainstem (0282). Wetland 30 Current Conditions: Wetland 30 is an uninventoried Class-2 system that lies on a portion of the historic delta of mainstem May Creek west of Lake Washington Boulevard North in the City of Renton. Because of the channelization of the delta reach of May Creek, most of the delta area is now technically outside of the May Creek basin because the creek can no longer wander across the breadth of the delta. It is included in this discussion because of its association with the historical delta of May Creek. Portions of the site were exposed after the lowering of Lake Washington. As is evident in 1936 aerial photographs. the wetland was originally a mosaic of scrub/shrub and forested wetland habitats. About half of the historic wetland was filled to accommodate lumber mill operations and other activities. The disturbed wetland site is currently denuded, has extremely compacted soils, and is continually disturbed by log storage activities. Portions of the site are contaminated with creosote, and are a priority clean-up site. The wetland receives water from precipitation, localized surface flow, and possibly shallow groundwater from Lake Washington. A small stream draining a small basin north of the May Creek basin is piped through this wetland directly into Lake Washington. Considering the intensively disturbed nature of this wetland, pollutant contamination in some locations, and its disconnectivity from streams, its principal functions are low. The wetland may provide small amounts of wildlife habitat. Future Conditions: This wetland is strategically located to provide a vegetative and habitat corridor between Lake Washington and May Creek Park. The site is highly suitable for restoration to a near -original condition. The wetland is currently zoned in the City of Renton for residential office park and other commercial development, although the presence of wetland soils on the site has relevance for building suitability. The future condition or fate of this wetland is uncertain, but it is likely to continue to be greatly affected by commercial activities. Wetland 34 Current Conditions: Wetland 34 is an uninventoried 2.4-acre Class-2 wetland that appears to straddle the basin boundary east of Jones Avenue NE and south of NE 43rd Place in the City of Renton. The wetland contains forested and scrub/shrub habitats, and receives water primarily as groundwater discharges from the base of steep slopes that adjoin the wetland to the east. Water flows through several small channels to created ditches along Jones Avenue NE; some of these ditch waters subsequently discharge to May Creek. The wetland has been severely impacted by historical and very recent filling, clearing, and ditching activities, including two large fills and one large cleared and ditched portion. Several industrial developments built on wetland fill suggest portions of the wetland may be receiving contaminants produced by those light industrial operations. Primary wetland functions include wildlife habitat, groundwater discharge, and toxicant retention. Chapter 9 Aquatic Habitat 9-47 Future Conditions: This wetland will likely continue to experience incremental acreage and habitat losses due to unpermitted fill and clearing activities. Low levels of toxicant contamination and trash dumping may continue. Forest vegetation could be removed from slopes above and adjacent to the wetland, resulting in increased flows and sedimentation in the wetland. However, this wetland does offer feasible opportunities for restoration and enhancement and, restored, would substantially supplement the valuable May Creek Park habitat corridor. Wetland 35 Current Conditions: This 1.2-acre uninventoried Class-2 wetland is located on the east side of Jones Avenue NE just north of where Jones Avenue turns into NE 31 st Street in the City of Renton. It contains scrub/shrub and forested habitats, and receives water from surface flows and groundwater discharges at the base of the adjacent steep slope. This wetland appears to have been deforested by 1936, but today is a relatively intact wetland. It is surrounded on all but one side by either steep slopes or Jones Road, and in fact may have been enlarged by obstructed drainage due to construction of Jones Road. The wetland functions primarily as wildlife habitat, but provides low levels of groundwater discharge and floodflow alteration. Future Conditions: This wetland appears to be sufficiently buffered against future changes as a result of adjacent steep, densely forested slopes. The wetland could be disturbed by a widening or realignment of Jones Road. Should land north of the wetland be developed, the Sensitive Areas Code will require buffer protection for both steep slopes and wetlands. Wetland 36 Current Conditions: This 2.1-acre uninventoried Class-2 wetland is the headwaters of a small unnamed tributary (0283A) to mainstem May Creek, located at NE 27th Street and east of Jones Avenue NE in the City of Renton. The 1936 aerial photographs show that more than half of this wetland was pasture at that time. Today, the wetland is predominantly deciduous forested and scrub/shrub habitat. Its water supply is derived from groundwater discharges and localized surface flow. Primary functions include wildlife habitat, groundwater discharge, and floodflow attenuation. The wetland has been disturbed by past filling activities, recent clearing, development without wetland buffering, human and pet intrusion, and trash dumping. Future Conditions: Existing forested areas around this wetland are currently for sale and will likely be cleared and developed into single-family homes. Increased runoff volumes, summer drying, nonpoint pollution, human and pet intrusion, and buffer removal are likely. Honey Creek (0285) Wetland 50 Current Conditions: This 2.6-acre Class-2 wetland inventoried by the City of Renton is the headwater to a very small tributary (0285A) to Honey Creek. The wetland is predominantly forested with deciduous trees, including aspen (Populus tremuloides). A small portion has been converted to lawn. The wetland provides moderate to high levels Chapter 9 Aquatic Habitat 9-48 of groundwater discharge, floodflow alteration, and wildlife habitat. In spite of these important functions, this wetland has been severely disturbed by filling and buffer removal. Residences appear to have been built in the wetland on fill, with cultivated backyards ending at the current wetland boundary. Cat and dog intrusion is intense, and considerable trash dumping has occurred. Future Conditions: This wetland occupies an important landscape position and provides significant beneficial functions. Because it is surrounded by residential development, this wetland will continue to be subjected to the same intensive disturbances it currently experiences, and will decline from ongoing vegetation removal, trash dumping, and the like. The wetland could benefit from a community clean-up and education effort. Boren and China Creeks (0287) Wetland 47 Current Conditions: This 3.7-acre Class-2 wetland is located in the bottom of a steep ravine on the east side of Coal Creek Parkway SE southeast of Lake Boren. This wetland is the headwater of Tributary 0287A which flows into Lake Boren. Though the western portion of the wetland was cleared for agricultural use in 1936, the wetland currently is dominated by deciduous forested habitat, with a smaller component of scrub/shrub habitat. Water enters the wetland primarily from groundwater discharges and local surface flows. Primary functions include groundwater discharge and wildlife habitat. The wetland has a well -developed forested buffer, which has been slightly affected by trash dumping. The wetland itself is relatively undisturbed, except that church and road developments at the north side discharge stormwater to the lower end of the wetland and its tributary. Future Conditions: Development will be restricted to the southwest edge of this wetland due to steep slopes elsewhere. However, development activity above the slopes on the east, north, and south sides of the wetland may cause increased runoff, nonpoint pollution, and human and pet visitation. Widening of Coal Creek Parkway SE may impact this wetland and its buffer along the west boundary. MAY VALLEY This subarea includes the mainstem of May Creek from RM 3.9 to RM 7.0. and the low - gradient (0.2 percent) area of May Valley from just below the beginning of the agricultural area to the area where the three forks of May Creek merge to form the main channel (just above the SR-900 crossing). It also includes the lower portions of the three channels (Map 2). The mouth areas of the three forks and all other tributary mouth areas entering this segment will be discussed as part of the Highlands and East Renton Plateau subareas. Chapter 9 Aquatic Habitat 9-49 Current Conditions: Stream Habitat Middle Mainstem (0282). The historical dredging and straightening of this low gradient, three -mile -long May Valley reach has grossly modified and degraded fish habitat. Channel narrowing has increased water depth and velocity in some areas. Activities within and upstream of this reach and the May Valley subarea have caused increased sedimentation and a loss of spawning gravels in most areas. Because the natural lateral migration of the channel has been halted, flows have been forced into a restricted area, causing the stream energy to increase during high flows. The fish habitat consists primarily of heavily sedimented riffles, plus glides and runs without many defined pools (Tables 9-5, 9-6, 9-7, and 9-8). Side channels and flood channels, where much spawning and rearing would normally occur, no longer exist in this subarea. Side channels, if they were present, would provide valuable summer rearing habitat and high flow refuge from floods for juvenile salmonids, particularly coho salmon (Naiman, 1992). Logging, many years of truck farming, and current impacts from cattle and horse grazing have left the valley floor almost devoid of any woody debris (Table 9-7). There are a few areas where willows and wetland grasses border the stream. At RM 5.6, a beaver dam adds some channel diversity, forcing the stream to spread outside the dredged channel banks. Current pasture management and livestock practices are exacerbating habitat problems. Livestock have direct access to the creek, causing bank erosion that adversely affects spawning, egg incubation, and rearing habitat. Large amounts of animal waste are also reaching the stream. Considerable documentation shows conclusively that grazing problems have contributed to extensive damage of western streams. The immediate effects of overgrazing are loss of streamside vegetation and trampling of stream banks. This damage eventually results in reduced fish populations (Armour et al., 1991). Trampling causes physical bank damage in the form of caving and sloughing that contributes to erosion and stream sedimentation. Also, damage to banks lessens the availability of protective cover in undercut areas (Hunter, 1991). Subsequent erosion may potentially lower the water table and reduce stream flows during critical low flow periods. Another serious consequence of overgrazing and the removal of streamside vegetation is the potential to elevate summer water temperatures to critical levels, causing fish stress, disease, growth impedance, and even death (Armour et al., 1991). High temperatures in the May Valley are a serious problem that will directly affect local and downstream fisheries resources. Despite these impacts, there is limited spawning and rearing use of this reach by salmonids. Coho fry from the Issaquah fish hatchery are stocked in this segment of the mainstem every year, and cutthroat trout and coho salmon have been seen spawning at bridge crossings where gravel deposition occurs. It is possible that sockeye and other stocks may use this area, but none were observed during the 1992-93 surveys. The lack of habitat diversity associated with channelization and elevated temperatures is potentially limiting salmonid production and sustainability. The problems of the already degraded fish habitat were compounded by the turbid runoff from the Sunset Materials's operations yard and quarry. This runoff was high in suspended solids and discharged directly to May Creek at the SR-900 bridge, along with Chapter 9 Aquatic Habitat 9-50 runoff from SR-900. May Creek turbidity and suspended solids were consequently elevated downstream. The habitat problems are futher compounded by the increased runoff and sediment load from tributaries that results from development in this region. Future Conditions: Stream Habitat The riparian area of the main channel in the May Valley is probably in better condition now than when intensive logging was occurring in the tributaries and active truck farming tilled the soil right up to the stream banks. The instream and riparian habitat remain unstable, however, because of poor livestock management practices, and increased residential encroachment around the Coalfield area and the south side of May Valley. The increasing water runoff from urbanization, sedimentation from bank instability, and upstream gravel mine runoff will continue to degrade habitat and increase flooding downstream. Increased erosion will continue to supply sediment into downstream fish habitat, causing increased channel aggradation and habitat degradation. Today, the only high -flow refuge available for juvenile salmonids is when water floods over the banks into the floodplain, opening up fringe habitat and creating local reductions in velocity. (However, fish that use such flood refuge areas are risk of stranding when peak flows subside.) During summer low -flow periods when many of the tributaries dry up and water temperatures increase, there will be more stress placed on the already affected reach because of the lack of shading and protective vegetation. Natural fish populations may ultimately be eliminated in this reach, with the exception of those that use the reach as a migration corridor. Current and Future Conditions: Wetland Habitat Wetland 5 Current Conditions: This inventoried Class-1 wetland fills most of the valley floor in the middle reach of May Creek, extending for nearly three miles along the main channel of May Creek from just west of 148th Avenue SE to just east of 188th Avenue SE (RM 4.3 to 7.1, and continuing along East Fork May Creek (0297) from RM 0.0 to 0.4). For purposes of this plan, Wetland 5 is considered to encompass the wetland upstream of the SR-900 crossing (the King County Wetlands Inventory —King County, 1990b—represents this area both as part of Wetland 5 and as a separate Class-2 Wetland 15), and as such totals 208 acres. In pre -settlement times, the wetland was probably dominated by forested swamps comprising western red cedar, Sitka spruce, and western hemlock. A small remnant of this mixed coniferous forested swamp habitat still remains east of SR-900 at SE May Valley Road, adjacent to the Sunset Materials quarry. Because of its historical value and important functions, this habitat remnant has been designated an LSRA. The remainder of the wetland has been so intensively disturbed by previous land uses that it does not meet the LSRA criteria. By 1936, this wetland had been almost entirely cleared, and drained and converted to agricultural use. May Creek itself had also been moved into a dredged and straightened Chapter 9 Aquatic Habitat 9-51 channel by that time. Today, the wetland remains in a highly disturbed condition due to past land -clearing and filling, agricultural use, and present-day animal grazing. These conditions have generated significant problems related to erosion, sedimentation, water quality, wildlife habitat, and stormwater conveyance. What in pre -settlement times was probably an expansive, diverse riparian and floodplain system has been converted for the most part to a highly degraded and functionally impaired wet pasture. However, the condition of this wetland has actually improved substantially since 1936 as a result of abandonment of agricultural land and natural restoration of relatively high -quality forested, scrub -shrub, and emergent wetland habitats in some locations. A tentative sighting of either a spotted frog or a red -legged frog was made in this wetland at RM 6.5 during habitat surveys conducted in Spring 1993. Future Conditions: While the Sensitive Areas Code will slow the rate and volume of filling, small violations will likely continue. In addition, as the land uses in the subarea change from a rural/agricultural base to a suburban commuting community, many of the pastures may be taken out of production (grazing), allowing natural successional processes or deliberate restoration of emergent, scrub -shrub, and forested wetland habitats to occur in some areas. The code could be effective at discouraging vegetation clearing in such areas. HIGHLANDS The Highlands Subarea tributaries all flow into the mainstem from the north side of May Valley. They include tributaries 0287D, 0289, 0292 and 0293, 0294, 0295, and 0297 of these streams originate in steep, undeveloped land underlain by bedrock on Cougar and Squak mountains. The lowest reaches of these tributaries are low -gradient channels that enter the May Valley Subarea floodplain and join the May Creek channel. The North Fork (0294) is the most important of the tributaries for fish because it supplies most of the flow to the mainstem and is more heavily used by fish than other tributaries. Habitat in the North Fork has been seriously affected by increased urbanization, road construction, and quarry sediment runoff. Current Conditions: Stream Habitat Tributary 0287D. This tributary enters May Creek at RM 4.4. It is a relatively small tributary ranging from four to seven feet in width, with moderate gradient (average eight percent). It begins from forested Wetland 55 four -tenths of a mile upstream. The lower stream (RM 0.0 to 0.1) flows through an alluvial fan in a horse pasture. The channel is a single long, low gradient riffle lacking any instream cover, riparian vegetation and bank structure due to heavy grazing along the stream. A local resident reports that the channel also dries up for part of the summer. Despite these conditions, the substrate is made up of clean gravels and is used by cutthroat trout for spawning. During floods, this channel is probably used by juvenile salmonids as a high -flow refuge. Upstream seasonal use of this tributary is limited by culverts near RM 0.1 that limit fish passage. The first culvert, downstream of SE May Valley Road, may block fish migration Chapter 9 Aquatic Habitat 9-52 during certain low flow periods. In addition, the SE May Valley Road culvert and a created pond spillway just upstream also block fish passage upstream. The pond is 122 feet long and has been stocked with trout by a private landowner. Some channel incision is occurring upstream of the pond, from RM 0.1 to 0.4. The channel is carving into compact clay, forming a series of plunge pools and step falls up to four feet high. This segment is heavily wooded. A bridle trail crosses the creek at RM 0.2, downstream of the wetland headwaters where the stream begins. The stream has a moderate mix of fast and slow water, and predominantly mixed coniferous and deciduous riparian habitat (Tables 9-7 and 9-9). Wetland 28b Current Conditions: This 8.0-acre inventoried wetland is the headwater to 0287D, and is located north of the intersection of 148th Avenue SE and SE May Valley Road at the base of steep slopes of the Newcastle Hills. This wetland was completely converted to agricultural (hay) production in 1936, and appears to have been ditched and partially drained for that purpose. Most of the wetland's buffer was cleared at that time as well. The wetland is currently forested, having been abandoned from agricultural use. Vegetation is composed of young red alder and cottonwood with an herbaceous understory; small areas of scrub -shrub and emergent habitats are also present. The wetland's main source of water is groundwater discharge along the base of adjacent steep slopes and local surface flow. The wetland is currently well -buffered from human intrusion except at the south edge where homes have been built. Its primary functions include wildlife habitat, groundwater discharge, and serving as a source of organic material for waters downstream. Future Conditions: Developable land currently surrounds the wetland except for steep slopes along the north side. Under the Sensitive Areas Code, development will require protection measures for the wetland, its outlet, and adjoining steep slopes. However, development in the wetland's upper catchment areas would severely disturb a substantial upland forested buffer valuable for wildlife habitat, and would cause increased runoff volumes and human and pet intrusion into the wetland. Long Marsh Creek (0289). Tributary 0289 enters May Creek at RM 4.6 and has an alluvial fan that is very similar to that of Tributary 0287D. It has been seriously degraded by horses and lacks channel stability, but has nice spawning gravels below SE May Valley Road. Cutthroat trout were documented using the spawning gravel during the 1993 survey. Fish access to habitat upstream is further limited by a culvert system that starts in a pasture downstream from the SE May Valley Road crossing. The first culvert, 260 feet upstream from the mouth, is 95 feet long and is piped under the pasture, increasing the pasture area for horse grazing. The second culvert, at RM 0.1, runs under SE May Valley Road. Other than the reach below SE May Valley Road, the stream has a high gradient for most of its length, often exceeding 10 percent. At RM 0.2, an eight -foot -high bedrock waterfall forms a natural fish barrier to anadromous fish. A small home-made dam at RM 0.3 impounds water for some form of irrigation or water diversion. Above the dam the stream flows through a deep, wooded Chapter 9 Aquatic Habitat 9-53 ravine dominated by large second growth conifers. Most of the stream above SE May Valley Road has high volumes of stable coniferous LWD that add to habitat diversity (Table 9-7). This upper reach is relatively good resident fish habitat, with a mixture of fast and slow water dominated by a stair -step longitudinal profile with a few segments of lower gradient, glide -dominated habitat. It is possible that this reach dries up in the summer, which could mean that no resident fish live above the falls. Wetland 11 Current Conditions: Class-2 Wetland 11 is located entirely within the Cougar Mountain Regional Park at the north -central edge of the May Creek basin. It is a major headwater of Long Marsh Creek and constitutes an important natural resource for the basin. As evidenced in 1936 aerial photographs, this 7.0-acre wetland appears to have remained in a presettlement condition despite the severe deforestation of its surrounding catchment and buffer. The wetland is predominantly forested with deciduous species, but also contains evergreen forested, scrub -shrub, emergent, and aquatic bed plant communities. The wetland appears to receive water from numerous small tributaries that drain upper catchment areas, as well as from groundwater. The wetland provides highly significant high -quality wildlife habitat, and contributes to the diversity and abundance of aquatic life and wildlife in the basin. The wetland is also important to groundwater discharge and provides a moderate benefit in floodflow alteration. Because of its significant functions and values, and undisturbed condition, this wetland has been designated an RSRA. Future Conditions: Because the wetland and a large contiguous buffer are contained within Cougar Mountain Regional Park and are managed for recreation and the protection of natural resources, it is probable that this wetland will remain in its current undisturbed condition. Country (0292) and Cabbage (0293) Creeks. Country Creek enters May Creek near RM 6.5. Cabbage Creek is its major tributary. The alluvial fan of Country Creek (RM 0.0 to 0.1) is in a pasture where cows have direct access to both the tributary and the mainstem of May Creek. Though the stream channel is generally less degraded than the other channels described above, Country Creek also lacks riparian cover, and the channel is wide and shallow with low banks. Nonetheless, spawning gravel is available and coho salmon and cutthroat trout redds have been found in this reach (Table 9-2). However, rearing habitat is limited. Upstream, near RM 0.1, the channel deepens and the stream has been rerouted alongside SE May Valley Road for approximately 200 feet, passing through four culverts. The stream gradient in this reach is moderate, averaging about four percent. At RM 0.1, the downstream side of a concrete block that was once the outflow of an upstream culvert has downcut and created a barrier that under all or most conditions blocks access of anadromous fish to the upper reaches of Country Creek and to any access to Cabbage Creek, which converges upstream of this point. Another relatively high -gradient culvert passes under SE May Valley Road a short distance upstream. Streamflow is depleted upstream of the confluence of Cabbage Creek, and local residents say the stream dries up in the summer. Local residents have observed chinook salmon and up Chapter 9 Aquatic Habitat 9-54 to 2'00 spawning coho in this reach and in lower Cabbage Creek. The current low returns of coho to the Lake Washington basin and the culvert barrier have reduced current use of these streams by coho; however, the half -mile -long reach below SE May Valley Road is still considered an LSRA. Upstream of the SE May Valley Road crossing, Country Creek has been armored and channelized, passes a few feet away from the edge of a house, and is part of a series of manmade containment ponds that are probably left over from the days when truck farms were dependent on irrigation. Just upstream from RM 0.2 a natural bedrock falls restricts upstream fish passage. This is the lowermost in a series of waterfalls that descend the steep valley wall slopes (gradient about 15 percent). New housing development upstream may be contributing to or causing increased runoff and flooding events downstream. Cabbage Creek flows into and provides most of the flow to lower Country Creek at RM 0.15. Upstream of the confluence with Country Creek, Cabbage Creek parallels SE May Valley Road for approximately 400 feet before passing under SE May Valley Road at RM 0.1. In this reach there is no riparian vegetation to buffer direct runoff from SE May Valley Road or to stop bank erosion. The gravel and cobble, combined with the flow, would be relatively good spawning habitat if the area were accessible to anadromous fish. During the large storms of 1990 the stream overtopped its banks in this reach and flowed across a farm field to May Creek (perhaps paralleling its original course to May Creek). Flow continued across this field until a riprap levee was placed along the roadside channel in this reach. Currently, the only vegetation along this riprap area consists of planted willows and volunteer red alders. At RM 0.07, the stream is routed under SE May Valley Road. Upstream of the road, the stream is enclosed within a forest of mixed conifer and deciduous trees. This stream segment has a high gradient (10 to 20 percent) and is dominated by fast water that forms a stair -step channel profile. Relatively good accumulations of stable LWD are present, and surface substrates are dominated by large gravels and small cobbles. Pocket water provides good holding areas for resident fish. At RM 0.1, the effects of increased residential development on the upper slopes become more apparent: the stream is downcutting, and the steep bank is eroding directly into the stream. Upstream from RM 0.2 the channel is dominated by bedrock and the habitat consists of a series of cascades, chutes, and falls. The upper banks of the channel have some residential development. Near RM 0.3, SE 108th Street crosses the stream channel. North Fork May Creek (0294). The North Fork merges with South Fork May Creek (0282) to form the mainstem of May Creek at RM 7.0. Most of the suitable gravel in the North Fork was used by spawning cutthroat trout during the 1993 field season (Table 9-2). The first 120 feet of the channel bottom is dominated by compact clay combined with gravel and sand. Two midchannel scour pools and relatively incised banks show signs of downcutting, possibly because of increased flows. This short segment is relatively well buffered by immature deciduous trees, but the stream channel is devoid of woody debris. Chapter 9 Aquatic Habitat 9-55 Upstream, the channel crosses SE May Valley Road at RM 0.1. The remaining lower reach from RM 0.1 to RM 0.8 is dominated by low -gradient (about 0.5 percent) glide habitat and flows through backyards and horse pastures and along dirt roads. The stream lacks LWD, habitat diversity, and riparian complexity (Tables 9-7 and 9-9). A small, homemade detention pond at RM 0.6 may impede upstream fish migration during low flow periods. However, both adfluvial cutthroat trout and coho salmon were seen above this partial barrier during the 1992-93 spawning surveys. WDFW annually stocks coho salmon fry in the upper reaches of the North Fork (personal communication, Chuck Baranski, WDF, Olympia, WA). Near RM 0.4 a small tributary (0294A) flows under SR-900 and into the North Fork. Landowners indicate that salmonid fry are trapped upstream of the road every summer, although Tributary 0294A is not regularly stocked by WDFW. The observations indicate that either some coho salmon are using the channel to spawn or possibly that stocked juvenile coho migrate up this channel. During the 1992-93 survey, cutthroat trout were seen spawning at the confluence of the North Fork and Tributary 0291A. From RM 0.8 to RM 1.0 (the confluence with Wilderness Creek 0295), the North Fork increases in flow, habitat diversity, and gradient (about two percent). Though limited in quantity, there are some pieces of LWD (Table 9-7). Despite the fact that this reach passes behind a few homes and then into the Issaquah Highlands campground, it is set away from the road and flows through a relatively well -established riparian corridor made up of both young and mature deciduous and coniferous trees. The substrate consists mainly of sand, but where gravel is found, it is clean and of good quality for spawning. Most gravel patches in this reach were utilized by adfluvial cutthroat trout during the 1992-93 spawning season, showing some of the highest density of use in the May Creek basin (Table 9-2). As a result of its high density of use and quality of habitat, the reach from RM 0.4 to RM 1.0 has been designated an LSRA. From RM 1.0 to RM 1.5 the North Fork is bordered by two rock quarries (Sunset Materials and Hazen Quarry) along the eastern side, and SR-900 immedately to the west. Though there are a few segments where the stream channel is buffered by dense brush, most of the reach is highly channelized and directly exposed to runoff from SR- 900 and the quarry driveways that cross the stream. The channel in this reach resembles a drainage ditch and contains a lot of fine sediment and sand, its gradient (about two to five percent) is suitable for coho salmon and in a few spots was utilized for spawning by coho salmon, adfluvial cutthroat trout, and brook lamprey during the 1992- 93 spawning season. At RM 1.5 the stream exits from Sunset Quarry: upslope, the stream has a high -gradient channel (greater than ten percent) that issues from a wetland further up the ridge above Sunset Quarry. The North Fork is affected by many problems, including the close proximity of SR-900, residential developments, deposition of fine sediment from upstream gravel quarries, limited habitat diversity and channel complexity, lack of well -established riparian vegetation in some areas, and a lack of LWD. Despite these characteristics, this stream is still used by cutthroat trout and coho salmon. The North Fork system also supports a population of freshwater mussels. They are considered a valuable biological resource that occurs only in unique and ecologically Chapter 9 Aquatic Habitat 9-56 complex locations. At RM 0.44, a moderate -sized population of mussels was located during the 1992-93 field season. Two additional smaller populations were located at RM 0.85 and at the confluence of Wilderness Creek at RM 1.0. NNPtInnri V Current Conditions: Wetland 13 is a 5.7-acre inventoried Class-1 system located along the valley bottom from just east of Wilderness Creek (0295) to the SE 109th Street bridge crossing of the North Fork. The wetland is paralleled along its entire length by SR--900 to the west and by steep slopes to the east, being narrowly constrained within the resulting narrow valley. Aerial photographs from 1936 indicate that the southern half of the wetland was in agricultural production and that the northern portion was densely forested. This wetland has a Class-1 rating because it provides potential habitat for bald eagles, although this rating is being reconsidered. The wetland is intimately associated with the North Fork of May Creek and provides excellent riparian support to the stream, particularly along the central part of the wetland. For this reason, and because the adjacent reach of the North Fork is designated an LSRA, Wetland 13 is also designated as an LSRA. The northern portion of the wetland consists of deciduous forest, while a created pond and emergent plant communities occupy the southern half of the wetland. The wetland receives water from May Creek and from groundwater discharges at the base of steep slopes to the east. The wetland provides high levels of aquatic and wildlife habitat, as well as moderate levels of floodflow alteration and sediment retention. Despite these notable characteristics, this wetland is being adversely affected on nearly all sides. Two quarries upstream are major sources of sediment to the May Creek system. Two major driveways cross the wetland and May Creek. One quarry has also intruded into the surrounding upland buffer. Likewise, SR-900 was built within the buffer of May Creek (prior to 1936) and contributes substantial amounts of sediment, nonpoint-source pollutants, noise, and litter to the wetland and associated reaches of May Creek. Future Conditions: The Washington State Department of Transportation's proposal to widen SR-900 adjacent to Wetland 13 could severely exacerbate the sedimentation, pollution, noise, and litter problems this area now experiences. The road -widening itself appears to require the relocation of May Creek within the highly confined valley bottom, thus presenting some difficult conditions for wetland and stream restoration in this area. Wilderness Creek (0295). This stream enters the North Fork of May Creek at RM 1.0. Immediately upstream from the confluence it crosses under SR-900 in a culvert. For most of its length above this point the stream is within the Cougar Mountain Regional Park, where a trailhead has been located immediately adjacent to the stream. Cutthroat trout were found spawning in the lower -gradient, fast -water stream channel, which is made up of gravels and cobbles. Above RM 0.2 the stream flows through a bedrock - controlled, steep -gradient (20 to 30 percent) channel with boulders dominated by cascades and falls. The stream's riparian area in this upper reach is well buffered by both conifers and deciduous trees, and the channel has large quantities of stable LWD. The local park ranger reports that seasonal fish use of this stream is limited by a series Chapter 9 Aquatic Habitat 9-57 of step falls and the fact that the stream dries up for extended periods of the year. Water that runs from this channel into the North Fork is cleaner and less turbid than other inflow, thereby helping to dilute some of the extreme turbidity of the North Fork. East Fork May Creek (0297). This tributary flows into the South Fork of May Creek (0282) at RM 7.1. Within the eastern portion of Wetland 5 from RM 0.0 to 0.4, the East Fork flows through a series of constructed ponds, berms, and a dredged channel under 188th Avenue SE, some of which are dry during the summer months. Upstream from the road the channel disappears amidst the blackberries and dense vegetation. At the eastern end of the wetland at RM 0.4 the stream channel has been trampled and degraded by a high concentration of horses in a paddock that straddles the channel. In this reach the banks of the stream have been broken down and riparian vegetation is lacking, resulting in a wide, flat spread of water across the paddock. Upstream, the channel is confined within failing gravel and chicken wire berms. Riprap routes the stream along SE May Valley Road through a series of culverts that are potential barriers to fish passage, across SE May Valley Road and up onto the slope of Squak Mountain which is dotted with private homes. Local residents report that the stream is dry for much of the year, and that it is probably not used by fish. Future Conditions: Stream Habitat Despite the fact that the North Fork of May Creek (0294) is seriously degraded by sediment and erosion from the quarries and runoff from SR-900, it still supports a fish resource. These fish are already stressed, and proposals to widen SR-900 would bring further impacts. Because of topographical constrictions, such roadway expansion would require the relocation of the already constrained stream channel. The presence and spawning use of the reach by salmonids, and the presence of freshwater mussels will require the roadway project designs to include measures for the protection of the stream and its resources. The lower regions of all Highlands Subarea streams enter May Valley, and will continue to be affected by the intensive livestock use of Wetland 5 and adjacent areas. This will continue to have negative effects on habitat quality and use by fish; however, new regulations governing fencing of the streams and limiting livestock access could significantly improve the existing situation in many locations. Upland development in the Highlands subarea will be less pronounced than in other parts of the basin, except for the headwaters of Cabbage Creek (0293) and the East Fork (0297). This will limit the detrimental effects of higher flows and increased sediment input. For those streams that experience future development, higher runoff will continue to cause either increased aggradation of sediment, which appears to be occurring in lower Country Creek (0292), or erosion such as in Cabbage Creek. Chapter 9 Aquatic Habitat 9-58 Current and Future Conditions: Wetland Habitat North Fork May Creek (0294) Wetland 75 Current Conditions: This 35.1-acre wetland includes inventoried Class-2 Wetland 14 and Wetlands 26b and 27b, as well as some uninventoried area in the floodplain north of SE May Valley Road and east of SR-900 at the foot of Squak Mountain. The wetland receives water from May Creek and from groundwater discharges at the base of steep slopes to the east. The North Fork of May Creek flows through the upper portion of the wetland, then at RM 0.5 the stream is directed sharply west by old berms and spoils present immediately south of the turn. The creek then turns south again, flowing through the western portion of the wetland and paralleling SR-900. At high flows the creek sometimes overflows its bank at RM 0.5 and sends part of the flow directly south. In the northern portion, north of the bend in the North Fork, the wetland is primarily used for pasture. Fill and a series of drainage ditches and berms were placed in the central area years ago, which is now developed with several residences and horse farms. To the east of this filled area the wetland supports a small seasonal pond. Vegetation consists of lawns, gardens, and close -cropped pasture, with some additional vegetation along and in the bottoms of the drainage ditches. To the west, where the stream parallels SR-900, the riparian and wetland area has thicker vegetation and deciduous tree, canopy. SR-900 was built prior to 1936 within the buffer of May Creek and now contributes substantial amounts of sediment, nonpoint-source pollutants, noise, and litter to this wetland and associated reaches of May Creek. The, drainage system originally collected at a small basin at the southwest corner, and flowed into the North Fork through a channel or feature of the terrain that was filled in the early 1980s by the downstream landowner. During the rainy season, water ponds for extended periods in the portions of the wetland south of the turn in the North Fork, until the level rises sufficiently to allow overland flow to the creek. During the rainy season, animal waste enters the stream from the flooded pastures. Future Conditions: The southern portion of Wetland 75 will remain in residential and livestock use. The drainage system will be need to be restored to full service if winter ponding is to be reduced. Residential development on the slopes of Squak Mountain will deliver more water and sediment to the wetland. Widening of SR-900 could have significant effects on the North Fork and the western portion of the wetland. EAST RENTON PLATEAU The East Renton Plateau subarea consists primarily of the South Fork of May Creek (0282) which drains Lake Kathleen, an unnamed tributary (0291A), and three very small tributaries (Greenes Creek 0288, Tributary 0291 B, and Hendrix Creek 0291 C) that contain minor aquatic resources. All stream mouths are in the May Valley Subarea (Map 2), but are discussed here to provide continuity. The two primary tributaries, 0282 and 0291A, have had moderate impacts from urbanization and gravel mining (lower reach of South Fork May Creek). The lower portions have been affected by livestock Chapter 9 Aquatic Habitat 9-59 and agricultural practices. Both of these streams are small and portions dry up in the summer, reducing their use as fish habitat. Current Conditions Tributary (0291A). This stream, which enters May Creek at RM 5.5, generally lacks LWD and consists predominantly of riffle habitat conditions for most of its surveyed length (Table 9-7). Livestock have access to only a limited area of the alluvial fan where the stream flows into May Creek. As a result of this limited livestock access, this creek has more intact riparian cover than any of the other East Renton Plateau tributaries. For its first 300 feet the stream is flat, wide, and lacks a definite channel. The banks are dominated by grasses and willows. Above this area the gradient increases but still remains moderate (one to three percent). Just upstream (RM 0.1 to 0.3), the channel becomes increasingly more scoured and the banks more defined, until the stream's incision into the floodplain terrace is about five feet deep. This indicates that increased runoff from urbanized areas is occurring upstream. The stream channel is heavily buffered by alders, willows, and blackberry bushes, making some areas impenetrable. A mixture of compact clay, gravel, and sand makes up the channel bottom. Gravel accumulations are found at channel meanders and at the tail end of plunge pools, caused by deep channel scouring. During 1992-93 surveys, both cutthroat trout and coho salmon were seen spawning in this segment (Table 9-2). Despite the lack of woody debris in this reach, scour/plunge pools as deep as three feet occur, supporting a range of fish at varying stages of their life cycles. This segment has been designated as an LSRA. Near RM 0.3, the stream is routed through a series of culverts, including the crossings under SE Renton -Issaquah Road (SR-900) culvert and a driveway for Coalfield Stables. The Coalfield Stable culvert is undersized and has potential to clog with debris, possibly limiting fish access. Just upstream (RM 0.3 to RM 0.4) the channel widens into a braided, gravel -dominated matrix of riffles and glides featuring fast and slow water. The riparian overstory is dominated by immature deciduous trees (Table 9-9). In the spring of 1993, coho fry were seen throughout this reach. Despite the amount of shaded cover in the reach, there is no understory vegetation to help stabilize the stream banks. Horses have access to the stream channel and horse trails meander through the stream floodplain. At RM 0.4 the stream constricts and forms one channel again. In this reach the habitat is fragmented due to residential development activities, including road and driveway construction, yard landscaping, and lot clearing. Many of the houses route storm water runoff directly to the stream. As a result, conditions that promote good stream habitat, such as a well vegetated riparian buffer, are slowly disappearing. At RM 0.5, a 60-foot- long culvert was placed 3.5 feet above the water surface to route water under 116th Street SE, thus halting upstream resident or anadromous fish passage. Upstream from this culvert the stream flows through residential backyards and is routed through culverts almost the entire distance to the outlet of Wetland 3 at RM 0.8. At the upper end of Wetland 3, just below the culvert leading under 164th Ave. SE, a 13-cm cutthroat trout was found during an electroshocking survey conducted by the County Roads Division in early 1994. Chapter 9 Aquatic Habitat 9-60 VVP1,1Anrl Current Conditions: This Class-2 inventoried wetland of approximately 11.7 acres is located north of SE 128th Street and east of 164th Avenue SE. It is closely associated with Tributary 0291A, and provides important riparian support to this stream. Historical photographs show that a large part of this wetland was filled by construction of the mini - mall east of 164th Avenue SE. The 1936 photographs also indicate that the portion of the wetland west of 164th Avenue SE has not been greatly modified since that time. The, wetland is currently a mixture of scrub -shrub and deciduous forested habitats. The north quarter of the wetland has been cleared and is being grazed by cows, which are causing much damage to the creek and wetland vegetation and soils. Coalfield Park (a recently completed King County park) was built within the buffer of this wetland and is a potential source of nutrient contamination from two intensively maintained athletic fields adjacent to the creek and wetland. Also, 164th Avenue SE, built through the wetland prior to 1936, is a source of sediment, pollution, and noise to the wetland and its associated stream. Water in this wetland comes primarily from Tributary 0291A and from localized groundwater discharges. The wetland provides relatively high -quality wildlife habitat, floodflow alteration, and sediment and toxicant retention functions. Future Conditions: This wetland is currently well buffered by an expansive upland forest along most of its west boundary. This forest is just now being converted to residential developments, and will likely be eliminated in the near term. Increased urban development will lead to increased intrusion by human visitors and their pets, and increased runoff volumes and associated pollutants levels. If 164th Avenue SE were to be widened, additional portions of the wetland might be filled and the creek relocated. Wetland 2 Current Conditions: This 11.8-acre Class-1 inventoried Wetland 2, locally known as Cemetary Pond, is located south of SE 128th Street at the intersection of 164th Avenue SE, at the headwaters of Tributary 0291A. Prior to settlement, and before SE 128th Street and 164th Avenue SE were constructed, the wetland was contiguous with Wetland 3 to the north. Wetland 2 has been substantially modified from its historic condition; aerial photographs indicate the wetland had been cleared by 1936, and that it may have been used for grazing or hay production around that time. The wetland has since been greatly reduced in size by road building and filling around its perimeter, and considerable diking and ditching had occurred before its acquisition by King County for a regional stormwater detention facility. Development of the site as an R/D pond apparently involved dredging two large open water features, and installation of an outlet control device. Currently, the wetland and its buffer are being intensively disturbed by people (pedestrians and motorbikes), and the wetland and its upland habitats have been frequently used for illegal dumping. SE 128th Street is also the source of a substantial amount of noise. Despite the intensive disturbance, the wetland does provide a relatively unusual mixture of open water, scrub -shrub, and forested habitats. Vegetation is young, but is beginning to provide suitable habitat for a broad variety of wildlife. Wetland hydrology is supported by a regional stormwater catchment network. As a result, the wetland provides important Chapter 9 Aquatic Habitat 9-61 floodflow alteration functions, and probably is moderately important for sediment removal and toxicant retention. Because this wetland is rated as a Class-1 system, this wetland is considered an LSRA. Future Conditions: Continued development in the wetland's catchment areas could place severe pressure on the resources and functions this wetland provides. Although it has already been subjected to substantial changes resulting from urban development, from a functional perspective this wetland may have begun to rebound from its lowest point. The illegal dumping should be greatly deterred by the placement of a barrier to vehicle entry. Despite possibilities of continued urban development in the upper subcatchment area, implementation of the Sensitive Areas Code and increased attention to and protection of wetland habitats in King County may result in large future gains in the quality and societal value of this degraded wetland. South Fork May Creek (0282). South Fork May Creek splits from the North Fork at RM 7.0. Like the North Fork's channel bottom, the South Fork is dominated by compact clay for 150 feet. A stream gage is located in this segment. Upstream of the gage, the stream channel begins to spread out and is lost in Wetland 5. In this region, the East Fork tributary (0297) intersects the South Fork (see the Highlands subarea for discussion of the East Fork tributary). The Sunset Materials quarry site borders the northeast side of the wetland. There is evidence of an oil spill coming from the same region, leaching into the wetland, which discharges into the stream channel. At the southwest side of the wetland at RM 7.3, the South Fork channel begins again. Upstream from the wetland the stream gradient begins to increase to about 10 to 15 percent. The channel bottom is made up of a mixture of gravel and cobble. There are some new homes and recent clearing near the stream channel, apparently part of a new residential development. Upstream of RM 7.4 the surrounding area changes from flatlands to that of a steep, densely wooded ravine at RM 7.4, and the channel becomes increasingly incised. From RM 7.4 to 7.7, the riparian corridor is well vegetated with a relatively high percentage of large conifer trees and a relative abundance of highly functional LWD. Both of these elements provide relatively stable and diverse habitat. The substrate is a mixture of cobbles, gravels, and boulders that complexity to the stream's riffle - dominated, pocket water matrix. A 128-foot culvert bisects this reach at the SE 128th Street crossing, potentially creating a partial fish barrier because of its length. The stream channel flattens out above RM 8.0 (gradient one to three percent) and enters what was once a cedar swamp. The wetland now has houses and lawns and the stream channel has been straightened and dredged. A series of roads and culverts cross the stream. In spite of these impacts, many of the large cedars are still intact and border the stream. Within this reach the channel is a heavily silted run that dries up during most summers. At RM 7.9 the stream channel is no longer protected by a cedar overstory. The wetland has been cleared and heavy equipment is stored near the stream. The stream channel disappears among blackberry brambles until it emerges at SE 134th Street, under which it is conveyed in an undersized culvert, and connects with Chapter 9 Aquatic Habitat 9-62 Lake Kathleen at RM 8.1. During the summer months, the water level in Lake Kathleen is too low for water to flow from the lake into the South Fork. The stream has approximately equal amounts of slow and fast water, with an average gradient of four to five percent. Most of the slow water occurs in Wetland 5 from RM 7.0 to 7.4, and most of the fast water occurs in the higher gradient segment from RM 7.4 to RM 7.7 (Table 9-7). Lake Kathleen. Lake Kathleen is a shallow, 38.5-acre lake that is mostly surrounded by single family homes. There is no public access to the lake, which is stocked annually with rainbow trout by WDFW. The lake is meso-eutrophic, but does not appear to be in immediate danger of increased eutrophication. Wetland 1 Current Conditions: Lake Kathleen and its associated wetlands form a 61.3-acre Class-1 inventoried system, located in the extreme southeast corner of the May Creek basin. Historical aerial photographs indicate that the main road infrastructure, first residences, and a straightened outlet channel had been constructed by 1936. Comparison of historical with current aerial photos shows that significant wetland losses have occurred at the outlet end and along the western shoreline of the lake. This lake —like most low - elevation lakes near large urban centers in western Washington —has been moderately to severely disturbed by residential development. Impacts include wetland filling, buffer modification, water quality degradation due to failing septic systems, increases in nonpoint loadings, and probable changes in wetland fauna. In spite of these changes, Lake Kathleen has a broad diversity of wetland habitat types, including aquatic bed, emergent, scrub -shrub, and forested habitats. The wetland vegetation at the southeast shoreline is of particular note. This forested wetland and its adjacent upland buffer appear to be unchanged since 1936, and may represent a rare example (for low -elevation lakes in western Washington) of a lakeshore environment that retains nearly pre -settlement appearance and conditions. Water derives mostly from localized surface flow. The lake and wetlands experience relatively high levels of recreational use such as swimming and boating. In addition, the lake and its wetlands provide high levels of floodflow alteration, sediment and toxicant detention, and nutrient removal and transformation. Because of the existing remnant of pre -settlement lakeshore environment and the generally significant functions that the Lake Kathleen system provides, this lake/wetland complex is considered an LSRA. Future Conditions: Residential development continues apace in the Lake Kathleen catchment. Future conditions will likely include further declines in water quality, greater human and pet intrusion, increased runoff volumes into the lake and its wetlands, and continued buffer modifications and conversions. The Lakeshore is mostly built -out, but a few areas still offer buildable lots, particularly on the southeast shoreline, which currently retains a unique wild and native character. Chapter 9 Aquatic Habitat 9-63 Future Conditions: Stream Habitat Given the existing land use pattern in the East Renton Plateau Subarea, most current impacts are likely to continue or worsen. Further fragmentation of the stream channels is probable with future buildout of already existing and future developments throughout the region. The agricultural impacts to the lower portions of the streams are likely to continue to degrade habitat conditions in those areas; however, new regulations governing fencing of the streams and limiting livestock access could significantly improve the existing situation in many locations. 9.7 KEY FINDINGS FISH RESOURCES • Coho salmon and steelhead, key native fish species, have decreased substantially in the basin. Sockeye salmon and lake -dwelling cutthroat trout appear to be increasing slightly. • Stream habitats in the basin have been severely degraded by a variety of poor management practices in the watershed. The major problems are: Channelization in the upper mainstem and in lower North Fork. Sedimentation in the lower mainstem from in -channel erosion in the upstream canyon; in the North Fork from livestock access and quarry operations; in Honey and Boren Creeks from channel erosion and poor development practices. Lack of woody debris in the lower mainstem, in the North Fork and in Honey and Boren Creeks. Lack of riparian cover in the upper mainstem, in Honey and Boren Creeks. In the upper mainstem, temperatures in late summer approach lethal limits for salmonids. Channel erosion from increases in peak flow in the mainstem canyon, in Honey Creek, in the South Fork and tributary 0291. Upstream fish passage on the mainstem can be blocked at a fishway at RM 2.9. The fishway is easily blocked by debris, and entrance conditions inhibit passage at low flows. Upstream passage to habitat reaches of one-half mile or more is limited by impassable (or nearly so) culverts in Boren and Honey creeks. Culverts also block access to short reaches of several small tributaries in the Highlands Subarea, and a culvert blocks passage in the resident fish zone of the South Fork. Chapter 9 Aquatic Habitat 9-64 • Few areas of comparatively "good" salmonid habitat are to be found in the basin. The lower mainstem through May Creek Park, and several tributaries in the Highland subarea account for most of the remaining good quality habitat areas. WETLANDS • More than 40 previously uninventoried wetlands were discovered during field investigations. • Virtually all wetlands in the basin have been disturbed by land management activities. An estimated 180 acres of wetland (about 30 percent) have been lost to filling or intensive commercial development in the basin since 1936. • Wetland 11 (Long Marsh), located within the Cougar Mountain Regional Park, appears to have remained in a nearly pre -settlement condition. VEGETATION • Forested riparian zones in the basin —where they are present —are dominated by deciduous rather than coniferous species. These forests appear to be mature, even senescent, with a low probability of conifer recruitment. These areas are increasingly invaded by weedy shrub species and even deciduous trees may not persist without intervention. Chapter 9 Aquatic Habitat 9-65 Chapter 10 Current and Future Conditions by Subarea Chapter 10 Current and Future Conditions by Subarea 10.1 INTRODUCTION The May Creek basin is a 14-square mile (8,989-acre) area of King County that lies east of Lake Washington and includes parts of the City of Renton and the future City of Newport Hills. For planning purposes the basin is divided into four subareas that are characterized by their natural features and land use patterns: the Lower Basin, May Valley, Highlands, and East Renton Plateau subareas. Each exhibits its own range of responses to changing conditions that will determine effective solutions to the problems of the subarea. This chapter summarizes the more significant conditions in each subarea. Further information is available in the individual chapters and Appendix A. DESCRIPTION The Lower Basin subarea encompasses 3,200 acres, or about 36 percent of the basin (see Appendix B, Map 2). It contains the mainstem of May Creek (0282) from the outlet to Lake Washington at RM 0.0 to the upper end of the canyon near RM 3.9, and all of the tributaries that flow into May Creek in this reach. Key natural features of the lower basin are the steep -walled, forested canyon, the delta downstream of the canyon and west of 1-405, and the major tributaries of Honey Creek and the Boren Creek system (including Boren Creek, Lake Boren, and China Creek). The Lower Basin subarea is the most urbanized portion of the basin, having 37 percent of the land in high -density single family residential uses and ten percent in low -density housing. Within this subarea, commercial and high -density residential development is concentrated in the vicinity of Lake Boren, on the delta by Lake Washington, and in the City of Renton in the Honey Creek drainage. The subarea is wholly contained within the Urban Growth Area, and expected future development and infill will further increase the areas allocated to high- and medium -density residential areas (to 50 and 19 percent, respectively). Despite the urban character of this subarea, a significant amount of forest area (currently 37 percent) is still present. The majority of the forested land is located within the May Creek and Honey Creek canyons and adjoining areas, with the remainder being largely undeveloped tracts within the rapidly developing northern portion of the subarea. Two-thirds of this forest area is expected to be removed as a result of future development and infill. Chapter 10 Current and Future Conditions 10-1 The increasing density of development and reduction of forest land in the subarea will lead to an increase in the total area covered by impervious surfaces. This hardened surface will contribute to a greater volume of stormwater runoff in the future. CURRENT AND FUTURE LOWER BASIN CONDITIONS Drainage and Flooding A reach of May Creek in the lower canyon, along Jones Ave. NE and NE 31 st Street, has been mapped as a FEMA floodplain. Existing houses will continue to be above the area of the 100—year flood of May Creek, although flood flows at this location will increase in the future primarily as a result of upstream development. Importantly, the long residence time of flood waters in May Valley directly contributes to reduced flow levels along May Creek in the canyon and at the delta. Removal of this substantial valley storage would result in further increases to downstream canyon flood flows. An abandoned railroad embankment impounds a small pond on Newport Hills Creek; the outlet works had not been maintained in years. Modeling indicates that under severe conditions, if the pond's outlet were to plug, the pond level could rise and, coupled with a failure of the embankment, could cause minor flooding for downstream houses. However, with reconditioning of the outlet from the pond, the pond level could be kept to where even in a very severe storm there would be no risk of flooding for downstream houses. On lower Gypsy Creek a culvert through an abandoned road crossing could potentially plug and fail. In a low area between 1-405 and Lake Washington Blvd. N., an undersized culvert causes water to pond when upslope runoff exceeds the capacity of the conveyance ditch and culvert. This frequently floods a local business. The City of Renton and the Washington State Department of Transportation are developing a series of measures to address this and related nearby water quantity and quality problems. Near the outlet from Lake Boren, a private access road is occasionally overtopped by flow from the lake. Increased flows into Lake Boren from additional upstream development will lead to more frequent overtopping of the road. Stormwater runoff from intensive residential development in the uplands in the Lake Boren and upper Honey Creek areas has led to a number of localized drainage, flooding, and water quality problems. Most are the immediate results of new construction and associated drainage alterations, including failure of builders to correctly hook up drainage systems, encroachment upon or complete blockage of drainage easements, inadequate maintenance of drainage features, and filling. Such localized problems will continue to sporadically occur as development proceeds in the areas. Chapter 10 Current and Future Conditions 10-2 Erosion and Sedimentation There is a continuing problem at the outlet to Lake Washington, where commercial operations are affected by sediment deposition, requiring an increasing frequency of dredging. The natural delivery of sediment to the delta has been augmented by increased upstream erosion and loss of functional channel structure in the canyons of the mainstem of May Creek and several Lower Basin tributaries, and deposition problems in the commercial have been worsened by constructed changes that slow the stream and prevent channel migration. Future development in the basin will increase flows in the canyon, worsening the stream channel erosion and delta deposition problems. New development along upstream reaches of China Creek has resulted in increased storm flows. These flows deepen and widen the ravine, and together with erosion and sediment washoff from construction sites, is delivering sediment that is partially filling some culverts and depositing at the inlet to Lake Boren. Water Quality This subarea contains most of the commercial, multi -family and high -density housing areas within the basin, a segment of 1-405, and several areas with pre -failing or failing septic systems. Not surprisingly, current and future concentrations of total phosphorous, total suspended solids, and fecal coliforms are of concern throughout much of the subarea. Metals in stormwater exceeded toxicity criteria at the mouth of May Creek and in Honey Creek. Also within the Lower Basin subarea are 14 small —quantity generators of hazardous waste and two large -quantity generators. The urbanization of this subarea is the primary reason for water contamination. Elevated metals concentrations are highest in the Honey Creek drainage, probably due to runoff from large areas of impervious surfaces. Similarly, urban activities are contributing to the degradation of water quality upstream from Lake Boren, where high total suspended solids, total phosphorous, and fecal coliform measurements were recorded. Honey Creek has a particularly high fecal coliform level, possibly caused by animal waste in the upper areas and failing septic tanks in the lower area. Major road crossings near the mouth of May Creek are major sources for the metals found in the vicinity. Additional development in the subarea is likely to exacerbate these current water quality conditions. Habitat Several habitat areas have been identified in the Lower Basin subarea that qualify as Locally Significant Resource Areas (LSRAs). These include the reach of May Creek from RM 0.2 to 3.9 and associated Wetlands 38, 39 and 40; Wetland 9 on Gypsy Creek; the lower reach of Honey Creek (RM 0.0 to 0.35); and several portions of the Boren/China Creek system, including the lower reach of Boren Creek (RM 0.0 to RM 0.5), Wetland 8 Chapter 10 Current and Future Conditions 10-3 (which includes Lake Boren) and Wetland 4 (associated with China Creek). See Map 1 in Appendix B, and Chapter 9: Aquatic Habitat and Fish. The reach of May Creek from RM 0.2 to 3.9 is in relatively good condition, considering its urban location, and is used by five species of salmonids. However, the reach generally lacks the large woody debris needed to maintain pools and habitat diversity, and its immature riparian area limits future sources of woody debris. The reach also receives a high load of sediment (see above). Honey and Boren creeks also contain usable anadromous fish habitat in their lower reaches. They, too, lack large woody debris, have limited sources for future recruitment of woody debris, and have high sediment loads. A fish ladder at the gas pipeline crossing of May Creek (RM 2.9) does not function under some conditions. When not functioning it becomes a barrier to the upstream passage and migration of fish. Several culverts on tributaries in the Lower Basin do not provide suitable fish passage under all conditions. 10.3 MAY VALLEY SUBAREA DESCRIPTION May Valley is the smallest of the four subareas, encompassing approximately one square mile (see Map 2 in Appendix B). The subarea includes the mainstem of May Creek above the head of the canyon at RM 3.9, as well as the lower portions of the three headwaters forks (the North, East, and South forks) above the crossing of the SE Renton -Issaquah Road (SR-900) at RM 7.0. Within the subarea is the flat valley bottomland, much of which is in the 100-year floodplain. Wetlands account for approximately 39 percent of the area, including the 208-acre May Valley Wetland 5. The area currently has very little commercial or high - density residential development, but about 31 percent of the land (193 acres) is devoted to low -density single-family residential use. Expected future land use changes will lead to a loss of slightly more than half of the grassland and remaining forest land as it is replaced with residential and commercial development. Flows originating in this area are not expected to increase significantly, but the area will be affected by development in the upland areas surrounding the valley. CURRENT AND FUTURE MAY VALLEY CONDITIONS Drainage and Flooding The May Valley has little topographical relief, drains slowly, and receives large flows from tributaries that drain the surrounding hillsides. Even before development, May Creek in the May Valley naturally overflowed its banks onto the large floodplain of the valley; as agricultural/livestock, residential, and roadway uses were located within the Chapter 10 Current and Future Conditions 10-4 valley; as agricultural/livestock, residential, and roadway uses were located within the floodplain, flooding and drainage problems resulted. The current flooding problems in May Valley are concentrated along the mainstem of May Creek and where major tributaries discharge onto the May Valley floodplain. Extensive flooding occurs annually during the storm season in the May Valley. A large number of pasture areas and other open areas are affected, with prolonged ponding of water in some locations. Approximately six houses, a commercial business, and several other buildings have been computed to be within the 100-year floodplain. There are also several reports of septic tank or well effects. Similar flooding occurs in the floodplains of the three forks of May Creek. On the North Fork a private runoff and drainage system for several short plats is not functioning properly, causing flooding of pastures and a barn, and prolonged ponding of water. Increased ponding of water is reported from the East Fork, exacerbated both by upstream development and by various private manipulations of an already indistinct drainage course. In two locations there is occasional bank overtopping and flooding of a house that is located near the entrance of a tributary into an alluvial fan or onto the floodplain of the May Valley. Flooding is exacerbated by various activities that have reduced the area and storage of the floodplain, such as filling, stream channelization, development within the floodplain, and sediment deposition; obstructions to drainage and flow, including vegetation in stream channel, backwater effects, and livestock trampling of banks; and increased stormwater runoff resulting from clearing and development of surrounding upland areas. New development on the hillsides to the north and south of the May Valley is predicted to result in increased floodwater volume delivered to the valley. While this will increase peak flows somewhat, because of the large storage capacity these volumes will more noticeably increase the frequency, depth and duration of flooding in existing locations. Modelling indicates that bridges at the crossing of May Creek at both 148th Avenue SE and 164th Avenue SE would be overtopped by a 25-year flood. Erosion and Sedimentation Farming (historically) and livestock raising/grazing (more recently) have removed and suppressed the riparian and wetland vegetation along many reaches of May Creek. Rainfall washes fines and manure from pastures and trampled streambanks, rapidly increasing the turbidity of May Creek even in light rains. Considerable suspended sediment is delivered from quarries in the Highlands and East Renton Plateau subareas, and also from tributaries discharging into the valley. Much of the sediment is retained in the valley, gradually filling -in the excavated channel. Sidecast spoils from past dredging still follow along much of the channel, and some spoils have Chapter 10 Current and Future Conditions 10-5 likely subsided back into the channel. There has also been substantial filling activity in the wetlands and floodplain. Future development on the hillslopes of the Highlands and East Renton Plateau subareas will deliver greater peak stormflows to the streams flowing into May Valley, and the greater erosive power of the streams will also deliver greater amounts of sediment to the valley. Water Quality Within this agricultural valley water quality is seriously degraded, due primarily to poor livestock management practices that contribute to high levels of total suspended solids, fecal coliform, total phosphorous, nitrates, and biological oxygen demand. Overgrazing and unrestricted animal access to May Creek results in trampled banks, and has virtually eliminated the riparian vegetation and shade in many locations (and has allowed water temperatures in the May Valley to reach critically high levels for salmonids during summer low -flow periods). Poor manure management and failing onsite sewage systems contribute fecal coliform bacteria to the water. Three quarries in Highlands and East Renton Plateau subareas have delivered elevated loads of total suspended solids, metals, and total phosphorous to the creek. One or two of these quarries may close and be reclaimed in the near future; however, continuing working sites must have better measures, upkeep of facilities, and compliance with water quality standards, and outflow from closed sites may still contribute to problems. Habitat One riparian wetland habitat segment of May Creek in the May Valley subarea qualifies as an LSRA: a portion of Class-1 Wetland 5 on the May Creek mainstem and South Fork. This area is located in a conifer forest remnant east of SE Renton -Issaquah Road (SR-900) and south of SE May Valley Road. The entire Wetland 5 is much larger than the qualifying portion: while most of it does not qualify for LSRA status, it is actually in better shape now than it was in the 1930s when agricultural use of the surrounding area was more intense. The stream habitats in the May Valley Subarea would formerly have provided some good coho salmon rearing habitats, but most have been severely degraded by actions within the subarea and along its feeder tributary streams. Two locations that still support coho spawning, Country Creek 0292, RM 0.09 to 0.14, and Tributary 0291A, RM 0.06 to 0.3 (partly within the subarea), are also identified as LSRAs. Livestock grazing and channelization have caused the loss of riparian and wetland vegetation, reducing the quantity and quality of the habitat. Problems in the area include a channel bottom that consists of silt, with almost no spawning habitat; heavy sediment loads from upstream areas and overland flow across adjacent sparsely vegetated areas; a lack of large woody debris (LWD) for fish habitat; collapsing stream banks caused by Chapter 10 Current and Future Conditions 10-6 livestock trampling; and elevated summer stream temperatures caused by a lack of streamside tree shading. 10.4 HIGHLANDS SUBAREA DESCRIPTION The 3,200-acre Highlands subarea lies to the north of May Valley and east of the Lower Basin subareas, encompassing the southern slopes of Cougar Mountain and southwest portion of Squak Mountain (Appendix B, Map 2). Major Highland tributaries include Long Marsh Creek, Country Creek, Cabbage Creek, and the North and East forks of May Creek. The Highlands subarea has steep, forested (81 percent) terrain, high precipitation, and shallow soils. The soils drain quickly and provide streamflow for the northern tributaries that empty into May Creek. Land use changes expected in this area will be dramatic. Short —plat development will convert 1,300 acres of forest land to low- and medium —density single—family residential use. This future development will increase stormwater runoff and delivery to downstream areas. CURRENT AND FUTURE HIGHLANDS CONDITIONS Drainage and Flooding Because of its higher rainfall, steep slope, and shallow soils, even in its undeveloped, forested state, this subarea produced more runoff than any developed area in the May Creek basin. Many of the Highlands subarea creeks will experience increases in peak flows as the currently undeveloped forest land is converted to single—family homes. The additional runoff resulting from land clearing, road building, and housing construction will be the largest addition to future peak flows in the basin, thereby adding to future May Valley flooding problems. Runoff from Squak Mountain as clearing and development proceed will also add to drainage and flooding concerns on the North and East forks of May Creek. Erosion and Sedimentation Long Marsh Creek currently has a stable channel, and is expected to retain this condition if the channel and valley wall vegetation can be maintained in the future. Additional runoff resulting from future development in the subarea will produce numerous erosion problems in other areas that currently have stable or nearly stable channels. Higher peak flows will expand the channels of Cabbage and Country creeks Chapter 10 Current and Future Conditions 10-7 and the North and East forks of May Creek, accelerating sediment production and contributing to the buildup of deposits in and near the stream confluences with May Creek. Water Quality Water quality within the northern tributaries (Long Marsh, Country , and Cabbage creeks) is relatively good; however, there is a currently unidentified source of nitrates. High phosphorus readings in the lower reaches are probably due to fertilizer use in these locations. Total suspended solids and metals concentrations in excess of standards have been measured at some locations along the North Fork of May Creek. The sediment loadings originate principally at the local quarries, which also account for most of the phosphorus. High metals concentrations probably result principally from runoff from SR-900. As a result of increased development, future loadings are expected to increase in several of the tributaries, including total suspended solids in the tributaries from Cougar Mountain, and TSS and lead levels along the North Fork. Habitat The Highlands subarea contains the only habitat feature in the basin that has been identified as a Regionally Significant Resource Area (RSRA): the Class-2 Wetland 11 at the headwaters of Long Marsh Creek. The Class-1 Wetland 13 on the North Fork of May Creek and the associated reach of the North Fork from RM 0.7 to 1.0 is identified as an LSRA. Many of the wetlands and upper tributaries are in moderately good to excellent conditions because of the limited amount of development that has taken place thus far. Fish usage in the tributary streams of the subarea is generally extremely limited due to the steepness of the stream channels land and natural barriers to upstream passage. Where artificial barriers are found, the length of stream that could be made accessible by barrier removal is generally small or negligible. The middle reach of the North Fork does have some accessible fish habitat, but the stream is adversely affected by a lack of LWD, livestock grazing in the lower areas, gravel pit operations that add suspended sediment and sand in the upper area, and channelization and runoff from SR-900 in the upper area. 10.5 EAST RENTON PLATEAU SUBAREA DESCRIPTION The East Renton Plateau subarea covers 2,000 acres, approximately 22 percent of the total basin (see Map 2 in Appendix B). It lies to the south of May Valley and east of the Lower Basin subareas, draining the draining the northern portion of the tableland Chapter 10 Current and Future Conditions 10-8 between the Cedar River and May Creek. The terrain is relatively flat, except where it slopes sharply down to the May Valley, and capped with relatively impervious till soils. Tributaries draining the plateau include Tributary 0291A, Greene's Creek, and the South Fork of May Creek, with Lake Kathleen situated at the eastern end of the subarea. The East Renton Plateau is currently divided primarily between forest land (744 acres, or 38 percent), low -density single family residential development (26 percent), and high - density single—family residential development (18 percent). Much of the currently developed area is located around Lake Kathleen and along the periphery of the subarea. Future development is expected to be primarily low -density single-family residential use, except where higher -density plats have already been approved. Under the revised County Comprehensive Plan, most of the plateau within the May Creek basin has been re -designated "Rural," limiting the future density of residential development in most of the area in this basin; however, portions of the May Creek basin and most of the plateau in the Cedar River basin immediately to the south have retained the "Urban" designation. Further residential development is also expected in the Lake Kathleen area. CURRENT AND FUTURE EAST RENTON PLATEAU CONDITIONS Drainage and Flooding The East Renton Plateau subarea is relatively flat, and natural drainage is often not well defined. Problems generally occur where new development alters, obstructs, or overloads the natural drainage, and where mitigation is inadequate to the conditions. Localized drainage and flooding problems arise periodically in the intensely developed area around Lake Kathleen. Along W. Lake Kathleen Drive SE, for example, some residential properties have in the past experienced drainage problems due to excess runoff from uphill development. Most are the immediate results of new construction and associated drainage alterations, including filling and loss of natural stormwater detention, alteration of natural drainage paths, failure of builders to correctly connect drainage systems, and encroachment upon or complete blockage of drainage easements. Such localized problems will continue to sporadically occur as development proceeds in the areas. Flooding has also occurred along the lakeshore and at the outlet, where outflow sometimes exceeds the outlet culvert capacity and flows over SE 134th Street. Future development on the plateau will result in additional localized drainage problems in various locations. Increased stormwater runoff from the additional development will contribute to problems in the May Valley. Drainage and flooding problems will also increase in the Lake Kathleen area in response to additional residential development around the lake. In the long term, as the lake continues to age and fill, its flood storage capacity will decrease, tending to increase the depth and duration of future flooding. Chapter 10 Current and Future Conditions 10-9 Erosion and Sedimentation Like the Highlands, the East Renton Plateau subarea is currently much less developed than it is expected to be in the future. The South Fork of May Creek currently is stable, and the primary effect of current sediment deposition is the aging of shallow, mesotropic Lake Kathleen. Future flow increases, however, are likely to lead to serious channel erosion problems in the South Fork, and increased deposition in its alluvial fan. Additional development upslope from Lake Kathleen is expected to increase the future nutrient and sediment load to the lake. Tributary 0291A and Greene's Creek are experiencing downcutting in some locations. Water Quality Relative to other parts of the basin, the East Renton Plateau subarea appears to have satisfactory water quality. Fecal coliform levels in Lake Kathleen occasionally exceeded the state standard when measurements were taken in 1979 and 1980. The lake is meso—eutrophic, but does not appear to be in immediate danger of increased eutrophication, in part because of the lack of significant drainage into the lake. Runoff from SE 128th Street is supplying metals to the South Fork. Some metals exceedances have also been observed for Tributary 0291A near the confluence with May Creek, which are probably due to runoff from SR-900. Habitat LSRAs in the East Renton Plateau subarea include the reach of Tributary 0291A from RM 0.06 to 0.26, where there is concentrated spawning of coho salmon; the Class-1 Wetland 2 at the headwaters of Tributary 0291A; and Class-1 Wetland 1, which includes Lake Kathleen. Lake Kathleen, like most low -elevation lakes near large urban centers in western Washington, has been moderately to severely disturbed by residential development, filling, buffer modification, and declining water quality due to failing septic systems and other nutrient input. Nonetheless, the lake supports a broad diversity of wetland types, including aquatic bed, emergent, scrub -shrub, and forested habitats. The forested wetland segment at the southeast shoreline and its adjacent buffer appear to be unchanged since the 1930s, and may represent a rare example for low -elevation lakes in this part of the state of a lakeshore environment that exhibits near pre -settlement conditions. Despite these and similar pockets of natural landscapes in the area, development has, in general, resulted higher amounts of stormwater runoff, streambank erosion, and reduced riparian habitat quality. Future development will continue this process. Chapter 10 Current and Future Conditions 10-10 Chapter 11 Coordination and Planning Chapter 11 Coordination and Planning 11.1 INTRODUCTION This Conditions Report has identified many water resource management problems affecting the May Creek basin, including flooding, damage to fish habitat and wetlands, erosion and sediment deposition. and degradation of water quality. These problems are the culmination of many years of development and other human activities that have had imparts on the basin's natural resources and processes. In response, there are a number of local, regional, state, federal, and tribal agencies. as well as special purpose districts and community programs, which are attempting to remedy these conditions and prevent further decline of the system. These organizations and their jurisdictions and roles are summarized in Table 11-1. From the standpoint of the responsible agencies and groups, several tools are needed to halt or reverse the decline of conditions and resources in the basin. First, resource agencies need a common interdisciplinary reference that documents conditions in the basin in sufficient detail that everyone can understand the resources issues and their interactions: the information provided in this Conditions Report fulfills that need. Second, the agencies and the public need a process through which they can jointly develop a single set of solutions. The May Creek basin planning process provides that opportunity, allowing all concerned to develop a common blueprint of actions to address the basin's existing problems and help keep them from getting worse. 11.2 PRIVATE SECTOR ACTIONS Both large- and small-scale private actions and personal activities can either contribute to the improvement of basin conditions and to the implementation of solutions, or to a worsening of water management problems. While some positive actions may require government regulation or incentives, others may be accomplished through individual and company actions and initiatives, and by education and community action programs. DEVELOPMENT ACTIVITY Development activity, involving substantial clearing and grading of vegetation and soils, can significantly influence surface -water conditions. For example, construction practices can allow large volumes of water and eroded soil to flow off the land during storm events. This runoff may reach nearby streams if erosion and sedimentation controls and other types of best management practices (BMPs) are not properly installed and maintained. As is discussed in Chapters 4 through 9, the eroded soil creates a myriad of problems including water quality degradation, disruption to fish spawning, loss of habitat cover, decreases in channel depth, increases in flooding, and others. Chapter 11 Coordination and Planning 11-1 Table 11-1. Government Agency Roles in Managing Resources of the May Creek Basin. Page 1 of 3 Local Governments City of Renton, City Administer within their jurisdictions development regulations for of Newcastle, and grading, drainage, and construction within and beyond shoreline King County areas; prepare and administer comprehensive plans and zoning regulations; prepare public works plans for stormwater, solid waste, and transportation; develop and implement plans to protect groundwater supplies. The County also administers its water quality ordinance. City of Renton Manages its sole source aquifer; provides sewer and water service to its customers in its service area. Regional Agencies King County Monitors stream quality in the basin; prepares area -wide plans for Department of water quality priorities; wastewater treatment and conveyance Metropolitan utility [there is no treatment of wastewater within the May Creek Services (Metro) basin]. Seattle -King Administers septic system regulations for small- to medium -scale County Department development, pesticide regulations, and groundwater protection of Public Health program. Indian Tribe Muckelshoot Indian Co -manages fishery resources in the basin with state resource Tribe management agencies. All waterbodies (streams, lakes, etc.) withing the Lake Washington drainage area are part of the Tribe's Usual and Accustomed fishing grounds. State Agencies Department of Regulates the use, transportation, and disposal of pesticides. Agriculture Department of Administers state and federal water quality regulations; provides Ecology technical assistance and oversight to local governments in the administration of the State Shoreline Management Act; reviews and comments on actions affecting wetlands; issues water quality certifications, NPDES and stormwater permits; provides technical assistance to local governments in wetlands management, nonpoint source pollution, and stormwater; approves local groundwater management plans. Department of Administers drinking water standards and septic system permit Health requirements for large developments. Department of Administers commercial forest practices regulations, including Natural Resources control of nonpoint pollution from forest practices; administers and regulates activities in the aquatic lands of Puget Sound and Lake Washington. Chapter 11 Coordination and Planning 11-2 Table 11-1. Government Agency Roles in Managing Resources of the May Creek Basin. Page 2 of 3 Department of Fish Administers the Hydraulic Code which regulates activities within and Wildlife the ordinary high water of streams and lakes, and administers regulations for the protection of federal- and state -listed threatened and endangered species. Manages fish and wildlife resources and habitat, sets fishing seasons. King Conservation Provides technical services and public educational programs District related to agricultural and livestock practices for preventing and correcting erosion and water quality problems; assists landowners in preparing individual farm plans. Puget Sound Water Develops and oversees implementation plans to protect and Quality Authority restore water quality from point and nonpoint sources in Puget (PSWQA) Sound and its tributary areas, including requirements for local governments to develop stormwater management plans; provides funding for public information and educational programs. [The PSWQA will end on June 30, 1996. The distribution of its responsibilities among continuing agencies is not yet determined, but many will probably be assumed by the Department of Ecology.] Department of Constructs and maintains state highways, including 1-405 and SR - Transportation 900. Federal Agencies Federal Emergency Provides technical assistance on flood prevention and Management management to local governments; determines requirements for Administration participation in the federal flood insurance program; administers flood insurance funds. US Army Corps of Administers regulations for activities in navigable waters, Engineers including Lake Washington; administers regulations for dredging and for projects involving placement of dredged and fill material in wetlands and waters of the U.S.; provides assistance through a variety of authorities to local governments and agencies in addressing various water resource problems, including floodplain management. US Environmental Develops and jointly enforces federal wetlands regulations with Protection Agency the U.S. Army Corps of Engineers; funds and manages the Quendal Logyard Superfund Clean-up site near the outlet of May Creek; regulates federal pesticide laws; provides technical assistance for nonpoint pollution problems. US Fish and Administers resource protection regulations for federally protected Wildlife Service threatened and endangered species; reviews and comments on actions affecting wetlands and waters of the U.S., including Lake Washington. Chapter 11 Coordination and Planning 1 1-3 Table 11-1. Government Agency Roles in Managing Resources of the May Creek Basin. Page 3 of 3 US Geological Conducts stream flow surveys and special drainage studies. Survey USDA Natural [formerly, the Soil Conservation Service] Provides technical Resources service and financial assistance to commercial agriculture Conservation operators for preventing and correcting soil erosion problems. Service King County/ Provides technical assistance for nonpoint pollution control. Washington State Univ. Extension Service USDA Agricultural Shares cost of water quality control measures on commercial Stabilization and farms; provides technical assistance on agricultural projects. Conservation Service Special Purpose Districts King County Sewer Provides sewer and water service to its customers within its and Water District service area; service area includes the City of Newcastle. 107 King County Water Provides water service to its customers within its service area. District 90 Chapter 11 Coordination and Planning 11-4 A study to assess the effectiveness of erosion -control BMPs on construction sites throughout King County was conducted by the King Conservation District (Tiffany et al., 1990), in which 86 site visits were made to 60 construction sites. The study found that three sites (five percent) had effective controls in place during the study period. The primary reasons specified for the remaining 95 percent having ineffective controls include inadequate installation, poor timing of installation with respect to weather conditions, and insufficient maintenance. A likely conclusion is that a majority of these sites contributed to erosion and sedimentation problems and water quality degradation in the surface waters of the basin. The level of performance in erosion control, sensitive areas protection, and others can be improved by education, which can provide instruction on proper practices for the companies and their employees, explain the purpose and function of protective measures, and secure a commitment to the better use of the control measures. Improvements in conditions can also be obtained by the periodic review and improve- ment of regulations to both better protect the resources and facilitate the proper selection and use of protective measures. and by the regular inspection and enforcement of the codes. BUSINESS AND FARMING ACTIVITIES Business and commercial activities often involve a substantial use of automobiles and trucks, both by the businesses and their customers, as well as the allocation of large areas to impervious surface. These businesses and developed areas can generate large volumes of stormwater runoff, and can introduce pollutants to the water from both point and ronpoint sources. However, the contamination of the water can be greatly reduced if certain measures and BMPs are employed and maintained. The King County Storrrnwater Pollution Control Manual (for existing operations) and the revised Surface Water Design Manual (for new construction) describe requirements, guidance and options for better controlling water pollution from commercial businesses. As is noted in Chapter 8, livestock is the principal source of agricultural pollution, and is a significant source of nonpoint pollution in the May Creek basin. Unrestricted access of livestock to the streams further contributes pollution from animal wastes and erosion, destroys aquatic habitat, and eliminates shading of the water (which in turn results in elevated stream temperatures). The King Conservation District and the King County/ Washington State University Extension Service provide educational and farm planning assistance to private landowners to improve operations, and to meet BMPs and the requirements of the Livestock Ordinance. INDIVIDUAL ACTIONS A significant contribution to conditions in the basin is made by the daily activities of the thousands of residents in the basin. For example, by their choices of mode of transportation (e.g., bus, carpool, bicycle, single -occupancy vehicle) and frequency of vehicular trips, individuals can greatly affect the generation of nonpoint pollutants in the basin and region. Further, the general public can improve stream and wetland quality as Chapter 11 Coordination and Planning 11-5 active stewards of the natural resource. By avoiding or minimizing such activities as the filling of wetlands, the rerouting or rip -rapping of streams, and the removal of large woody debris and streamside vegetation; by reducing the use of fertilizers and pesticides; by employing livestock and pasture BMPs; and by properly caring for and maintaining septic systems, people individually and collectively can have a substantial beneficial effect on the streams, lakes, and wetlands of the basin. 11.3 ROLE OF GOVERNMENT AND PUBLIC AGENCIES LOCAL GOVERNMENTS Local jurisdictions and their surface water management programs are generally the first to respond to water resource problems. In the May Creek basin there are three such jurisdictions: the City of Renton, with about 12 percent of the area, the City of Newcastle, with 20 percent of the area, and King County, which includes the unincorporated 68 percent of the basin. Potential future annexation areas for the cities of Renton and Newcastle extend east of the current city boundaries to the Urban Growth Area boundary, and are included in the comprehensive plans for the cities. King County and the cities of Renton and Newcastle have surface water management codes that specify development standards to address stormwater runoff, and programs that respond to existing drainage problems by evaluating conditions in the system and developing responsive measures. These measures can include capital improvement projects such as stormwater detention ponds or water quality control facilities. Less intensive and nonstructural approaches can include land -use controls and development regulations, public education, incentives to encourage improved stewardship and assistance in implementing best management practices, the development of conservation plans for individual landowners, and others. The effectiveness of existing and proposed regulations and plans will be improved by coordination between the jurisdictions, and will depend on the level of priority and funding that is given for education and assistance, permit review, development inspections, and code enforcement within each jurisdiction. King County uses several measures to address the harmful surface water effects of development: • The Surface Water Design Manual and Drainage Code that describe surface and stormwater runoff analysis and specific design requirements, procedures, and guidance for development (a revision of the manual will be completed in 1995); • The Sensitive Areas Ordinance and Code that protect wetlands, steep slopes, streams, and other sensitive areas through the application of limits and controls on development in these environmentally sensitive areas; and • The Water Quality Ordinance and Code that require best management practices and controls on existing and new pollution sources such as contaminated stormwater discharge, hazardous waste, and failing septic systems. To describe Chapter 11 Coordination and Planning 11-6 the controls and regulations, and to assist in the design and implementation of measures, King County has developed a Stormwater Pollution Control Manual that will be adopted by the Council in 1995. In 1993, King County adopted a Public Rule that designates the May Creek basin as a "critical drainage area" (CDA). The Public Rule places some requirements in addition to those in the Design Manual on new development in the basin, particularly in the rural areas. This Public Rule and CDA will expire when the basin plan is adopted. The City of Renton also has developed several means for addressing harmful effects of development on surface water, including: • The City has developed a critical areas ordinance with maps identifying wetlands, areas of "geologic hazards," and other critical areas, and added measures for protection to the building regulations code; • Currently, the City is working on a new Comprehensive Storm and Surface Water Drainage Plan (in the interim the City is using the 1990 Surface Water Design Manuan; and • The City has adopted regulations to safeguard the water supply in its sole -source aquifer, and developed an Infiltration/Inflow Program to address wastewater collection and conveyance issues. The City of Newcastle has adopted an interim comprehensive plan and inventory of sensitive areas; this plan and its inventories and supportive ordinances will be further developed before final adoption. The City has also adopted a surface water runoff policy and management program, which adopt most of the analysis and specific design requirements and procedures of the County's 1990 Design Manual. STATE, FEDERAL AND TRIBAL AGENCIES The state and federal agencies and tribes that are identified in Table 11-1 manage or make decisions about the natural resources in the basin. Most also have a role in protecting these resources from adverse effects of development through the conditioning of permits according to individual agency policies and regulations and the enforcement of the regulations, and by conducting programs to manage the land and water resources. For example, the Washington Department of Ecology and the US Environmental Protection Agency regulate water quality, and the US Environmental Protection Agency and US Army Corps of Engineers regulate many of the developmental activities in streams and wetlands. The 'various agencies address different resource concerns and are guided by separate missions and objectives, as is shown in Table 11-1. These different concerns, missions, and authorities can conflict and create gaps in regulatory coverage for certain resources. Failure to correct problem conditions may result from a lack of technical capability to Chapter 11 Coordination and Planning 11-7 mitigate for development impacts, or from limited authority to protect the resources. Most frequently, however, it is due to insufficient funding to keep pace with expanding development pressures. In some cases the multiplicity of regulations and policy objectives can lead to inconsistent management of the resources. A primary goal of the May Creek Basin Plan is to coordinate with agencies and tribes to help establish a unifying direction and to identify the priority needs for the comprehensive management of the basin's surface water resources. 11.4 RELATED PLANS, PROGRAMS, AND REGULATIONS KING COUNTY GROWTH MANAGEMENT PLANNING POLICIES In accordance with the directives of the State of Washington's Growth Management Act, in June 1992 the King County Council and the cities in the county adopted county -wide planning policies to provide a framework for managing growth by all of the jurisdictions in the county. The interjurisdictional Growth Management Planning Council and the County approved a new interim Urban Growth Area (UGA) boundary, defining the areas in which urban growth would be allowed in the basin in the next 20 years and where urban level services, such as sewer and water, would be provided. Those areas outside of the UGA line were designated Rural and assigned a low -density zoning. These policies and interim UGA boundary were incorporated and further revised by the County in the 1994 update to the Comprehensive Plan. KING COUNTY COMPREHENSIVE PLAN UPDATE In 1995 the King County Council adopted a revised and updated Comprehensive Plan to reflect the requirements of the Growth Management Act and the county -wide planning policies noted above, and to revise the urban/rural boundary and new development policies and regulations. Public meetings and workshops were held throughout the county in July and August of 1993 to collect ideas on how to manage growth, provide affordable housing, transportation, and protect the quality of life for the next 20 years. A supplemental environmental impact statement (SETS) on the impacts of the update was prepared in 1994, building on the environmental information contained in the EIS for the 1985 Comprehensive Plan and the EIS for Vision 2020. As was noted above, the UGA boundary defines the areas in which urban growth and urban -level services will be allowed and provided in the county in the next 30 years; moreover, the Comprehensive Plan assumes that land use in the areas west of the UGA will ultimately proceed to high -density residential or other urban densities and uses, unless there are environmental or legal limitations. Those areas outside of this line are designated Rural and assigned a low -density zoning. After 30 years, the UGA could be extended into the Rural -designated areas to accommodate future growth. The revision of the Comprehensive Plan and the UGA boundary resulted in the May Creek basin in the redesignation of two large areas north and south of the May Valley floodplain from Urban to Rural (see Map 3 in Appendix B; see also the discussion in Chapter 3: Land Use and Land Cover). Many policies were updated and revised, and Chapter 11 Coordination and Planning 11-8 some new ones, such as provision for consideration of Regionally and Locally Significant Resource Areas in County planning, were developed. The May Creek Basin Plan will be developed consistent with the planning and policy direction in the revised Comprehensive Plan. KING COUNTY ZONING CODE REVISIONS After the adoption of the 1985 King County Comprehensive Plan the zoning code was revised to more accurately implement the plan's countywide goals and policies. The next major code revision was in June 1993, in which revisions were made to simplify regulations and satisfy the Growth Management Act requirements. King County is now revising the zoning code to apply new zone categories, to implement the changes in the Comprehensive Plan, and to reduce the number of P-suffix conditions on zoning, and is preparing new zoning maps for use by the county, communities, citizens, and agencies. All existing zones have a new zoning designation which is equivalent to the previous category. The May Creek Basin Plan will be developed consistent with the new zoning. KING COUNTY PUBLIC BENEFIT RATING SYSTEM King County offers an incentive to preserve open space on private property by providing a tax reduction if the land contains one or more open space resources. The incentive establishes a "current use taxation" property tax assessment for the portion of the property that is approved as open space land. This taxation generally reduces the taxable value 50-90 percent below that of the "highest and best use" tax assessment. The Public Benefit Rating System allows lands to be evaluated and scored for the presence of open space resources, and a calculation of the current use taxation value to be made. Management and retention of the open space resource continues to be the responsibility of the property owner. KING COUNTY PARKS, RECREATION, AND OPEN SPACE COMPREHENSIVE PLAN The 1988 King County Open Space Plan proposed two trail connections through May Creek basin. One trail is proposed to connect May Creek near the east end of May Creek, Park to Cougar Mountain through the proposed plat of The Highlands in Newcastle (formerly, Whitegate). A second proposal would connect the Cedar River Trail to the south with the Lake Sammamish Trail to the north, using a route that would generally follow the Puget Sound Power and Light transmission line right-of-way. A new King County Parks, Recreation, and Open Space Plan will be adopted by the Council in 1995 that defines future needs for parks, recreation, and open space in King County, and the role the County will play in providing services and public open spaces to keep pace with population growth. Chapter 11 Coordination and Planning 11-9 KING COUNTY CODE AND COMMUNITY PLAN AMENDMENTS In the solutions phase of the development of the basin plan, changes in land -use regulations and zoning may be proposed to address anticipated future surface water problems. These changes could be implemented through revisions to surface water management and zoning codes, by an amendment to the Newcastle Community Plan, or other appropriate processes. Any such changes would require staff analysis by and coordination with County and city planning units, public review, and adoption by the King County Council. KING COUNTY SURFACE WATER MANAGEMENT STEWARDSHIP PROGRAM King County Surface Water Management has developed a program of basin stewardship to provide assistance and help educate the residents, and to help implement the recommendations of the basin plans. Some of the responsibilities of basin stewards include: providing technical assistance to basin residents to prevent nonpoint pollution, revegetating disturbed areas, assisting in water quality monitoring and habitat conditions, education, and identifying code violations. The May Creek basin will be included in the stewardship responsibilities for the Cedar River/Lake Washington watershed area. CITY OF RENTON COMPREHENSIVE PLAN The City of Renton has updated its comprehensive plan to meet the requirements of the Growth Management Act, and has adopted new zoning. The Land Use Element of the plan, and the proposed zoning to implement the plan policies, encourage high density and commercial development in the city's downtown area, and industrial development in north Renton. Single-family neighborhoods will have an overall density of eight to ten dwelling units per acre, and multifamily development may occur in identified multifamily areas. Development in environmentally sensitive areas and urban separators will be limited to low- and medium -density residential housing. The current and future land use/cover maps for this Conditions Report (see Maps 4 and 5 in Appendix B) were developed with the assistance of the City of Renton, and incorporate information developed for the comprehensive plan. CITY OF RENTON GROUNDWATER MANAGEMENT PLANNING The City of Renton has a number of programs that are underway to evaluate the quality and quantity of groundwater in Renton's sole source aquifer. The aquifer lies predominantly in the Cedar liver Valley, just east of downtown Renton, although one wall is within the May Creek basin. The May Creek Basin Plan will identify surface water policies and programs that can assist in protecting groundwater supplies and quality in the future. Chapter 11 Coordination and Planning 1 1-10 CITY OF RENTON COMPREHENSIVE PARK, RECREATION, AND OPEN SPACE PLAN The Park Plan for the City of Renton was adopted by the City Council in 1993. It defines existing and future park needs, identifies development and facility standards, makes recommendations, and identifies strategies for funding improvements. Specific open space areas, trails, and sites are recommended in the May Creek basin. The May Creek Basin Plan will be able to coordinate its surface water recommendations with those parks needs. CITY OF RENTON SENSITIVE AREA ORDINANCES The City of Renton has a series of ordinances which regulate development and protect sensitive areas. These areas include wetlands, aquifers, floodplains, and areas of steep slope, landslide hazard, seismic hazard, erosion hazard, volcanic and coal mine hazard, agricultural and mineral resource land, and wildlife habitat. The City applies these regulations to lands in the basin within its jurisdictional boundary. CITY OF RENTON COMPREHENSIVE SURFACE WATER UTILITY PLAN The City of Renton has completed the first phase of its comprehensive water utility plan for the corporate limits and adjoining unincorporated areas out to the Urban Growth Boundary. Phase I includes a description of existing policies, regulations, and gaps; Phase II defines new policies, a surface water quality and public education program, staff needs for operation and maintenance, and a six -year capital improvement program schedule for implementation. Information from the May Creek Basin Plan and Conditions Report can be used to supplement information in the City's utility plan. HONEY CREEK AND MAY CREEK INTERCEPTORS The City of Renton and King County Department of Metropolitan Services (Metro) are currently considering a new sanitary sewer interceptor line for the Honey Creek area, to connect to the Metro trunk line near Lake Washington Boulevard via a connecting Metro interceptor line. The two principal groups of alternatives are 1) a gravity -line that would construct the Metro interceptor line in the May Creek canyon downstream from Honey Creek, and 2) a force -main route over the Renton Highlands that would use existing lines for most of its length and would require pumping, but would avoid the sensitive areas of the May Creek canyon. The canyon gravity -line route could link with and help service parts of the District 107 sanitary sewer system; however, current District plans envision using a route down the Coal Creek drainage, and this route would be used if a Renton Highlands interceptor route were chosen. Information from this conditions report and the basin plan will be used in the planning, analysis, design and implementation of the interceptor projects. Chapter 11 Coordination and Planning 1 1-11 CITY OF NEWCASTLE INCORPORATION Voters in 1994 approved the incorporation of a new city located, in large part, in the May Creek basin. The city was initially designated as Newport Hills but was renamed as the City of Newcastle in late 1994. The city includes about 1,800 acres or 20 percent of the May Creek basin, and is located in the north and northwestern portion of the basin. The City of Newcastle, King County, and the City of Renton will be conferring as the basin plan and its elements are being developed, and will need to develop interlocal agreements for the implementation of some of the measures in the basin plan. CITY OF NEWCASTLE COMPREHENSIVE PLAN The City of Newcastle has adopted an interim Comprehensive Plan which encourages the continuation of high -density residential development where utility facilities exist or may be extended, while most commercial and industrial development would occur outside of the city. Where sensitive areas or other environmental constraints are present, development would be limited to medium (suburban -level) densities. Multifamily development would generally be limited to the vicinity of existing multifamily areas, and adjacent to commercial and office uses. The Cougar Mountain area would remain for the present as a growth reserve area, in which the City encourages clustered development at overall low density for the present. This allocation will be examined again in an update to the plan, and is likely eventually to be developed to higher densities. Current and future land use/cover maps in this Conditions Report (see Maps 4 and 5 in Appendix B) were developed based on Renton and County planning prior to the incorporation. With minor exceptions they continue to reflect the densities allowable under the interim Newcastle plan. EAST KING COUNTY COORDINATED WATER SYSTEM PLAN In 1989, pursuant to the state's Public Water Supply Act, east King County was designated as a critical water supply area. The City of Seattle has recently updated its Comprehensive Water Supply Plan, and individual water purveyors in the county have been updating their water service plans, defining their service areas consistent with existing land use plans, and studying options for future water supplies and distribution. WASHINGTON DEPARTMENT OF ECOLOGY STORMWATER PERMITTING The Department of Ecology has begun to regulate stormwater discharges on a watershed (Water Quality Management Area) basis. Five-year NPDES (National Pollutant Discharge Elimination System) permits will be issued for King County and eight other large and medium counties/municipalities in Washington. The permits require the implementation of five-year programs to address and finance priority needs for the quality of stormwater. King County has three permits that began in July 1995, one of which (the Cedar/Green) includes the May Creek basin. The County's water quality Chapter 11 Coordination and Planning 11-12 code, and the Surface Water Design Manual (see above) have been revised to assist businesses in protecting water quality and to assist the County in meeting its responsibilities under these permits. Some commercial and industrial enterprises, based on SIC (Standard Industrial Classification) codes, will also need to obtain stormwater permits and develop Stormwater Pollution Prevention Plans (SWPPPs). WASHINGTON STATE DEPARTMENT OF TRANSPORTATION HIGHWAY PLANNING The Washington State Department of Transportation (WSDOT) has proposed widening SR-900, easterly and northerly from Duvall Avenue within the Renton city limits to 1-90 in Issaquah. In 1992 the WSDOT published a Design Analysis Study that included three different project concepts; while no specific decisions have been made to date, evaluations of future land use/cover for this Conditions Report assumed that widening to at least four lanes will occur. The realignment of the intersection of SR-900 and SE May Valley Road to address safety concerns, and the reconstruction of the crossing of May Creek, will be completed in 1995-6. For the larger future project, the area of greatest environmental concern in the basin is the drainage of the North Fork of May Creek. In this subcatchment, the widening and realignment of SR-900 will affect Class-1 and -2 wetlands and Class-2 streams with salmonids, and in some locations it may be difficult to find sufficient room for both creek and roadway needs. Information from this conditions report and the basin plan will be valuable in the planning, analysis, design and mitigation of this project. Improvements have also recently been made to 1-405 for High Occupancy Vehicle (HOV) lane development. In connection with this project and others, old drainage problems near the May Creek crossing are being investigated and addressed by WSDOT and the City of Renton. Information from this conditions report has been useful in the development of this project. Chapter 11 Coordination and Planning 11-13 Chapter 12 References References CHAPTER 2 - INTRODUCTION Huckell/Weinman Associates, Inc. 1993. Final Environmental Impact Statement, Vol. 1, Fig. 2. King County. 1980. May Creek Basin Plan. King County Department of Planning and Community Development. Seattle, WA. CHAPTER 3 - LAND USE AND LAND COVER Buerge, David. 1984. Indian Lake Washington. The Weekly, August 1-7, 1984. City of Renton. 1991. Greater Renton Map. Renton Chamber of Commerce, Renton, WA. Fish, Edward R. 1969. The Past at Present in Issaquah, WA. GeoEngineers. 1991. City of Renton Critical Areas Maps. Renton, WA. King County. 1992. Annual Growth Data Book. King County Department of Parks, Planning and Resources. Seattle, WA, May 1992. King County. 1990a. Wetlands Inventory. 3 volumes. King County Department of Planning and Community Development. Seattle, WA. King County. 1990b. Sensitive Areas Map Folio. King County Department of Planning and Community Development. Seattle, WA. King County. 1983. Newcastle Community Plan and Area Zoning. King County Department of Planning and Community Development. Seattle, WA, December 1983. King County. 1979. Newcastle Community Plan Profile. King County Department of Planning and Community Development. Seattle, WA, February 1979. CHAPTER 4 - GEOLOGY AND GROUNDWATER Atwater, B.F., and A.L. Moore. 1992. A tsunami about 1,000 years ago in Puget Sound, Washington. Science 258: 1614-17. Atwater, B.F. 1987. Evidence for Great Holocene earthquakes along the outer coast of Washington State. Science 236: 942-44. References 12-1 Algermissen, S.T, D.M. Perkins, P.C. Thenhaus, S.L. Hanson, and B.L. Bender. 1990. Acceleration and Velocity Maps for the United States and Puerto Rico. U. S. Geological Survey Miscellaneous Field Studies Map, 1:7,500,000 scale. Armstrong, J.E., D.R. Crandell, D.J. Easterbrook, and J.B. Noble. 1965. Late Pleistocene stratigraphy and chronology in southwestern British Columbia and northwestern Washington. Geological Society of America Bull. 76: 321-30. Booth, D.B. 1987. Timing and processes of deglaciatiopn along the southern margin of the Corrdilleran ice sheet. Pages 71-90, In: Ruddiman, W F., and Wright, H.E., Jr., eds. North America and Adjacent Oceans during the Last Deglaciation. Vol. K- 3 of The Geology of North America. Boulder, Colorado: Geological Society of America. Booth, D.B. 1992. Geologic Map of the Maple Valley 7.5' Quadrangle, King County, Washington. Unpublished draft map, US Geological Survey. Booth, D.B. and J. P Minard. 1992. Geologic Map of the Issaquah 7.5' Quadrangle, King County, Washington. Miscellaneous Field Studies Map MF-2206, United States Geological Survey. Bretz, J.H. 1913. Glaciation of the Puget Sound region. Washington Geological Survey Bull. 8. 244 pp. Bucknam, R.C., E. Hemphill -Haley, and E.B. Leopold. 1992. Abrupt uplift within the past 1,700 years at southern Puget Sound, Washington. Science 258: 1611-14. Foster, H.L., and TN.V. Karlstrom. 1966. Ground Breakage and Associated Effects in the Cook Inlet Area, Alaska, Resulting from the March 27, 1964, Earthquake. U.S. Geological Survey Professional Paper 543-A. Galster, R.W, H.A. Coombs, and H.H. Waldron. 1989. Engineering geology in Washington: introduction. Washington Division of Geology and Earth Resources Bull. 78: 3-12. Goverment Land Office (GLO). 1865. Map of Township No. 24 North., Range No. 5 East. Gower, H.D., J.C. Yount, and R.S. Crosson.1985. Seismotectonic Map of the Puget Sound Region, Washington. Miscellaneous Investigations Map 1-1613, U.S. Geological Survey Hall J.B., and K.L. Othberg. 1974. Thickness of Unconsolidated Sediments, Puget Lowland, Washington. Map GM-12, Division of Geology and Earth Resources, Washington Department of Natural Resources. Heaton, T.H., and S.H. Hartzell. 1987. Earthquake Hazards on the Cascadia Subduction Zone. Science 236: 162. References 12-2 Hopper, M.G., et al. 1975. A Study of Earthquake Losses in the Puget Sound, Washington Area. U.S. Geological Survey Open -File Report 75-375. Jacoby, G.C., P.L. Williams, and B.M. Buckley. 1992. Tree ring correlation between prehistoric landslides and abrupt tectonic events in Seattle, Washington. Science 258: 1621-3. Karlin, R.E., and S.E.B. Abella. 1992. Paleoearthquakes in the Puget Sound Region recorded in sediments from Lake Washington, U.S.A. Science 258: 1617-20. King County. 1993. Cedar River Current and Future Conditions Report, King County Surface Water Management Division, Seattle, WA. Liesch, B.A., C.E. Price and K.L. Walters. 1963. Geology and Ground -water Resources of Northwestern King County, Washington, Water -Supply Bulletin No. 20, Dept. of Water Resources, WA, 260pp. Luzier, J. E..1969. Geology and Ground -water Resources of Southwestern King County, Washington, Water -Supply Bulletin No. 28, Dept. of Water Resources, WA, 260pp. McCulloch, D.S. 1966. Slide -induced Waves, Seiching and Ground Fracturing Caused by the Earthquake of March 27, 1964, at Kenai Lake, Alaska. Geological Survey Professional Paper 543-A. Mullineaux, D.R. 1965. Geologic Map of The Renton Quadrangle, King County, Washington. Geologic Quadrangle Map GQ-405, United States Geological Survey. Noson, L.L., A. Qamar, and G. W. Thorsen. 1988. Washington state earthquake hazards. Washington Division of Geology and Earth Resources Information Circular 85, 77p. Rosengreen, TE. 1965. Surficial Geology of the Maple Valley and Hobart Quadrangles, Washington. M.S. Thesis, University of Washington, 71 pp. Schuster, R.L., R.L. Logan, and PT Pringle. 1992, Prehistoric Rock Avalanches in the Olympic Mountains, Washington. Science 258: 1620-1. Walsh, T.J. 1982. Coal rank and thermal maturation in King County, Washington. Washington Geologic Newsletter 10(1): 11. Walsh, T. 1990. Geologic history of the Tiger Mountain State Forest, Washington. Geologic Newsletter 18(1): 35-6. Waldron, H.H., B.A. Liesh, D. R. Mullineaux, and D.R. Crandell. 1962. Preliminary Geologic Map of Seattle and Vicinity, Washington. Miscellaneous Geologic Investigations Map 1-354, US Geological Survey. References 12-3 Yount, J.C., G.R. Dembroff, and G.M. Barats. 1985. Map Showing Depth to Bedrock in the Seattle 30' by 60' Quadrangle, Washington. Miscellaneous Field Studies Map MF-1692, US Geological Survey. CHAPTER 5 - HYDROLOGY AQUA TERRA Consultants. 1991. Hydrological Simulation Program —Fortran, User's Manual for Release 10. US Environmental Protection Agency, Athens, GA. AQUA TERRA Consultants. 1993. May Creek Basin Plan Hydrology Calibration Report. King County Surface Water Management and City of Renton Surface Water Utility. Dinicola, R.S. 1990. Characterization and Simulation of Rainfall -Runoff Relations for Headwater Basins in Western King and Snohomish Counties, Washington. Water - Resources Investigations Report 89-4052. US Geological Survey, Tacoma, WA. Federal Emergency Management Agency (FEMA). 1989. Flood Insurance Study, King County, Washington and Incorporated Areas. Washington, DC. U.S. Water Resources Council. 1981. Guidelines for Determining Flood Flow Frequency, Bulletin #17B of the Hydrology Committee. Washington, DC. CHAPTER 6 - FLOODING AQUA TERRA Consultants. 1993. May Creek Basin Plan HEC-2 Calibration Report. King County Surface Water Management and City of Renton Surface Water Utility. Booth, D.B. 1991. Urbanization and the Natural Drainage System —Impacts, Solutions, and Prognoses. Northwest Environmental Journal 7: 93-118. Entranco. 1995. Gypsy Subbasin Analysis: Technical Memorandum No. 2. City of Renton Surface Water Utility. Federal Emergency Management Agency (FEMA). 1989. Flood Insurance Study, King County, Washington and Incorporated Areas. Washington, DC. INCA Engineers, Inc. 1993. Valley cross -sections, May Creek Basin Plan. Bellevue, WA. King County. 1993. May Creek floodplain survey. Seattle, WA. United States Army Corps of Engineers Hydrologic Engineering Center. 1991. HEC-2 Water Surface Profiles User's Manual. Davis, CA. Washington State Department of Transportation (WSDOT). 1992. Feasibility Study for SR 900 Expansion. Olympia, WA. References 12-4 CHAPTER 7 - SEDIMENT EROSION AND DEPOSITION Bathhurst, J.C. 1987. Critical conditions for bed material movement in steep, boulder - bed streams. In: Erosion and Sedimentation in the Pacific Rim. Proceedings of the Corvallis Symposium, Aug. 1987. IAHS Publ. No. 165. City of Renton. 1993. Honey Creek sewerline access road interim repairs, Project No. S-2029. Leopold, L.B., and D.L. Rosgen. 1990. Movement of Bed Material Clasts in Gravel Streams. Applied Fluvial Geomorphology, short course manual. Lepp, L.R., C.J. Koger, and J.A. Wheeler. 1993. Channel erosion in steep -gradient, gravel -paved streams. Bull. Assoc. Engin. Geol. 30(4): 443-54. United States Geological Survey (USGS). 1983. 1:25,000-scale metric topographic-bathymetric map of Bellevue South, Washington. US Geological Survey and National Ocean Service. United States Geological Survey (USGS). 1983. 1:25,000-scale metric topographic-bathymetric map of Renton, Washington. US Geological Survey and National Ocean Service. CHAPTER 8 - WATER QUALITY Bell, Milo C. 1986. Fisheries Handbook of Engineering Requirements and Biological Criteria. US Army Corps of Engineers, North Pacific Division, Portland, OR. Bennett, T, King County Surface Water Management Division, personal correspondence, July 9, 1993. Carriveau, U.S. Environmental Protection Agency, personal communication, March 24, 1994. CH2M Hill. 1988. Delineation of Aquifer Protection Areas for City of Renton Wells 4 and 5A. Letter report from S.M. Brown to Ron Olsen, City of Renton, June 14, 1988. City of Seattle Water Department Water Quality personnel, personal correspondence, May 1982 as cited in Galvin D.V and Moore R.K. (1982). Environmental Systems Research Institute (ESRI(H)). 1991. Surface Modeling with TINT"' Galvin, D.V. and R.K. Moore. 1982. Toxicants in Urban Runoff. Metro Toxicant Program Report #2. Toxicant Contol Planning Section Water Quality Division, Municipality of Metropolitan Seattle (Metro). References 12-5 Gammon, J.R. 1970. The effect of inorganic sediment on stream biota, EPA 18050 DWC 12/70, Washington D.C., as cited in King County (1993). GeoEngineers. 1992. Summary Report, Critical and Resource Areas Evaluation, City of Renton, Washington. Draft, January 22, 1992. Griffin et al., 1980, as cited in Galvin and Moore (1982). Hall, K.J., and B.C. Anderson. 1988. Toxicity and chemical composition of urban stormwater runoff. Can. J. Civil Eng. 15: 98 - 106. Harr, R.D., and R.L. Fredriksen. 1988. Water quality after logging small watersheds within the Bull Run watershed, Oregon. Water Resources Bull. 24: 1103 - 1111. Hicks, B.J., J.D. Hall, PA. Bisson, and J.R. Sedell. 1991. Responses of Salmonids to Habitat Changes. In: W.R. Meehan, ed. Influences of Forest and Rangeland Management on Salmoid Fishes and their Habitats. Am. Fish. Soc. SPEC 19: 483- 518. Horner, R. 1990. Current and projected status of wetlands in the East Lake Sammamish Planning Area. Puget Sound wetlands and Stormwater Management Research Program, University of Washington, Seattle, WA. King County. 1992. Small Farm Nonpoint Pollution Project, Small Farms Program. King County Conservation District. Renton, WA. King County. 1980. May Creek Basin Plan. King County Department of Planning and Community Development. Seattle, WA. King County. 1990. East Lake Sammamish Basin Conditions Report —Preliminary Analysis. King County Surface Water Management Division, Seattle, WA. King County. 1991. Protecting ground water —A strategy for managing agricultural pesticides and nutrients. Draft, July 1991. King County. 1993a. Cedar River Current and Future Conditions Report. King County Surface Water Management Division, Seattle, WA. King County. 1993b. Forestry assessment for May Creek basin. King County Environmental Division. King County. 1994. Changes in Cedar River Water Quality and Potential Impacts on Lake Washington Water Quality, Fisheries, and Habitat. King County Surface Water Management Division, Seattle, WA. Kirkpatrick, D. 1990. Evaluating the Effectiveness of Stormwater Management Policies in Protecting Streams. M.S. Thesis, University of Washington. References 12-6 Lloyd, D.S. 1987. Turbidity as a Water Quality Standard for Salmonid Habitats in Alaska. North American Journal of Fisheries Management. 7: 34-45. Metropolitan Washington Council of Governments, Water Resources Planning Board. 1983. Pollutant removal capability of urban best management practices in the Washington metropolitan area. Final Report. Novotny, V , and H. Olem. 1994. Water Quality: Prevention, Identification and Management of Diffuse Pollution. Van Nostrand Reinhold, New York. Omernick, 1977, as cited in Kirkpatrick (1990). O'Shea, M.L., and R. Fields. 1992. The Detection of Pathogens in Storm Generated Flows: Water Environment Federation 65th Annual Conference and Exposition, New Orleans, LA. Persaud D., R. Jaagumagi, and A. Hayton. 1991. The provincial sediment quality guidelines, Water Resources Branch, Ontario Ministry of the Environment. Draft. Puget Sound Cooperative River Basin Team (PSCRBT). 1992. Lower Cedar River Watershed, King County Washington. Lacey, WA. Puget Sound Water Quality Authority (PSWQA). 1989. Puget Sound Water Quality Management Plan, Seattle, WA. Purell, Washington Department of Ecology, personal communication, March 25, 1993. Reinelt, L., and R. Horner. 1994. Pollutant removal from stormwater by palustrine wetlands based on a comprehensive budget. In: Ecological Engineering. Sartor et al., 1974 as cited in Galvin and Moore (1982). Sato, B., 1994, Washington Department of Ecology, personal communication, August 1994. Schlorff E., 1993, Washington Department of Ecology, personal communication as cited in King County (1993). Schueler, 1987, as cited in Kirkpatrick (1990). Seattle Engineering Department. 1993. Pipers Creek Bacteriological Source Tracking Investigation. Seattle -King County Department of Public Health (SKCDPH). 1992. Status of Ground Water Management Programs in King County —March 28, 1992. Seattle -King County Department of Public Health (SKCDPH). 1993a. May Creek Basin Report on Small Quantity Hazardous Waste Generators. References 12-7 Seattle -King County Department of Public Health (SKCDPH). 1993b. May Creek Basin Report on Underground Storage Tanks. Seattle -King County Department of Public Health (SKCDPH). 1993c. On -site septic system studies for the May Creek Basin. Seattle -King County Department of Public Health (SKCDPH). No date. Appendix A. Recharge Potential Mapping Criteria and Rationale. Storer, R., King County Surface Water Management Division, personal correspondence to Mick Zevart, March 30, 1993. Terrell, C.R., and PB. Perfetti. 1991. Water Quality Indicators Guide: Surface Water. USDA, Soil Conservation Service, SCS-TP-161. United States Environmental Protection Agency (EPA). 1977. Guidelines for the pollutional classification of Great Lakes harbor sediments. EPA, Region V, April, 1977. United States Environmental Protection Agency (EPA). 1983, as cited in Kirkpatrick (1990). United States Environmental Protection Agency (EPA). 1986. Quality criteria for water, 1986, EPA 440/5-86-001, Washington D.C. United States Environmental Protection Agency (EPA). 1988a. Must for UST's. EPA 530/UST-88, Washington D.C. United States Environmental Protection Agency (EPA). 1988b. Interim sediment criteria values for nonpolar hydrophobic organic contaminants. SCD 17. Washington, D.C. United States Environmental Protection Agency (EPA). 1995. Draft Watershed Analysis, CWA/Aquatic Module Integration Considerations. 25 pp. United States Geological Survey (USGS). 1986. Quantity and Quality of Storm Runoff from Three Urban Catchments in Bellevue, WA. Water Resources Investigations Report 86-4000. Washington Department of Ecology (WDOE). 1988a. Draft nonpoint pollution assessment and management program: Water quality program. Olympia, WA as cited in King County (1993). Washington Department of Ecology (WDOE). 1988b. Fact Sheet: Proposed Consent Decree on a Phase I Remedial Investigation and Feasibility Study for the Quendall Terminals Site. Washington Department of Ecology (WDOE). 1991. Summary of criteria and guidelines for contaminated freshwater sediments, September 1991. References 12-8 Washington Department of Ecology (WDOE). 1993. Underground storage tank listing, January 4 and February 10. Welch, E.B. 1992. Ecological Effects of Wastewater, 2nd ed. Chapman & Hall, London. Wetzel, R.G. 1975. Limnology. W.B. Saunders Co., Philadelphia. Wilber and Hunter, 1977, as cited in Kirkpatrick (1990). Wisconsin Department of Natural Resources (WDNR). 1985. Report of the technical subcommittee on determination of dredge material suitability for in -water disposal. Wisconsin Department of Natural Resources (WDNR). 1990. Development of sediment quality criteria for the Little Menomonee River/Moss-American Superfund Site. Memo from D. Schuettpelz to M. Giesfeldt. Zinner, L., Washington Department of Ecology, personal communication, August 24, 1993. CHAPTER 9 - AQUATIC HABITAT AND FISH Armour, C.L., D.A. Duff and W. Elmore. 1991. The effects of livestock grazing on riparian and stream ecosystems. Fisheries 16(1): 7-11. Askins, R.A. 1995. Hostile landscapes and the decline of migratory songbirds. Science 267: 1956-7. Beschta, R.L., and W.S. Platts. 1986. Morphological features of small streams: significance and function. Water Resources Bull. 22(3): 369-79. Bilby, R. E. 1985. Influence of stream size on the function and characteristics of large organic debris. In: Proceedings of the West Coast Meeting of the National Council of the Paper Industry for Air and Stream Improvement, Portland, OR. Bilby, R.E., and J.W. Ward. 1989. Changes in characteristics and function of woody debris with increasing size of streams in western Washington. Trans. of the American Fisheries Soc. 118: 368-378. Bilby, R.E., and J.W. Ward. 1991. Characteristics and function of large woody debris in streams draining old -growth, clear-cut, and second -growth forests in southwestern Washington. Can. J. Fisheries and Aquatic Sciences 48: 2499-2508. References 12-9 Bisson, PA. 1987. Large woody debris in forested streams in the Pacific Northwest: past, present , and future. Pages 143-90, In: E.O. Salo and TW Cundy, eds. Symposium on Streamside Management: Fishery and Forestry Interactions. Coll. For. Res., Contr. No. 57, University of Washington, Seattle, WA. Bisson, P.A., TP Quinn, G.H. Reeves, and S.V Gregory. 1992. Best management practices, cumulative effects, and long-term trends in fish abundance in Pacific Northwest river systems. Pages 189-232, In: R.J. Naiman, ed. Watershed management: Balancing Sustainability and Environmental Change. Springer- Verlag, NY Bjornn, TC., et al. 1977. Transport of Granitic Sediment in Streams and its Effects on Insects and Fish. Bull. 17. Moscow, ID: University of Idaho; Forest, Wildlife, and Range Experiment Station. Booth, D.B. 1991. Urbanization and the natural drainage system -impacts, solutions, and prognosis. Northwest Environmental Journal 7(1): 93-118. Brown, E.R., ed. 1985. Management of Wildlife and Fish Habitats in Forests of Western Oregon and Washington. U.S.D.A. Forest Service, Corvallis, OR. Cedarholm, C.J., and E.O. Salo. 1979. The Effects of Landslide Siltation on Salmon and Trout Spawning Gravels of Steqauleho Creek and the Clearwater River Basin, Jefferson County, Washington, 1972-1978. Seattle, WA: University of Washington; 1979; Final Report, Part III, Fisheries Research Institute, FRI-UW-7915. Cooper, J.W. 1987. An overview of estuarine habitat mitigation projects in Washington State. Northwest Environmental Journal 3(1): 112-127. Franklin, J.F. 1992. Scientific basis for new perspectives in forests and streams. Pages 25-72, In: R.J. Naiman, ed. Watershed management: Balancing Sustainability and Environmental Change. Springer-Verlag, NY. Franklin, J.F., and C.T. Dyrness. 1973. Natural Vegetation of Oregon and Washington. Pacific Northwest Forest and Range Experiment Station., USDA Forest Service, Corvallis, OR. Hicks, B.J., J.D. Hall, PA. Bisson, and J.R. Sedell. 1991. Response of salmonids to habitat changes. In: W.R. Meehan, ed. Influences of Forest and Rangeland Management on Salmoid Fishes and their Habitats. American Fisheries Society Special Publication 19. Am. Fish. Soc. SPEC 19: 483-518. Hunter, C.J. 1991. Better Trout Habitat: A Guide to Stream Restoration and Management. Island Press, Washington D.C. 320 pp. King County. 1980. May Creek Basin Plan. King County Surface Water Management Division, Seattle, WA. King County Environmental Division. 1990a. King County Sensitive Areas Folio. References 12-10 King County Environmental Division. 1990b. King County Wetland Inventory. King County. 1990c. Hylebos/Lower Puget Sound Conditions Report. King County Surface Water Management Division, Seattle, WA. Kunz, Kathy, M. Rylko, and E. Somers. 1988. An assessment of wetland mitigation practices pursuant to Section 404 permitting activities in Washington state. Pages 515-531, In: Proceedings, First Annual Meeting on Puget Sound Research, March 18-19, Vol. 2. Puget Sound Water Quality Authority, Seattle. Lloyd, D.S. 1987. Turbidity as a Water Quality Standard for Salmonid Habitats in Alaska. North American Journal of Fisheries Management. 7: 34-45. Luchetti, G.L., and R.B. Fuerstenberg. 1993. Urbanization, habitat conditions and fish communities in western King County with implications for management of wild coho salmon. Proc. American Fish. Soc. Coho Workshop, Nanaimo, British Columbia, May 1992. MacDonald, L.H., A.W. Smart and R.C. Wissmar. 1991. Monitoring Guidelines to Evaluate Effects of Forestry Activities on Streams in the Pacific Northwest and Alaska. CSS/EPA. Marcus, M.D., M.K. Young, L.E. Noel, and B. A. Mullan. 1990. Salmonid-habitat Relationships in the Western United States: A Review and Indexed bibliography. USDA Forest Service, General Technical Report RM-188. Naiman, R.J., ed. 1992. Watershed Management: Balancing Sustainability and Environmental Change. Springer-Verlag, NY Puget Sound Water Quality Authority. 1986. Issue Paper: Habitat and Wetlands Protection. Seattle, WA. Reiser, D.W., M.P. Ramey, and TA. Weshe. 1992. Flushing flows. Pages 91-138, In: J.A. Gore and G.E. Petts, eds. Alternatives in Regulated River Management. CRC Press, Inc. Boca Raton, FL. Reppert, R.T., W. Sigelo, E. Stakhiv, L. Messman, and C. Meyer. 1979. Wetland Values: Concepts and Methods for Wetlands Evaluation. IWR Research Report 79- R-1, U.S. Army Corps of Engineers, Institute for Water Resources, Fort Belvoir, VA. Richter, K.O., A. Azous, S.S. Cooke, R.W. Wissman, and R.R. Horner. 1991. Effects of stormwater runoff on wetland zoology and wetland soils characterization and analysis. Puget Sound Wetlands and Stormwater Management Research Program: Fourth Year of Comprehensive Research. Robinson, S.K., F.R. Thompson III, T.M. Donovan, D.R. Whitehead, and J. Faaborg. 1995. Science 267: 1987-90. References 12-11 Rylko, M. and L. Storm. 1991. How much wetland mitigation are we requiring? or, Is no net loss a reality? In: Proceedings, Second Annual Meeting on Puget Sound Research. Puget Sound Water Quality Authority, Seattle. Schlosser, I.J. 1991. Stream fish ecology: a landscape perspective. BioScience 41: 704-712. Sedell, J.R., and F.H. Everest. 1991. Historic changes in pool habitat for Columbia River Basin salmon under study for TES listing. Draft report. USDA, Forest Service, Corvallis, OR. Terborgh, J. 1989. Where Have All the Birds Gone? Essays on the Biology and Conservation of Birds that migrate to the American tropics. Princeton University Press. Thorne, R.E., and J.J. Ames. 1987. A note on the variability of marine survival of sockeye salmon (Oncorhynchus nerka) and the effects of flooding on spawning success. Can. J. Fish. Aq. Sci. 44. United States Fish and Wildlife Service (FWS). 1985. National Wetland Inventory. Washington Department of Fisheries. 1992. Salmon 2000 Technical Report phase 2: Puget Sound Washington Coast and Integrated Planning. Washington Department of Fisheries, Washington Department of Wildlife, and Western Washington Treaty Indian Tribes. 1993. 1992 Washington State Salmon and Steelhead Stock Inventory (SASSI). Olympia, Washington. March 1993. CHAPTER 11 - COORDINATION AND PLANNING Tiffany, C., G. Minton, and R.F. Thomas. 1990. Erosion and sedimentation control: an evaluation of BMPs on construction sites in King County, Washington, January 1988 - April 1989. References 12-12 Appendices APPENDIX A OBSERVED CONDITIONS SUMMARY Appendix A May Creek Basin Observed Conditions Summary Page 1 of 17 Title Primary Secondary Description Subject Subject Basinwide 1. Habitat aquatic water quality Wetland habitats are generally in poor ecological health, resulting from a variety of Degradation habitat and impacts. Riparian areas cleared or substantially altered in many locations. There is a land cover scarcity of instream LWD throughout the basin; recruitment of large woody debris #' (LWD) is poor due to past removal of riparian forest and domination of existing riparian forests by deciduous trees. This is particularly the case in May Cr. canyon, where there is insuffici-ent LWD to maintain pools. Two-thirds of existing forest vegetation in the basin will likely be lost to future residential development. In many locations the streamcourses, wetlands, and ravines are being used to dump yard waste, old appliances, and other debris. Basinwide 2. Livestock -keeping water quality aquatic Pastures are, in general, overgrazed throughout the rural and suburban areas. Animal Practices * habitat, density is too high in many pastures. BMPs are absent in many locations, and animals erosion have direct access to streams and wetlands in many locations, with consequent destruction of streambank vegetation, stream channels, and fish habitat, and water temperature elevation. Fecal matter and eroded soil are entering the streams, contributing to coliform pollution, elevated phosphorus, and other problems. R:l .invvide 3. Fecal Coliform water quality Fecal coliform concentrations during storm events exceeded state criteria at all Pollution + stations. Both livestock manure and pet wastes can contribute to the fecal coliform loading. Onsite sewage systems in several locations are in failing or pre -failing condition. Basinwide 4. Urban and Road- water quality Copper, lead, and zinc are entering the water from road runoff and the urbanized related Nonpoint ,r Honey Creek area. High levels of total suspended solids are being released by new Pollution construction sites and quarry operations. Phosphorus levels are higher than is good for streams and lakes: contributors include fecal matter, construction runoff, quarry runoff. Basinwide 5. Future land use water Stormwater runoff and peak stream flows will increase due to future development. Stormwater ,r,r quality, The urban areas (currently in the western and southern portions of the basin) will infill Runoff drainage, to suburban (medium) and urban (high, multifamily, and commercial) densities. flooding Residential use will double basinwide: 2/3 of existing forest vegetation will likely be lost to this development. Re -location of the Urban Growth Boundary westward in the basin will help to control future increases in stormwater flow, but additional rural -density development will still add considerable amounts of impervious surface and runoff to the basin. •,r* Most Significant ** Very Significant * Significant [no starsl Less Significant Page 2 of 17 Subarea Tributary & River Primary Secondary Description Number Mile Subject Subject Lower Basin May Creek n.H. water quality Urban area and urbanization impacts on water quality. Locations with the highest 0282 and + readings were also generally among the highest in the basin. its Fecal coliform counts were above standard in all locations, but highest in Honey tributaries Creek and China creeks, and near the mouth of May Creek. Loadings of metals were elevated in a number of locations, particularly in Honey Creek, the stormline at NE 27th Street, and downstream from 1-405. Total Phosphorus exceeded guidelines, and was highest in China Creek, May Creek mouth, and Honey Creek. Total Suspended Solids were also highest at these three locations. Lower Basin May Creek 0.0 to sediment flooding, Bedload and sediment naturally deposit on the delta, but deposition has increased at 0282 0.4 deposition erosion, outlet of May Creek and at a right-angle bend at RM 0.2. Increased peak flows in May * water Creek deliver more sediment, and the right-angle turn slows the stream velocity and quality reduces sediment -carrying capacity. Creek is channelized, and natural channel migration across delta is prevented. Frequency of dredging has increased to enable commerce to continue. Riprap is also eroding in places in peak storms. Future: increased sedimentation levels will continue or worsen with increased peak flows and development. Lower Basin May Creek 0.0 to aquatic Riparian vegetation, habitat diversity , cover are lacking in lower 0.2 mile. 0282 0.2 habitat Future: mitigation for dredging activities at the creek mouth will restore some of this vegetation. Lower Basin May Creek 0.2 to erosion water One of two sets of alignments for a new Metro sewage interceptor line would place a 0282 2.1 , * quality, gravity -feed sewage line within the canyon of May Cr., from RM 0.1 to RM 2.1, LSRA aquatic where it would link with Renton's Honey Cr. interceptor. The gravity line would also from 0.2 habitat collect from current or future parts of the District 107 sewage system. The second to 3.9 set of alternatives would convey a pumped line over the Renton Highlands. The gravity sewer line and its supportive access roads and facilities would result in impacts to the creek, wetlands, and riparian areas due to filling, bank armoring, and changes in hydrology. The sewer line would be excavated into the valley wall in several locations, and has the potential to worsen some of the current sites of slumps, rotations, slides, and seeps, and to initiate new problem sites; slope failure could result in system failure. Construction, access roads, hydrologic and hydraulic changes, erosion and sedimentation all could adversely affect both fish and wildlife populations and habitat in the LSRA. Future: a possible Phase-2 extension of the line would go further up the canyon to the rural boundary. Lower Basin May Creek 0.2 to aquatic The riparian forest lacks conifers, and the understory has few or no young trees. 0282 3.6 habitat There is insufficient LWD to maintain pools. The channel from RM 0.2 to 0.5 LSRA apparently was straightened in the past. from 0.2 Future: the lack of young trees in understory may lead to gradual loss of forest to 3.9 canopy as mature deciduous trees die. Current LWD deficiencies may worsen and stream habitat quality may decline. Page 3 of 17 Subarea ributary & FT River Primary Secondary Description Number Mile Subject Subject Lower Basin May Creek 0.4 drainage flooding An 18" culvert passing under 1-405 is undersized. Runoff flows into ditch prior to 0282 LSRA * entering 12" culvert, which then empties to ditch and May Cr. Water backs up and from 0.2 floods property between 1-405 and L. Washington Blvd. N. up to two feet in depth. to 3.9 Future: current work by WSDOT in connection with 1-405 HOV lane may resolve this problem. Lower Basin May Creek 0.4 to aquatic Large area of Wetland 34, along eastern edge of May Creek Park, was filled. 0282 0.65 habitat Future: without effective enforcement of regulations, incremental wetland acreage LSRA losses will likely continue due to unpermitted activities. from 0.2 to 3.9 Lower Basin May Creek 0.6 to erosion May Creek flows through a canyon cut into the glacial till and outwash soils. Perched 0282 3.9 aquifers provide hydrostatic pressure that leads to slope movements along the valley LSRA walls. from 0.2 Future: slope movements are a natural feature of the canyon and will continue. to 3.9 Additional routing of drainage and runoff to canyon edge or additional utility crossings could increase these movements. Lower Basin May Creek 0.8; 1.8; water quality aquatic Pipes and hoses were found crossing May Creek at these locations; further 0282 3.9; habitat investigation needed. LSRA from 0.2 to 3.9 Lower Basin May Creek 1.2 ; erosion water quality Drainage and storm flow from apartment complex has been concentrated over valley 0282 LSRA ,r wall. Washout and gully is approximately 50 feet wide with total volume of approx. from 0.2 2,600 cu. yds. Chronic erosion and deposition of fines into May Creek is occurring, to 3.9 affecting LSRA and downstream sediment deposition. Lower Basin May Creek 1.2 erosion Six to eight feet of fill are encroaching on edge of canyon wall. The fill is unable to 0282 LSRA revegetate due to steepness and looseness of material. from 0.2 to 3.9 Lower Basin May Creek 1.4 to erosion Culverted road crossing is being undermined along NE 31st St. in lower section of 0282 1.6 canyon. LSRA Future: peak flows will increase in canyon. from 0.2 to 3.9 Lower Basin May Creek 1 .5, 2.1 erosion Motor and mountain bike use is degrading stream banks and trails. 0282 LSRA from 0.2 to 3.9 Page 4 of 17 Subarea Tributary & River Primary Secondary Description Number Mile Subject Subject Lower Basin May Creek 1.8 erosion Site of storm sewer pipeline failure (caused by slumping of saturated fill) has not fully 0282 LSRA revegetated, allowing erosion to continue. from 0.2 to 3.9 Lower Basin May Creek 1.8 erosion Trash, concrete, yard waste, and soil have been dumped over valley wall into an old 0282 LSRA landslide area. A berm of soil, yard waste, etc. has accumulated and will probably from 0.2 also be shoved or fall over the hillside. to 3.9 Lower Basin May Creek 1.9 elusion drainage An 18" corrugated metal pipe has separated at the joint, creating two failure areas 0282 LSRA • totalling approx. 600 cubic yards. Sediment is delivered to LSRA. from 0.2 to 3.9 Lower Basin May Creek Near 2.3 erosion drainage Erosion of outwash soils in canyon due to runoff piped to canyon rim in May Creek 0282 LSRA Park near SE 95th Way and 122nd Ave. SE. from 0.2 to 3.9 Lower Basin May Creek 2.4 erosion aquatic Motor bike access along natural gas pipeline is causing erosion from the steep, open 0282 LSRA habitat embankment into May Creek. Revegetation is prevented; damage to salmon redds is from 0.2 possible. to 3.9 Lower Basin May Creek 3.0 11 aquatic Natural gas pipeline is not buried sufficiently at crossing of May Creek, creating a fish 0282 LSRA habitat passage barrier that is mitigated by a fish ladder. This ladder is a key access point for from 0.2 + anadromous fish passage for seven months. Depending on the instream flows and to 3.9 sediment loads, the ladder can cease functioning and itself become a fish passage barrier, causing upper basin to become inaccessible to upstream passage of anadromous fish for unknown lengths of time. Field observations indicate that ladder monitoring and maintenance are inadequate. Lower Basin May Creek 3.0 erosion aquatic Pipeline and electric utility corridor has steep slopes that are being used by all -terrain 0282 LSRA habitat vehicles. This use keeps part of the slope bare of vegetation, and the exposed gravel from 0.2 and dirt is eroding from the steep slope into May Creek. Clearing for the utility lines to 3.9 has removed all trees and riparian vegetation. Future: conditions will continue or worsen without corrective action. Lower Basin May Creek 3.7 erosion water quality House construction near stream. Creek bank slumps about 50 feet from house, 0282 LSRA exposing compact glacial advance outwash sediments. from 0.2 to 3.9 Page 5 of 17 Subarea Tributary & River Primary Secondary Description Number Mile Subject Subject Lower Basin Trib. 0283A 0.0 to aquatic Trib. 0283A is tightlined for a substantial distance; the remaining riparian area is 0.2 habitat greatly disturbed. Impacts to Wetland 36 from filling, grazing, dumping, and by removal of buffer vegetation. Lower Basin Gypsy 0.0 to erosion sediment Gypsy Creek is deeply incised into erosive outwash sands below RM 0.35. From RM Creek 0284 0.5 + deposition, 0.35 to RM 0.5 the channel has recently incised into compacted till. Increased runoff water quality from upstream urbanization is encouraging this channel downcutting. Together with bank sloughing in some locations, the erosion is creating a wide channel. Large amounts of suspended sand and sediment are delivered to May Creek, affecting the LSRA and downstream sediment deposition. Future: Downcutting will worsen as remaining unbuilt areas are developed and more stormwater runoff is generated. Lower Basin Gypsy 0.2 drainage erosion, The creek is conveyed under an old road (probably for logging) crossing by a four -foot Creek 0284 ,r flooding, culvert with 15 feet of loose fill dirt on top. At times the culvert can be suspended aquatic above stream and be a barrier to upstream fish passage. (However, upstream channel habitat is downcut, largely barren of fish habitat with no pools and little LWD). Future: If the culvert were to clog, backed -up water could blow out the culvert and fill, with possible flooding and damage downstream at the alluvial fan. Lower Basin Gypsy 0.5 to water quality Future: Wetland 9 is vulnerable to increases in nonpoint pollution loading and runoff Creek 0284 0.8 as development progresses in the area. Wetland 9 LSRA erosion Lower Basin Honey 0.2 to water Renton sewage pipeline road has oversteepened sidecast fill that encroaches on the Creek 0285 1.4 + quality, floodway of Honey Cr., directing creek flow into valley wall. Sidecast road fill and LSRA aquatic valley wall are eroding and slumping, introducing fines into the creek and downstream from 0.0 habitat LSRAs. Drain pipes and ditches are plugging and existing controls are failing in some to 0.4 locations. . Lower Basin Honey 0.35 erosion water Former gravel pit site is open to the public and used by all -terrain vehicles (ATVs) Creek 0285 quality, which cut trails through advance outwash and sand, and cause erosion and discharge aquatic of sediment fines into the creek. habitat Lower Basin Honey 0.35 aquatic Culvert blocks upstream fish passage under some flow conditions. Approximately 0.7 Creek 0285 habitat mile of usable habitat is available upstream of barrier. Lower Basin Honey 0.5 erosion Road is eroding away and riprap in stream is collapsing around bridge. Creek 0285 Page 6 of 17 Subarea Tributary & River Primary Secondary Description Number Mile Subject Subject Lower Basin Homey 0.5 erosion water quality Large landslide has been deeply incised (a 20-foot channel into the bank) and delivers Creek 0235 . sediment to the creek and downstream LSRAs. Future: this erosion will continue and worsen unless stabilized. Lower Basin Honey 0.6 erosion Erosion is occurring due to lack of culvert across pipeline access road. Creek 0285 Lower Basin Honey 0.8 erosion Fill is eroding around culvert. Creek 0285 Lower Basin Honey 0.9 and erosion Renton sewer pipeline exposed in creek bed. Creek 0285 1.0 Lower Basin Honey 1.0 erosion Recreational bike activity causing erosion down pipeline track. Creek 0285 Lower Basin Honey 1.1 to aquatic Entire instream channel has been riprapped from gas/powerline crossing to 130th Creek 0285 1.4 habitat Ave. SE, destroying fish habitat and reducing diversity. Lower Basin Honey 1.25 sediment erosion Partially blocked culvert due to sediment deposition from upstream erosion. Creek 0285 deposition Lower Basin Honey 1.4 to aquatic Honey Creek is tightlined through a heavily developed commercial area. The pipe is a Creek 0285 2.0 habitat barrier to fish movement. Lower Basin Honey Near 2.0 drainage Drainage alterations, construction and increased runoff have caused several localized Creek 0285 flooding problems in this area. Lower Basin Honey Near 3.0 drainage flooding Filling, drainage alterations, construction, clearing, and associated runoff have caused Creek 0285 several localized flooding problems in this area. Lower Basin Trib. 0285A 0.1 to aquatic • drainage Substantial amounts of fill material have been placed in Wetland 50; filling has 0.2 habitat reduced storage and increased runoff. Buffers have been cleared of vegetation. Lower Basin Newport 0.0 to erosion Some channel incision and sedimentation was observed downstream of the road Hills Creek 0.4 crossing at RM 0.4, both upstream and downstream of the railroad fill and pond at 0286 RM 0.2. Page 7 of 17 Subarea Tributary & River Primary Secondary Description Number Mile Subject Subject Lower Basin Newport 0.2 dramage erosion, An old railroad crossing ("landfill trestle") impounds a pond (Wetland 12). The outlet Hills Creek ,r+ aquatic from the pond is a vertical standpipe with horizontal screen, and could easily plug. 0286 habitat, The standpipe connects to a larger horizontal clay pipe that outlets at the water quality downstream face of the embankment; the end of the pipe has cracked and caused some erosion, but the remainder of the pipe is intact. A portion of the creek's inflow to the pond seeps through the fill instead of exiting through the outlet pipe. A dam - break analysis indicates that remedial action should be taken to prevent debris blockage at the outlet: if this is done, downstream houses would not be threatened or flooded by a failure of the embankment for all reasonable rainfall and flood events up to and including the WDOE design event. The railroad fill is also a fish passage barrier. Lower Basin Newport 0.5 drainage sediment A culvert has filled with sediment and is partially blocked. Hills Creek deposition, structure (a 24" clay pipe) is broken and has caused some erosion next to the lower 0286 erosion face. Lower Basin Boren and 0.0 to aquatic Channel to RM 0.5 is incised into and constrained by steep valley walls. Lack of LWD China 2.4 habitat throughout this stream reach has resulted in poor channel structure. creeks LSRA 0287 from 0.0 to 0.5; Wetlands 4and 8 LSRAs Lower Basin Boren Creek 0.2 erosion drainage A concrete culvert has separated and collapsed along Coal Creek Parkway SE. 0287 LSRA • Sections have separated, partially blocking flow and resulting in significant erosion from 0.0 and bank sloughing into the stream. 30-ft. landslide from the creek up to the road to 0.5 elevation. The Parkway's sidecast fill is oversteepened and raveling, and encroaches onto the creek's floodway. Lower Basin Boren Creek 0.2 to drainage ' water Evergreen Terrace subdivision at SE 91 st Street is located on shallow soils that can 0287 0.4 quality, become saturated, leading to problems with drainage, septic system overloads, and LSRA erosion erosion. Ad hoc changes to local drainage by residents and contractors have also led from 0.0 to problems. to 0.5 Future: sewer service could be provided in future by combination of further development to southeast and local assessment to the subdivision. Lower Basin Boren Creek 0.4 water quality aquatic Pipes and hoses were found crossing Boren Creek; further investigation needed. 0287 habitat Lower Basin Boren Creek 0.5 to aquatic Wetland 7 is impacted by grazing and by removal of buffer vegetation. 0287 0.8 habitat Future: vegetation impacts are likely to continue. The wetland could be impacted by Coal Creek Parkway SE improvements. Page 8 of 17 Subarea Tributary & River Primary Secondary Description Number Mile Subject Subject Lower Basin Boren Creek 0.5, aquatic Culvert under SE 89th PI . is potentially a fish passage barrier in high flows or when 0287 0.75, 0.8 habitat debris collects at intake. Culvert under private driveway is a fish passage barrier to 1.7 miles of upstream habitat. Long and complex culvert under SE 84th Way is a potential fish barrier. Lower Basin Lake Boren 0.9 to water quality sediment The water quality has decreased in Lake Boren. The lake had a natural seasonal (Boren 1.4 . deposition, cloudiness from winter runoff, but the cloudiness is persisting for longer periods than Creek Wetland erosion, in the past. Lake Boren receives water from China Creek, which is high in total system 8 is an aquatic phosphorus, total suspended solids, and fecal coliforms. Therefore, while the water 0287) LSRA habitat quality in Lake Boren appears to be relatively good now, it has the potential for degradation in the future if urban runoff to China Creek is not controlled. Sediment deposition has formed a delta at the pipe inlet of China Creek. The lake has had high readings (with some seasonal and yearly fluctuations) for total suspended solids, phosphorus, and fecal coliforms. Intense residential development is occurring in all of the uplands around the lake: development in the China Creek catchment is particularly of concern because all runoff is received by the lake. Class-1 Wetland 8 (Lake Boren and wetland fringe) and buffers are also impacted by agricultural use, clearing, and filling activities. Intensive grazing at headwaters of Trib. 0287E results in fecal coliform contamination in Wetland 49. Future: Lake turbidity and phosphorus will continue or worsen due to further intensive residential development in the China Creek catchment, and from long-term removal of vegetation. The remaining farming activities in the area will be replaced by residential development. High -density residential development, and increased use of the park, will increase flows and nonpoint loadings to the lake and wetland. Lower Basin Lake Boren 1.0 flooding At high lake level, flow at the outlet from Lake Boren floods private driveway and (Boren Cr. Wetland ,r creek crossing (sole access to two homes). system 8 is an 0287) LSRA Lower Basin Lake Boren Near 0.7 drr,irmq(e flooding, Runoff from intensive residential development in the uplands in the Lake Boren area (Boren to 1.2 erosion, has led to a number of localized drainage, flooding, and water quality problems. Most Creek water quality are immediate results of new construction and associated drainage alterations, system including failure of builders to correctly hook up drainage systems, encroachment 0287) upon and complete blockage of drainage easements, inadequate maintenance of drainage features, and filling. Lower Basin China Creek 1.2 aquatic Stream has been channelized, straightened, and lined with cement for 1,000 feet; 0287 habitat stream banks have been denuded of riparian vegetation. Outlet Lower Basin China Creek 1.2 drainage sediment Partially blocked culvert due to sediment deposition; erosion is occurring. 0287 deposition, erosion Lower Basin China Creek FT drainage erosion, Smaller culvert inside a larger culvert is creating a partial blockage and erosion. 0287 flooding Page 9 of 17 Subarea Tributary & River Primary Secondary Description Number Mile Subject Subject Lower Basin China Creek 1.9 erosion drainage There has been a slope failure within the steep ravine of China Cr. Erosion from the 0287 open face is adding sediment to the stream and lake. The landslide is normal event in the steep ravine, although downcutting/widening can increase the frequency of such events. Lower Basin Trib. 0287B 0.2 to water quality aquatic Intensive grazing at headwaters of Trib. 0287B results in fecal coliform contamination 0.3 habitat from animal wastes in Wetland 49. Future: this is part of the possible West Village residential site, per the Newcastle Community Plan. May Valley May Creek n.a. water quality aquatic Rural area and livestock impacts on water quality. 0282 * habitat A combination of historic clearing, intense farming, unrestricted animal access to the riparian area has removed most streamside cover and shade, and as a result water temperatures in most of the subarea reach critically high levels for cold -water fish during Summer low -flow periods. Fecal coliform counts were highest in mid -valley (one of the highest readings in the basin), and above standard in all locations. Total Phosphorus exceeded guidelines. There were some metals exceedances close to road crossings. May Valley May Creek 4.0 to water quality aquatic Pipes and hoses were found crossing May Creek; further investigation needed. 0282 7.0 habitat (several locations) May Valley May Creek 4.1 erosion Flood waters cut at bank below home; loss of two large trees and yards of soil in 0282 1990 Page 10 of 17 Subarea Tributary & Number River Mile Primary Subject Secondary Subject Description May Valley May Creek 4.3 to aquatic drainage, Class-1 Wetland 5, the May Creek stream channel, and their buffers have been 0282 7.1; habitat flooding, extensively altered and intensively disturbed now and in the past. May Valley section condition ** water quality of May Creek was formerly dredged, forming a straight ditch with sidecast spoils. s Dredging ceased in 1940s, and channel has been accumulating sediment from continue sediment deposition and spoils subsidence. The area suffers from extensive filling, on N., E., clearing, grazing and livestock access to the creek. The streambanks in many places & S. partially or completely lack riparian vegetation. Channelization has left the stream forks devoid of habitat diversity and limits salmonid production and sustainability. Large within amounts of manure eventually enter the May Creek system. Lack of stream shading May results in elevated water temperatures in late summer. Valley Maximum temperatures in the open May Valley are above the preferred range for the subarea; salmonids, and are at or approaching the upper lethal limits in late Summer. Lower Wetland temperature ranges were recorded both upstream and downstream of the open May 5 is Cl. 1 Valley reach, rarely exceeding 20°C.Temperature is therefore a limiting factor for fish passage and survival in the open May Valley reach in the Summer months. Future: channel will continue to infill with sediment, reducing capacity and leading to increased flooding. Existing and future flows will deliver more water than current channel can handle. The May Valley is a working landscape that will continue to have rural uses in the riparian and wetland areas; however, without mitigative measures, impacts will continue or worsen. M,IV Valley May Creek 4.5 drainage flooding 148th Ave. SE bridge will not pass the 25-yr. flow. Overtopping and flow across road 0282 * reported for 1990 flood event. Page 11 of 17 Subarea Tributary & Number Rives Milo Primary sulj;i Secondary Subject Description May Valley May Creek 4.5 to flrmwiiny water quality Extensive flooding of pastures occurs annually in the May Valley during most of the 0282 7.0 *+ storm season. Most of the land between SE May Valley Road and SR-900 historically was within the floodplain, and much is still within the floodplain as modified by historic and recent filling. Flooding is exacerbated by illegal filling and channelization that reduce floodwater storage; runoff from development and clearing of surrounding upland areas; sediment and vegetation that fill in the stream channel and impede its flow; and livestock trampling of banks (also causing erosion and water quality problems). Approximately five homes and seven outbuildings —storage sheds, garages, animal shelters and barns —are located in the modelled 100-year floodplain of May Creek, and two others are affected by tributary flows just above where they enter the floodplain. Flood velocities and depths are low, so that public safety in May Valley is not a significant issue. There is prolonged ponding of water in pasture land in floodplain of May Creek in area of RM 4.6 to 5.0 upsteam of 148th Ave. SE. Prolonged wet soil conditions in part of fields restricts livestock use of the area. Reed canarygrass is thick in the channel of RM 4.6 to RM 4.7. Just below 164th Ave. one property has stables that get water, and a garage, well, and septic tank that are also occasionally affected; one house gets water under it in large floods. Upstream of 164th Ave. SE there is widespread pasture and open -land flooding, and some long -duration ponding in various places. One residence is located in an obvious low spot, and has reported frequent water under the foundation with occasional property damage in the larger events (such as 1990). A feed store is located on fill in the floodplain just upstream of 164th, and has one or two buildings that get floodwaters during large peak events. At least one other residence has complained of septic tank problems related to flooding. Future: the area is a working landscape with homes, barns, rural businesses and pastures located in or adjacent to floodplain and wetland area. It will continue to have rural uses; however, without remedial measures the impacts will continue and worsen. The width of the 100-year floodplain, and therefore the number of homes in it, is not expected to increase significantly under future land use conditions. Increased flood volumes in the valley will instead result in longer durations of floodwater inundation, greater frequency of flooding, and slightly greater flood depths. May Valley May Creek 5.8 to drainage flooding, The 164th Ave. SE bridge will probably not pass the 25-yr. flow. Congestion in the 0282 5.9 + sediment creek channel (vegetation and siltation) and at the bridge. deposition Page 12 of 17 Subarea Tributary & River Primary Secondary Description Number Mile Subject Subject May Valley May Creek 6.9 to water quality drainage, Sunset Materials has many long-standing drainage and water quality problems. 0282; S. 7.0; S. * erosion, Earthmoving and gravel operations on the unclassified use portion of the property are Fork May Fork from aquatic producing and releasing substantial volumes of turbid, sediment -laden water. The Creek 0282 7.0 to habitat sediment pond is not properly designed or maintained, and discharges water with 7.2) considerable amounts of suspended sediment. Ad hoc channels have also been dug to LSRA enable drainage from the staging area and other areas to by-pass the sediment pond from 7.0 and to discharge untreated sediment -laden water to May Creek. Both pond and ad to 7.2 hoc discharges flow into drainage ditches along SR-900, then discharge into May Creek and Class-1 Wetland 5. Sediment has plugged a culvert near the outlet from the sediment pond, isolating part of the roadside ditch. Oil and suspended sediment are being discharged from the nonconforming use area into the LSRA portion of Wetland 5 and the S. Fork of May Creek. Oil containment measures are improperly sited and poorly maintained. Sediment settling and removal measures, and erosion control measures are inadequate and poorly maintained. Future: Unclassified use permit has expired and the gravel operation will be closed: area needs proper reclamation. The nonconforming use area will continue, and will need to be brought into and kept in compliance with regulations and operating plans. May Valley May Creek 7.0 sediment aquatic Sediment has partially blocked a culvert. 0282 deposition habitat May Valley North Fork 0.0 to drainage aquatic North Fork channel has been moved and straightened. Most wetlands have been & Highlands May Creek 0.7 habitat extensively filled, drained, or grazed. 0294 LSRA Future: the area is a working landscape with homes, barns, rural businesses and from 0.0 pastures. It will continue to have rural uses in the riparian and wetland areas. to 0.1, and 0.4 to 1.0; Wetland 13 LSRA May Valley North Fork Near 0.2 drainage flooding, Private runoff and drainage system for several short plats is not functioning properly, May Creek to 0.5 * water causing flooding of pastures, two barns, garden, and manure piles, and prolonged 0294 LSRA quality, ponding of water. Most properties not on fill are within 100-yr floodplain. Flooding is from 0.4 erosion exacerbated by sediment deposition in sole outlet which has filled the channel at its to 1.0; lower end. Runoff from Squak Mt. has apparently increased: drainage features on Wetland hillside are showing first signs of increased flow. Runoff from north side of SE May 13 LSRA Valley Rd., together with some runoff from lower Squak Mt., is flowing down to a low area where it contributes to the problem. An old highway culvert under SE May Valley Rd. is reported to have formerly conveyed water under the road, but no such outlet now exists. Fill for private road 186th Ave. SE may be causing some backwater effects on upstream properties. Future: runoff will increase as more single-family homes are constructed on Squak Mt. Problem will worsen without reconditioning of drainage system and addressing of road runoff problems. Page 13 of 17 Subarea Tributary & River Primary Secondary Description Number Mile Subject Subject May Valley East Fork 0.0 to aquatic Disturbance and alteration to Class-1 Wetland 5, channel, and buffers from dredging, May Creek 0.4 habitat filling, grazing, and clearing. 0297 May Valley E. Fork May 0.2 drainage erosion Culvert is falling apart, partially blocking flow and causing erosion. Creek 0297 May Valley East Fork 0.2 to flooding aquatic A large volume of water and debris came down stream in 1990, and stormflows have May Creek 0.4; this habitat, reportedly been higher in recent years. Larger areas of ponded water, together with 0297 portion drainage dying and toppling of trees (perhaps due to prolonged soil saturation or clearing of of some neighboring tracts), are reported. Stream channel lacks definition in this area. Wetland Both channel and wetland have been greatly altered by local landowners, particularly 5 is an in vicinity of 188th Ave. SE, although accounts of events and causation vary. Some LSRA stream enforcement actions taken by County DDES. Diversion of stream channel at RM 0.4 by constructed berm, to prevent flooding of pasture adjacent to stream on east side of 188th Ave. SE. May Valley East Fork 0.5 drainage erosion, Significant risk that main culvert under SE May Valley Rd. could plug from debris and May Creek * flooding, sediment, and lead to overtopping of the road and erosion along the road. 0297 sediment deposition May Valley South Fork 7.3 aquatic Length and slope of 130-foot-long culvert at SE 128th St. (RM 7.3) may be partial or May Creek Wetland habitat complete fish passage barrier. A natural barrier —a steep, incised ravine —is located at 0282 5 from RM 7.4 to 7.7. Stream flow is subsurface for portions of the year. 7.0 to 7.3 LSRA May Valley Trib. 0.0 (near aquatic water quality Alluvial fans of Tributaries 0287D, 0289, 0291 A are heavily grazed and lack riparian 028713; the con- habitat or upland vegetation. Compound alluvial fan of 0292 (shared with Cabbage Creek Long Marsh fluences 0293, which has been diverted into Country Creek at RM 0.15) has a stream channel Creek with May that is less degraded than are other downstream tributaries in May Valley, but the fan 0289; Trib. Cr.: RM is heavily grazed in some portions. Direct animal access to stream corridor in these 0291 A; 4.4, areas destroys redds and rearing habitat. Country 4.65, Creek 0292 5.5, 6.5 May Valley Trib. 0287D 0.05; aquatic Culvert below SE May Valley Road may block passage during low flows, and culvert 0.07; habitat for SE May Valley Road at RM 0.07 is a fish passage barrier. Just upstream of the 0.11 (RM road culvert is an impoundment whose spillway draws water vertically through three- 4.4 on to -five-foot deep outlet pipe and out of a culvert. Fish cannot pass this barrier. Natural May Cr.) step -falls barrier at RM 0.13 May Valley Trip. 0287D 0.05 (RM flooding One house had some basement flooding from Trib. 0287D during 1991-2 storms. 4.5 on May Cr.) Page 14 of 17 Subarea Tributary & River Primary Secondary Description Number Mile Subject Subject May Valley Greene's 0.0,(RM erosion aquatic The tributary has cut into glacial advance outwash soil to a depth of 15 to 20 feet at Creek 0288 4.5 on habitat upper end of section. The deposited silt fan is about 10 feet wide, 30 feet long, and May Cr.) 1.5 feet deep. May Valley Indian 0.04 (RM aquatic water quality Fish are unable to pass through two -foot -long culvert in pasture. Overgrazed pasture Meadows 4.9 on habitat and paddocks are eroding into creeks. A natural barrier (waterfall) is at RM 0.2. Creek 0291 May Cr.) May Valley Hendrix 0.05 (RM flooding drainage One house is outside of the May Creek 100-year floodplain, but receives floodwater Creek 6.4 on that is comes from Hendrix Creek, possibly with contribution of runoff from SR-900. 0291 C May Cr.) It has had basement flooding several times in last five years, with damage to personal effects and appliances. May Valley Cabbage 0.0 to drainage flooding, Cabbage Creek is diverted 90-degrees to join Country Creek (0292). Floodwaters Creek 0293 0.1 sediment bring sediment and debris that deposits in the channel bend and in the backwater of deposition culverts. This in turn can cause the creek to jump the bank and flow to other portions of the alluvial fan, flooding pastures. Some basement flooding of one house (near the right-angle turn) has occurred. Future: Increasing flows will bring more sediment and debris, plugging culverts and channels and causing channel shifting. Highlands Subarea- n.a. drainage land use, The majority of water that is delivered to the May Valley comes from this subarea. Wide • erosion Future development will greatly increase the amount of runoff. Because most development is low -density residential in earlier, vested plattings, mitigation requirements are low and will be largely ineffective in reducing additional runoff generated by this development. Highlands northern n.a. water quality aquatic Rural area, quarrying, and livestock impacts on water quality. tributaries ,r habitat Water quality in the North Fork is the principal concern, where excessive Total to May Phosphorus, Total Suspended Solids, and metal loadings have been measured. Fecal Creek coliform counts were also high in the N. Fork. Three tributaries have high NO3 levels. Highlands Country & 0.14 aquatic Fish passage barrier (under most flow conditions) due to erosion immediately below Cabbage LSRA habitat the lip of cement driveway and retaining wall. This blockage prevents access to upper creeks from Country and Cabbage creeks. A second barrier is a high -gradient culvert immediately 0292 and 0.09 to upstream under SE May Valley Rd, with a natural barrier at RM 0.2. [Natural barrier 0293 .14 on Cabbage Creek is at RM 0.2 above the joining with Country Creek.l Creeks run parallel to SE May Valley Rd. in a riprapped drainage ditch. Highlands North Fork 0.1 to drainage aquatic SR-900 may be expanded to 4 or 5 lanes in this topographically constrained area. May Creek 1.6 . habitat Fish habitat in this reach is generally poor due to channelization and rip -rapping, and 0294 LSRA lack of deep water, cover LWD, and habitat diversity; nevertheless, some salmonid from 0.4 use and spawning has been observed in the North Fork. to 1 .0; Future: SR-900 expansion needs to address impacts to North Fork May Creek and to Wetland salmonid habitat, including probable relocation of the creek and effects on class-1 13 LSRA wetland. Page 15 of 17 Subarea Tributary & River Primary Secondary Description Number Mile Subject Subject Highlands North Fork 0.7 to water quality, aquatic Runoff from two quarries (Sunset Quarry and Hazen Quarry) and the Issaquah Sand May Creek 2.2 erosion habitat, and Gravel stockpile runs directly into May Creek. Driveways from all three sites cross 0294 LSRA * drainage the creek, and dirt is eroded into the stream. Mud tracked onto SR-900 by large from 0.4 vehicles is later washed into the creek. to 1.0; Sunset Quarry's entrance gets very muddy and slopes downhill to the Tibbetts Divide, Wetland sending muddy water to Tibbetts and May creeks; stormwater heading for Tibbetts 13 LSRA has potential to divert to May in heavy flows. New stockpiles near the entrance have inadequate erosion control, sending silt into May Creek. Hazen Quarry has been observed releasing chocolate -colored water from the large staging area: some water flows around the barriers at the entrance, other discharges through a ditch dug past the office trailers and into May Creek. Stormwater flows over the driveway at the entrance to Issaquah Sand and Gravel stockpile because the culvert is undersized. The driveway from the Issaquah Highlands Campground also crosses the creek, and probably also contributes some sediment. Future: Hazen Quarry may be mined -out, in which case it will need to be properly reclaimed. Sunset Quarry is seeking to expand operations. Highlands North Fork 1.6 to drainage Gravel operations in the Sunset Quarry have breached the drainage divide between May Creek 2.2 + Tibbetts and May creeks in several locations. On a site visit in Aug. 1994 actual 0294 breaks in the berming between the drainages were observed in two locations, which would allow some runoff that would normally drain to the Tibbetts Creek basin to be diverted to the May Creek basin. The quarry's R/D system was overwhelmed in Jan. 1990 storm and sent a large volume of water and sediment south to May Creek. Future: Berming in several locations has the potential to breach during some storms. R/D system still appears to have the potential to send water to May Creek. Sunset Quarry is currently seeking to expand operations. Highlands East Fork 0.8 to erosion aquatic Upstream development on SE 1 18th and 198th streets has caused an increase in May Creek 1.0 habitat both flow volume and erosion. Some residents have reported that summer flow in the 0297 creek is lower than in the past. Highlands Trib. 0287D 0.3 erosion A bridle trail crosses through stream. Highlands Indian 0.1 water quality Runoff from a small lumber mill located on the edge of Trib. 0291 introduces fines Meadow and organic materials into the creek. Creek 0291 Highlands Country Cr. 1.0 drainage erosion, Development uphill of several plats on the south face of Cougar Mountain may result 0292 & flooding in increased erosion of stream channels and increased flow downstream. Potential for Cab-bage 0.14 future flooding problems. Cr. 0293 East Renton n.a. drainage flooding The area is relatively flat, and natural drainage is often not well defined and easily Plateau obstructed or destroyed by development activities. Future: flooding problems will occur where new development alters, obstructs, or overloads natural drainage, and where mitigation is inadequate or not required. Page 16 of 17 Subarea Tributary & River Primary Secondary Description Number Mile Subject Subject East Renton subarea- n.a. drainage Future development in this subarea will increase the amount of runoff to May Valley. Plateau wide This subarea is second to the Highlands subarea for both current contribution and future increase in that contribution. East Renton southern n.a. water quality Rural area, urbanization, and livestock impacts on water quality. Plateau tributaries Trib. 0291 A is contributing some metals and fecal coliforms to the Valley. Total to May Phosphorus is above guideline, and Fecal coliforms exceed standard. Metal are elevat Creek ed in the S. Fork downstream of SE 128th Street. East Renton 0282, n.a. drainage aquatic SR-900 may be expanded to 4 or 5 lanes in this area. Undersized culverts are present Plateau 0291 A, habitat along SR-900 at several locations, partially blocked culverts are in need of 02918, maintenance along SR-900 at multiple sites, and detention ponds are needed along 0291 C, SR-900 at four locations, as described in WSDOT Design Analysis Study (Concept A). 0288, 0285 Future: SR-900 expansion needs to address impacts. East Renton S. Fork May 7.7 to drainage aquatic Channel has been dredged and straightened in the past, and silt has accumulated in Plateau Creek 0282 8.1 habitat it. The stream dries or goes subsurface in summer. East Renton South Fork 8.0 to aquatic Wetland 1 and Lake Kathleen have been impacted by development around the lake Plateau May Creek 9.0 habitat and upslope, including some old filling and one large recent and currently vacant fill. 0282 Some buffer areas have been removed, and there has been filling, clearing, mowing around lake by residents. East Renton South Fork 8.2 drainage flooding Lake Kathleen outlets through two undersized culverts under SE 134th St.. Channel Plateau May Creek + immediately downstream is constricted, causing rise of Lake Kathleen and some 0282 flooding of lakeshore property. At 3.5 feet of rise, the road is overtopped, currently causing inconvenience for east -side lake residents. Future: additional development and consequent runoff may cause more frequent lake level rise and road overtopping, and eventual road instability and possible safety problem. East Renton Lake 8.2 to sediment water quality The lake is naturally shallow and mesotrophic. Sediment deposition and growth of Plateau Kathleen 8.5 deposition• aquatic vegetation are exacerbated by delivery of runoff and nutrients associated with Wetland the development of the lakeshore and hillsides. 1 and L. Future: natural eutrophication of the lake will continue; over time, the runoff storage Kathleen of the lake will decrease. LSRA East Renton South Fork Near S.5 drainage flooding Development and filling has caused an increase in runoff from W. Lake Kathleen Dr. Plateau May Creek to 8.7 SE and SE 136th St, overflowing ditches and draining onto private property. 0282 and Trib. 0282A East Renton Greene's 0.1 to erosion drainage Channel is expanding in some reaches as it erodes through outwash. Upper reaches Plateau Creek 0288 0.6 of the creek have been straightened. Page 17 of 17 Subarea Tributary & River Primary Secondary Description Number Mile Subject Subject East Renton Greene's 0.2, and drainage flooding, Runoff from uphill development in area of on 146th Ave. SE, SE 100th PI. and 147th Plateau Creek 0288 near 0.4 erosion Ave. SE is causing downstream flooding of private property. Similar problem near 147th Ave. SE and SE 104th St. East Renton Trib. 0291A 0.3 flooding sediment Driveway culvert for Coalfield Stables is undersized and partially filled with sediment, Plateau LSRA from deposition and may clog. Reduced conveyance together with increased peak flow from 0.06 to 0.3 development can cause flooding. Stables's culvert may block fish access. 0.3 aquatic Three-foot concrete box culvert under SR-900 has shallow flows and is a possible fish habitat passage barrier. A 60-foot-long culvert under 116th St. SE is perched 3.5 feet above the stream, 0.5 blocking fish passage upstream. Note: upstream from RM 0.8 the stream is culverted aquatic almost continuously through residential yards. habitat East Renton Trib. 0291 A 0.3 erosion water quality Trib. 0291 A has cut as much as five feet into flood terraces, indicating increased Plateau LSRA from + runoff from upstream development. Surface erosion from road edges, ditches and 0.06 to 0.3 gravel driveways is also adding fines to creek, which affect a coho-spawning area and LSRA downstream. East Renton Trib. 0291 A 0.8 to aquatic water quality Once contiguous, Wetlands 2 and 3 have been impacted by extensive fill, dredging, Plateau 1.4 habitat drainage, and trash dumping. Runoff from neighborhood commercial site and 128th Wetland Ave. SE enters Trib. 0291 A and Wetland 2. Wetland 3 has been modified with an 2 LSRA outlet flow regulator to act as regional stormwater R/D facility (Cemetery Pond). East Renton Trib. 0291 D Near 0.2 drainage flooding Runoff from clearcut property uphill, together with mislaid and mis-sized drainage Plateau system and lack of gradient has led to localized flooding of streets, open land, and some flood damage to houses. A phase-1 Neighbor -hood Drainage Assistance Project study was done for this site, near 156th Ave. SE and SE 124th St. East Renton Trib. 0291 B Near 0.2 drainage Runoff from uphill properties flows through an undersized private drainage system Plateau causing localized flooding of house built over drainage pathway on the corner of 164th Ave. SE and SE 116th St. East Renton n.a. drainage flooding, Runoff from uphill properties (and some drainage alterations) have caused drainage Plateau erosion, sed. and flooding problems near 179th Ave. SE and SE 121st Pl., SE 114th St. near deposition 152nd Ave. SE, and 166th Ave. SE. .r• Most Significant ++ Very Significant • Significant [no starsl Less Significant APPENDIX B MAPS f.. Map 2 i Subarea Boundaries , h\ wash*a. '`J i NEWCASTLE May Creek Basin Lake .o \0 r ♦ �.4 - I \ 0 , B9 m v4 `' _ • I HIGHLANDS o?e, I o10Q Y.h i rsp �. LOWER BASIN i_— L_ --�'' 81 zf .� .� 2 C I A� n RENTON�% ♦ * rN �YI ♦ �zo ♦ I , m� EAST �� % j I j I RENTON ♦ PLATEAU o ♦ • . . - ` • o MAY . ♦.-• � o . „ VA ♦ a I (� 019 I D I N . #o ► Basin Boundary . - ♦ Subarea Boundary f Stream Lake loneLake Kathleen 0 /2 1 Mile - --- I Incorporated Area NEWCASTLE I r- I :I RENTOON�N� _ Commercial/Institutional 0 Multifamily Single Family High Density 0 Single Family Low Density Grass Single Family Low Density Forest Quarry Grass Forest 0 Clearcut Wetlands Lake Stream Roads f• May Creek Basin Boundary — — Renton & Newcastle City Boundaries Map 4 Existing Land Use/Land Cover May Creek Basin B I I q r L 12,E ` jl a I �n t � r 7 G I h Si \ a ` h 0 Yz t Mile " Map 5 Future y NEWCASTLE Land Use/Cover - i Lake 4 , May Creek Basin Romn si CYPsY A F f RENTON - ' I z V ` �o lz _ Commercial/Institutional Multifamily T A Z. 0 Single Family High Density I I Nf r 0 Single Family Medium Density - - Single Family Low Density _ ® Quarryb f 0 Grass 0 Forest Wetlands N Lake _ Stream ake Roads athteen f� May Creek Basin Boundary - 0 Renton & Newcastle City Boundaries '/a 1 Mile m. Map 8 Subcatchment Was Boundaries LBU May Creek Basin GYP 11 11wcn / > / h/noNH3 1 k WT4 BNB 1 LBL \ \ CN4\ I` CCP LMC Qsv \ r / Gte I harsh Glt a rI I 1 I ► / / �- COU CAC CN2 1 --I / ti 1 HCL I \ / 1-- 2 � / MVL i \ I p/ — -- HCM '1 �/ \ y / 0 I � 1 \ A l ^.f eek I NFK HCU \ \\\ A iPSC 1 I Bost Fes. EFK Alp C, Itk / 1 \/ a \ / \ J s \ CFD Pf LKC ti \ n \ _ � n N Basin Boundary Stream LKA • O Lake — — Subcatchment Boundary Lake Kathleen 0 vz 1 Mile CN2 Subcatchment Name Map 10 Septic Systems May Creek Basin Garden c c of Eden (r G I L SE 89th - Lake Boren - 4 I Ia o e to � c - e IN. YACI Sierra (Evergreen � Hei hts 9 Terrace 151 st y St. 7y " SE May k ' - Valley Road �' c•'` \ -Z� NE 1 th St. 160th Ave. SE _ 148th Ave. SE e & SE 1 17th St. ax 156th c" SE 122th I AvP. SE St. po 0 .-oo— Basin Boundary SE 128th �l Stream N 164th Ave. SE its Lake C Target area Lake O System with a history of failure Kathleen ■ System in prefailure or failure at time of inspection 0 Yi t Mile � O System exhibiting both characteristics above ../— Basin Boundary Stream •O Lake ,1111800 Wetland Newcastle Landfill Quarries • Small Quantity Generator (SKCDPH) Underground Storage Tank ❑ Permitted Hazardous Waste Activities ■ Quendall Site Map 12 Hazardous Waste Generators & Underground Storage Tanks May Creek Basin ce4 n 1. � An ❑ f'r ❑ G'e Lake sso Map 14 Lower Basin Conditions nA May Creek Basin l f 0a ti7C 6 LS \0 £3 od Lake 028J,q ? • r` o In Boren • - �2 o o O C:eek ED �� _,�. — • i QZ , 0289 5 9 6t ' rr • m •` o•• _',� r' �- ` ' ��� '•� _ .SE Mo 81 oybq�arsh e¢Y vo CP °q D 0282 R <91 �Ty7 a l - v� �� r� ♦ G� -.l nri/Qn �,N r Ff I `� - - e�eek 029, ^ ft�. Basin Boundary u I __ �n Subarea Boundary `" I ♦ D 0_�9 Stream &Stream Number F ro _ - \ _..._, �� Lake ` / „ \ ♦ Wetland N _ Concentrated Spawning Area > CP o Q• /0 Problem Area ` 0 LS Locally Significant Resource Area ♦ li Wetland Habitat Problem Stream Habitat Problem N Flooding Problem V Water Quality Problem li UM, Erosion Problem ' 0 Yz 1 Mile n�A Sediment Deposition Problem �J Map 15 SE orsy 9 May Valley Conditions May Creek Basin -- -`♦ A A m CO r�''�dO 029, 0289 c� OIv 0 0 j N f+ Basin Boundary o `%♦ • ,k LJ.�y • • �, 1 r, - Subarea Boundary a ♦ 1 ;, , ; ; _ �.! 1 0'119 Stream & Stream Number v ♦'� ... - .. "- - Wetland a. ♦�., - ._ .. _ �.., . :-.., : :� Concentrated Spawning Area D � • Q/0 Problem Area ®nA �,♦ LS �� _ k ti10 � k Locally Significant Resource Area N n ♦♦ < - _ - / \\% Wetland Habitat Problem rn ♦♦ :__: 0297 ♦♦ D 9�N: -► • 3-7 Stream Habitat Problem 3 o fir. IV Flooding Problem JG Water Quality Problem x Erosion Problem N Q 0 IA h Mile N ` , Sediment Deposition Problem K lop .� 00 �♦ — — O0 --51 J O 1] u Creek S E _ �prsh 09 Map 16 Highlands Conditions May Creek Basin May ♦` yp Cr { r G r f • ry �/e a O _ w o N m It o�D f► Basin Boundary . o- Subarea Boundary of, Stream & Stream Number Wetland Concentrated Spawning Area 0 Problem Area 0 LS locally Significant Resource Area 0 RS Regionally Significant Resource Area Wetland Habitat Problem Stream Habitat Problem Flooding Problem Water Quality Problem Erosion Problem D� o Q j O .O 11 M ' 1 o b - _ 29 _- % k Irn a t n it N o a 2 0 1/1 1 Mile Map 17 SE Creek y Roll - ��113'69 East Renton Plateau e 0282 _ Y R Conditions May Creek Basin Cr � Q, - 029� a ♦ _ qa �D rn ` p'f i �Noney N:F 1 1 .0 H % 4 LS - Lse pOftft y • N o _ - '- _ a ♦ - w - �qs/ \\ Greg ark\ • 0 f• Basin Boundary I 'ram Dr \ . i'► Subarea Boundary SE 128th STD \ o`er Stream & Stream Number a qWO Lake Wetland f . m N _<2::v Concentrated Spawning Area Q / Problem Area • Locally Significant Resource Area • Wetland Habitat Problem N Stream Habitat Problem ® O f LS Erosion Problem Lake AFlooding Problem ''- Kathicoi 0 Yz 1 Mlle l�l Sediment Deposition Problem 1 1 gK h �Ce W \ Me '� n UIV Ct U 0?89 n s Im ♦ `` a ��. Basin Boundary i Subarea Boundary a`J9, Stream & Stream Number 100 Year Floodplain Area Map 18 May Valley 100 Year Floodplain May Creek Basin m ♦ �� of ♦�, \,,,� ` p o ♦ Q ♦ ;♦` Sc 0' 1 I �, =olley ry P ` q 0 1 1 1 1 1 1 D `� `'r• Fork ` n � o � ND N 0 /< 1/2 Mile APPENDIX C HYDROLOGY Table C-1. Percentage of Effective Impervious Area Associated with Different Land Uses. Dwelling Total Total Effective Units Impervious Impervious Area Impervious Land Use per Acre Area (%) Effectivel/ (%) Areal/ (%1 Commercial 90 95 85 Multi -Family > 7 60 80 48 High Density Single 3-7 40 65 26 Family Medium Density Single 1-3 20 50 10 Family Low Density Single < 1 10 40 4 Family Quarry 90 2 2 Clear Cut 0 0 0 Grass 0 0 0 Wetland 0 0 0 Forest 0 0 0 1/ Total impervious area (TIA) effective is the percent of TIA connected to a drainage system. 2/ Effective impervious area (EIA) equals TIA times the percent of TIA effective. Table C-2. Watershed Segmentation by PERLNDs. I. May Creek Current Land Use Conditions TFF' TFM TFS OF TGF TGM TGS OG SA LAKES EIA TOTAL % (acres) (ac) (ac) (ac) (ac) (ac) (ac) (ac) (ac) (ac) (ac) (ac) EIA Highlands Subarea EFK 10 39 204 31 6 5 26 41 38 0 6 406 1.5 NFK 17 107 779 34 2 21 89 63 45 0 6 1,164 0.5 CAC 16 123 318 0 0 2 1 1 0 0 5 466 1.0 COU 16 101 197 4 0 0 1 1 3 0 1 324 0.4 LMC 17 100 275 44 0 4 2 5 16 0 2 465 0.4 WT4 35 60 38 0 16 12 1 0 4 0 2 168 1.1 East Renton Plateau Subarea LKA 94 56 1 0 65 36 1 0 25 49 26 353 7.5 LKC 58 39 8 34 17 23 0 2 11 0 3 195 1.3 PSC 100 74 4 7 129 44 1 12 4 0 35 410 8.6 RHC 89 100 4 5 45 92 3 2 28 0 34 402 8.4 May Valley Subarea CFD 64 102 98 77 65 80 27 62 81 0 36 691 5.2 MVM 2 23 49 13 0 0 6 34 16 0 5 149 3.6 MVL 26 79 148 12 14 10 24 29 59 0 8 410 2.1 CCP 35 129 129 55 32 29 7 51 12 0 22 500 4.3 Lower Basin Subarea CN5 6 12 4 34 3 1 0 12 0 0 7 79 8.7 LBU 11 72 74 8 47 94 66 35 11 17 66 502 13.2 LBL 19 21 49 53 2 21 36 63 17 0 28 307 9.0 CN4 2' 11 4 37 4 2 1 12 0 0 4 77 5.2 NHC 3 27 53 14 5 22 24 3 6 0 13 171 7.4 CN3 8 4 18 47 2 2 2 36 4 0 8 130 6.0 HCU 74 40 5 9 48 40 2 17 8 0 37 281 13.2 HCM 10 12 5 9 95 15 3 81 5 0 107 342 31.4 HCL 28 23 46 26 87 18 11 15 2 0 47 303 15.6 CN2 1 1 19 19 24 13 1 94 4 0 41 217 18.8 GYP 18 31 28 25 16 18 14 27 11 0 24 210 11.3 CN1 1 4 20 79 1 2 1 49 6 0 23 186 12.1 BNB 4 3 1 11 6 4 1 24 1 0 26 80 31.9 TOTAL 764 1,394 2,577 685 % of basin Forested = 5,420 acres = 60.3% 734 612 350 770 Grass = 2, 466 acres = 27.4% 416 66 621 8,989 6.9 4.6% 0.7% 6.9% 1/ TFF = Till soil, Forested, Flat (0-5%) slope; TFM = same, with Moderate (5-15%) slope; TFS = same, with Steep (>15%) slope; TGF, TGM, TGS = same progression, but vegetation type is Grass; OF = Outwash soil, Forested, all slopes; OG = same, with Grass; SA = Saturated soils, all vegetation types, all slopes; EIA = Effective Impervious Area Table C-3. Watershed Segmentation by PERLNDs. 11. May Creek Future Land Use Conditions TFF' TFM TFS OF TGF TGM TGS OG SA LAKES EIA TOTAL % (acres) (ac) (ac) (ac) (ac) (ac) (ac) (ac) (ac) (ac) (ac) (ac) EIA Highlands Subarea EFK 4 15 92 28 8 28 132 46 37 0 16 406 4.0 NFK 10 68 552 27 8 54 300 56 41 0 47 1,164 4.0 CAC 10 79 183 1 6 43 130 1 0 0 13 466 2.8 COU 7 50 79 2 8 48 108 2 3 0 16 324 4.9 LMC 14 91 244 43 3 12 31 6 16 0 6 465 1.3 WT4 11 25 20 0 36 41 18 0 4 0 14 168 8.2 East Renton Plateau Subarea LKA 34 17 0 0 121 73 2 0 25 49 33 353 9.4 LKC 22 19 3 21 50 41 5 14 11 0 8 195 4.0 PSC 36 10 0 0 175 99 4 18 3 0 65 410 15.7 RHC 30 44 2 3 96 142 4 4 28 0 49 402 12.3 May Valley Subarea CFD 36 49 37 28 88 126 78 94 80 0 75 691 10.9 MVM 1 7 20 7 2 16 33 35 16 0 13 149 8.8 MVL 9 29 64 12 29 55 100 29 58 0 26 410 6.3 CCP 0 2 51 13 62 142 77 86 12 0 53 500 10.7 Lower Basin Subarea CN5 0 2 3 15 8 9 1 28 0 0 13 78 16.7 LBU 6 20 15 4 47 132 103 36 11 17 110 502 22.0 LBL 0 0 23 9 19 37 57 98 17 0 48 307 15.7 CN4 0 0 0 26 2 9 4 22 0 0 14 77 17.6 NHC 1 1 6 13 6 42 61 4 6 0 30 171 17.5 CN3 4 0 12 38 3 5 7 41 4 0 16 130 12.6 HCU 1 0 0 0 109 71 4 18 8 0 69 281 24.6 HCM 0 0 0 0 90 18 6 78 5 0 145 342 42.3 HCL 2 4 23 , 14 105 33 30 22 2 0 70 303 23.1 CN2 0 0 16 18 24 14 3 91 4 0 47 217 21.8 GYP 4 4 7 12 26 37 30 38 11 0 41 210 19.6 CN1 0 2 13 33 1 3 6 74 6 0 48 186 25.6 BNB 1 3 1 5 3 4 1 26 1 0 36 80 45.0 TOTAL 243 542 1,466 370 1,136 1,334 1,334 966 410 66 1,122 8,988 % of basin Forested = 2,620 acres = 29.2% Grass = 4,770 acres = 53.1 % 4.6% 0.7% 12.5% 1/ TFF = Till soil, Forested, Flat (0-5%) slope; TFM = same, with Moderate (5-15%) slope; TFS = same, with Steep (>15%) slope; TGF, TGM, TGS = same progression, but vegetation type is Grass; OF = Outwash soil, Forested, all slopes; OG = same, with Grass; SA = Saturated soils, all vegetation types, all slopes; EIA = Effective Impervious Area Table C-4. Final Calibration Parameter Values. PERLND' Num- Name LZSN INFILT LSUR SLSUR KVARY AGWRC INFEXP INFILD DEEPFR BASETP AGWETP CEPSC UZSN NSUR INTFW IRC LZETP ber 10 TFF 4.5 0.16 400 0.030 0.5 0.996 2.0 2.0 0.0 0.0 0.0 0.2 2.0 0.35 7.0 0.5 0.70 11 TFF 4.5 0.16 400 0.030 0.5 0.996 2.0 2.0 0.0 0.0 0.0 0.2 2.0 0.35 7.0 0.5 0.70 14 TFM 4.5 0.16 400 0.100 0.5 0.996 2.0 2.0 0.0 0.0 0.0 0.2 1.0 0.35 7.0 0.5 0.70 15 TFM 4.5 0.16 400 0.100 0.5 0.996 2.0 2.0 0.0 0.0 0.0 0.2 1.0 0.35 7.0 0.5 0.70 17 TFS 4.5 0.16 200 0.200 0.5 0.996 2.0 2.0 0.0 0.0 0.0 0.2 0.6 0.35 15.0 0.3 0.70 18 TFS 2.5 0.05 200 0.200 0.5 0.996 2.0 2.0 0.0 0.0 0.0 0.2 0.6 0.35 15.0 0.2 0.70 20 TGF 4.5 0.06 400 0.030 0.5 0.996 2.0 2.0 0.0 0.0 0.0 0.1 1.0 0.25 7.0 0.5 0.25 21 TGF 4.5 0.06 400 0.030 0.5 0.996 2.0 2.0 0.0 0.0 0.0 0.1 1.0 0.25 7.0 0.5 0.25 24 TGM 4.5 0.06 400 0.100 0.5 0.996 2.0 2.0 0.0 0.0 0.0 0.1 0.5 0.25 7.0 0.5 0.25 25 TGM 4.5 0.06 400 0.100 0.5 0.996 2.0 2.0 0.0 0.0 0.0 0.1 0.5 0.25 7.0 0.5 0.25 27 TGS 4.5 0.06 200 0.200 0.5 0.996 2.0 2.0 0.0 0.0 0.0 0.1 0.3 0.25 15.0 0.3 0.25 28 TGS 2.5 0.04 200 0.200 0.5 0.996 2.0 2.0 0.0 0.0 0.0 0.1 0.3 0.25 15.0 0.2 0.25 30 OF 5.0 2.00 400 0.050 0.3 0.996 2.0 2.0 0.0 0.0 0.0 0.2 0.5 0.35 9.0 0.5 0.70 31 OF 5.0 2.00 400 0.050 0.3 0.996 2.0 2.0 0.0 0.0 0.0 0.2 0.5 0.35 9.0 0.5 0.70 40 OG 5.0 0.80 400 0.050 0.3 0.996 2.0 2.0 0.0 0.0 0.0 0.1 0.5 0.25 9.0 0.5 0.25 41 OG 5.0 0.80 400 0.050 0.3 0.996 2.0 2.0 0.0 0.0 0.0 0.1 0.5 0.25 9.0 0.5 0.25 50 4.0 2.00 100 0.001 0.5 0.996 10.0 2.0 0.0 0.0 0.0 0.1 3.0 0.5 4.0 0.5 0.80 51 4.0 2.00 100 0.001 0.5 0.996 10.0 2.0 0.0 0.0 0.0 0.1 3.0 0.5 4.0 0.5 0.80 1/ TFF = Till soil, Forested, Flat (0-5%) slope; TFM = same, with Moderate (5-15%) slope; TFS = same, with Steep (>15%) slope; TGF, TGM, TGS = same progression, but vegetation type is Grass; OF = Outwash soil, Forested, all slopes; OG = same, with Grass Table C-5. R/D Requirements by Subcatchment for Mitigated -Future Scenario Total Detention Pond Storage Volume RCHRES Number Subcatchment (acre-ft) (watershed inches)" 11 LKA 1.92 0.065 15 LKC 0.49 0.030 25 EFK 1.20 0.035 35 N FK 10.33 0.106 45 CAC 2.50 0.064 55 COU 7.24 0.268 60 CFD 9.14 0.159 70 MVM 0.57 0.046 75 RHC 3.62 0.108 80 MVL 1.94 0.057 85 PSC 10.66 0.312 95 LMC 2.70 0.070 100 CCP 12.53 0.301 101 WT4 4.93 0.352 103 LBU 10.15 0.243 105 LBL 7.63 0.298 110 CN5 2.52 0.388 120 CN4 2.26 0.352 125 NHC 5.45 0.382 130 CN3 3.79 0.350 131 HCU 12.14 0.518 133 HCM 8.46 0.297 135 HCL 7.34 0.291 140 CN2 2.70 0.149 145 GYP 5.63 0.322 150 CN1 12.81 0.826 160 BNB 2.21 0.332 Total 152.86 0.2042J 1/ Computed per acre of subbasin area for each individual subbasin. 2/ Computed per acre of entire May Creek basin. Table C-6. Detention Pond Contributing Area by Subcatchment for Mitigated -Future Scenario PERLND Type RCHRES Subcatch- TFF TFM TFS TGF TGM TGS OF OG SA EIA Total Number ment (acres) (ac) (ac) (ac) (ac) (ac) (ac) (ac) (ac) (ac) (ac) 11 LKA 0.0 0.0 0.0 24.0 0.0 0.0 0.0 0.0 0.0 2.4 26.4 15 LKC 0.0 0.0 0.0 6.4 0.0 0.0 0.0 0.0 0.0 0.8 7.2 25 EFK 0.0 0.0 0.0 0.0 0.0 3.2 0.0 3.2 0.0 2.4 8.8 35 NFK 0.0 0.0 0.0 0.0 0.0 3.2 0.0 4.0 0.0 19.2 26.4 45 CAC 0.0 0.0 0.0 0.0 32.0 0.0 0.0 0.0 0.0 4.0 36.0 55 COU 0.0 0.0 0.0 0.0 8.0 80.0 0.0 0.0 0.0 9.6 97.6 60 CFD 0.0 0.0 0.0 16.0 0.0 0.0 0.0 12.0 0.0 24.0 52.0 70 MVM 0.0 0.0 0.0 0.0 0.0 4.8 0.0 4.8 0.0 0.8 10.4 75 RHC 0.0 0.0 0.0 0.0 28.0 0.0 0.0 0.8 0.0 8.0 36.8 80 MVL 0.0 0.0 0.0 0.0 0.0 5.6 0.0 1.6 0.0 14.4 21.6 85 PSC 0.0 0.0 0.0 80.0 0.0 0.0 0.0 13.6 0.0 22.4 116.0 95 LMC 0.0 0.0 0.0 1.6 9.6 20.0 0.0 2.4 0.0 4.0 37.6 100 CCP 0.0 0.0 0.0 48.0 112.0 29.6 0.0 48.8 0.0 27.2 265.6 101 WT4 0.0 0.0 0.0 24.0 24.0 9.6 0.0 0.0 0.0 8.8 66.4 103 LBU 0.0 0.0 0.0 0.0 40.8 40.0 0.0 8.8 0.0 25.6 115.2 105 LBL 0.0 0.0 0.0 4.0 24.0 24.0 0.0 37.6 0.0 16.8 106.4 110 CN5 0.0 0.0 0.0 4.0 6.4 0.0 0.0 16.0 0.0 5.6 32.0 120 CN4 0.0 0.0 0.0 1.6 7.2 3.2 0.0 10.4 0.0 8.0 30.4 125 NHC 0.0 0.0 0.0 0.0 32.0 33.6 0.0 0.8 0.0 13.6 80.0 130 CN3 0.0 0.0 0.0 1.6 3.2 3.2 0.0 14.4 0.0 7.2 29.6 131 HCU 0.0 0.0 0.0 80.0 29.6 0.0 0.0 8.8 0.0 27.2 145.6 133 HCM 0.0 0.0 0.0 18.4 0.0 0.0 0.0 6.4 0.0 31.2 56.8 135 HCL 0.0 0.0 0.0 39.2 0.0 0.0 0.0 4.8 0.0 18.4 62.4 140 CN2 0.0 0.0 0.0 1.6 0.0 0.0 0.0 9.6 0.0 6.4 17.6 145 GYP 0.0 0.0 0.0 8.0 16.0 12.0 0.0 3.2 0.0 13.6 52.8 150 CN1 0.0 0.0 0.0 0.0 2.4 4.8 0.0 20.8 6.0 20.0 48.0 160 BNB 0.0 0.0 0.0 0.0 1.6 0.0 0.0 1.0 0.0 8.8 11.4 Total 0.0 0.0 0.0 358.4 376.8 276.8 0.0 233.8 0.0 350.4 1,597.0 1/ TFF = Till soil, Forested, Flat (0-5%) slope; TFM = same, with Moderate (5-15%) slope; TFS = same, with Steep (>15%) slope; TGF, TGM, TGS = same progression, but vegetation type is Grass; OF = Outwash soil, Forested, all slopes; OG = same, with Grass; SA = Saturated soils, all vegetation types, all slopes; EIA = Effective Impervious Area Table C-7. Flood Frequency Analysis for all Land -use Scenarios 2-year Flood 10-year Flood 100-year Flood RCHRES Subcatch- Forested Current Future Future Mit- Forested Current Future Future Mit- Forested Current Future Future Mit- Number ment (cfs) (cfs) (cfs) igated (cfs) (cfs) (cfs) igated (cfs) (cfs) (cfs) (cfs) igated (cfs) (cfs) 11 LKA 5 5 6 6 6 8 11 11 8 13 20 20 15 LKC 11 17 20 19 17 26 31 30 24 36 48 47 25 EFK 35 42 69 67 57 68 101 99 89 102 144 141 35 NFK 105 123 176 169 175 199 248 242 268 296 332 328 45 CAC 43 46 82 78 77 81 132 124 126 133 206 193 55 COU 24 26 55 35 42 46 85 63 70 77 127 108 60 CFD 151 170 202 193 250 285 359 348 396 461 601 590 70 MVM 143 164 191 183 242 276 332 322 385 445 532 523 75 RHC 17 33 43 39 27 51 68 62 42 76 104 96 80 MVL 141 165 195 188 245 285 347 339 397 468 569 562 85 PSC 10 26 41 32 18 42 66 51 31 68 106 82 95 LMC 40 42 50 43 71 75 85 78 118 125 139 130 100 CC P 173 208 253 243 299 357 438 429 482 582 727 706 101 WT4 7 9 15 10 12 15 26 20 20 25 42 38 103 LBU 16 23 28 26 28 43 54 50 47 72 101 92 105 LBL 21 36 51 42 36 62 86 76 60 103 144 137 110 CN5 175 210 258 245 301 361 443 435 485 589 734 716 120 CN4 195 245 309 285 337 420 529 509 546 687 874 861 125 NHC 6 12 21 14 10 20 34 22 16 31 54 34 130 CN3 200 255 328 297 346 435 554 528 560 707 905 894 131 HCU 7 19 34 22 13 30 53 34 21 45 81 52 133 HCM 13 43 50 46 23 52 51 52 37 60 52 57 135 HCL 20 63 81 69 36 85 101 90 59 109 123 113 140 CN2 217 316 415 363 377 521 657 615 617 794 1,013 1,012 145 GYP 6 16 25 18 10 25 39 29 16 38 60 44 150 CN1 223 336 447 389 387 548 699 652 633 825 1,058 1,055 160 BNB 223 341 452 391 389 556 706 652 636 835 1,069 1,059 APPENDIX D FLOODING Table D-1. Lower May Creek Water Surface Elevations from HEC-2 Modelling 10-yr. Flood 100-yr. Flood Cross-section Current Scenario Future cenano Current Scenario Future -Scenario Number Location Taken Flow Elevation Flow Elevation Flow Elevation Flow Elevation by (cfs) (ft) (cfs) (ft) (cfs) (ft) (cfs) (ft) 0.0 Lower Mill Br. SWIVI 556 15.91 652 1 4 1059 17.16 16 Lower Mill Br. SWM 556 16.50 652 16.79 835 17.29 1059 18.61 139 SWM 556 17.49 652 17.81 835 18.40 1059 19.35 209 Mill Foot Br. SWM 556 17.86 652 18.06 835 18.42 1059 19.31 213 Mill Foot Br. SWM 566 18.24 652 18.45 835 18.83 1059 19.39 332 SWM 566 19.33 652 19.58 835 20.00 1059 20.45 495 Upper Mill Br. SWM 566 20.56 652 20.80 835 21.19 1059 21.63 512 Upper Milll Br. SWM 566 21.78 652 22.46 835 23.04 1059 23.47 634 SWM 566 22.13 652 22.74 835 23.31 1059 23.76 1030 INCA 566 23.85 652 24.20 835 24.77 1059 25.26 1103 Railroad Br. INCA 566 25.58 652 25.93 835 26.52 1059 27.17 1110 Railroad Br. INCA 566 25.63 652 25.99 835 26.58 1059 27.25 1140 INCA 566 25.60 652 25.95 835 26.51 1059 27.15 1165 Lk. Wash. Blvd. INCA 566 26.12 652 26.48 835 27.11 1059 27.82 1195 Lk. Wash. Blvd. INCA 566 26.22 652 26.57 835 27.20 1059 27.92 1285 INCA 566 26.62 652 26.90 835 27.47 1059 28.18 1478 SWM 566 28.26 652 28.52 835 28.80 1059 29.50 1862 interp. 566 32.04 652 32.35 835 32.97 1059 33.27 2246 INCA 548 35.43 652 35.71 825 36.10 1055 36.60 2328 INCA 548 36.21 652 36.60 825 37.15 1055 37.82 2641 interp. 548 39.79 652 40.13 825 40.65 1055 41.25 2954 SWM 548 42.96 652 43.27 825 43.74 1055 44.27 3710 interp. 548 52.65 652 52.96 825 53.40 1055 53.93 4088 INCA 548 58.10 652 58.41 825 59.10 1055 59.66 4518 SWM 548 64.78 652 65.09 825 65.33 1055 65.73 5293 SWM 548 75.45 652 75.65 825 76.21 1055 76.73 5993 SWM 548 84.92 652 85.30 825 85.71 1055 86.24 6573 INCA 548 94.80 652 95.07 825 95.50 1055 95.99 6673 31st St. INCA 548 96.81 652 97.15 825 97.62 1055 98.13 6703 31st St. INCA 548 96.86 652 97.21 825 97.70 1055 98.24 6893 INCA 548 99.85 652 100.15 825 100.60 1055 101.14 7101 private br. INCA 548 102.99 652 103.30 825 103.76 1055 103.58 7116 private br. INCA 548 103.25 652 103.61 825 104.11 1055 104.80 7271 INCA 521 104.53 615 104.95 794 105.59 1012 106.38 7345 interp. 521 106.22 615 106.52 794 107.02 1012 107.76 7405 31st St. INCA 521 106.93 615 107.48 794 108.47 1012 109.59 7429 31st St. INCA 521 109.33 615 110.46 794 111.50 1012 112.91 7444 interp. 521 110.65 615 111.98 794 112.29 1012 113.24 7642 INCA 521 111.18 615 112.37 794 112.80 1012 113.62 7899 INCA 521 112.88 615 113.19 794 113.72 1012 114.42 8020 private br. INCA 521 114.27 615 114.46 794 114.84 1012 115.21 8036 private br. INCA 521 114.44 615 115.01 794 115.59 1012 115.99 8153 INCA 521 118.14 615 117.40 794 118.32 1012 118.48 9353 INCA 521 135.15 615 136.04 794 136.09 1012 136.19 Table D-2. May Valley Water Surface Elevations from HEC-2 Modelling 10-yr. Flood 100-yr. Flood Cross-section Current Scenario Future Scenario Current Future Scenario Scenario Number Location Taken Flow Elevation Flow Elevation Flow Elevation Flow Elevation by (cfs) (ft) (cfs) (ft) (cfs) (ft) (cfs) (ft) 0.1 below CoalCr Pwy FEMA 357 265.85 4 4 30 Coal Cr. Pkwy. SE FEMA 357 266.98 429 267.32 582 267.91 706 268.31 650 FEMA 357 276.52 429 276.74 582 277.18 706 277.50 1440 FEMA 357 289.12 429 289.45 582 290.05 706 290.46 2440 FEMA 357 298.47 429 298.76 582 299.32 706 299.73 2725 FEMA 357 302.73 429 303.01 582 303.55 706 303.94 2736 143rd Ave. SE FEMA 357 302.88 429 303.16 582 303.67 706 304.02 2746 143rd Ave. SE SWM 357 303.08 429 303.42 582 304.10 706 304.54 2756 SWM 357 303.16 429 303.51 582 304.18 706 304.72 3061 FEMA 357 305.49 429 305.96 582 306.76 706 307.32 3571 FEMA 357 309.05 429 309.33 582 309.80 706 310.13 3591 146th Ave. SE FEMA 357 309.10 429 309.39 582 309.87 706 310.21 3602 146th Ave. SE SWM 357 309.14 429 309.44 582 309.96 706 310.32 3622 SWM 357 309.23 429 309.56 582 310.15 706 310.59 4047 FEMA 357 309.60 429 309.98 582 310.70 706 311.25 4397 FEMA 357 309.64 429 310.02 582 310.74 706 311.28 4507 148th Ave. SE FEMA 285 309.66 339 310.02 468 310.70 562 311.22 4530 148th Ave. SE SWM 285 309.67 339 310.03 468 310.83 562 311.44 4580 FEMA 285 309.93 339 310.34 468 311.23 562 311.54 4630 INCA 285 309.93 339 310.34 468 311.23 562 311.54 4825 FEMA 285 310.00 339 310.39 468 311.28 562 311.59 5305 Cottom's Stbls Ln FEMA 285 310.11 339 310.47 468 311.32 562 311.63 5316 Cottom's Stbis Ln SWM 285 310.26 339 310.52 468 311.31 562 311.61 5366 FEMA 285 310.65 339 310.96 468 311.44 562 311.71 6041 FEMA 285 310.80 339 311.08 468 311.56 562 311.84 6646 pvt. bridge FEMA 285 310.79 339 311.11 468 311.59 562 311.86 6658 pvt. bridge FEMA 285 310.88 339 311.10 468 311.58 562 311.85 6708 FEMA 285 310.93 339 311.17 468 311.64 562 311.91 7123 FEMA 285 311.14 339 311.25 468 311.70 562 311.97 7618 FEMA 285 310.96 339 310.95 468 311.35 562 312.04 7628 pvt. bridge FEMA 285 311.05 339 311.10 468 313.23 562 312.49 7640 pvt. bridge SWM 285 311.51 339 311.90 468 313.25 562 312.91 7650 SWM 285 312.23 339 312.67 468 313.28 562 313.06 8835 FEMA 285 312.42 339 312.79 468 313.38 562 313.25 9985 FEMA 276 312.68 322 313.01 445 313.56 523 313.56 10935 FEMA 276 315.26 322 315.30 445 315.49 523 315.71 11435 FEMA 276 316.25 322 316.48 445 316.91 523 317.04 11735 INCA 276 318.53 322 318.76 445 319.07 523 319.25 11835 164th Ave. SE FEMA 276 319.05 322 319.34 445 320.01 523 320.39 11863 164th Ave. SE FEMA 276 319.39 322 319.75 445 320.30 523 320.56 11963 FEMA 276 319.41 322 319.77 445 320.32 523 320.58 12323 FEMA 276 319.47 322 319.78 445 320.33 523 320.59 13143 FEMA 276 319.48 322 319.80 445 320.34 523 320.60 13893 FEMA 276 319.50 322 319.81 445 320.36 523 320.61 14608 FEMA 276 319.57 322 319.72 445 •320.36 523 320.62 15488 FEMA 276 321.92 322 321.98 445 321.98 523 322.03 16148 FEMA 276 322.86 322 322.97 445 323.26 523 323.39 16953 FEMA 276 323.75 322 323.85 445 324.05 523 324.17 17563 FEMA 276 324.07 322 324.33 445 324.98 523 325.36 17573 SR-900 FEMA 293 324.50 371 324.93 445 325.24 523 325.63 17631 SR-9001' SWM 293 326.69 371 327.58 445 328.48 523 329.44 17641 FEMA 293 326.94 371 327.95 445 329.07 523 329.36 17741 INCA 293 327.27 371 328.32 445 329.43 523 329.83 18026 FEMA 293 327.31 371 328.33 445 329.44 523 329.84 18216 INCA 293 329.93 371 330.00 445 330.07 523 330.13 18316 SE May Valley Rd. FEMA 199 331.39 242 331.59 296 331.71 328 331.87 18329 SE May Valley Rd. INCA 199 331.63 242 331.89 296 332.15 328 332.34 18429 INCA 199 332.23 242 332.55 296 322.93 328 333.17 18734 FEMA 199 332.40 242 332.69 296 333.04 328 333.26 19514 FEMA 199 334.21 242 334.26 296 334.38 328 334.38 20444 FEMA 199 338.34 242 338.40 296 338.40 328 338.40 21144 FEMA 199 342.58 242 342.90 296 343.26 328 343.62 1/ Modeled elevations at SR-900 were based on a computer routine that has now been superseded. Further analysis suggests the elevations in this table are too high by approximately 2.5 feet due to inaccuracies in the representation of friction losses through the culvert structure. This revised analysis indicates road overtopping at SR-900 is unexpected for all modeled events, up to and including the 100-year. APPENDIX E WATER QUALITY Table E-l. Guidelines for Freshwater Sediment. Page 1 of 3 Tex( reference=> A B C D E F G (Hart et al., (EPA, 1988) EPA Interim (Anon., 1988) Ont. Min. Environ. (Persaud et al., 1991) Provincial (WDNR.85.9 1988) (EPA. 1977) EPA Region V Guidelines for (Neff et al., Sed• Criteria for Nonpolar Disolved Material Disposal Classification Sediment Quality Guidelines 0) Wisconsin Sediment the Pollutional Class of Harbor Seds. 1986) SLC Organics Criteria Dept. of Quality for Lowest Severe Natural Guidelines Non Moderately Heavily Freshwater Chronic Residue Open Unrestricted Restricted Compound Name PP Mol Wt. No Effect Effect Effect Resources Polluted Polluted Polluted Sediments Basis Basis Water Land Land METHODS=> EQP SLC SLC Note I BKG BKG BKG METALS UNITS=> mg/kg dry mg/kg dry mg/kg dry mg/kg dry mg/kg dry mg/kg dry Antimony Y 121.8 - - - - - Arsenic Y 74.9 6 33 10 BKG 17 SLC <3 3-8 >8 Barium N 137.3 - 500 BKG - <20 20-60 >60 Cadmium Y 112.4 0.6 10 1 BKG 2.5 BID - - >6 Chromium Y 52.0 26 I10 100 BKG 100 BID <25 25-75 >75 Cobalt N 58.9 50. - - - - Copper Y 63.5 16 I10 100 BKG 85 BID <25 25-50 >50 Iron (%) N 55.8 2 4 - 5.9 BKG <1.7 1.7-2.5 >2.5 Lead Y 207.2 31 250 50 BKG 55 BKG <40 40-60 >60 Manganese N 54.9 460 I100 - 1200 BKG <300 300-500 >5W Mercury Y 200.6 _ 0.2 2 0.1 BKG 0.6 BKG < 1 - > 1 Nickel Y 58.7 16 75 100 BKG 92 SLC <20 20-50 >50 Selenium Y 79.0 - - 1 BKG - - - Silver Y 107.9 0.5' - - Zinc Y 65.4 120 820 100 BKG 143 BKG <90 90-200 >200 PESTICIDES/CHLOR. ORGS. mg/kg dry mg/kg dry mg/kg OC mg/kg OC PCB Y M 0.01 0.07 530 0.05 BKG 4.00 SLC PCB-1016 Y M 0.007 53 0.75 SLC PCB-1248 Y M 0.03 150 3.50 SLC PCB-1254 Y M 0.06 34 5.75 SLC PCB-1260 Y M 0.005 24 2,3,7,8-TCDD Y 322.0 - - 3.3 EA EQP 2,3,7,8-TCDF N 306.0 - - < 1.0 Pg/g Aldrin Y 362.0 0.002 8 0.01 BKG 0.20 SLC BHC Y 288.0 0.003 12 - 0.32 SLC a-BHC Y 288.0 0.006 10 0.60 SLC b-BHC Y 288.0 0.005 21 0.50 SLC g-BHC (Lindane) Y 288.0 0.0002 0.003 1 0.05 BKG 0.30 SLC Chlordane Y M 0.005 0.007 6 0.01 BKG 0.75 SLC g-Chlordane Y 409.8 - 0.05 SLC Chlorpyrifos N 351.0 SLC EQP EQP Note 2 mg/kg dry mg/kg dry mg/kg dry 8 14 20 1 1.6 4 25 120 120 50 20 25 25 100 10D 1 NA 3.5 50 NA 500 0.3 NA 0.5 25 17 60 - 14 2 0.5 - - 100 220 500 mg/kg OC mg/kg OC mg/kg OC mg/kg dry mg/kg dry mg/kg dry 0.29 0.05 NA >2.0 19.5 - 0.157 0.098 3.22 Table E-1. Guidelines for Freshwater Sediment. Page 2 of 3 Text reference -> A 11 C D E F G (Hart et al., (EPA, 1988) EPA Interim (Anon., 1988) Ont. Min. Environ. (Persaud et al., 1991) Provincial (WDNR.85.9 1988) (EPA, 1977) EPA Region V Guidelines for (Neff et al., Sed. Criteria for Nonpolar Disolved Material Disposal Classification Sediment Quality Guidelines 0) Wisconsin Sediment the Pollutional Class of Harbor Seds. 1996) SLC Organics Criteria Dept. of Quality for Lowest Severe Natural Guidelines Non Moderately Heavily Freshwater Chronic Residue Open Unrestricted Restricted Compound Name PP Mol Wt. No Effect Effect Effect Resources Polluted Polluted Polluted Sediments Basis Basis Water land Land Dieldrin Y 378.0 0.0006 0.002 91 0.01 BKG 1.90 SLC 0.021 19.9 0.13 Endrin Y 379.0 0.0005 0.003 130 0.05 BKG 0.30 SLC 1.04 0.0532 Hexachlorobutadiene Y 260.7 0.01 0.02 24 - - - - Heptachlor Y 370.0 0.0003 - 0.05 BKG 0.20 SLC - 0.11 Hetachlor epoxide Y 386.0 - 0.005 5 - - 0.008 - Mirex N 545.6 - 0.007 130 - 0.70 SLC - - - - - - - - DDT (total) Y M - 0.007 12 0.01 BKG 0.50 EQP - - - 0.19 - 0.928 - - o.p'-DDT Y 352.0 - - - - - - op -pp -DDT Y M 0.008 71 - p.p'-DDD Y 318.0 0.008 6 0.80 SLC p.p'-DDE Y 316.0 0.005 19 0.50 SLC p.p'-DDT Y 354.5 - - - - 0.6,0.9 SLC - - - - - - - - Ethyl parathion N 291.3 0.081 Toxaphene Y M - - - 0.05 BKG - - - - - - - - Chloroform Y 119.4 2.7 EQP Methylene chloride Y 94.9 - - - 126 EQP - - - - - - - - - PAH mg/kg dry mg/kg OC mg/kg OC mg/kg OC PAH (total) - M - 2 I1000 89 EQP - - - - - - - - - - LPAH M - - - - - - - - - - - - - - Naphthalene Y 128.2 - - - 1240 EQP - - - - - - - - - - 2-Methy1napthalene N 142.2 - - - - - - - - - - - - - - Acenapthylene Y 152.2 - - - - - - - - - - - - - - Acenapthene Y 154.2 - - - 92 EQP - - - - - 732 - - - - Fluorene Y 166.2 - - Phenanduene Y 178.2 - - - - - - - - - 139 - - - - Anthracene Y 178.2 - - - - - - - - - - - - - - HPAH M - - Fluoranthene Y 202.3 1216 EQP 1893 Pyrene Y 202.3 - 1311 Benzo(a)anthracene Y 228.3 - - - - - - - - - 1317 - - - - Chrysene Y 228.3 - BenzoOuoranthenes Y 252.0 - - - - - - - - - - - - - - Benzo(a)pyrene Y 252.3 89 EQP 1063 Table E-1. Guidelines for Freshwater Sc(limcnt. Page 3 of 3 Text reference=> :1 It C D I[ F G (Hart et al., (EPA, 1988) EPA Interim (Anon., 1988) Ont. Min. Environ. (Persaud et al., 1991) Provincial (WDNR.85.9 1988) (EPA, 1977) EPA Region V Guidelines for (Neff et al., Sed. Criteria for Nonpolar Disolved Material Disposal Classification Sediment Quality Guidelines 0) Wisconsin Sediment the Pollutional Class of Harbor Seds. 1986) SLC Organics Criteria Dept. of Quality for Lowest Severe Natural Guidelines Non Moderately Heavily Freshwater Chronic Residue Open Unrestricted Restricted Compound Name PP Mol Wt. No Effect Effect Effect Resources Polluted Polluted Polluted Sediments Basis Basis Water Land Land Ideno(1,2,3<,d)pyrene Y 276.0 - - - - - - - - - - - - - - Benzo(g,h,i)perylene Y 276.0 - - - - - - - - - - - - - - Dibenzo(a,h)anthracene Y 278.0 - - - - - - - - - - - - - - OTHER mg/kg dry mg/kg dry mg/kg dry mg/kg dry mg/kg dry mg/kg OC mg/kg dry Oil & Grease N M 1500, 1000 BKG <1000 1000-2000 >2000 15W Volatile Solids (%) N M - - <5 5.8 >8 Loss on Ignitition (%) N M - - - - - - - - - - - 6 - - COD N M - <40000 40000.80000 > 800W - Cyanide Y 26.0 0.1• <0.10 0.10-025 >0.25 0.1 Total Phosphorous N M 6W 2000 <420 42G-00 >650 1000 Ammonia N 17.0 - 100• - - - <75 75-200 >200 - - - 100 - - TOC (%) N M - 1 10 - - - - - - - - - - - Total Kjeldahl Nitrogen N M 550 4800 <1000 1000-2000 >2000 2000 Aniline N 93.1 - - 0.0662 Toluene Y 92.2 5250 EQP Eth Thenzene Y 1062 1100 EQP Y BKG - Background Method mg/kg = ug/g = parts per million PP - Priority Pollutant SLC - Screening Level Method mg/kg dry = mg/kg dry weight M = Mixture, precise molecular weight is indeterminable EQP - Equilibrium Partitioning Method mg/kg OC = mg/kg organic carbon BIO - Bioassay Method (Spiked) METHODS> Means all entries in that column were derived using the method indicated. Methods used by WDNR (1985, 1990) and Beak Consultants (Hart et al., 1988) are listed individually. See Note 1. None 1: BKG derived values reported in mg/kg dry weight. EQP derived values reported in mg/kg organic carbon. Note 2: Methods data not currently available. For Provincial Sediment Quality Guidelines, indicates values borrowed from Ministry of Environment Dredged Disposal Criteria. NA Data not available Compiled by Washington State Department of Ecology. Version 1, September 1991. IMPORTANT: Publication of these numbers and methods does NOT imply endorsement or recommendation by the Department of Ecology. Table E-2. Groundwater Quality Criteria (Table 1 in WAC 173-200). GROUND WATER QUALITY CRITERIA CONTAMINANT CRITERION PRIMARY AND SECONDARY CONTAMINANTS RADIONUCLIDES A. PRIMARY CONTAMINANTS Barium* 1.0 Cadmium* Chromium* Lead* Mercury* Selenium* Silver* Fluoride Nitrate (as N) Endrin Methoxychlor 1, 1, 1 -Trichloroethane 2-4 D 2,4,5-TP Silvex Total Coliform Bacteria B. SECONDARY CONTAMINANTS Copper* Iron* Manganese* Zinc* Chloride Sulfate Total Dissolved Solids Foaming Agents pH Corrosivity Color Odor C. RADIONUCLIDES Gross Alpha Particle Activity Gross Beta Particle Radioactivity Gross Beta Activity Tritium Strontium-90 Radium 226 & 228 Radium -226 H. CARCINOGENS Acrylamide Acrylonitrile Aldrin Aniline Aramite Arsenic* Azobenzene Benzene Benzidine Benzo(a)pyrene Benzotrichloride Benzyl chloride Bis(chloroethyl)ether Bis(chloromethyl)ether Bis(2-ethylhexyl) phthalate Bromodichloromethane Bromoform Carbazole Carbon tetrachloride Chlordane Chlorodibromomethane Chloroform 4 Chloro-2-methyl aniline 4 Chloro-2-methyl anaine hydrochloride 0.01 0.05 0.05 0.002 0.01 0.05 4 10 0.0002 0.1 0.20 0.10 0.01 1/100 AND milligrams/ liter (mg/1) mg/1 mg/1 mg/l mg/l mg/l mg/1 mg/l mg/1 mg/I mg/l mg/l mg/1 mg/l ml 1.0 mg/1 0.30 mg/1 0.05 mg/1 5.0 mg/1 250 mg/I 250 mg/I 500 mg/l 0.5 mg/1 6.5-8.5 noncorrosive 15 color units 3 threshold odor units 15 50 20,000 8 0.02 0.07 0.005 14 3 0.05 0.7 1.0 0.0004 0.008 0.007 0.5 0.07 0.0004 6.0 0.3 5 5 0.3 0.06 0.5 7.0 0.1 0.2 pico Curie/ liter (pCi/1) pCi/l pCi/l pCi/l pCi/l pCi/l micrograms/ liter µg/l µg/l µg/l µg/l µg/1 (µg/4 µg/I µg/1 µg/1 µg/I µg/l l+g/l µg/l µg/I µg/l µg/l µg/l µg/I µgIl µg/l µg/1 µg/1 µg/l µg/1 o-Chloronitrobenzene 3 µg/l p-Chloronitrobenzene 5 µgll Chlorthalonil 30 µg/l Diallate I µg/l DDT (includes DDE and DDD) 0.3 µg/l 1,2 Dibromoethane 0.001 µg/1 1,4 Dichlorobenzene 0.4 µg/1 3,3' Dichlorobenzidine 0.2 µg/l 1,1 Dichloroethane 1.0 µg/1 1,2 Dichloroethane (ethylene chloride) 0.5 µg/l 1,2 Dichloropropane 0.6 µg/l 1,3 Dichloropropene 0.2 µg/l Dichlorvos 0.3 µg/I Dieldrin 0.005 µg/l 3,3' Dimethoxybenzidine 6 µg/I 3,3 Dimethylbenzidine 0.007 1,2 Dimethylhydrazine 60 µg/l 2,4 Dinitrotoluene 0.1 µg/I 2,6 Dinitrotoluene 0.1 µg/l 1,4 Dioxane 7.0 µg/l 1,2 Diphenylhydrazine 0.09 µg/l Direct Black 38 0.009 µg/l Direct Blue 6 0.009 14g/1 Direct Brown 95 0.009 µg/l Epichlorohydrin 8 µg/l Ethyl acrylate 2 µg1l Ethylene dibromide 0.001 µg/l Ethylene thiourea 2 µg/l Folpet 20 µg/1 Furazolidone 0.02 µg/1 Furium 0.002 µg/l Furmecyclox 3 µg/l Heptachlor 0.02 µg/1 Heptachlor Epoxide 0.009 µg/l Hexachlorobenzene 0.05 µg/l Hexachlorocyclohexane (alpha) 0.001 µg/I Hexachlorocyclohexane (technical) 0.05 µgll Hexachlorodibenzo-p-dioxin, mix 0.00001 µg/l Hydrazine/Hydrazine sulfate 0.03 µg/I Lindane 0.06 µg/l 2 Methoxy-5-nitroaniline 2 µg/l 2 Methylaniline 0.2 µg/l 2 Methylaniline hydrochloride 0.5 µg/l 4,4' Methylene bis(N,N'-dimethyl) aniline 2 µgh Methylene chloride (dichloromethane) 5 µg/l Mirex 0.05 µg/1 Nitrofurazone 0.06 µg/l N-Nitrosodiethanolamine 0.03 µg/1 N-Nitrosodiethylamine 0.0005 µg/1 N-Nitrosodimethylamine 0.002 µg/l N-Nitrosodiphenylamine 17 µg/l N-Nitroso-di-n-propylamine 0.01 µg/1 N-Nitrosopyrrolidine 0.04 µg/1 N-Nitroso-di-n-butylamine 0.02 µg/1 N-Nitroso-N-methylethylamine 0.004 µg/1 PAH 0.01 µg/l PBBs 0.01 µg/l PCBs 0.01 µg/l o-Phenylenediamine 0.005 µg/I Propylene oxide 0.01 µg/l 2,3,7,8-Tetrachlorodibenzo- p-dioxin 0.0000006 µg/l Tetrachloroethylene (perchloroethylene) 0.8 µg/1 p,a,a,a-Tetrachlorotoluene 0.004 µg/l 2,4 Toluenediamine 0.002 µg/l o-Toluidine 0.2 µg/l Toxaphene 0.08 µg/l Trichloroethylene 3 µg/l 2,4,6-Trichlorophenol 4 µg/l Trimethyl phosphate 2 µg/l Vinyl chloride 0.02 µg/l *metals are measured as total metals Table E-3. Repair Rates and Ages of Septic Systems in May Creek. Total A B C D E F G H I J K L M N Total number 995 127 65 72 29 21 134 43 88 38 37 17 212 14 98 of Systems Repair Rate* 18% 16% 51% 33% 21% 19% 20% 35% 15% 21% 19% 12% 8% 0% 18% Multiple 2% 1% 9% 6% 4% 5% 4% 5% 1% 0% 0% 0% 1% 0% 0% Repair Rate Record of 14% 17% 14% 19% 14% 24% 19% 12% 9% 16% 11% 6% 10% 21% 14% Pumping Average Age 21.7 20.3 21.4 28.7 22.7 15.3 26.7 21.5 18.5 25.8 21.8 16.9 19.4 16.2 19.5 (Years) Systems 36 % 33 % 29 % 32 % 31 % 33 % 31 % 33 % 68 % 34 % 32 % 76 % 32 % 36 % 29 % Inspected Systems 6% 2% 10% 17% 0% 0% 2% 7% 0% 15% 17% 31% 4% 0% 4% Failing or Prefailing** * Includes multiple repairs made to a specific system ** Percentage of those systems inspected Table E-4. King County Water Quality Data for 17 Stations During Storm Flow Conditions. Page 1 of 6 Sample ID 1 2 12/5/91 1/28/92 4/17/92 1/18/93 * 1/19/93 1/28/92 4/17/92 1/19/93 12/5/91 Sample Date Total Dissolved Total Dissolved Total Dissolved Total P (mg/1) 0.186 0.368 0.587 <0.10 0.054 0.088 0.089 0.115 0.064 SRP (mg/1) 0.019 0.034 0.045 0.013 0.03 0.032 0.046 0.015 NO3 & NO2 (mg/1) 0.807 1.27 0.65 2.2 1 1.43 0.152 0.314 0.918 Hardness (mg CaCO3/1) 42.1 37.7 29.5 64 39 29.1 30.5 39 52.1 FOG (mg/1) <0.25 <0.25 TSS (mg/1) 127.0 137 254 < 10 11 22 18 2.5 26 Turbidity (NTU) 29.0 36 37 < 1.0 4.6 22 3.2 1.4 8.8 Aluminum 0.82 <0.1 0.5 0.3 Antimony <0.05 <0.05 Arsenic <0.05 <0.05 <0.05 <0.05 <0.05 <0.05 Barium 0.011 0.0082 0.018 0.02 Beryllium <0.005 <0.005 <0.001 <0.001 <0.001 <0.001 Cadmium <0.005 <0.005 <0.003 <0.003 <0.003 <0.003 Calcium 9.2 11 9.2 9.9 Chromium <0.01 <0.01 <0.005 <0.005 <0.005 <0.005 Copper (mg/1) 0.0125 0.0112 <0.01 <0.01 <0.001 0.001 0.0065 0.002 0.003 0.0079 Iron 0.91 0.1 0.34 0.27 Lead (mg/1) 0.0143 0.0078 <0.003 <0.003 0.003 <0.001 0.0032 0.003 0.003 0.0036 Magnesium 4 4.5 3.8 4.2 Manganese 0.051 0.024 0.063 0.069 Mercury <0.0002 <0.0002 Molybdenum <0.02 <0.02 <0.02 <0.02 Nickel <0.01 <0.01 <0.02 <0.02 <0.02 <0.02 Potassium <2 <2 2 2 Selenium <0.05 <0.05 <0.05 <0.05 <0.05 <0.05 Silver <0.005 <0.005 <0.004 <0.05 <0.004 Sodium 5.5 5.6 7.3 7.2 Thallium <0.1 <0.1 <0.2 <0.2 <0.2 <0.2 Zinc (mg/1) 0.149 0.042 <0.01 <0.01 0.01 0.008 0.009 0.007 0.01 0.342 Fecal Colif. (#/100ml) > 1360 440 170 EST 100 58 660 Chloride (mg/1) 3.88 6.14 Ammonia (mg/1) <0.05 TDS (mg/1) 200 TKN (mg/1) 0.22 TOC (mg/1) 3.8 Fecal Strep (#/100ml) * ATI DATA 3/23/93 10:47 AM Page 2 of 6 Sample 11) 4 5 Sample Date 12/5/91 1/28/92 4/17/92 1/19/93 12/5/91 1/28/92 4/17/92 1/19/93 Total I)i.ssolved Total 1 Tota12 Diss. 1 Diss.2 Total P (mg/1) 0.079 0.106 0.523 0.248 0.093 0.169 0.49 0.048 SRP (mg/1) 0.016 0.03 0.028 0.019 0.016 0.034 0.034 0.014 NO3 & NO2 (mg/1) 0.504 1.27 0.353 0.716 0.017 1.37 0.771 1.17 Hardness (mg CaCO3/1) 24 30.1 16.9 57 10 40.2 36.9 48 41 FOG (mg/1) <0.25 <0.25 TSS (mg/1) 37 48 321 144 51 80 16s 8 Turbidity (NTU) 19 14 40 34 21 22 34 4 Aluminum 9.3 <0.1 0.61 0.58 <0.1 <0.1 Antimony Arsenic <0.05 <0.05 <0.05 <0.05 <0.05 <0.05 Barium 0.078 0.0082 0.0077 0.0077 0.0055 0.0087 Beryllium <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 Cadmium <0.003 <0.003 <0.003 <0.003 <0.003 <0.003 Calcium 12 8.8 12 10 12 12 Chromium 0.02 <0.005 <0.005 <0.005 <0.005 <0.005 Copper (mg/1) 0.0042 0.0058 0.024 <0.003 0.0058 0.0138 <0.001 <0.001 <0.001 <0.001 Iron 14 0.2 0.62 0.57 0.1 0.1 Lead (mg/1) 0.0058 0.0063 0.04 <0.001 0.0074 0.0159 0.001 0.001 <0.001 <0.001 Magnesium 6.5 4.2 4.3 3.7 4.3 4.3 Manganese 0.63 0.033 0.04 0.038 0.013 0.014 Mercury Molybdenum <0.02 <0.02 <0.02 <0.02 <0.02 <0.02 Nickel <0.02 <0.02 <0.02 <0.02 <0.02 <0.02 Potassium 3 <2 <2 <2 <2 <2 Selenium <0.05 <0.05 <0.05 <0.05 <0.05 <0.05 Silver <0.004 <0.004 <0.004 Sodium 7.7 6.1 6.7 5.7 6.1 6.2 Thallium <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 Zinc (mg/1) 0.095 0.041 0.17 0.02 0.052 0.044 0.01 0.005 0.006 <0.005 Fecal Colif. (#/100nil) EST 1400 EST 1200 4400 EST 80 EST 300 77 Chloride (mg/1) <0.50 6.53 2.43 Ammonia (mg/1) <0.010 0.016 0.016 TDS (mg/1) TKN (mg/1) 0.633 1.06 TOC (mg/1) Fecal Strep (#/100ml) 5000 960 * ATI DATA 3/23/93 10:47 AM Page 3 of 6 Sample ID 6D 6U 7 12/5191 1/28/92 4/17/92 1/19/93 12/5191 1/28/92 4/17/92 1/19/93 12/5/91 1/28/92 4/17/92 1/19/93 Sample Date Total Dissolved Total Dissolved Total Dissolved Total P (mg/1) 0.146 0.08 0.101 0.192 0.211 0.081 0.096 0.192 0.075 0.058 0.138 0.103 SRP (mg/1) 0.019 0.028 0.023 0.013 0.016 0.025 0.038 0.013 0.025 0.024 0.091 0.024 NO3 & NO2 (mg/1) 0.21 1.19 0.106 0.172 0.218 1.31 0.098 0.234 0.549 0.898 0.424 0.421 Hardness 17 24.5 6.42 23 23 26.1 7.42 28 47.7 54.2 35.1 40 (mg CaCO3/1) FOG (mg/1) 1.3 2 <0.25 TSS (mg/1) 35 22 53 89 61 19 45 92 15 8 35 38 Turbidity (NT" 47 16 15 34 29 18 9.2 32 7.2 6. 28 11 Aluminum 4.5 <0.1 5 <0.1 3.3 <0.1 Antimony Arsenic <0.05 <0.05 <0.05 <0.05 <0.05 <0.05 Barium 0.043 0.015 0.051 0.015 0.024 0.007 Beryllium <0.001 <0.001 <0.001 <0.001 <0.001 <0.00 Cadmium <0.003 <0.003 <0.003 <0.003 <0.003 <0.00 Calcium 6.1 6 7.4 6.1 11 10 Chromium 0.01 <0.005 0.01 <0.005 <0.005 <0.005 Copper (mg/1) 0.0053 0.0054 0.02 0.002 0.0063 0.0068 0.021 0.004 0.0023 0.0041 0.008 0.001 Iron 8.2 1.1 10 0.55 3.4 0.1 Lead (mg/1) 0.0126 0.007 0.05 0.001 0.0152 0.006 0.06 <0.001 0.0012 0.0018 0.004 <0.001 Magnesium 2 1.3 2.4 1.2 3 2.5 Manganese 0.28 0.23 0.32 0.19 0.54 0.11 Mercury Molybdenum <0.02 <0.02 <0.02 <0.02 <0.02 <0.02 Nickel <0.02 <0.02 <0.02 <0.02 <0.02 <0.02 Potassium 2 2 4 3 2 <2 Selenium <0.05 <0.05 <0.05 <0.05 <0.05 <0.05 Silver <0.004 <0.004 Sodium 4.3 3.9 5 4.4 5.3 4.3 Thallium <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 Zinc (mg/1) 0.05 0.047 0.13 0.094 0.056 0.042 0.19 0.11 u.u11 0.006 0.025 0.037 Fecal Colif. (#/100ml) > 1680 44O 76 EST 220 EST 180 220 > 1 160 EST 200 110 Chloride (mg/1) Ammonia (mg/1) TDS (mg/1) TKN (mg/1) TOC (mg/1) Fecal Strep (#/100ml) • ATI DATA 3/23/93 10:47 AM Pan 4of6 Sample ID 8 9 IOB 10 12/5/91 1/28/92 4/17/92 1/19/93 12/5/91 1/28/92 4/17/92 1/19/93 4/17/92 1/28/92 1/19/93 Sample Date Total Dissolved Total Dissolved Total Dissolved Total P (mg/1) 0.197 0.335 0.662 0.141 0.093 0.112 0.221 0.052 1.29 0.042 0.026 SKP (ing/1) 0.012 0.046 0.04 0.02 0.012 0.035 0.04 0.015 0.028 0.011 0.008 NO3 & NO2 (mg/1) 0.414 1.31 0.286 0.494 1.03 1.38 0.525 1.02 3.37 2.17 Hardness (mg CaCO3/1) 59.1 47.8 36.5 86 48.1 30.9 35.5 36 32.1 30 FOG (mg/1) <0.25 <0.25 <0.25 TSS (mg/1) 116 99 353 87 20 22 50 10 12 1.6 Turbidity (NTU) 54 71 76 41 13 28 25 4.9 1.9 0.39 Aluminum 6.7 <0.1 0.58 <0.1 0.2 <0.1 Antimony Arsenic <0.05 <0.05 <0.05 <0.05 <0.05 <0.05 Barium 0.048 0.017 0.0062 0.0087 0.002 0.0068 Beryllium <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 Cadmium <0.003 <0.003 <0.003 <0.003 <0.003 <0.003 Calcium 23 25 9.6 12 8.7 9.9 Chromium 0.006 <0.005 <0.005 <0.005 <0.005 <0.005 Copper (mg/1) 0.0106 0.0104 0.01 0.002 0.0045 0.0055 <0.001 <0.001 0.0043 <0.001 <0.001 Iron 6.4 0.08 0.65 0.2 0.08 <0.05 Lead (mg/1) 0.0053 0.0053 0.008 0.001 0.0019 0.0028 <0.001 <0.001 0.0025 <0.001 <0.001 Magnesium 7 6.6 2.9 3.7 2 2.3 Manganese 0.48 0.047 0.1 0.12 0.003 0.003 Mercury Molybdenum <0.02 <0.02 <0.02 <0.02 <0.02 <0.02 Nickel <0.02 <0.02 <0.02 <0.02 <0.02 <0.02 Potassium 2 <2 <2 <2 <2 <2 Selenium <0.05 <0.05 <0.05 <0.05 <0.05 <0.05 Silver Sodium 43 50 5.5 6.5 5 5.1 Thallimn <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 Zinc (mg/1) 0.081 0.026 .0.047 0.02 0.065 0.02 <0.005 <0.005 ).U1 1 <0.005 <0.005 Fecal Colif. (N/100ml) > 2140 EST 590 780 420 120 < 20 140 1400 Chloride (mg/1) 5.89 4.61 Ammonia (mg/1) 0.032 0.36 TDS (mg/1) TKN (mg/1) 1.28 0.933 TOC (mg/1) Fecal Strep (k/100►n1) 540 740 * ATI DATA 3/23/93 10:47 AM Page 5 og 6 Sample ID 11 12 12/5/91 1/28/92 4/17/92 1/19/93 12/5/91 1/28/92 4/17/92 1/18/93 * 1/19/93 Sample Date Total Dissolved Total Total Diss.1 Diss.2 Total P (mg/1) 0.104 0.103 0.402 0.105 0.119 0.119 0.345 <0.10 0.094 SRP (mg/1) 0.013 0.035 0.03 0.011 0.01 0.018 0.03 0.018 NO3 & NO2 (mg/1) 1.94 1.63 0.528 1.25 1 1.26 0.529 0.991 1.4 Hardness (mg CaCO3/1) 28.4 24.1 18.9 32 57.1 40.2 36.1 58 53 56 FOG (mg/1) <0.25 <0.25 TSS (mg/1) 37 44 127 45 45 52 139 10 35 Turbidity (NTU) 14 13 32 16 28 54 63 7 12 Aluminum 3.9 <0.1 1.7 3.2 <0.1 <0.1 Antimony <0.05 Arsenic <0.05 <0.05 <0.05 <0.05 <0.05 <0.05 <0.05 Barium 0.036 0.012 0.012 0.017 0.0094 0.0057 Beryllium <0.001 <0.001 <0.005 <0.001 <0.001 <0.001 <0.001 Cadmium <0.003 <0.003 <0.005 <0.003 <0.003 <0.003 <0.003 Calcium 8.5 7.7 14 15 13 14 Chromium <0.005 <0.005 <0.01 <0.005 <0.005 <0.005 <0.005 Copper (mg/1) 0.0039 0.006 0.003 0.002 0.0047 0.0085 <0.01 0.002 0.007 0.001 0.001 Iron 3.1 0.09 1.7 2.8 0.2 0.1 Lead (mg/1) 0.002 0.0033 0.0059 <0.001 0.0007 0.0036 <0.003 0.002 0.003 <0.001 <0.001 Magnesium 2.6 2 4.2 4.4 3.7 Manganese 0.38 0.048 0.15 0.19 0.11 0.1 Mercury <0.0002 Molybdenum <0.02 <0.02 <0.02 <0.02 <0.02 <0.02 Nickel <0.02 <0.02 <0.01 <0.02 <0.02 <0.02 <0.02 Potassium <2 <2 <2 2 <2 <2 Selenium <0.05 <0.05 <0.05 <0.05 <0.05 <0.05 <0.05 Silver <0.005 Sodium 7.1 6.6 7.9 8.1 7.3 7.3 Thallium <0.2 <0.2 <0.1 <0.2 <0.2 <0.2 <0.2 Zinc (mg/1) 0.045 0.38 0.032 0.01 0.038 0.051 <0.01 <0.009 0.02 <0.005 0.01 Fecal Colif. (#/100m1) EST 260 760 190 680 EST 380 160 Chloride (mg/1) 4.95 4.61 Ammonia (mg/1) 0.029 0.02 0.06 TDS (mg/1) 100 TKN (mg/1) 1.84 0.766 0.31 TOC (mg/1) 2.3 Fecal Strep (#/100nil) 360 680 > 1770 * ATI DATA 3/23/93 10:47 AM Pan 6of6 Sample 1D 16 17 FIELD REP 1215/91 1/28/92 4/17/92 1/19/93 12/5/91 1128/92 4/17/92 1/19193 12/5/91 1/28/92 4/17/92 1/19/93 Sample Date Total Dissolved Total Dissolved Total Dissolved Total P (mg/1) 0.159 0.105 0.606 0.091 0.125 0.065 0.179 0.077 0.124 0.141 0.628 0.442 SRP (mg/1) 0.004 0.017 0.03 0.008 0.007 0.043 0.024 0.006 0.01 0.013 0.047 0.003 NO3 & NO2 (mg/1) 0.18 1.77 0.7 1.12 1.93 1.58 0.713 0.52 1.93 1.63 0.018 0.208 Hardness 56.1 41 37.7 65 30 22.9 22.1 26 28 22.9 29.5 120 (mg CaCO3/1) FOG (mg/1) <0.25 <0.25 <0.25 TSS (mg/1) 154 01) 524 40 41 22 90 24 37 45 259 243 Turbidity (NTU) 87 40 61 24 _IX 14 48 34 48 13 40 348 Aluminum 5 <0.1 2.4 <0.1 29 <0.I Antimony Arsenic <0.05 <0.05 <0.05 <0.05 <0.05 <0.05 Barium 0.019 0.004 0.029 0.013 0.17 0.019 Beryllium <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 Cadmium <0.003 <0.003 <0.003 <0.003 <0.003 <0.003 Calcium 18 15 6.6 5.5 25 18 Chromium <0.005 <0.005 <0.005 <0.005 0.038 <0.005 Copper (mg/1) 0.0214 0.0086 0.009 <0.001 0.0066 0.0043 0.006 0.001 0.006 0.006 0.045 0.003 Iron 3.6 <0.05 2.1 0.07 29 0.2 Lead (mg/1) 0.0027 0.0042 0.003 <0.001 0.0093 0.0033 0.0046 <0.001 0.0109 0.0051 0.019 <0.001 Magnesium 5.2 2.2 15 Manganese 0.16 0.025 0.035 0.004 1.4 0.93 Mercury Molybdenum <0.02 <0.02 <0.02 <0.02 <0.02 <0.02 Nickel <0.02 <0.02 <0.02 <0.02 0.04 <0.02 Potassium <2 <2 <2 <2 5 <2 Selenium <0.05 <0.05 <0.05 <0.05 <0.05 <0.05 Silver Sodium 14 12 5.3 4.4 28 22 Thallium <0.2 <0.2 <0.02 <0.2 <0.2 <0.2 Zinc (mg/1) 0.219 0.03 0.02 0.01 0.0ol) 0.025 0.02 0.01 0.074 0.035 0.092 0.02 Fecal Colif. (N/100ml) 540 EST 340 140 740 700 140 1120 900 3 Chloride (mg/1) Ammonia (mg/1) TDS (mg/1) TKN (mg/1) TOC (mg/1) Fecal Strep (///100m1) * ATI DATA Table E-5. King County water quality data for 2 stations during base flow conditions. Sample ID 1 12 12A 1/18/93 3/2/93 1/18/93 3/2/93 Sample Date Total Dissolved Total Dissolved Total P (mg/1) <0.10 0.033 <0.10 0.035 SRP (mg/1) 0.01 0.016 NO3 & NO2 (mg/1) 2.2 1.12 0.839 Hardness (mg CaCO3/1) 64 64.4 58 53.6, 51 FOG (mg/1) TSS (mg/1) < 10 3 10 4.9 Turbidity (NTU) < 1.0 1.8 7 6.1 Aluminum 0.3 Antimony <0.05 <0.05 <0.05 Arsenic <0.05 <0.05 <0.05 <0.05 Barium 0.0059 Beryllium <0.005 <0.005 <0.005 <0.001 Cadmium <0.005 <0.005 <0.005 <0.003 Calcium 14 Chromium <0.01 <0.01 <0.01 <0.005 Copper (mg/I) <0.01 <0.01 <0.01 0.004 0.002 Iron 0.79 0.46 Lead (mg/1) <0.003 <0.003 <0.003 <0.001 <0.001 Magnesium 3.9 4.3 Manganese 0.14 0.14 Mercury <0.0002 <0.0002 <0.0002 Molybdenum <0.02 Nickel <0.01 <0.01 <0.01 <0.02 <0.02 Potassium <2.0 <2.0 Selenium <0.05 <0.05 <0.05 <0.05 Silver <0.005 <0.005 <0.005 <0.004 Sodium 6.8 7 Thallium <0.1 <0.1 <0.1 <0.2 <0.2 Zinc (mg/1) <0.01 <0.01 <0.01 <0.005 0.005 Fecal Colif. (#/100ml) Chloride (mg/1) Ammonia (mg/1) <0.05 0.019 0.06 0.061 TDS (mg/1) 200 100 TKN (mg/1) 0.22 0.355 0.31 0.493 TOC (mg/1) 3.8 3.22 2.3 5.26 Fecal Strep (N/100ml) G:\WP16\4248\MAYCK\07421A ♦ 3-27-95 Table E-6. Recharge potential of SCS soil series. Abbreviation Soil Series Name Recharge Potential Factor AgB Alderwood gravelly sandy loam, 0-6 % slopes M AgC Alderwood gravelly sandy loam, 6-15 % slopes M AgD Alderwood gravelly sandy loam, 15-30% slopes M AkF Alderwood & Kitsap soils, very steep M AmC Arents, Alderwood material, 6-15% slopes M BeC Beausite gravelly sandy loam, 6-15 % slopes H BeD Beausite gravelly sandy loam, 15-30% slopes H Bh Bellingham silt loam L EvB Everett gravelly sandy loam, 0-5 % slopes H EvC Everett gravelly sandy loam, 5-15 % slopes H EvD Everett gravelly sandy loam, 15-30% slopes H InC Indianola loamy fine sand, 4-15% slopes H KpB Kitsap silt loam, 2-8 % slopes M Ma Mixed alluvial land M No Norma sandy loam M OvC Ovall gravelly loam, 0-15% slopes H OvD Ovall gravelly loam, 15-25 % slopes H OvF Ovall gravelly loam, 40-75 % slopes H Py Puyallup fine sandy loam M RdC Ragnar-Indianola association, sloping H RdE Ragnar-Indianola association, moderately steep H Rh Riverwash H Sh Sammamish silt loam M Sk Seattle muck M Sm Shalcar muck L Tu Tukwila muck M Lake (Lakes -- not a soil series) H on (Ponds -- not a soil series) H Quar (Quarries -- not a soil series) H G:\WP16\4248\MAYCK\07421A ♦ 3-27-95 Table 1-7. Recharge potential of geologic map units Abbreviation Geological Map Unit Age Recharge Potential Factor m Modified Land Holocene M Qls Landslide Deposits M Qaf, Qf Alluvial / Debris Fan Deposits H Qyal Younger Alluvium M Qmw Mass Wastage Deposits M Qvr Recessional Outwash Deposits Vashon stade, Fraser Glaciation (Pleistocene) H Qvt Till L [Qvr + Qvt] Mixed Till and Recessional Outwash M Qva Advance Outwash Deposits M Qvi Ice Contact Deposits H Qtb Transitional Beds Early or Pre- Fraser Glaciation (Pleistocene) L Tr Renton Formation Puget Group Be Bedrock (Tertiary) M Tt Tukwila Formation L [Qvt + Tt] mixed till and Tukwila Formation L G:\WP16\4248\MAYCK\07421A • 3-27-95 Table E-8. Comparison of Existing Site Water Quality with Federal Critera and State Standards. Page 1 of 6 Sample ID Sample Date 1 2 3 4 12/5/91 1/28/92 4/17/92 4/17/92 1/19/93 1/28/92 4/17/92 1/19/93 12/5/91 12/5/91 1/28/92 4/17/92 1/19/93 Field Rep Copper Measured Value (ug/1) Total 12.5 11.2 15.8 14.1 < 1 6.5 1.5 2.0 7.9 4.2 5.8 22.8 24 Assumed Dissolved 3.36 3.01 4.25 3.80 11` t .75 0_404 3* 2.13 1.13 1.56 6.14 3" Acute Criteria Federal(ug/1) 7.84 7.07 5.61 5.61 7.30 5.54 5.79 7.30 9.59 4.62 5.72 3.32 10.44 State (ug/1) 6.76 6.09 4.84 4.84 6.29 4.78 4.99 6.29 8.27 3.98 4.93 2.86 9.00 Chronic Criteria Federal (ug/1) 5.65 5.14 4.17 4.17 5.29 4.12 4.29 5.29 6.77 3.49 4.24 2.59 7.31 State (ug/1) 4.87 4.43 3.59 3.59 4.56 3.55 3.69 4.50 5.84 3.01 3.65 2.23 6.30 Lead Measured Value (ug/1) Total 14.3 7.8 34.2 30.6 3 3.2 4.6 3 3.6 5.8 6.3 51.4 0.04 Assumed Dissolved 2.96 1.61 7.08 6.33 < 1 * 0.66 0.952 3* 0.745 1.20 1.30 10.6 < 1 * Acute Criteria Federal(ug/1) 27.14 23.58 17.26 17.26 17.26 16.96 18.01 24.62 35.60 13.27 17.71 8.49 39.92 State (ug/1) 18.65 16.20 11.86 11.86 11.86 11.65 12.37 16.92 24.46 9.12 12.16 5.83 27.42 Chronic Criteria Federal (ug/1) 1.06 0.92 0.67 0.67 0.96 0.66 0.7u 0.96 t .3'? 0.52 0.69 0.33 1.56 State (ug/1) 0.73 0.63 0.46 0.46 0.66 0.45 0.48 0.36 0.47 0.23 1.07 Zinc Measured Value (ug/l) Total 149.0 42 77 73 10 9 72 7 342 95 41 240 0.17 Assumed Dissolved 86.3 24.3 44.6 42.3 8* 5.2 41.7 1ti' 198 55.1 23.8 139 20* Acute Criteria Federal(ug/1) 56,22 51.20 41.60 41.60 52.70 41.12 42.79 52.70 67.35 34.92 42.31 25.95 72.68 State (ug/1) 50.10 45.62 37.06 37.06 46.95 36.64 38.12 46.95 60.11 31.12 37.70 23.12 64.76 Chronic Criteria Federal(ug/1) 50.92 46.38 37,67 37.67 47.73 37.24 38.75 47.73 61.00 31.63 38.32 23.50 65.83 State (ug/1) 1 45.37 41.321 33.57 33.57 42.531 33.181 34.53 42.53 1 54.35 28.181 34.15 1 20.941 58.65 * Actual Values Table E-8. Comparison of Existing Site Water Quality with Federal Criteria and State Standards. Page 2 of 6 Sample ID 5 6D 6U 12/5/91 1/28/92 4/17/92 1119/93 12/5/91 1/28/92 4/17/93 1/19/93 12/5/91 1/28/92 4/17/92 1/19/93 Sample Date 1 2 Copper Measured Value (ug/1) Total 5.8 13.8 7.2 < 1 < 1 5.3 5.4 4.7 20 6.3 6.8 3.9 21 Assumed Dissolved 1.56 3.71 1.94 < 1 * < 1 * 1.43 1.45 1.27 2* 1.70 1.83 1.05 4* Acute Criteria Federal (ug/1) 2.02 7.51 6.93 8.88 7.65 3.34 4.71 1.33 4.44 4.44 5.00 1.53 5.34 State (ug/1) 1.75 6.47 5.97 7.65 6.60 2.88 4.06 1.15 3.83 3.83 4.31 1.32 4.60 Chronic Criteria Federal (ug/1) 1.65 5.43 5.04 6.32 5.52 2.60 3.55 1.13 3.37 3.37 3.75 1.28 3.98 State (ug/1) 1.42 4.68 4.35 5.44 4.76 2.24 3.06 0.98 2.90 2.90 3.23 1.10 3.43 Lead Measured Value (ug/1) Total 7.4 15.9 10.3 1 1 12.6 7 19.3 50 15.2 6 12.8 60 Assumed Dissolved 1.53 3.29 2.13 < 1 * < 1 * 2.61 1.45 3.99 1* 3.15 1.24 2.65 < 1 * Acute Criteria Federal (ug/1) 4.35 25.59 22.95 32.07 26.24 8.56 13.63 2.48 12.57 12.57 14.77 2.98 16.15 State (ug/1) 2.99 17.58 15.77 22.03 18.03 5.88 9.36 1.70 8.64 8.64 10.15 2.05 11.09 Chronic Criteria Federal (ug/l) 0.17 1.00 0.89 1.25 1.02 0.33 0.53 0.10 0.49 0.49 0.58 0.12 0.63 State (ug/1) 0.12 0.69 0.61 0.86 0.70 0.23 0.36 0.07 0.34 0.34 0.40 0.08 0.43 Zinc Measured Value (ug/I) Total 52 44 28 10 5 50 47 58 130 56 42 36 190 Assumed Dissolved 30.1 25.5 16.2 6* < 5* 29.0 27.2 33.6 94* 32.5 24.3 20.9 110* Acute Criteria Federal(ug/1) 16.63 54.07 50.28 62.83 54.98 26.08 35.54 11.43 33.69 33.69 37.50 12.92 39.80 State (ug/1) 14.82 48.17 44.80 55.98 48.98 23.23 31.67 10.18 30.01 30.01 33.41 11.51 35.46 Chronic Criteria Federal(ug/1) 15.07 48.97 45.54 56.91 49.79 23.62 32.19 10.35 30.51 30.51 33.96 11.70 36.05 State (ug/1) 1 13.421 43.63 1 40.581 50.71 1 44.371 21.041 28.681 9.221 27.19 27.191 30.261 10.42 32.12 * Actual Values Table E-8. Comparison of Existing Site Water Quality with Federal Criteria and State Standards. Page 3 of 6 Sample ID Sample Date 7 8 9 10 12/5/91 1/28/92 4/17/92 1/19/93 12/5/91 1/28/92 1 4/17/92 1/19/93 12/5/91 1/28/92 4/17/92 1/19/93 4/17/92 Copper Measured Value (ug/1) Total 2.3 4.1 2.8 8 10.6 10.4 14.3 10 4.5 5.5 3.5 < 1 Assumed Dissolved 0.62 1.10 0.75 1 * 2.85 2.80 3.85 2* 1.21 1.48 0.94 < 1 Acute Criteria Federal (ug/1) 8.82 9.95 6.61 7,48 10.80 0.06 15.38 8.89 5.86 6.68 6.77 State (ug/1) 7.61 8.58 5.70 6.44 9.31 7.62 5.91 13.26 7.67 5.05 5.70 5.84 Chronic Criteria Federal (ug/1) 6.28 7.01 4.83 5.40 9 5.i)0 10.39 6.33 ?C 4.88 4.94 State (ug/1) 5.41 6.04 4.17 4.00 6.50 5.42 4.31 8.96 5.45 3.74 4.21 4.26 Lead Measured Value (ug/l) Total 1.2 1.8 2.6 4 5.3 5.3 13.3 8 1.9 2.8 4.5 < 1 Assumed Dissolved 0.25 0.37 0.54 < 1 * 1.10 1.10 2.75 1 * 0.39 0.58 0.93 < 1 * Acute Criteria Federal(ug/1) 31.82 37.44 21.53 25.43 41.80 31.90 22.63 67.38 32.16 18.31 21.85 22.24 State (ug/1) 21.86 25.72 14.79 17.47 28.72 21.92 15.55 46.29 22.09 12.58 15.01 15.28 Chronic Criteria (ug/q 1.24 1.46 Q Q5Federal 0.87 State (ug/1) 0.85 I .UU 0.58 0.68 1.12 0.85 t#>) 1.80 0.86 0,49 £#S 0.60 Zinc Measured Value (ug/1) Total 11 6 7 25 81 26 45 47 o, 20 9 < Assumed Dissolved 6.4 3.5 4.1 37* 46.9 15.1 26.1 20* 37.7 11.6 5.2 <5* Acute Criteria Federal (ug/1) 62.50 69.64 48.20 53.84 74 94 62.61 49.82 102.98 62.94 43.26 48.66 49.24 State (ug/1) 55.69 62.05 42.94 47.97 66.77 55.79 44.39 91.76 56.08 38.55 43.36 43.87 Chronic Criteria Federal(ug/1) 56.61 63.08 43.65 48.76y8 56.71 45.12 93.28 57.01 39.18 44.07 44.60 State (ug/1) 50.44 56.20 38.89 43.45 60.48 50.53 40.21 83.11 50.80 34.91 39.27 39.74 * Aclual Values Table E-8. Comparison of Existing Site Water Quality with Federal Criteria and State Standards. Page 4 of 6 Sample ID 10 11 12 1/28/92 4/17/92 1/19/93 12/5/91 1/28/92 1/28192 4/17/92 1/19/93 12/5/91 1128/92 4/17/92 1/19/93 Sample Date 1 2 Field Rep Copper Measured Value (ug/1) Total 4.3 3.1 < 1 3.9 6 6 7 3 4.7 8.5 9.1 2 7 Assumed Dissolved 1.16 0.83 < 1 * 1.05 1.62 1.62 1.88 2* 1.27 2.29 2.45 1* 1* Acute Criteria Federal(ug/1) 6.08 5.90 5.70 5.41 4.64 44.2 3.69 6.06 10.45 7.5.1. 6,19 9.75 10.26 State (ug/1) 5.24 5.08 4.91 4.67 4.00 3.81 3.18 5.22 9.01 6.47 5.85 8.40 8.85 Chronic Criteria Federal (ug/I) 4.48 4.36 4.23 4.03 1,34, 4.47 7.32 5 ,43 CO. 6.87 7.20 State (ug/1) 3.86 3.76 3.64 3.48 3.02 2.89 2.45 3.85 6.31 4.68 4.27 5.92 6.21 Lead Measured Value (ug/1) Total 2.5 6.7 < 1 2 3.3 5.1 15.2 5.9 0.7 3.6 6 2 3 Assumed Dissolved 0.52 1.39 < 1 * 0.41 0.68 1.06 3.15 < 1 * 0.14 0.74 1.24 < 1 * < 1 * Acute Criteria Federal (ug/1) 19.22 18.46 17.63 16.44 13.34 12.50 9'tI 19.14 40.01 25.59 22.32 36.39 39.03 State (ug/1) 13.20 12.68 12.11 11.30 9.17 8.59 6.73 13.15 27.48 17.58 15.33 25.00 26.81 Chronic Criteria Federal (ug/1) (75i Q 72 0.69 0 64 ...... 0 5..:2 ... 0;49 4 38 .. 0:75 1.56 1 0t .. 0.8 ... _ i 42 t .52 _ ... State (ug/1) 0.. 51 b 4.9.. 0.47 0.44 36 f1.33 026 0.51 1.07 4 69 O.Gb 0.97 1.04 Zinc Measured Value (ug/1) Total 14 13 <5 45 38 35 43 32 38 51 20 <9 20 Assumed Dissolved 8.1 7.5 <5* 26.1 22.0 20.3 24.9 10* 22.0 29.6 11.6 <5* 10* Acute Criteria Federal (ug/1) 44.68 43.50 42.19 40. 28 35.05' 33.56 29.52 ........... 44.56 72.79 54.07 49.36 68.34 71.60 State (ug/1) 39.81 38.76 37.59 35.89 31.23 29.90 25.42 39,71 64.85 48.17 43.98 60.89 63.79 Chronic Criteria Federal (ug/1) 40.47 39.40 38.22 36AS ...I...... 31141 .......I... 50.40 ........... 25 84 ........... 40.36 65.93 48.97 44.70 61.89 64.85 State (ug/1) 36.06 35.10 34.05 32.50 28.28 27.09 23142 35.96 58.74 43.63 39.83 55.15 57.78 * Actual Values Table E-8. Comparison of Existing Site Water Quality with Federal Criteria and State Standards. Page 5 of 6 Sample ID 13 14 15 16 Sample Date 1/28/92 1 4/17/92 l/19/93 1/28/92 4/17/92 1/19/93 12/5/91 1/28/92 4/17/92 1/19/93 12/5/91 1/28/92 4/17/92 1/19/93 Copper Measured Value (ug/1) Assumed Dissolved 5.1 1.8 < 1 3 6.4 1 3.8 4.3 23 2 21.4 8.6 36.5 9 Total 1.37 0.48 1 0.81 1.72 <1 1.02 1.16 6.19 1' 5.76 2.32 9.83 <1* Acute Criteria Federal (ug/1) 6.88 6.82 6.95 7.51 636 6.95 12.17 2,,84 ( 8.00 10.28 7,65 7.07 11.81 State (ug/1) 5.93 5.88 5.99 6.47 5.48 5.99 10.49 2.41 6.64 6.90 8.8o 6.60 G.Ov 10.18 Chronic Criteria Federal (ug/p 5.01 4.97 5.06 5.43 4.67 5.06 8.41 2.2 5-55 5.75 7.'2 5.52 5.1-1 8.18 State (ug/1) 4.32 4. 29 4.36 4.68 4.02 4.36 7.25 1.91 4.79 4.90 6.22 4.76 4.43 7.05 Lead Measured Value (ug/1) Total 3.3 3.2 <1 2.2 5.4 <1 1.3 2.3 9.9 <1 2.7 4.2 13.5 3 Assumed Dissolved 0.68 0.66 < 1 * 0.46 1.12 2 * 0.27 0.48 2.05 < 1 * 0.56 0.87 2.71) < I Acute Criteria Federal (ug/1) 22.71 22.47 23.03 25.59 20.45 23.03 49.13 6.74 26.49 27.88 39.12 26.24 23.58 47.18 State (ug/1) 15.60 15.44 15.82 17.58 14.05 15.82 33.75 4.63 18.20 19.16 26.87 18.03 16.20 32.41 Chronic Criteria Federal (ug/)) il.$9 01..88 0.90 to 080 0.90 1.91 0' 26 '<ti 1.09 11.52 1.02 0.92 1.84 State (ug/1) 0.61 U.60 0.62 0.69 0,62 1.32 0.18 U.71 0.75 1.05 0.70 0.63 1.26 Zinc Measured Value (ug/1) Total 26 9 <5 9 12 <5 45 19 32 5 219 30 56 20 Assumed Dissolved 15.1 5.2 <5* 5.2 7.0 <5* 26.1 11.0 18.5 126.9 17.4 32.5 10* Acute Criteria Federal (ug/1) 49.93 49.59 50.40 54.07 46.56 50.40 83.45 22.25 55.32 57.24 71.71 54.98 51.20 81.24 State (ug/1) 44.49 44.18 44.90 48.17 41.49 44.90 74.36 19.83 49.29 51.00 63.89 48.98 15.o2 72.38 Chronic Criteria Federal(ug/1) 45.23 44.91 45.65 48.97 42.17 45.65 75.59 20.16 50.10 51.85 64.95 49.79 46.38 73.58 State (ug/1) 1 40.301 40.021 40.671 43.631 37.581 40.671 67.351 17.961 44.64 46.191 57,871 44.371 41.32 1 65.56 * Actual Values Table E-8. Comparison of Existing Site Water Quality with Federal Criteria and State Standards. Page 6 of 6 Sample ID Sample Date 17 12/5/91 12/5/91 1/28/92 4/17/92 1/19/93 Field Rep Copper Measured Value (ug/1) Total 6.6 6 4.3 5.1 6 Assumed Dissolved 1.78 1.62 1.16 1.37 1* Acute Criteria Federal (ug/1) 5.70 5.34 4.42 State (ug/1) 4.()1 4.60 3.81 3.68 4.29 Chronic Criteria Federal (ug/1) 4.23 1 A. 3.36 3115 3, . 74, State (ug/1) 3.64 3.43 2.89 2.81 3.22 Lead Measured Value (ug/1) Total 9.3 10.9 3.3 10.0 4.6 Assumed Dissolved 1.92 2.26 0.68 2. t 9 < 1 * Acute Criteria Federal (ug/1) 17.63 16.15 12.50 11.95 14.70 State (ug/1) 12.11 11.09 8.59 8.21 10.10 Chronic Criteria Federal (ug/1) 0,69 0.63 0,57 State (ug/1) ()A 1 0.39 Zinc Measured Value (ug/1) Total 69 74 25 28 20 Assumed Dissolved 40.0 42.9 14.5 16.2 10* Acute Criteria Federal (ug/1) 42,19 30.80 33.56 32.57 37.37 State (ug/1) 37,59 35.4.E 29.90 29.02 33.30 Chronic Criteria Federal (ug/1) U. 12 M 30.40 29.50 33.85 State (ug/1) 305, 32.12 27.09 26.281 30.161 * Actual Values Table E-9. Ratio of Criteria to Measured Total Concentration Relative to Federal Standard, and Assumed Dissolved Concentration Relative to State Standards. Station Total Copper Copper Lead Lead Zinc acute Zinc number of acute chronic acute chronic chronic samples (S & F) 1 4* S: S: ---1 S: S: 2-15 S: 1-2 S: 1-2 F: 1-2 F: 2-3 F: 2 F: 8-51 F: 1-3 F: 2-3 2 3 S: S: S: S: 1-5 S: ---1 S: —1 F: --1 F: —1 F: F: 3-7 F: —2 F: 2 3 1 S: S: S: S: S: 3 S: 4 F: F: --1 F: F: 3 F: 5 F: 6 4 4 S: 3 S: 3 S: 2 S: 2-46 S: 2-6 S: 2-7 F: 1-7 F: 1-11 F: 6 F: 9-156 F: 3-9 F: 1-10 5 4 S: S: --1 S: S: 3-12 S: 2 S: 2 F: 1-2 F: 1-3 F: 2 F: 4-16 F: 3 F: 3 6D 4 S: --1 S: —1 S: 2 S: 3-57 S: 1-3 S: 1-4 F: 1-5 F: 2-7 F: 2-8 F: 13-193 F: 2-5 F: 2-5 6U 4 S: --1 S: ---1 S: --1 S: 3-33 S: 1-3 S: 1-3 F: 1-4 F: 2-7 F: 1-4 F: 12-106 F: 1-5 F: 1-5 7 4 S: S: S: S: S: S: F: —1 F: —1 F: F: 1-4 F: F: 8 4 S: S: S: S: 1-5 S: S: F: 1-2 F: 1-3 F: F: 3-15 F: --1 F: --1 9 4 S: S: S: S: 1-2 S: S: F: F: —1 F: F: 2-6 F: --1 F: ---1 10 3 S: S: S: S: 1-3 S: S: F: F: F: F: 3-10 F: F: 11 4* S: S: S: S: 2-12 S: S: --1 F: 1-2 F: 2-3 F: 2 F: 3-40 F: 1-2 F: 1-2 12 4 S: S: S: S: 1-2 S: S: F: --1 F: 2 F: F: 1-7 F: F: --1 13 3 S: S: S: S: --1 S: S: F: F: —1 F: F: 4 F: F: 14 3 S: S: S: S: 2-3 S: S: F: --1 F: —1 F: F: 2-7 F: F: 15 4 S: S: —1 S: S: 3 S: S: F: 2-3 F: 2-4 F: F: 8-10 F: F: 16 4 S: —1 S: 2 S: S: 1-4 S: 2 S: 2 F: 2-5 F: 1-7 F: F: 2-26 F: 1-3 F: 1-3 17 4* S: S: S: S: 2-7 S: --1 S: ---1 F: —1 F: 1-2 F: F: 7-23 F: 2 F: 2 S = State; F = Federal Table E-10. May Creek Water Quality Data: Ratio of Dissolved to Total Metal Concentrations. Page 1 of 2 Sample ID 1 2 4 5 6D 6U 7 8 9 10 11 12 1/19/93 1/19/93 1/19/93 1/19/93 1/19/93 1/19/93 1/19/93 1/19/93 1/19/93 1/19/93 1/19/93 1/19/93 Sample Date 1 2 1 2 Aluminum 0.12 0.60 0.01 0.16 0.17 0.02 0.02 0.03 0.01 0.17 0.50 0.03 0.06 0.03 Antimony Arsenic Barium 0.75 1.11 0.11 0.71 1.13 0.35 0.29 0.29 0.35 1.40 3.40 0.33 0.78 0.34 Beryllium Cadmium Calcium 1.20 1.08 0.73 1.00 1.20 0.98 0.82 0.91 1.09 1.25 1.14 0.91 0.93 0.93 Chromium 0.25 0.50 0.50 0.83 Copper (mg/1) 1.50 0.13 0.10 0.19 0.13 0.20 0.67 0.50 0.14 Iron 0.11 0.79 0.01 0.16 0.18 0.13 0.06 0.03 0.01 0.31 0.63 0.03 0.12 0.04 Lead (mg/1) 0.33 1.00 0.03 1.00 1.00 0.02 0.02 0.25 0.13 0.17 0.50 0.33 Magnesium 1.13 1.11 0.65 1.00 1.16 0.65 0.50 0.83 0.94 1.28 1.15 0.77 0.88 Manganese 0.47 1.10 0.05 0.33 0.37 0.82 0.59 0.20 0.10 1.20 1.00 0.13 0.73 0.53 Mercury Molybdenum Nickel Potassium 1.00 0.67 1.00 0.75 1.00 1.00 1.00 Selenium Silver Sodium 1.02 .099 0.79 0.91 1.09 0.91 0.88 0.81 1.16 t .18 1.02 0.93 0.92 0.90 Thallium Zinc (mg/1) 0.80 1.43 0.12 0.60 1.00 0.72 0.58 1.48 0.43 0.31 0.50 Hardness (mgCaCO3/1) 39 39 57 48 41 23 28 40 86 36 30 32 53 56 Table E-10. May Creek Water Quality Data: Ratio of Dissolved to Total Metal Concentrations. Paee 2 of 2 Sample ID Sample Date 13 14 15 16 17 Mean Ratio 1/19/93 1/19/93 1/19/93 1/19/93 1/19/93 Aluminum 1.00 0.33 0.13 0.02 0.04 0.08 Antimony Arsenic Barium 1.50 1.00 0.83 0.21 0.45 0.58 Beryllium Cadmium Calcium 0.94 0.91 1.00 0.83 0.83 0.97 Chromium 0.48 Copper (ing/1) 1.00 0.50 0.11 0.17 0.27 Iron 0.25 0.48 0.01 0.03 0.09 Lead (mg/1) 0.33 0.22 0.21 Magnesium 0.90 Manganese 0.67 0.68 0.16 0.11 0.37 Mercury Molybdenum Nickel Potassium 0.91 Selenium Silver Sodium 0.86 0.85 0.87 0.86 0.83 0.93 Thallium Zinc (mg/1) 0.50 0.50 0.58 Hardness (mgCaCO3/1) 37 37 43 65 26 40.72 Table E-11. Selected Toxicity Criteria for Fresh Waters in the State of Washington'. Acute Criteria Chronic Criteria Substance (Ng/L except where noted.)" (Ng/L except where noted.)" chloride (dissolved in association with sodium) copper4/ lead4l zinc4/ 860.0 mg/L S (0. 862) (e(0.9422[In(hardness)]-1.464)) S (0.687)(e(1.273[In(hardness)}1.460)) 5 (0.891 )(e(o.847[In(hardness)]+0.860)) 230.0 mg/L S (0.862)(e(0.8 545[In(hardness)]-1.465)) 5 (0.687)(e(1.273[In(hardness)}4.705)) S (0.891) (e(0.847[In (hardness)]+0.761)) 1/ Subset of toxic substance regulations in WAC 173-201A-040. 2/ A one -hour average concentration not to be exceeded more than once every three years on the average. 3/ A four -day average concentration not to be exceeded more than once every three years on the average. 4/ Based on the dissolved fraction of the metal. Table 1-12. Full Report of Lake Water Quality Data. MINOR LAY.ES MONITORS NO PROJECT -- MASTER FILE TABLE I OF 2 SAMPLE DEPTH WIND SPEED MIND BEAR AMB CLD-COV TEMP TRANS DO COND TURB ALK MG STATION NUMBER GATE PROJ H TIME MATRIX M/SEC DEG STORM TEMP C M _____ MG/L ____ PH __ UMHOS/CM NTU CACO3/L ________ ____ _______ _______ ______ A710 791304, ______ 790516 ____ BLS _____ 1.0 ____ 831 ______ 9OLD _____ 0 ____ 0 _____ ____ .0 _______ 100 ____ 18.5 3.0 9.0 6.1 43 .0 7913046 190516 BLS 2.5 829 9OLD 0 0 .0 17.2 .0 8.6 6.6 42 .0 7913049 790S16 BLS S.0 625 9OLD 0 0 .0 12.6 .0 3.6 6.1 47 .0 7913080 790716 BLS 1.0 1145 90LD 0 0 .0 24.0 1.4 7.4 6.3 36 .0 7913081 790716 BLS 2.5 1142 9OLD 0 0 .0 19.8 .0 4.1 6.2 34 .0 7913082 790716 BLS 5.0 1135 SOLD 0 0 .0 17.6 .0 1.4 6.1 42 .0 791313S 790918 BLS 1.0 1122 9OLD 0 0 .0 15 20.5 2.5 6.8 7.1 43 .0 7913136 790910 BLS 2.5 1120 90LD 0 0 .0 18.9 .0 6.4 7.0 45 .0 7913137 790918 BLS 5.0 1115 90LD 0 0 .0 15.0 .0 .1 6.S 68 .0 791318S 791113 BLS 1.0 951 90LD 0 0 .0 100 7.2 1.9 7.6 6.5 45 .0 7913186 791113 BLS 2.5 950 90LD 0 0 .0 7.5 .0 7.6 6.5 45 .0 7913187 791113 BLS S.0 945 90LD 0 0 .0 7.0 .0 7.7 6.6 46 .0 8011010 800114 BLS 1.0 1045 90IJ C 0 .0 100 2.0 2.0 10.6 6.9 46 .0 8013011 800114 BLS 2.5 1052 9CLD 0 0 .0 3.6 .0 10.4 6.6 49 .0 9013012 800114 BLS 5.0 1100 90LD 0 0 .0 4.0 .0 9.5 6.5 51 .0 8013080 800310 BLS 1.0 1040 90LD 0 0 .0 100 8.2 3.0 9.9 6.6 60 .0 BCI3C01 C00I10 3LS 2.S 1C35 9C_D T C 8.0 •.0 9.9 6.7 51 .0 8013062 800310 BLS 5.0 103C 90LD 0 ♦ .0 8.0 .0 10.0 6.8 S: .0 M.INOF. LAKES MONITO?_tw'. FROJECT -- MASTER FILE TA -- 1 OF 2 N I::J WIND SAMPLE CE?i7i SP_EJ BFJ+? AIMS CLD-COV TEMP TRANS DO CO, 10 TUP.B ALl: MG STAT1011 NUMBER DATE PROJ M. TIME MATRIX M;S=_ DEG STDRM TEMP A C M MG/L PH UMHOS/CM NTU CACO3/L A-10 7113106 730805 BPI 1.0 1110 90LD 0 C .0 24.9 2.0 7.8 6.4 60 .0 7113109 7306C5 BPL 3.0 1105 9OLD 0 0 .0 18.2 .0 1.5 6.3 5P .0 7113110 710805 BPI I.I 1055 90LL C 0 .1 13.5 .0 .1 6.2 12 .0 721309-0 720224 BPI 1.0 1150 90LD 0 0 .0 6.6 2.4 11.7 6.8 <1 1.0 34 7213099 72C224 EFL 3.0 1200 SOLD 0 G .0 6.2 .0 11.1 6.5 35 1.1 17 7213100 720224 BPL 7.0 1209 90LD 0 0 .0 6.2 .0 11.1 6.4 39 1.2 9 7213438 720419 BPI 1.0 131S 9OLD 0 0 _0 10.0 2.9 8.7 6.7 39 2.1 7213439 720419 BP- 3.0 1318 90LD 0 0 .0 8.7 .0 8.7 6.8 SO 2.7 7213440 720419 BPI 7.0 1321 9OLD 0 0 .0 8.3 .0 7.6 6.7 39 1.7 721366S 720526 BPI 1.0 1025 90LD 0 0 .0 18.0 3.5 8.8 6.9 40 1.4 7213666 720526 BPI 4.0 1040 90LD 0 0 .0 15.8 .0 6.0 6.7 40 2.5 7213667 720526 BPI 7.0 1035 SOLD 0 0 .0 12.9 .0 3.0 6.4 44 3.3 7513001 750205 BPI 1.0 I1S5 90LD 0 C .0 3.0 2.5 12.7 5.6 46 1.0 7 7513002 750205 BPI 3.0 1208 90LD 0 0 .0 2.9 .0 12.6 6.4 44 1.0 8 7513003 75020S BPI 6.0 1159 90LD 0 0 .0 3.1 .0 12.6 6.5 44 1.0 7 7513038 750224 BPI 1.0 1010 9OLD 0 0 .0 4.7 2.1 12.5 6.8 49 2.0 7 7513039 750224 BPI 3.0 1015 90LD 0 0 .0 5.0 .0,.12.5 6.7 50 2.5 7 - 11040 7SO224 BPI 6.0 1020 9OLD 0 0 .0 S.0 .0 12.0 6.5 50 2.5 8 7513086 75C305 BPI 1.0 1000 90LD 0 0 .0 6.0 .0 12.1 6.7 45 1.0 8 7513087 7SO305 BPL 3.0 1010 90LD 0 0 .0 6.4 .0 11.6 6.7 44 1.1 8 7513088 7S030S BPI 6.0 1015 9OLD 0 0 .0 6.3 .0 11.8 6.7 45 1.0 8 7513127 750319 BPI 1.0 940 9OLD 0 0 .0 6.4 2.1 11.4 7.0 43 1.2 9 7513128 750319 BPI 3.0 945 9CLD 0 0 .0 6.3 .O 11.3 6.9 42 3.5 9 7513129 750319 BPL 6.0 935 906D 0 0 .0 6.5 .0 11.3 6.9 41 3.8 9 MINOR LAKES MONITORING PROJECT -- MASTER FILE TABLE 1 OF 2 SAMPLE STAT30N NUMBER LATE PROJ _______ ______ ______ ____ DEPTH N _____ TIME MATRIX ____ ______ MIND SPEED M/SEC _____ WIND BEAR DEC ___ AMH CLD-COV TEMP TRANS DO 51'ORX TEMP 9 C M MG/L PH COND TUBB ALK MG UNMOS/CM NTU CAC03/L A 10 751335_ 9 750108 BPL 1.0 1301 SOLD 0 0 _____ ____ _______ .0 ____ 8.9 _____ 2.7 ____ 10.4 __ 6.4 ________ 47 __ _ 1.7 _______ B 7513160 7SO406 BPL 3.0 1100 90LD 0 0 .0 8.7 .0 10.4 6.4 46 3.0 B 7513161 750408 BPL 6.0 1055 90LD 0 0 •0 8.5 .0 10.0 6.4 60 2.9 B 7513191 750422 BPL 1.0 925 90LD 0 0 .0 11.9 2.5 9.6 6.3 67 1.5 B 7513192 750422 BPL 3.0 93S 90LD 0 0 .0 10.7 .0 8.4 6.2 41 1.3 8 7513293 750422 BPL 6.0 92S 90LD 0 0 .0 9.5 .0 6.1 6.2 41 1.9 9 7513211 7SO506 BPL 1.0 1350 90LD 0 0 .0 12.0 2.3 9.4 7.1 57 .7 B 7513212 750506 BPL 3.0 1400 90LD 0 0 .0 12.0 .0 8.5 6.8 43 .6 10 7513213 7SO506 BPL 6.0 1350 90LD 0 0 .0 9.8 .0 2.2 6.5 43 1.4 9 7S132SS 7SOS20 BPL 1.0 2020 9OLD 0 0 .0 16.8 2.4 9.1 6.3 40 1.4 20 7513256 7SO520 BPL 3.0 1025 90LD 0 0 .0 13.2 .0 9.2 6.1 47 2.0 10 7513257 750520 BPL 6.0 1030 90LD 0 0 .0 12.2 .0 1.S 6.1 42 2.6 13 7513293 7SO603 BPL 1.0 920 90LD 0 0 .0 21.0 2.0 B.1 7.3 41 ,4 5 7513284 750603 BPL 3.0 930 SOLD 0 0 .0 20.0 .0 7.8 7.2 40 .6 8 7513285 750603 BPL 6.0 935 SOLD 0 0 .0 19.2 .0 7.5 7.1 40 .5 E 7513309 7SO619 BPL 1.0 84S 90LD 0 0 .0 17.2 2.8 7.8 7.2 42 ,_ E 7513310 750619 BPL 3.0 850 9CLD 0 0 .0 16.3 .0 5.8 6.6 70 1.2 6 7513311 750619 BPL 6.0 645 9OLD 0 0 .0 23.1 .0 2 6 6.6 85 4.0 1. 7S.3334 75070E EPL 1.0 930 90LD 0 0 •0 24.5 3.2 9.2 7.0 42 _. E 751333S 750706 BPL 3.0 920 90LD 0 0 .0 10.0 .0 5.6 6.E 44 .E 9 7513336 750708 EFL 6.0 905 901•D 0 0 .0 16.4 .0 2.6 6.5 51 1.9 1: 7513357 750722 BPL 1.0 920 9CLI- 0 0 .0 22.3 2.1 8.2 6.B 41 .7 9 75/3358 750722 BPL 3.0 940 9CLD 0 0 .0 20.9 .0 5.8 6.6 41 .9 l0 7513359 750722 EPL 6.0 930 90L^, 0 0 .0 15.8 .0 1.1 6.3 80 4.9 15 M=110R LAKES MONITORING PROJECT -- MASTER FILE TABLE 1 OF 2 SAMPLE WIND WIND STAT1011 NUMBER. PATE DEFTH SPEED BEAR AMB CLD-COV TEMP TRANS DO COND TUFB ALK MG ---- ---- M TIME MATRIX M/SEC DEC; STORY TEMP 9 C M MG/L PH UMMOS/CM NlV CAC03/L ___ ____ ____ ______ _____ _ _____ ____0 _ _____ _ A730 7513370 750804 BP-- 1.0 SOLD 0 0 _ ________ ____ _______ • 22.3 2.1 6.2 6.8 .7 7SI3371 750604 BPL 3.0 SOLD 0 0 .0 20.9 .0 5.9 6.6 ,9 7SI3372 7$0804 BFL 6,0 901G 0 0 .0 15.6 .0 7513404 750819 BPL 1.0 935 9OLD 0 0 ,0 39.2 2.5 7.1 6.7 12 3.0 8 7SI340S 750819 BPL 3.0 945 9GLD 0 0 .0 19.2 .0 5.4 6.3 82 .8 9 7513406 750819 BPL 6.0 950 90LD 0 0 .0 13.5 .0 1.7 6.2 S1 3.8 74 7513416 750906 BPL 1.0 915 9OLD 0 0 .0 19.2 1.S 9.0 6.4 43 .8 7 7513417 7SO908 BPL 3.0 930 9GLD 0 0 .0 27.0 .0 7.6 6.6 43 .7 7 7513418 750908 8PL 6.0 91D 90LD 0 0 .0 14.8 .0 2.1 6.2 S3 4.6 13 7513440 750922 BPL 1.0 930 9GLD 0 0 .0 38.3 2.5 8.4 6.8 48 .7 6 7513441 750922 EPL 3.0 940 90LD 0 0 .0 17.6 .0 7.6 6.S 39 .5 7 7SI3442 750922 BFL 6.0 920 90LD 0 0 .0 14:5 .0 4.5 6.3 43 1.9 12 7513481 751105 BPL 1.0 2020 90LD 0 0 .0 9.9 2.6 9.1 6.2 46 .7 9 7S13482 751305 BPL 3.0 2020 SOLD 0 0 .0 9.8 .0 0.9 6.2 40 7.0 9 7513483 751105 BPL 6.0 1020 90LD 0 0 .0 9.1 .0 0.4 6.2 38 .6 9 7513511 751204 BPL 1.0 920 90LD 0 0 .0 6.7 2.2 10.8 6.S 37 .8 11 7513512 7SI204 8PL 3.0 930 90LD 0 0 .0 6.7 .0 10.4 6.6 38 .9 9 I>13513 751204 BPL 6.0 920 90LD 0 0 .0 C.- .0 10.6 6.6 39 .9 7 7523530 751215 BPL 1.0 926 9CLD 0 0 ,0 4.9 1.9 10.2 6.7 38 .8 6 7513532 751215 BPL 3.0 918 90LD 0 0 .0 4.9 .0 10.1 6.4 38 1.0 7 7S13S32 751215 BPL 6.0 91S 90LD 0 0 .0 5.2 .0 10.1 6.5 46 .9 7 7613D01 760105 BPL 1.0 925 9GLD 0 0 ,0 3.8 3.8 11.0 6.5 75 1.1 11 7613002 760105 BPL 3.0 933 90LD 0 0 .0 4.1 .0 10.7 5.6 40 1.1 12 7E13003 760105 BPL 6.0 924 90LD 0 0 ,0 3.9 .0 30.E 5.9 40 1.2 1C MINOR LAXES MONITORING PROJECT -- MASTER FILE TABLE 1 OF 2 SAMPLE STATION NUMBER _______ ______ DATE ______ PROD ____ DEPTN M _____ TIME MATRIX ___ ______ MIND SPEED M/SEC _____ MIND BEAR DEG ____ AME CLD-COV TdP TRANS DO STORM TEN % C M MG/L _____ PM CONO TORE UMNOS/CM NTU ALX MG CACO3/L A710 761I074 760119 BPL 1.0 915 SOLD 0 0 ____ _______ .0 ____ 4.4 _____ 2.3 ____ 11.2 __ 6.8 ________ 41 _ 2.2 8 7611035 760119 BPL 3.0 920 SOLD 0 0 .0 4.4 .0 11.1 6.8 42 1.4 9 761,3036 760119 BPL 6.0 915 SOLD 0 0 .0 4.4 .0 10.8 6.7 39 3.3 8 7613067 760202 8PL 1.0 91S SOLD 0 J .0 5.2 2.0 10.7 6.7 56 3.0 8 7613068 760202 8PL 3.0 925 SOLD 0 0 .0 5.2 .0 10.4 6.9 41 1.6 9 7613069 760202 BPL 6.0 920 SOLD 0 0 .0 5.2 .0 9.6 6.4 41 1.9 8 6710 7113111 710805 BPL 1.0 1125 SOLD 0 0 .0 25.0 2.2 .0 6.5 47 ,0 7213101 720224 BPL 1.0 1226 SOLD 0 0 .0 6.5 .0 11.4 6.4 48 .6 11 7213441 720419 BPL 1.0 1326 SOLD 0 0 .0 10.2 3.2 8.0 6.6 43 1.6 7213666 720526 BPL 1.0 1110 SOLD 0 0 .0 18.0 3.3 0.8 6.9 46 1.7 7513011 750205 8PL 1.0 2216 SOLD 0 0 .0 2.8 .0 13.0 6.6 43 1.0 E 7513045 750224 BPL 1.0 1036 SOLD 0 0 .0 4.5 .0 .0 .0 .0 7SI3096 7SO305 8PL 1.0 955 SOLD 0 0 .0 6.6 .0 .0 .0 .0 C710 7113112 710805 BPL 1.0 1150 SOLD 0 0 .0 25.2 2.1 .0 6.5 65 .0 7213102 720224 BPL 1.0 1215 SOLD 0 0 .0 6.5 .0 11.0 6.4 42 1.0 13 7_13442 720419 BPL 1.0 1334 SOLD 0 0 .0 10.0 .0 7.4 6.7 3E 2.4 7212669 72052E BFL 1.0 '100 SOLD 0 0 .0 18.0 .0 8.6 6.9 41 2.4 ' 7513014 750205 BFL 1.0 1:12 SOLD 0 .0 2.9 .0 12.[ 6.7 45 :.0 E 7513047 75022: BPL 1.0 1045 SOLD 0 C .0 4.7 .0 .0 .0 .0 75.3099 750305 EFL 1.0 1020 SOLD 0 0 .0 6.2 .0 .0 .0 .0 D710 7113113 710605 BPL 1.0 1135 SOLD 0 0 .0 25.0 1.0 .0 6.S 6E .0 72:2103 720224 BFL 1.0 1222 SOLD 0 0 .0 6.6 .0 11.5 6.6 43 1.0 13 7213443 720419 BF_ 1.0 13C2 9C;LD 0 0 .0 10.5 .0 10.3 6.6 29 1.9 72:3670 720526 EFL 1.0 1005 901-D 0 0 .0 17.2 .0 8.7 6.9 40 1.6 M:::OF. LAKES M.ONITOP.ING PROJECT -- MASTER FILE 'ABLE 1 OF 2 MIND M:;1D SA:!F:E DEFT- SPEED BEAR AME CLD-COV TEMP TRIJJS DO CO::_- Tl=e MS STATION _______ 1:�-Y.EL ______ DATE ______ FP.OJ ____ M _____ TIY.E ____ M_ F.1% ______ M/SEC _____ DEG_ STOP." T-MP % C M MG/L PH 'l;XH:3/C- N= CAC03/L D710 75.2017 7SO205 BPL 1.0 11.5 SOL: 0 ________ 0 ____ _______ .0 ____ 3.0 _____ .0 ____ 12.9 __ 6.E ______ 44 1.0 ____ E 7513049 7SO224 EPL 1.0 1032 SOLD 0 0 .0 5.1 .0 .0 .0 .0 75.3102 750305 BFL 1.0 1030 SOLD 0 0 .0 6.0 .0 .0 .0 .0 I710 7512053 750224 BPL 1.0 1042 SOLD 0 0 .0 S.2 .0 9.5 .0 60 .0 75:3107 750305 BFL 1.0 1025 SOLD 0 0 .0 4.5 .0 10.3 6.4 60 1.0 E 7513139 750319 BPL 1.0 945 SOLD 0 0 .0 5.0 .0 8.7 6.5 41 6.2 8 7513171 75040E BPL 1.0 1110 SOLD 0 0 .0 8.0 .0 8.4 6.0 44 2.9 8 7513203 750422 BPL 1.0 945 SOLD 0 0 .0 10.5 .0 8.1 6.2 41 3.2 9 7513223 750506 PPL 1.0 1407 SOLD 0 0 .0 13.2 .0 9.2 6.6 42 1.4 9 751326S 750520 EPL 1.0 1035 SOLD 0 0 .0 15.5 .0 8.9 6.2 49 2.0 6 7513293 750603 BPL 1.0 945 SOLD 0 0 .0 19.4 .0 7.7 7.2 4D .S 10 7513319 750619 EPL 1.0 840 SOLD 0 O .0 16.0 .0 6.7 6.7 E6 .8 11 7513344 750708 BPL 1.0 935 SOLD 0 0 .0 23.5 .0 7.2 6.6 41 1.3 8 7513542 751215 BPL 1.0 SOLD 0 0 .0 .0 .0 .0 6.5 41 1.0 7 0710 7213444 720419 BPL 1.0 1255 SOLD 0 0 .0 11.0 .0 10.6 6.7 38 1.5 7213671 720526 EPL 1.0 1015 SOLD 0 0 .0 17.0 .0 6.6 6.8 45 2.4 7513021 750205 BPL 1.0 1230 SOLD 0 0 .0 4.2 .0 12.6 6.8 47 1.0 6 7513050 750224 BFL 1.0 __C7 SOLD 0 0 .0 5.4 .0 11.8 .0 49 .0 7513112 750305 EPL 1.0 1035 SOLD 0 0 .0 6.6 .0 11.6 6.7 150 1.0 8 7513144 750319 BPL 1.0 95S SOLD 0 0 .0 6.0 .0 10.8 6.8 40 4.S 8 7513176 75040E BPL 1.0 1120 SOLD 0 0 .0 10.0 .0 10.6 6.4 46 21.0 8 7513208 7SO422 BPL 1.0 940 SOLD 0 0 .0 10.7 .0 9.6 6.5 41 1.4 6 7513228 7SO5D6 BPL 1.0 1420 9O1.0 0 0 .0 12.0 .0 9.4 6.6 49 .8 9 7SI3268 75052C BPL 1.0 1015 SOLD 0 0 .0 16.5 .0 8.8 6.5 41 2.1 8 MINOR LAKES MONI7ORING PROJECT -- MASTER FILE TABLE 1 OF 2 WIND MIND SAMPLE DEPTH SPEED BEAR AMB CLD-COV TEMP TRANS DO COND TURB ALR MG STATION NUMBER DATE PROJ M TIME MATRIX M/SEC DEG SPDRM TEMP 9 C N WGIL PH UMHOS/CM muCAC03/L ______ ______ ____ _____ ____ ______ _____ ____ _____ ____ _______ ____ _____ ____ __________ ___________ 0710 751329S 150603 BPL 1.0 9SS 9OLD 0 0 .0 19.5 _0 7.4 7.1 93 .8 9 7S13320 7SO619 BPL 1.0 900 90LD 0 0 .0 16.2 .0 8.4 6.8 63 .8 e 7513493 7SI10S BPL 1.0 1300 90LD 0 0 .0 20.2 .0 0.8 6.2 26 1.5 9 7513S27 752206 BPL 1.0 1000 90LD 0 0 .0 6.; .0 10.5 6.6 61 2.6 8 7S13567 7S1215 8PL 1.0 946 90L13 0 0 .0 6.6 .0 10.8 .0 .0 7613017 76010S BPL 1.0 944 90LD 0 0 .0 6.0 _0 10.9 5.8 38 1.8 9 7613050 760219 BPL 1.0 925 9OLD 0 0 .0 6.2 .0 11.3 6.7 81 2.0 6 7613083 760202 BPL 1.0 930 90LD 0 0 .0 S.0 .0 10.2 6.4 63 4.3 7 MINOR LAKES MONITORING PROJECT -- MASIFR FILE TABLE 1 OF 2 WAND WIND SAMPLE DEPTH SPEED BEAR AMB CLD-COV TEMP TRANS DO CCND TURD AW. MG STATION NUMBER DATE PROJ M TIME MATRIX M/SEC DEG STORM TEMP 9 C M MC/L PH UMHOS/CM NTU CAC03/L _______ ______ ______ ____ _____ ____ ______ _____ ____ _____ ____ _______ ____ _____ ____ __ ________ ____ _______ A780 8800486 880SO4 ES3321 1.0 1300 MBA 0 0 N 16.4 80 10.6 6.0 .0 .0 .0 8005979 86OS16 E53321 1.0 1300 MBA 0 0 S 13.0 100 16.0 2.S .0 .0 .0 8806338 880606 853321 2.0 1250 AABA 0 0 N 21.0 65 16.0 2.5 .0 .0 .0 8606937 880621 B53321 1.0 2000 AABA 0 0 N 21.1 20.0 2.8 .0 .0 .0 6607233 88070S ES3321 1.0 900 AABA 0 0 S 10.0 100 17.8 3.0 .0 .0 .0 8807259 800719 B53321 1.0 1000 AAB1. 0 0 N 2S.0 20.0 3.8 .0 .0 .0 860633S 990801 B53323 1.0 11SO AAEA 0 0 N 20.6 90 20.6 2.5 .0 .0 .0 8906361 880815 B53322 1.0 1300 AABA 0 C N 18.3 300 19.4 2.8 .0 .0 .0 8809006 880906 B53321 2.0 1310 AABA 0 0 N 18.9 96 20.0 4.5 .0 .0 .6 8809032 880939 B5332: 1.0 1020 MBA 0 0 N 12.8 100 26.1 3.0 .0 .0 .0 8809838 881003 B53321 1.0 1030 MBA 0 0 N 12.8 100 15.6 .0 .0 .0 .0 0903912 990301 B53321 1.0 930 AAEA 1 25 N 1.0 100 3.0 3.1 11.0 6.8 49 .0 8903913 8903C1 B53321 3.0 534 AAEA 1. 25 N 1.0 100 3.0 .0 12.3 6.66 65 .0 6906S78 690323 E53321 1.0 1030 MBA 1 230 N 9.0 30 .0 2.1 12.6 6.9 49 .0 0904579 890323 B53322 3.0 3032 AAEA 1 230 N 9.0 30 6.0 .0 12.5 7.0 50 .0 8905811 890509 B53321 1.0 3000 AAEA 0 0 N 15.6 100 17.2 3.S .0 .0 .0 090S236 89OS23 253321 1.0 1155 AAEA 0 0 N 14.6 50 16.7 3.0 .0 .0 .0 $905861 890606 ES332: 1.0 3:9 AAEA 0 0 N 16.0 100 21.0 3.6 .. .0 .0 890SO86 890621 853321 1.0 MBA 0 0 .0 .0 .0 .0 .0 .0 6904470 890712 B53321 1.0 1236 MBA 0 0 N 24.0 1 23.0 1.7 .0 .0 .0 6906495 690725 ES332: 1.0 1330 AAEA 0 0 N .0 .0 6.6 .0 .0 .0 0907416 890637 B53321 1.0 121C AABA 0 0 N 27.6 1 22.6 2.6 .D .0 .0 8907656 890905 653321 1.0 015 MBA 0 0 N 16.7 100 17.8 2.9 .0 .0 .0 8907688 890919 BS3321 1.0 1118 AAEA 0 0 N 28.3 10 18.3 3.6 .0 .0 .0 MINOR LAKES MONITORINC PROJECT -- MASTER FILE TABLE I OF 2 SAMPLE SEATS ON NUMBER DATE DEPTH MIND WIND SPEED BEAR AMB CLD-CON TEMP TRANS DO GO:D TURB ALK PP.OJ _____ ______ ______ ____ M T1 Y.E MATRIX M/SEC DEG STORM TEMP 9 _____ C M MG/L PH /Ma UIUNCS/CM N1V GC03/L L A 40 0908645 091009 853321 ____ ______ 1.0 1300 AABA _____ 0 ____ _____ 0 N ____ _______ 17.0 3 ____ 17.5 _____ 3.1 ____ _ __ .0 ______-_ ____ .0 9004629 900226 B53321 1.0 1180 MBA 5 160 N 8.0 6.0 .7 11.3 6.9 160 .0 9004630 900226 653321 6.0 1162 MBA S 160 N 8.0 S.5 .0 11.2 7.0 140 .0 9004631 900226 8531:1 0.0 1145 MBA 5 160 N 8.0 4-5 .0 11.0 7.0 135 .0 9106014 910226 653323 1.0 1308 MEA 5 180 N 17.0 7.8 2.0 .0 .0 122 .0 9106015 910226 B53321 6.0 1306 MBA 5 160 N 17.0 7.2 .0 .0 .0 126 .0 9106016 910226 BS3322 8.0 3300 MBA 5 180 N 17.0 7.2 .0 9.6 .0 129 .0 9106034 910319 B53321 1.0 1269 MBA 0 0 N 11.0 S00 7.5 1.6 11.6 7.2 118 .0 9206835 910319 853321 6.0 1250 MBA 0 0 N 11.0 100 7.0 _0 10.6 7.2 119 .0 9206936 910319 B53321 8.0 1267 AABA 0 0 N 11.0 100 6.3 .0 10.1 7.2 116 .0 9207364 920226 B53321 1.0 1528 AABA 1 130 N 12.0 100 7.9 1.8 10.0 6.9 132 .0 920736S 920224 ES332: 4.0 1S34 AA SA 1 130 N 12.0 100 7.0 .0 9.6 6.9 133 .0 9207366 920228 85332: 6.0 1537 AABA 1 130 N 12.0 100 6.9 .0 6.4 7.0 137 .0 920053S 920331 BS3321 1.0 1315 An OA 5 150 N 17.0 10 13.0 3.9 10.0 7.6 153 .0 920BS36 920331 253321 4.0 1342 AABA 0 0 .0 10.0 .0 8.6 7.1 15e .0 9208537 920331 BS3321 8.0 1340 MBA 0 0 .0 8.0 .0 S.2 6.9 1SC .0 MINOR LAKES MONITORING PROJECT -- MASTER FILE TABLE 2 OF 2 TOTAL S'USP CHLOR ORTH TOT FECAL ENTERO- SAMPLE DEPTH SOL A PHAEO NH3 PO4 NO2-MO3 PO4 FC COLI 6N[ERO COCCUS STATION NUMBER DATE ______ M _____ !SG/L UG/L UG/L MG/L MG/L MG/L MG/L CODE /100HL CODE ORG/IOOML _______ ______ A710 7923047 790S16 1.0 ----- .0 _____ 2.10 ----- .10 __-- .000 -___ .001 ------- .000 ____ __-_ .017 ------ ------ --------- 10 7923046 790516 2.5 .0 .00 .00 .000 .001 .000 .021 7913049 190516 5.0 .0 .00 .00 .000 .001 .000 .021 7913080 790716 1.0 .0 .90 2.40 .000 .002 .000 .024 30 , 7913081 790716 2.5 .0 .00 .00 .000 .002 .000 .022 7913092 790716 5.0 .0 .00 .00 .000 .003 .000 .032 7913135 790918 1.0 .0 2.40 .20 .000 .004 .000 .011 11 7913136 790918 2.5 .0 .00 .00 .000 .005 .000 .019 7913137 790918 5.0 .0 .00 .00 .000 .012 .000 .042 7913165 791113 1.0 .0 .00 .00 .000 .004 .000 .019• 10 , 7913186 792113 2.5 .0 .00 .00 .000 .004 .000 .027 7913187 791113 5.0 .0 .00 .00 .000 .003 .000 .040• 6013010 900114 1.0 .0 5.20 .20 .000 .009 .000 .032 19 8013011 800114 2.5 .0 .00 .00 .000 .012 .000 .027- 8013012 600114 5.0 .0 .00 .00 .000 .000 .000 .023 9013080 800310 1.0 .0 1.50 1.70 .000 .008 .000 .015. 10 8013081 900310 2.5 .0 .00 .00 .000 .005 .000 .012 8013082 60031-0 5.0 .0 .00 .00 .000 .004 .000 .012 MINOR LAKES MONITORING PFOJEC'I -- MASTER FILE TABLE 2 OF 2 Tj-AL Si1SP CELOR OP.TH TOT FECAL E71.sO- SAMFLT_ DEPTH S A PHAEO NH3 PO4 NO2-NO3 PO4 FC COLI ENIERO COC _'S STATION NUMBER _______ ______ DATE M MG/L UG/L UG/L MG/L MG/L MG/L MG/L CODE /100ML CODE ORG/100ML A710 7113106 ______ 710805 _____ _____ 1.0 .0 _____ .00 .00 -___ .020 ____ .000 _______ .010 __-_ ____ .000 ______ --------------- 7123109 71090S 3.0 .0 .00 .00 .020 .000 .010 .000 7113110 710805 7.0 .0 .00 .00 .35^ .000 .020 .000 7213090 720224 1.0 .0 .00 .00 .010 .000 .520 .000 7213099 720224 3.0 .0 .00 .00 .010 .000 .530 .000 7223100 720224 7.0 .0 .00 .00 .010 .000 .S30 .000 7213438 720419 1.0 .0 2.70 .00 .050 .000 .280 .000 7213439 720419 3.0 .0 .00 .00 .050 .000 .260 .000 7213440 720419 7.0 .0 .00 .00 .040 .000 .260 .000 7213665 720526 1.0 .0 .90 .00 .050 .000 .100 .000 7213666 720526 4.0 .0 .00 .00 .050 .000 .100 .000 7213667 720526 7.0 .0 .00 .00 .120 .000 .080 .000 7513001 750205 1.0 .0 7.80 .00 .007 .008 .692 -040 20 7513002 7SO205 3.0 .0 8.80 .00 .005 .003 .690 .0SO- 7511003 75020S 6.0 .0 .00 .00 .006 .006 .698 .050 7513038 750224 1.0 .0 3.70 3.20 .006 .006 .709 .070 20 7S13039 750224 3.0 .0 .00 .00 .006 .007 .702 .070 7S13040 750224 6.0 .0 8.50 1.50 .0.v .010 .686 .060 7513006 75030S 1.0 .0 4.30 3.60 .004 .007 .639 .040 20 7513097 750305 3.0 .0 2.70 5.20 .003 .000 .639 .040 7513089 750305 6.0 .0 5.30 11.10 .004 .007 .622 .050 7513127 750319 1.0 .0 2.90 4.70 .019 .009 .517 .030' - 20 7513126 750319 3.0 .0 2.10 2.00 .011 .008 .524 .030 7S13129 750319 6.0 .0 6.40 7.40 .008 .008 .524 .030 MINOR LAKES MONITORING PROJECT -- MASTER FILE TABLE 2 OF 2 TOTAL SAMPLE STATION NUMBER DATE DEPTH SUSP SOL GHLOR A PHAEO NH3 ORTH PO4 TOT NO2-NO3 Po4 FG FECAL _ EME710 ---- ------ ------ M ----- NG/L UG/L UG/L MG/L MG/L MG/L MC/L CODE /100ML CENTTERO A710 7513159 7SO400 1.0 .0 2.20 1.00 0AOGC/100ML .035 .005 .392 .020 - 7513160 750408 3.0 .0 .SO 3.20 .034 .004 .391 .030 7513161 7SO408 6.0 .0 .SO 3.20 .034 .004 .376 .040 7SI3191 750422 1.0 .0 .60 3.30 .042 .010 7SI3192 7SO422 3.0 .0 .50 3.20 .037 .007 .297 .285 .020 .030 20 . 7513193 750422 6.0 .0 .10 3.30 .046 .007 .261 .040. 7SI3211 750506 1.0 .0 .00 6.30 .041 .003 7513212 750506 3.0 .0 5.30 6.90 .034 .003 .209 .196 .040 .050- 20 7513213 750506 6.0 .0 .00 7.20 .102 .005 .128 .060 7513255 7SO520 1.0 .0 .70 2.10 .013 .003 .121 7513256 750520 3.0 .0 .80 4.00 .040 .002 .124 .020 .020 20 . 7513257 7SO520 6.0 .0 1.20 2.30 .114 .004 .060 .040 7513293 750603 1.0 .0 1.50 1.20 .027 .003 .076 7513284 7SO603 3.0 .0 3.70 17.60 .024 .002 .056 .020 .040 20 7513285 7SO603 6.0 .0 3.30 5.20 .022 .003 .OS6 .020 7513309 7$0619 1.0 .0 .10 .90 .026 .003 7Si3330 750619 3.0 .0 2.90 .10 .043 .003 .025 .020 .020 .020 20 7513311 750619 6.. .0 3.20 5.00 .212 .006 .005 .050 7513334 750708 1.0 _0 .SO 1.50 .007 _003 7513335 750708 3.0 .0 2.50 3.20 .033 .003 .003 .00S .020 .OSo. 20 7513336 750708 6.0 .0 8.10 4.40 .1:: .005 .002 .060 7SI3357 7Sp722 1.0 .t .50 1.80 .014 .004 .001 751335E 750722 3.0 .0 1.30 7.10 .001 .003 .001 .030 .030 20 7S133S9 750722 6.0 .0 9.00 18.20 .144 .O06 .00i .060 MINOR LAKES M01JIT0RING PROJECT -- MASTER.. FILE TABLE 2 OF 2 TV AL SUSP CHLCR CRTH TOT FECAL e7EP.0- SAMPLE IRMBE?. DATE DEPTH M SOL MG/L A UG/L PH:.EO NH3 PO4 tM2-NO3 Po4 FC COLI E^ERO COCCUS UG/L MC/L MG/L MG/L MG/L CODE /100ML CODE ORG/100ML A.30 7513370 750804 1.0 _0 SO 3.80 .p1B .004 .001 .010 __ 7SI3371 750804 3.0 .0 2.30 7.10 .00: .002 .001. .010 7513372 750804 6.0 .0 9.80 18.20 .005 .004 .001 .050 7SI3404 750819 1.0 .0 1.30 4.00 .014 .007 .004 .020 43 7513405 750819 3.0 .0 1.60 5.10 _002 .005 .001 .020 7513406 750019 6.0 .0 .00 .00 .021 .007 .001 .040 7513416 750908 2.0 .0 .00 .00 .005 .010 .001 .040 20. 7513417 750908 3.0 .0 .00 .00 .004 .007 .001 _040 7513416 750908 6.0 .0 .00 .00 .084 .008 .001 .220 7513440 750922 1.0 .0 .80 2.00 .014 .004 .002 .040 20 7513441 750922 3.0 .0 1.10 3.80 .004 .004 .001 .020 7513442 750922 6.0 .0 30.40 6.80 .004 .002 .001 .040 7513481 751105 1.0 .0 3.30 .10 .074 .016 .300 :'060 20 . 7513482 751305 3.0 .0 2.90 .10 .056 .013 .267 .060 7513463 751105 6.0 .0 .00 .00 .053 .010 .119 .050 7513511 751204 1.0 .0 1.50 1.40 .074 .016 .422 .020 -88 7SI3512 751204 3.0 .0 1.30 1.50 .060 .015 .394 .020 7SI3513 751204 6.0 .0 1.60 2.00 .060 .012 .385 .030 7523530 751215 1.0 .0 2.00 .SO .077 .016 .SO9 .060 23 7513531 751215 3.0 .0 1.60 .50 .069 .015 .504 .060 7513532 7SI215 6.0 .0 1.60 2.30 _066 _013 .504 .060 7613001 760105 1.0 .0 1.50 2.60 .071 .015 .534 .010 20 7613002 760105 3.0 .0 2.90 4.20 .OS7 .020 .525 .030 7613003 760105 6.0 .0 6.00 .10 .05S .010 .525 .020 MINOR LAKES MCNITORING PROJECT -- MASTER FILE TABLE 2 OF 2 TOTAL SAMPLE DEPTH SUSP SOL CMLOR A PMAEO NH3 ORTR PO4 TOT M02-NO3 PO4 FC FECAL ENTERO_ COLI NUMBER _______ ______ DATE ______ M _____ MG/L _____ UG/L _____ UG/L MG/L MG/L MG/L MG/L CODE ENTER COCCUSSTATION /SOOML CODE ORG/100ML A730 7613034 760119 1.0 .0 4.70 _____ 1.50 ____ .047 ____ .019 _______ .526 ____ ____ .050 ____20 ______ _________ 761303S 760119 3.0 .0 5.30 2.60 .035 .012 .SIB .060 7613036 76011- 6.0 .0 2.10 .80 .046 .012 .526 .070 7613067 760202 1.0 .0 4.80 1.70 .021 .012 .496 .040 20 7613068 760202 3.0 .0 4.00 1.60 .014 .007 .496 .050 7613069 760202 6.0 .0 1.60 1.80 .015 .006 .496 .040 8710 7113111 71080S 1.0 .0 .00 .00 .OSO .000 .010 .000 7213101 720224 1.0 .0 .00 .00 .010 .000 .520 .000 7213441 720419 1.0 .0 .00 .00 .040 .000 .260 .000 7213668 720526 1.0 .0 .00 .00 .040 .000 .100 .000 7513011 7SO205 1.0 .0 .00 .00 .004 .000 .010 .000 20 751304S 750224 1.0 .0 .00 .00 .004 .000 .010 .000 20 7513096 750305 1.0 .0 .00 .00 .004 .000 .010 .000 20 C710 7113112 71080S 1.0 .0 .00 .00 .020 .000 .010 .000 7213102 720224 1.0 .0 .00 .00 .010 .000 .460 .000 7213442 720419 1.0 .0 .00 .00 .040 .000 .260 .000 7223669 720S26 1.0 .0 .00 .00 .040 .000 .090 .000 7513014 75020- 1.0 .0 .00 .00 .004 .000 .008 .00. 20 7513047 750224 1.0 .0 .30 .00 .004 .000 .0D6 .000 20 7513093 750305 1.0 .. .DD .00 .004 .000 .006 .000 20 D710 7113113 710805 1.0 .0 .00 .00 .020 .000 .010 .000 7213103 720,24 1.0 .0 .;9 .00 .010 .000 .530 .000 7213443 7204_9 1.0 .. .00 .00 .040 .000 .260 .000 7213670 720S:6 1.0 .. .,,, .00 .040 .000 .100 .000 M:NS?. L;iFES Y.0'11 TOR:NO PRO.lECT -- MASTEF. FILE TABLE 2 OF 2 TOTAL SUSP Cn_C_. ORTH TCT FECAL ENTER - SAMPLE DEPTei SOL. A P-AEO NH3 PO4 NO2-NO3 PO4 FC COLI EITE?O COCCUS STATION _______ NUMBEP GATE M MG/L =/L UG/L MG/L MG/L MG/L MG/L COCE /100ML CODE OP.G/100M_ D710 ______ 7513017 ______ 750205 _____ 1.0 _____ .0 _____ .00 _____ .00 ____ .004 ____ .000 _______ .010 ____ ____ .000 ______ ______ _________ 20 7513045 750,14 1.0 .0 .00 .00 .004 .000 .010 .000 20 7513101 7S0305 1.0 .0 .00 .00 .004 .000 .010 .000 20 1710 7513053 750224 1.0 .D .00 .00 .014 .005 2.590• .120 250 7SI3107 7SO305 1.0 .0 .0C .00 .010 .004 2.190 .060. 67 . 7513139 7SO319 1.0 4.0 .00 .00 .020 .013 1.306 .060 40 7513171 750409 1.0 2.4 .00 .00 .060 .030 .253 .090 20 7S13203 750422 1.0 2.7 .00 .00 .031 .009 .215 .030 29 7513223 7SOS06 1.0 .6 .00 .00 .034 .003 .157 .050 20 . 7513265 75OS20 2.0 3.5 .00 .00 .012 .003 .097 .020 20 7S13293 IS0603 1.0 1.5 .00 .00 .017 .002 .049 .020 7513319 750619 1.0 1.0 .00 .00 .017 .002 .01E .020 41 7SI3344 750708 1.0 .1 .00 .00 .004 .003 .001 .040 20 7513542 751215 1.0 .1 .00 .00 .004 .003 .001 " .040 0710 7213444 720419 1.0 .0 .00 .00 .040 .000 .260 .000 7213671 72OS26 1.0 .0 .00 .00 .040 .000 .100 .000 7513021 75020S 1.0 4.0 .00 .00 .008 .006 .672 .050 70 7513058 7SO224 1.0 .0 .00 .06 .006 .003 .693 .050 20 7513112 750305 1.0 .0 .00 .00 .005 .005 .230 .040 20 _ 7513144 750319 1.0 1.2 .00 .00 .016 .009 .510 .030 20 7513176 750408 1.0 14.6 .00 .00 .031 .006 .371 .040 • 20 - 7513208 750422 1.0 .0 .00 .00 .033 .006 .280 .040 20 7513226 750506 1.0 2.0 .00 .00 .036 .001 .187 .050 20 7513260 7SOS20 1.0 12.5 .00 .00 .018 .004 .077 .020 83 MINOR LAKES MONITORING PROJECT -- MASTER FILE TABLE 2 OF 2 TOTAL SUSP CHLOR ORTH TOT FECAL ENTERO- SAMPLE DEPTH SOL A PHAEO NH3 PO4 NO2-NO3 PO4 FC COLI ENTERO COCCUS STATION NUMBER DATE M MG/L UG/L UG/L MG/L MG/L MG/L MG/L CODE /100ML CODE ORG/100ML ------- ------ ------ ----- ----- ----- ----- ---- ----------- ---- ---- ------ --------------- A740 8908645 891009 1.0 .0 1.84 24.12 .000 .000 .000 .018 9004629 900226 1.0 .0 .59 .23 .000 .000 .000 .046- 9004630 900226 4.0 .0 .00 .00 .000 .000 .000 .039 9004631 900226 8.0 .0 .00 .00 .000 .000 .000 .034 9106014 910226 1.0 .0 9.18 4.70 .000 .000 .000 .030 910601S 910226 4.0 .0 .00 .00 .000 .000 .000 .024 . 9106016 910226 8.0 .0 .00 .00 .000 .000 .000 .026 9106834 910319 1.0 .0 8.44 1.58 .000 .000 .000 .026 9106835 910319 4.0 .0 .00 .00 .000 .000 .000 .024 9106836 910319 8.0 .0 .00 .00 .000 .000 .000 .022 9207364 920224 1.0 .0 3.52 1.20 .000 .000 .000 .047 9207365 920224 4.0 .0 .00 .00 .000 .000 .000 .030 9207366 920224 8.0 .0 .00 .00 .000 .000 .000 .027 9208535 920331 1.0 .0 .00 .00 .000 .000 .000 .000 . 9208536 920331 4.0 .0 .00 .00 .000 .000 .000 .017 9208537 920331 8.0 .0 .00 .00 .000 .000 .000 .029 . MINOR LAKES MONITORING PROJECT -- MASTER FILE TABLE 2 OF 2 TOTAL SUSP CHLOR ORTH TOT FECAL ENTERO- SAMPLE DEPTH SOL A PHAEO NH3 PO4 NO2-NO3 PO4 FC COLI ENTERO COCCUS STATION NUMBER ------- ------ DATE ------ M ----- MG/L UG/L UG/L MG/L MG/L MG/L MG/L CODE /100ML CODE ORG/100ML 0710 7513295 750603 1.0 ----- 1.5 ----- .00 ----- .00 ---- .023 ---- .002 ------- .033 ---- -'-- .020 ------ --------------- 24 7513320 750619 1.0 2.5 .00 .00 .018 .002 .024 .020 49 7513493 751105 1.0 2.7 .00 .00 .043 .007 .145 .050 34 7513527 751204 1.0 4.4 .00 .00 .064 .012 .394 .030 83 7513547 7SI215 1.0 .0 .00 .00 .082 .011 .468 .000 20 7613017 760105 1.0 3.6 .00 .00 .050 .008 .512 .010 37 7613050 760119 1.0 4.S .00 .00 .035 .013 .507 .070 20 7613083 760202 1.0 3.2 .00 .00 .024 .006 .462 .050 20 MINOR LAKES MONITORING PROJECT -- MASTER FILE TABLE 2 OF 2 TOTAL SUSP CHLOR ORTH TOT FECAL ENTERO- SAMPLE DEPTH SOL A PHAEO NH3 PO4 NO2-NO3 PO4 FC COLI ENTERO COCCUS STATION NUMBER DATE M MG/L UG/L UG/L ----- MG/L MG/L MG/L MG/L CODE /100ML CODE ORG/100ML ------ ------- ------ A740 8800486 ------ 880504 ----- 1.0 ----- .0 ----- 1.96 .23 ---- .000 ---- .000 ------- .000 ---- ---- ------ --------- .013 880S979 880516 1.0 .0 2.35 .94 .000 .000 .000 .028 8806338 880606 1.0 .0 6.76 1.88 .000 .000 .000 .020 8806937 880621 1.0 .0 1.47 1.10 .000 .000 .000 .008 8807233 880705 1.0 .0 1.76 1.12 .000 .000 .000 .012 8807259 880719 1.0 .0 2.40 2.01 .000 .000 .000 .017 8808335 880801 1.0 .0 3.46 1.38 .000 .000 .000 .014 8808361 880815 1.0 .0 2.42 2.66 .000 .000 .000 .014 8809006 880906 1.0 .0 2.64 .23 .000 .000 .000 .011 8809032 880919 1.0 .0 3.52 2.85 .000 .000 .000 .016 8809838 881003 1.0 .0 4.11 3.0E .000 .000 .000 .013 8903912 890301 1.0 .0 3.67 2.75 .000 .000 .000 .022 8903913 890301 3.0 .0 .00 .00 .000 .000 .000 .024 8904578 890323 1.0 .0 .00 .00 .000 .000 .000 .035 8904579 890323 3.0 .0 .00 .00 .000 .000 .000 .040 890S811 890509 1.0 .0 1.76 .09 .000 .000 .000 .013 8905836 890523 1.0 .0 .39 2.62 .000 .000 .000 O15 890S861 890606 1.0 .0 .8° .01 .000 .000 .000 .018 8905886 890621 1.0 .0 83.41 38.30 .000 .000 .000 .060 8906470 890712 1.0 .0 .00 .00 .000 .000 .000 .021 . 8906495 890725 1.0 .0 .89 .77 .000 .000 .000 .013 8907418 890607 1.0 .0 1.96 3.52 .000 .000 .000 .037 - 8907656 890905 1.0 .0 2.45 2.01 .000 .000 .000 .017 8907688 890919 1.0 .0 4.33 1.95 .000 .000 .000 .011 ' MAY CREEK BASIN STUDY AmC Bh BOD EEC AgC, A AgC AgB N" k .. _ U. AgC - No CNU A6C AgC ..- t (1dcU AgD IJh r BeD ABC e_ U C _ .. FREQUENCY SOL-CODE RECLASS 19 AgC 2 16 AyyD 2 2 AkF 2 3 AmC 2 8 BeC 3 5 BeD 3 4 EvB 3 12 EvC 3 1 1nnC 3 3 EAKE 3 4 No 2 1 OvC 3 1 Ov0 3 2 POOrND 3 3 0UAR 3 Rd[ 3 1 Rh 3 Sk 5 2 3 Sm 1 I ru 2 AgC EvC AgU Bh RdC AgU .. EvC. EvC A AmC C. KpB AgC, No Tu AgJ) P,rB AgC UlJAR A Bh SOIL RECHARGE POTENTIAL FACTOR ! High (RECLASS = 3) C Medium (RECLASS = 2) 0 Low (RECLASS = 1) NILF 0 1 .,AK Figure E-1: Influence of soil properties on potential aquifer recharge areas. July 0/, 1995 /swl/mC4-94/mayaeek/ebasco/acquder/bw-soiLaml SLOPE RECLASS 0-40% 3 40-80% 2 80-100% 1 SLOPE RECHARGE POTENTIAL FACTOR High (RECLASS = 3) C Medium (RECLASS = 2) C� Low (RECLASS = 1) I MILE Figure E-3: Influence of slopes on potential aquifer recharge areas. July UI. IM/srl/mc4-94/maycreek/eDasco/ocauiler/DM-sloo.aml 40 CAW / ) ° �\ f 0 zia y_ 'per �7 \ P p MILE. Figure E-4: Map of estimated depth to groundwater in May Creek Basin. ily 07, 1995 /srl/mc4-94/maycreek/ebasco/ocquiler/deplh2gr/gwconl.aml DEPTH 10 GW RECLASS 0-25 feet 3 25-75 feet 2 >75 feet 1 DEPTH TO GROUNDWATER RECHARGE POTENTIAL FACTOR High (RECLASS = 3) Medium (RECLASS = 2) 0 Low (RECLASS = 1) f MILE 0 1 Figure E-5: Influence of groundwater depth on potential aquifer recharge areas. My ur, IUD isn/Inca-a+imoycretk/eoosco/ocquner/DW-gM.umi 0 Figure E-6. Water Temperature Monitoring Results by Location. North Fork at SE May Valley Road 30 ci 25 20 15 - — — - ° ■ �od0 p ° o o- ■ ■ ■ ■ d'v E15 : ■ ■ ■ ■ ■ ■ 0 1-Oct 1-Nov 2-Dec 1-Jan 1-Feb 3-Mar 3-Apr 3-May 3-Jun 3-Jul 3-Aug 2-Sep 3-Oct O Water Year 1993 0 Water Year 1994 164th Avenue SE 30 c> 25 ■ ° e o 9P 20 ■ .- — - ■ (�o 15 ■ a 10 ■ ■ ■ ■ ■ ■ E 5 0 1-Oct 1-Nov 2-Dec 1-Jan 1-Feb 3-Mar 3-Apr 3-May 3-Jun 3-Jul 3-Aug 2-Sep 3-Oct 148th Avenue SE 30 ci t_ 2 5 � o 20 15 — - - - -°�_ ° o "" o ° a10 ■ ■ ■■ E 5 ■ ■ ■ ■ ■ ■ 0 1-Oct 1-Nov 2-Dec 1-Jan 1-Feb 3-Mar 3-Apr 3-May 3-Jun 3-Jul 3-Aug 2-Sep 3-Oct NE 31st Street 30 U 25 = 20 2 15 --°-O ■ o ®° °■ o 060 o m ■ 10 ■ ■ ■ ° c. E 5- ■ ■ ■ 0- 1-Oct 1-Nov 2-Dec 1-Jan 1-Feb 3-Mar 3-Apr 3-May 3-Jun 3-Jul 3-Aug 2-Sep 3-Oct Tahle F,-13. Full Renort of Mav Creek Sediment Oualitv Data. Page 1 of 4 Sample ID r 1 IA 4 Sample Date 9/15/92 9117/92 9115/92 9/17/92 9/15192 9/17/92 (mg/kg) TPH 63.3 195.0 24.3 FOG 120.0 316.0 39.7 4-Methylphenol 0.32 Phenanthrene 0.1 0.3 Di-n-Butylphthalate 0.17 0.32 Fluoranthene 0.2 0.65 Pyrene 0.16 0.48 Butylbenzylphthalate EST 0.1 Benzo(a)Anthracene EST 0.065 0.18 bis(2-Ethylhexyl)Phthalate 0.26 0.7 Chrysene 0.091 0.29 Benzo(b)Fluoranthene EST 0.066 Benzo(k)Fluoranthene 0.098 Benzo(b+k)Pyrene 0.44 Benzo(a)Pyrene EST 0.062 0.17 Indeno(1,2,3-cd)Pyrene 0.13 Benzo(ghi)Perylene EST 0.095 Aroclor-1260 EST 0.03 0.1 Aluminum 8175.0 16076.0 9919.0 Cadmium <0.2 0.869 <0.2 Chromium 18.5 40.7 28.1 Copper 22.7 36.5 18.7 Lead 14.8 26.5 4.0 Zinc 51.1 119.0 55.3 Total P 716. 716.0 901.0 Table C-13. Full Report of Mav Creek Sediment Qualitv Data. Page 2 of 4 Sample 1D 6 7 9 Sample Date 9/15/92 9/17/92 9/15/92 9/17/92 9/15/92 9/17/92 (mg/kg) TPII 935.0 20.8 FOG 1474.0 23.6 106.0 4-Methylphenol Phenanthrene Di-n-Butylphthalate Fluoranthene Pyrene Butylbenzylphthalate Benzo(a)Anthracene b is (2-Ethylhexy I) Phthalate Chrysene Benzo(b)Fluoranthene Benzo(k)Fluoranthene Benzo(b+k)Pyrene Benzo(a)Pyrene Indeno(1,2,3-cd)Pyrene Benzo(ghi)Perylene Aroclor-1260 Aluminum 21943.0 16399.0 13718.0 Cadmium 1.69 <0.2 <0.2 Chromium 54.6 23.1 24.9 Copper 106.0 19.1 16.7 Lead 255.0 11.0 6.1 zinc 551.0 44.5 45.0 Total P 3365.0 288.0 350.0 Appendix E. Calculation of Annual Total Phosphorus Loads to Lake Washington from Selected Basins To gain an understanding of relative contributions of total phosphorus to Lake Washington, annual loads were calculated for six streams discharging to the lake: May, Coal, Kelsey and Thornton Creeks, Cedar River, and Sammamish River. Water quality and flow data were collected from a variety of sources and were used to compute the total phosphorus loads. An attempt was made to use the best available data and provide consistency where possible; however, due to the variability in monitoring programs, it is recommended that these loading estimates be used in a relative comparison for planning purposes and not for more precise applications. The following report describes the methods and results of the loading calculations for the six selected stream systems. Data Sources and Calculations of Total Phosphorus Loads Water Quality Data The water quality data that were used to calculate total phosphorus loads to Lake Washington were obtained from Metro and the Department of Ecology (WDOE). Both the Metro samples, usually collected on the same day of each month, and the WDOE samples, collected monthly or twice monthly, are from routine sampling programs and include both baseflow and storm events. The premise is that by sampling on the same day of the month, capturing both base and storm events, over a long period of time the monitoring will represent "average" conditions. To augment the Metro routine sampling data, Metro storm specific data was included at some sites. In addition, for those sites that had supplemental samples, there was some variation to which storms were sampled. Sampling stations for phosphorus load calculations were selected based on the proximity to the mouth of the system (see the location map). For the Cedar River, WDOE water quality data was used instead of Metro data because it was nearer the United States Geological Survey (USGS) flow gauge located at the mouth. Due to data availability, the station for Kelsey Creek is located at the mouth of the basin, upstream of the Mercer Slough Basin. The sources of both water quality and flow data for all six stations are as follows: Stream Water Quality Data Flow Monitoring Data May Creek Metro King Co Coal Creek Metro Bellevue Kelsey Creek Metro USGS Thornton Creek Metro Metro Cedar River WDOE USGS Sammamish River Metro USGS21 1/ Measured King County flow incorporated with HSP-F simulated flow. 2/ Regression equation applied with USGS data at Woodinville. Flow Data The USGS supplied flow data for Kelsey Creek and the Cedar and Sammamish rivers. A regression equation (Lebman, John, Aspects of Nutrient Dynamics in Freshwater Communities, Ph.D. Dissertation, Univ. Washington, 1978), together with data from an upstream station at Woodinville, was used for the computation of flow at the mouth of the Sammamish River (see Calculations below). Because of numerous gaps in the King County May Creek measured data, periods of missing flow were replaced with Hydrological Simulation Program —FORTRAN (HSP-F) data (see Chapter 5: Hydrology). The Bellevue Storm and Surface Water Utility flow records were acquired for Coal Creek. For the period of interest, continuous Thornton Creek flow data downstream of the confluence of the north and south tributaries were not available. Because of this, recorded Metro flow data were linearly interpolated between routine sampling days to approximate daily flows. Calculations To calculate approximate daily total phosphorus loads, continuous flow records were multiplied by concentrations linearly interpolated between sampling dates. Daily loads were summed separately for the approximate water years 1991 and 1992 (beginning on October 21 st and ending on October 20th) and then combined to obtain an averaged yearly load. In addition, for each of these sites, an average daily loading was calculated based on the entire long term record. This allowed for a comparison of the two year period to a longer and more inclusive record. Due to data availability and the desire to overlap the period of record, for the purpose of this report, water years start on October 20th instead of October 1st. To include the greatest number of sampling days, and because the long term record did not always include an entire water year, the listed values for the long term record are calculated from an average daily value multiplied by 365 days. Table E-14 lists these average yearly loads in addition to flow and concentration values. Table E-14. Mean Daily Flow and Total Phosphorus Daily Concentrations and Annual Loads for Six Stream Systems that Contribute to Lake Washington. May Coal Kelsey Thornton Cedar Sammamish Creek Creek Creek Creek River River 2-Year Data Record 10/21/90 - 10/20/92 Mean Daily Flow 21 24 22 12 689 399 (cfs/day) Mean Daily Total P 0.046 0.071 0.102 0.082 0.018 0.051 concentration (mg/Uday) 1990-91 Loading 2,290 5,538 4,764 1,764 37,772 47,037 (Ibs/yr) 1991-92 Loading 1,103 2,183 3,870 3,147 16,721 27,154 (Ibs/yr) Average Annual 1,697 3,860 4,317 2,455 27,247 37,095 Loading (Ibs/yr) Long-term Data Record Starting Date 1/11/89 10/16/90 9/16/87 9/15/87 9/23/87 10/10/88 Ending Date 3/22/93 10/20/92 9/21/93 10/20/92 11/18/92 9/20/93 Years of Record 4.2 2.0 6.0 5.1 5.2 4.9 Mean Daily Flow 21 24 20 11 604 379 (cfs/day) Mean Daily Total P 0.044 0.072 0.096 0.074 0.021 0.053 concentration (mg/L/day) Average Annual 1,696 3,905 3,988 1,811 30,129 36,918 Load/ (Ibs/yr) 1/ Calculated from average daily loads multiplied by 365. To calculate total phosphorus loads for the Sammamish River, it was necessary to use a regression equation to approximate flow at the mouth because the present operating USGS gauge nearest the mouth is at Woodinville. To validate this procedure, for an identical period of time, loads calculated from the regression equation were compared with loads using linearly interpolated WDOE flow and concentration values from an upstream site near Bothell. The results were similar as is seen below: Calculated Total Phosphorus Data Sources Loads (Ibs/year) 1990-91 1991-92 Regression Equation with USGS 47,037 27,154 at Woodinville and Metro Concentrations at Mouth Department of Ecology Flow 42,232 26,754 and Concentrations near Bothell Because a continuous flow record was desired, the regression equation was selected for all further analysis of Sammamish River loadings. Starting in water year 1991 there is a lower limit of approximately 22 cfs for Bellevue flow data. Before this time water volumes measured by Bellevue fluctuate below this point. In addition, for water year 1991 and beyond, measured Metro volumes are also lower than 22 cfs. For these reasons, when Bellevue flow is 22 cfs or lower it is superseded with interpolated Metro flow data as long as the Metro flow data is also below 22 cfs. As was previously noted, Kelsey Creek loads do not account for any flow or phosphorus loads from the downstream Mercer Slough Basin. Because some basins had a greater number of supplemental Metro storm specific data (approximately two to four additional samples each for May, Kelsey and Thornton creeks, twice this many for Coal Creek, and none for the Sammamish and Cedar rivers), some of these loads may be artificially elevated above other basins. Limits of Analysis The purpose of this analysis was to present relative annual total phosphorus loads to Lake Washington from May, Coal, Kelsey, and Thornton creeks, and the Cedar and Sammamish rivers. To calculate the complete loading to the lake, loads from the many additional smaller streams in the Lake Washington watershed should be analyzed. The loads presented herein approximate values based on available —though limited —data, and were developed for planning purposes. A more accurate loading estimation would require an enhanced and uniform monitoring program. Table E-15. Water Temperatures in May Creek North Fork 164 Ave. SE 148 Ave. SE NE 31st Street DATE MIN Pres MAX MIN Pres MAX MIN Pres MAX MIN Pres MAX 6/10/93 12 13 13 13 6/16/93 11 15 15 10.5 16 16 11 17 17 11 17 18 6/19/93 12.5 16 16 12.5 19.5 19.5 13 21 21 18 18 6/22/93 11 12.5 17 11 13.5 21 12 14 22.5 12.5 12.5 21 6/25/93 10.5 16 16 11 20 20 12 21 21 11 17.5 17.5 7/1/93 10.5 18 18 11 22 22 13.5 21.5 22 12 13 19.5 7/9/93 11.5 13 16.5 13 15 22 14 15 22 12.5 15 18.5 7/16/93 12 14 15 12.5 16 19 13 16 18 12 16 16 7/23/93 12 14 16.5 12 15 21 13 15 21 15 7/30/93 12 14 16 11.5 18 21 12.5 18 20.5 12.5 15.5 16.5 8/6/93 12 16 20 12 18.5 25.5 14 17 25 12 16 19 8/13/93 13 14.5 17 12.5 16 21 14 14 19.5 12.5 14 17 8/20/93 13 17 19 13 21 24 12 16 17 8/25/93 12 12 18 11.5 12 22 13 11.5 12 18 9/3/93 10.5 18.5 19 10.5 22.5 23.5 12 23.5 24 10 15.5 16 9/10/93 13.5 16.5 19 12 22 24 14.5 16 12 15.5 16.5 9/16/93 10 14.5 21 9.5 19.5 23.5 12 13 19 10 13.5 16.5 9/24/93 11 13.5 8.5 10.5 16 8 11 14.5 10/1/93 13 18 10 12 16 9 12 13 10/14/93 8 12 14 8 13.5 18.5 9 12 14 8.5 12.5 13.5 11 /5/93 6 8 13 6 10 15 6.5 8 14 6.5 8 13 11/19/93 2.5 6.5 8.5 3.5 8 10.5 3.5 5.5 8.5 4 7 9 12/6/93 0 5 8.5 1 5 10 0 2 6.5 4 10 12/21/93 2.5 4 8.5 2 4 9 1.5 2 6.5 2 3 9 1/6/94 1 6 8 1.5 6 7.5 0.5 4 6 1 5 1/25/94 5 7.5 9 5 7.5 9 3.5 6 7 4 7 2/4/94 2 4 8 2 5 8 1.5 3 6 2 3 8 3/22/94 0 7 12 0 7 12.5 0 6 11 5.5 3/30/94 5 10 13 4.5 10.5 14.5 4 9.5 13 2.5 11 12.5 6/2/94 7 13 16 6.5 17 21 7 16.5 20.5 14 7/8/94 11 16.5 18 11.5 22.5 24 11 19 23.5 - 10 16 17 7/22/94 12 21 14 21 22 15 22 25 11.5 18 18 7/29/94 13.5 16 15 19 26.5 18 18 24 12 15 19 8/19/94 13 17 18.5 14.5 21 24.5 16.5 17.5 22 12 15.5 16.5 9/13/94 9.5 10.5 18 11 12 23 13 13.5 18 10 11.5 16.5 Table E-16. Pollutant Yield Coefficients by Land -use Category Total Total Fecal Land -use Category Suspended Phosphorus Total Coliformsi/ Solidsi/ 1 (kg/ha-yr) Zinc2/ (#/ha-yr) (kg/ha-yr) (kg/ha-yr) Commercial/Institutional Forest Grass Impervious Quarry3/ Low -density Single-family Forested (Current Land Use) Low -density Single-family Grass (Current Land Use) Multifamily High -density Single Family Medium -density Single Family (Future Land Use) Low -density Single Family (Future Land Use) 242 0.688 1.00 1.7+E9 26 0.095 0.02 1.2+E9 80 0.010 0.06 4.8+E9 133 0.588 0.63 6.3+E9 80 0.010 0.60 4.8+E9 404/ 0.1404/ 0.804/ 1.4+E941 60 0.457 0.80 2.8+E9 133 0.588 0.63 6.3+E9 97 0.540 0.40 4.5+E9 74 0.419 0.24 3.3+E9 50 0.298 0.80 2.1+E9 1/ Horner, 1990, unless noted otherwise. 2/ Novonty, V. and Olem, H., 1994. 3/ For comparision of current to future conditions, quarries are assumed to be closed with a cap and revegetated with grass. This eliminates the variability inherent in quarry operations. 41 Reinelt, L. and Horner, R., 1994. to