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HomeMy WebLinkAboutL2STA-StreamDRSegA_2015 04 15Lake to Sound Trail—Segment A Stream Discipline Report Prepared for King County Parks Division 201 South Jackson, Seventh Floor Seattle, WA 98104 Prepared by Parametrix 719 2nd Avenue, Suite 200 Seattle, WA 98104 T. 206.394.3700 F. 1.855.542.6353 www.parametrix.com CITATION Parametrix. 2015. Lake to Sound Trail—Segment A Stream Discipline Report. Prepared by Parametrix, Seattle, Washington. April 2015. TABLE OF CONTENTS 1. INTRODUCTION 1-1 1.1 PROJECT OVERVIEW 1-1 1.2 PROJECT FEATURES 1-5 1.3 PROJECT AREA AND SETTING 1-5 1.4 PROJECT PURPOSE AND NEED 1-6 2. METHODOLOGY 2-1 2.1 METHODS OF ANALYSIS 2-1 2.2 STUDIES AND COORDINATION 2-1 2.2.1 Review of Existing Information 2-1 2.2.2 Field Investigation 2-1 2.2.3 Regulations 2-2 3. AFFECTED ENVIRONMENT 3-1 3.1 STUDY AREA 3-1 3.2 GREEN/DUWAMISH RIVER BASIN SUMMARY 3-1 3.3 GREEN RIVER 3-2 3.3.1 Stream Type 3-2 3.3.2 Fish Habitat 3-2 3.3.3 Water Quality Conditions 3-2 3.3.4 Biological Conditions 3-2 3.4 BLACK RIVER 3-4 3.4.1 Stream Type 3-4 3.4.2 Fish Habitat 3-4 3.4.3 Water Quality Conditions 3-4 3.4.4 Biological Conditions 3-5 3.5 SPECIAL STATUS SPECIES 3-5 4. ENVIRONMENTAL CONSEQUENCES 4-1 4.1 CONSTRUCTION EFFECTS 4-1 4.1.1 Permanent Effects 4-1 4.1.2 Temporary Effects 4-2 4.2 OPERATIONAL EFFECTS 4-2 5. MITIGATION 5-1 5.1 AVOIDANCE AND MINIMIZATION MEASURES 5-1 5.2 RESTORATION OF TEMPORARY EFFECTS 5-1 5.3 COMPENSATORY MITIGATION 5-2 6. REFERENCES 6-1 LIST OF FIGURES 11 Vicinity Map 1-3 4-1 Stream Buffer Impacts 4-5 APPENDICES A Site Photographs ACRONYMS AASHTO American Association of State Highway and Transportation Officials BMP best management practice BNSF Burlington Northern Santa Fe Corps U.S. Army Corps of Engineers CWA Clean Water Act DBH diameter at breast height Ecology Washington State Department of Ecology ESA Endangered Species Act FEMA Federal Emergency Management Agency FHWA Federal Highway Administration HPA Hydraulic Project Approval LWD large woody debris OHWM ordinary high water mark NEPA National Environmental Policy Act PHS Priority Habitats and Species RM river mile SMP Shoreline Master Program TESC temporary erosion and sediment control WDFW Washington Department of Fish and Wildlife WDNR Washington Department of Natural Resources WRIA Water Resource Inventory Area WSDOT Washington State Department of Transportation INTRODUCTION This discipline report is intended to provide information in support of the Washington State Department of Transportation (WSDOT) Environmental Classification Summary form for the National Environmental Policy Act (NEPA) Documented Categorical Exclusion process, assist project planning, and facilitate permitting. This report describes streams and aquatic resources in the area of a proposed 1.2-mile non-motorized trail, which includes two fish-bearing streams. This report also evaluates potential impacts to streams and stream buffers from the proposed project, and presents avoidance and minimization measures included in the project design and conceptual mitigation for unavoidable impacts. Project Overview King County, together with the Cities of Renton and Tukwila, WSDOT, and the Federal Highway Administration (FHWA), is proposing to develop a 1.2-mile segment of what would ultimately be the 16 mile Lake to Sound Trail. The 1.2-mile segment is referred to as Segment A of the Lake to Sound Trail. Segment A extends from Naches Avenue SW, runs parallel to the railroad tracks north of the Black River Riparian Forest, across a proposed non-motorized pedestrian bridge northeast of Monster Road and under two railroad bridges to the Green River Trail at the north end of the Starfire Sports Complex in Fort Dent Park (Figure 1-1). Segment A, as well as the longer Lake to Sound Trail, would be part of a Regional Trail System that provides non-motorized, alternative transportation and a recreation corridor for multiple trail users, including bicyclists, pedestrians, skaters, and others. A goal of the Lake to Sound Trail is to provide non-motorized transportation facilities to economically disadvantaged communities in southwest King County that have been historically underserved by such facilities. Once complete, Segment A would become part of a larger planned system that would serve employment and residential centers in South King County and connect to regional trails in Seattle and the greater Regional Trail System network. Segment A would provide a much needed trail connection between the regional growth centers of Renton and Tukwila, and safe passage under the heavy rail lines. In addition to the Green River Trail, Segment A would connect to the Interurban Trail to the south, and in the future to the Cedar River Trail. Figure 11. Vicinity Map Project Features Segment A is typically approximately 12 feet of asphalt pavement bounded by two 2-foot-wide shoulders and 1-foot-wide clear zones, in accordance with American Association of State Highway and Transportation Officials’ (AASHTO) guidelines. The project includes: Constructing a 12-foot-wide asphalt pavement trail with soft-surface (gravel) shoulders Performing minor grading to construct the trail (approximately 1,410 cubic yards of cut and 2,980 cubic yards of fill, disturbing an area of approximately 0.72 acre outside the proposed trail footprint) Performing ground improvements, which will disturb an area of approximately 0.17 acre in addition to other disturbances from the trail Constructing a new non-motorized pedestrian bridge, including abutments, over the Black River, northeast of Monster Road, which cannot be improved to safely accommodate the envisioned trail use Installing a pedestrian-actuated signal crossing of Monster Road south of the bridge Constructing an undercrossing feature beneath two railroad bridges to protect trail users from potential falling debris Installing one box culvert for terrestrial habitat enhancement Building retaining walls near the south approach to Monster Road, north of the proposed pedestrian bridge over the Black River, and on either side of the box culvert Installing split-rail fencing and plantings to discourage incursions into sensitive areas and to improve visual screening for sensitive wildlife Constructing two approximately 10-foot by 20-foot pull-out rest areas (one at the northern perimeter of the Black River Riparian Forest and one east of Monster Road and northwest of the Black River pump station) Project Area and Setting The Segment A project area is a linear corridor mostly within an existing trail corridor (see Figure 1-1). Segment A is located in Section 13, Township 23 North, Range 4 East, Willamette Meridian. Two parallel railroad tracks (Burlington Northern Santa Fe [BNSF] and Union Pacific) cross the western quarter of the proposed trail corridor on elevated bridges heading north-south. Another set of BNSF railroad tracks are located north of the eastern three-quarters of the proposed trail corridor with an east-west bearing. These tracks tie into the north-south tracks north of the project area. East of the railroad bridges, the proposed trail alignment is within the City of Renton; west of the railroad bridges the proposed trail alignment is within the City of Tukwila. The project area is described from east to west below. The east terminus is located at a cul-de-sac on Naches Avenue SW near an office park. The eastern three-quarters of the proposed trail alignment from Naches Avenue SW to the new pedestrian bridge northeast of Monster Road (approximately 4,100 linear feet) follows an existing gravel maintenance road south of the BNSF east-west railroad tracks and north of the Black River, along the northern perimeter of the Black River Riparian Forest (see the Lake to Sound Trail—Segment A: Vegetation and Wildlife Discipline Report [Parametrix 2015a] for a more detailed description of the Black River Riparian Forest and the wildlife communities it supports). The gravel maintenance road is commonly used for walking and pet exercise. The existing road surface in most of this portion consists of compacted gravel and ranges from 10 to 12 feet wide. Areas immediately outside the edge of the existing gravel surface generally consist of grasses, low-growing annual plants, blackberry thickets, and native riparian trees. Uses outside this portion of the project area include a concrete recycling plant and an area zoned for light industrial uses just north of the railroad tracks. The proposed trail alignment crosses over the Black River using a proposed new non-motorized pedestrian bridge northeast of Monster Road Bridge, then crosses Monster Road south of the river. For the western quarter of the proposed trail alignment, west of Monster Road, the alignment lies south of the Black River. For the first 150 feet west of Monster Road, the alignment is on existing paved surfaces, and then it follows a dirt footpath that joins an existing dirt road beneath the railroad bridges for 650 feet. The westernmost 600 feet of the proposed trail alignment is on maintained lawns associated with Fort Dent Park. West of the railroad bridges, the area south of the proposed trail alignment is dominated by Fort Dent Park and the Starfire Sports Complex. The confluence of the Black and Green rivers is located just north of the west end of the Segment A project area. Commercial businesses are north of the Black River and south of the trail corridor. Project Purpose and Need The purpose of the Segment A project is to design and construct an alternative non motorized transportation corridor and multi-use recreational trail between Naches Avenue SW in Renton and the Green River Trail in Tukwila. Segment A would provide non-motorized access to recreation and employment centers and complete a link in the Regional Trail System network. The trail is intended to safely accommodate a variety of groups such as bicyclists, pedestrians, runners, wheelchair users, and skaters. Trail design standards will safely accommodate different ages and skill levels within those groups. Completion of Segment A would provide the following benefits: Serve local and regional non-motorized transportation needs and provide access to the trail for local communities. Help satisfy the regional need for recreational trails and provide safe recreational opportunities to a wide variety of trail users. Provide a critical link in the Regional Trails System. Provide economic and health benefits to communities along the trail. METHODOLOGY Methods of Analysis This study is based on a review of existing information and field investigations. The goal of these efforts was to document existing information to reflect current site conditions and to collect new information to assess potential impacts. Potential impacts on fish and aquatic resources were calculated by overlaying the proposed design onto the project base maps showing wetland, stream and buffer locations. Affected areas were determined as the area of overlap of the two sets. In some areas, multiple impact types (e.g., stream buffer and wetland buffer) were present in a single location. In this document, all stream and riparian buffer impacts are reported, although for purposes of compensatory mitigation, overlapping impacts were assigned based on the following hierarchy: wetland, stream (below ordinary high water mark [OHWM]), wetland buffer, and stream buffer impacts. Studies and Coordination Review of Existing Information Prior to conducting fieldwork, Parametrix reviewed maps and materials including, but not limited to: Priority Habitats and Species data (Washington State Department of Fish and Wildlife [WDFW] 2015a) Washington State Department of Natural Resources (WDNR) Natural Heritage Program database Salmonscape database (WDFW 2015b) A catalog of Washington streams and salmon utilization, Volume 1, Puget Sound Region (Williams et al. 1975) Water Resource Inventory Area (WRIA) 9 (Green/Duwamish River) Limiting Factors Analysis (Kerwin and Nelson 2000) Field Investigation The information on streams and aquatic habitat presented within this report is based primarily on the results of site investigations conducted by project biologists. The stream surveys characterized the project area streams within and immediately adjacent to the project right-of-way. The stream investigation involved qualitative evaluations of instream habitat features, riparian vegetation, streambank stability, and fish passage obstructions within the study area (where right-of-entry allowed access). Field investigations within the Segment A project area occurred on February 1, 2011. Selected site photographs are presented in Appendix A. In addition, coordination occurred with the authors of the wetland discipline report and critical area study for this project (Parametrix 2011, 2015b), who also collected available information on ecological resources and performed field studies. Regulations Streams associated with the project (Green River and Black River) in the City of Tukwila (west of the railroad bridges) are regulated under TMC 18.44, while in the City of Renton (east of the railroad bridges), the Black River and all of the Black River Riparian Forest is regulated under RMC 4-3-090 (Shoreline Master Program [SMP] Regulations). Land use permits will be required by the cities. Streams, wetlands, and other sensitive resources in the project vicinity are also subject to federal and state regulations. The information in this report is intended to facilitate project planning and to support acquisition of a Hydraulic Project Approval (HPA) from the WDFW, a Clean Water Act (CWA) Section 404 permit from the U.S. Army Corps of Engineers (Corps), and a CWA Section 401 Water Quality Certification from the Washington State Department of Ecology (Ecology), as necessary. AFFECTED ENVIRONMENT This section describes existing conditions of the streams and buffers within the study area, as well as the overall site conditions. A total of two streams (Black River and Green River) and six wetlands (Wetlands 1 through 6) (see the Lake to Sound Trail—Segment A Critical Area Study [Parametrix 2015b] for detailed wetland descriptions) are located within the Segment A project area. Surface water runoff from the concrete recycling plant north of the project area drains under the BNSF railroad tracks and then across the existing gravel maintenance road to Wetland 3. The water has eroded a short channel through the existing gravel and then sheet flows over the wetland, where much of the water infiltrates. (As part of the trail project, a drainage culvert would be constructed to convey this runoff under the trail (Figure 11).) Study Area The study area for the Lake to Sound Trail—Segment A stream investigation is defined as the area within 200 feet of the Black and Green Rivers, from Naches Avenue SW, parallel to the railroad tracks north of the Black River Forest, across Monster Road and under two railroad bridges to the Green River Trail at the north end of the Starfire Sports Complex in Fort Dent Park (see Figure 1-1). The study area also includes the Black River Riparian Forest, which is designated as a Shoreline under the City of Renton code. The following sections describe the aquatic habitat and species within the study area. This includes an overview of general site characteristics and descriptions of individual streams and aquatic habitat areas, as well as fish distribution and habitat use in each stream. Green/Duwamish River Basin Summary The project site is located within WRIA 9, the Green-Duwamish River basin. The Duwamish River is defined as the portion of the Green/Duwamish River system downstream from the confluence of the Black River (River Mile [RM] 11.0) to Elliott Bay (RM 0.0), while the Green River extends upstream from the Black River. For this report, the term ‘Duwamish River’ pertains to the first 11 miles of the river system, while the term ‘Green River’ pertains to both the portion of river above RM 11.0 and the river system as a whole. Historically, the Green, White, Black, and Cedar Rivers flowed into the Duwamish River, and the system drained an area of over 1,600 square miles. In the early 1900s, the Black, White, and Cedar Rivers were diverted, reducing the Green River drainage over 60 percent to just 483 square miles (Blomberg 1988). Also, in 1913 the City of Tacoma constructed a diversion dam on the Green River, near the town of Palmer, at about RM 50.0. In 1963, the Howard Hansen Dam was built at RM 53.0. Both of these structures completely blocked fish migration to the upper Green River and its tributaries. Flow in the Green River is regulated by the operation of the Howard Hanson Dam. River velocities are dissipated as the river widens and currents converge with tidal pressures. Characterized by wet and dry seasons, discharge of the river varies seasonally. The wet season extends from November to July, and the dry season from August to October. The mean monthly flow rate in the lower Duwamish varies from 400 cubic feet per second (cfs) in August to 2,600 cfs in January. Stream banks are sloped and diked to contain flows of up to 11,000 cfs (Williams et al. 1975). According to the Federal Emergency Management Agency (FEMA), the maximum regulated flow for the 100-year recurrence interval is 12,000 cfs at the project site. The Lower Green River basin begins at the Auburn Narrows (RM 31) and continues to just downstream of the confluence with the Black River in Tukwila (RM 11). The lower Green River basin is composed of two areas that are split by the Black River basin to the north and the Mill Creek basin to the south. It is mostly on the urban side of the urban growth boundary and contains portions of the cities of Kent, Auburn, Tukwila, Federal Way, and SeaTac. Land uses include residential, commercial, industrial, and agricultural, as well as some major highways, including Interstate 5. There are extensive areas of office/commercial and multi-family residential development. This area has developed rapidly over the past 20 years. Green River Stream Type The project alignment intersects the Green River at about RM 11.0 on the right bank of the river (see Figure 1-1). According to the WDNR stream typing system, the Green River is a Type S stream, designated as a shoreline of the state. Within the project area, the stream is located within the local jurisdiction of the City of Tukwila, which also classifies the Green River as a Type S stream. The shoreline jurisdiction extends 200 feet from the river OHWM. According to Tukwila SMP (Section 7.7), “the buffer will extend 125 feet landward from the ordinary high watermark, determined at the time of development or redevelopment of the site or when levee replacement or repair is programmed.” The remaining 75 feet landward of the buffer is also regulated under the Tukwila SMP. Fish Habitat Identified limiting habitat factors in the lower Green River watershed include (1) urbanization, water diversions, and revetments that have resulted in disconnection of the river from floodplain off-channel habitats such as sloughs and adjacent wetlands, (2) reduction of large woody debris and associated instream complexity, such as pools and riffles, (3) creation of adult salmon migration problems due to low flows, (4) chronic water quality problems, and (5) severe reductions in riparian habitats and associated functions (Kerwin and Nelson 2000). Currently, the reach within the study area is used by all native anadromous salmonid species for rearing and migration. Water Quality Conditions The Green River has no listed exceedances on the 2012 Ecology 303(d) list within or immediately adjacent to the project limits (Ecology 2015). A 303(d) reach is located over 0.5 mile upstream from the project area, with recorded exceedances for stream temperature, dissolved oxygen, and fecal coliform. Biological Conditions Fish Presence The Duwamish and lower Green Rivers serve as a migration and rearing area for anadromous salmonids, with no spawning habitat available (Williams et al. 1975). Three Pacific salmon species inhabit the Green/Duwamish River basin in significant numbers: Chinook (Oncorhynchus tshawytscha), coho (O. kisutch), and chum (O. keta) salmon. Pink (O. gorbuscha) and sockeye (O. nerka) salmon may occasionally be seen in the Green River basin, but the Green River is primarily a chum, coho, and Chinook salmon stream (Williams et al. 1975). Although sockeye salmon are occasionally seen in streams that are not tributaries to lakes, sockeye almost always require a rearing lake below or near their spawning area (Foerster 1972). Other anadromous fish using these waters include steelhead (O. mykiss), sea-run cutthroat trout (O. clarki clarki), Dolly Varden (Salvelinus malma), and bull trout (Salvelinus confluentus). Studies of juvenile salmonids in the Duwamish and lower Green River (Williams et al. 1975; Weitkamp and Campbell 1980; Weitkamp and Schadt 1982; Warner and Fritz 1995) have demonstrated the species presence, their timing within the project vicinity, and various characteristics of the fish. These investigations show that subyearling Chinook and chum salmon use shallow-water shoreline habitats of various characteristics during their migration to the ocean. Juvenile pink salmon are likely to be found in the same areas during their spring migration period. The young salmon appear to prefer relatively protected shorelines with gradual slopes and depths of less than about 6 feet. However, they are also found along hard, steep to vertical substrates that are either natural or man-made. The young salmon tend to remain close to the shoreline but apparently cross deep water at night (Stober et al. 1973; Bax et al. 1979). Yearling Chinook, steelhead, and coho also use shoreline areas but appear to be less shoreline-oriented than the subyearling migrants. The substantially larger yearlings are commonly found in the near-surface water well away from the shoreline. Subadult and adult bull trout and Dolly Varden are likely to forage within the project vicinity during their late spring to summer migrations into Puget Sound. Juvenile salmon migrating past the project site include Chinook produced from the Soos Creek Hatchery, located about 39 miles upstream from the site. The juvenile migration period potentially extends from late February through mid-June. During this period, wild fish commonly occur further upstream and are more numerous in tributaries, compared to hatchery fish. Stream Buffer Conditions Overstory riparian vegetation on the right bank of the river is generally limited to a relatively narrow (20 to 50 feet wide) zone with a sparse overstory of deciduous and coniferous trees. Trees include scattered Douglas-fir (Pseudotsuga menziesii), black cottonwood (Populus balsamifera), western redcedar (Thuja plicata), and nonnative alder (Alnus spp.) and spruce (Picea spp.) species. Understory vegetation consists primarily of shrubs, with sumac (Rhus spp.), poison hemlock (Conium maculatum), red-osier dogwood (Cornus sericea), bitter cherry (Prunus emarginata), and substantial amounts of Himalayan blackberry (Rubus armeniacus). Invasive vegetation dominates the outer portion of the riparian zone, including a large amount of Himalayan blackberry and various grass species. A single line of ornamental trees is present on the south edge of the riparian zone, directly adjacent to Fort Dent Park. In addition, portions of the riparian zone consist of patches of bare ground. The vegetation is not adequate to provide the full range of riparian functions, although low to moderate levels of stream shading, large woody debris (LWD) recruitment, leaf litter production, and bank stability are provided by the existing riparian zone. Much of the shrub vegetation overhangs the river, offering some overhead cover for fish. Black River Stream Type According to the WDNR stream typing system, the Black River is a Type S stream, designated as a shoreline of the state. Within the project area, the stream is located within the local jurisdictions of the Cities of Tukwila and Renton (see Figure 1-1), although the majority of the Black River is within Renton. Within Renton, the Black River is classified as a Class 1 water (shoreline of the state) (RMC 4-3-090F.1). The regulated buffer within shoreline jurisdictional (the Standard Vegetation Conservation Buffer width) includes lands within 100 feet, as measured on a horizontal plane, from the OHWM. Within Tukwila, the stream is classified as a Type S (shoreline of the state) stream. The regulated shoreline jurisdiction extends 200 feet from the river OHWM. According to Tukwila SMP (Section 7.7), “the buffer will extend 125 feet landward from the ordinary high watermark, determined at the time of development or redevelopment of the site or when levee replacement or repair is programmed.” The remaining 75 feet landward of the buffer is also regulated under the Tukwila SMP. Fish Habitat The Black River enters the Green River near Tukwila, on the right bank, at RM 11.0. On the Black River, a dam and pump station, which is approximately 600 feet upstream of Monster Road, prevent tidal upstream inundation of the river channel and maintain downstream flow, regardless of tidal influences. A Denil fishway allows upstream fish passage at the pump station, and an air lift pump arrangement aids downstream migrants in passing the structure during the spring months (Harza 1995). The project site is located in a developed setting, zoned industrial, with large amounts of impervious surface within the project vicinity. A large gravel pit (Stoneway Concrete) is located north of the Monster Road Bridge, warehouses and an industrial operation are located to the north and south of the trail alignment, and railroad tracks run both parallel and perpendicular to the trail alignment. Instream habitat within the project area is dominated by run-type channel morphology, with maximum stream depths of greater than 6 feet. At the time of the site visit (February 2011), the wetted width was approximately 25 feet, and no pools or riffles were observed. Bank-full width was estimated at 30 feet. Streambed material consists almost exclusively of sands and silts. The streambanks are relatively steep (approximately a 50-degree angle) and bank condition appears to be relatively stable. Underneath the Monster Road Bridge, both streambanks are 100 percent armored with riprap, from the edge of the water to the bridge deck. No LWD was observed in the study area, and the presence of the pump station above the project site precludes LWD recruitment from upstream. Overall, the quality of fish habitat is poor, with little habitat diversity. Within the study area, the Black River would probably be used for migration or possibly rearing, although instream cover is somewhat limited. Water Quality Conditions The Black River from RM 0.25 to 1.44 is on the 2012 Ecology 303(d) list for exceeding the fecal coliform criteria (Ecology 2015). This exceedance includes the reach of the Black River between Monster Road Bridge and the Black River pump station. Biological Conditions Fish Presence WDFW (2015a, b) data indicate that Chinook salmon, chum salmon, coho salmon, steelhead trout, and cutthroat trout all have been documented in the Black River within the study area. The type of use is listed as migration for all species except coho, which use the lower Black River for juvenile rearing. Conditions favorable for Chinook salmon spawning and rearing do not exist in the project area, and recent information, as well as historical records (Harza 1995; Williams et al. 1975), indicate that Chinook do not use this area for spawning and rearing. However, very small numbers of adult fall Chinook migrating up the Green River occasionally stray into the Black River and become trapped above the Black River pump station (the pump station cannot pass adult salmon downstream). In the fall of 1997, adult Chinook were observed entering the Black River and attempting to spawn near the SW 27th Street culvert in Springbrook Creek, 2.3 miles upstream of the project area (Kerwin and Nelson 2000). Bull trout are not known to occur in the Black River, and there have been no documented occurrences of spawning (WDFW 1998). Water temperatures in the Black River basin are too high to support reproduction by this species (Harza 1995; Rieman and Chandler 1999). Stream Buffer Conditions The stream buffers of the Black River within the project area are relatively degraded, of limited widths, and composed primarily of herbaceous, shrub, and nonnative species. Downstream of Monster Road Bridge, the width of the vegetated buffer ranges between 50 and 100 feet on the north side of the river and about 75 to 150 feet on the south side. Upstream of the bridge, the width of the vegetated averages from 100 to 150 feet on both sides of the Black River. The vegetated buffer consists of lightly forested and herbaceous plant communities, although the forested zone is restricted to within 50 feet of the river. Vegetation includes red alder (Alnus rubra), tall fescue (Schedonorus phoenix), salmonberry (Rubus spectabilis), reed canarygrass (Phalaris arundinacea), Himalayan blackberry, black cottonwood, western redcedar, western swordfern (Polystichum munitum), bigleaf maple (Acer macrophyllum), red elderberry (Sambucus racemosa) and snowberry (Symphoricarpos albus). Under existing conditions, the riparian corridor is not fully functioning, but it does provide some functions that support aquatic species, including some level of small woody debris or LWD recruitment, overhead stream cover, bank stability, leaf litter recruitment, and water quality maintenance. Special Status Species Three fish species that are listed as threatened or endangered under the Endangered Species Act (ESA) occur within the project area. ESA-listed salmonid populations within the Green River and the Black River are the Puget Sound evolutionarily significant unit of Chinook salmon and the Puget Sound steelhead distinct population segment. Also, small numbers of bull trout may be present within the mainstem Green River, although habitat conditions in the Black River would not support these species. No species that are candidates for listing under ESA are present in the study area; however, the Puget Sound/Strait of Georgia population of coho salmon is listed as a species of concern by the National Oceanic and Atmospheric Administration Fisheries and is present in the study area. Priority fish species include all State-listed endangered, threatened, sensitive, and candidate species, and species of recreational, commercial, or tribal importance that are considered vulnerable. No fish species with State candidate status occur in the study area. No State-listed sensitive, threatened, or endangered fish species occur in the study area. Coastal cutthroat trout, which are designated as priority species, may occur within the study area (WDFW 2015a). ENVIRONMENTAL CONSEQUENCES Construction Effects This section describes the extent and type of temporary and permanent effects on streams and aquatic resources that could occur as a result of construction activities associated with the proposed project. Permanent Effects The project does not include construction activities below the OHWM of any stream; therefore, the project would not result in any stream fill, nor would alterations to fish passage structures be required. Permanent effects on stream buffers would occur where the proposed trail alignment encroaches into currently vegetated areas within the regulatory buffers on the Green River and the Black River, including areas within the construction footprint for the proposed pedestrian bridge. As previously discussed, there is some overlap between stream buffers and wetland buffers. The total amount of riparian buffer that would be subjected to permanent impacts would be approximately 31,641 square feet (0.73 acre) (Figures 4-1 through 4-5). Of this area, 0.13 acre (5,715 square feet) also falls within wetland buffers and are identified as wetland buffer impacts for regulatory purposes. For this analysis, therefore, the project would result in 0.60 acre (25,926 square feet) of permanent impacts to riparian buffers. Further details on these impacts are provided in this project’s Critical Area Study (Parametrix 2015b). Permanent riparian buffer impacts would occur primarily along the Black River; approximately 2,400 square feet of the affected area would be within the Green River riparian buffer. In almost all cases, the quality of the riparian buffer that would be permanently displaced is low to moderate. Much of the riparian impact area along the Black River consists of grass or nonnative herbaceous and shrub species. The City of Renton has determined that all trees within 10 feet of the paved edge of the trail should be removed, as should all cottonwood trees within 20 feet of the paved edge of the trail, for the protection of public safety and the trail surface. Approximately 51 trees within the regulatory buffer of the Black River in the City of Renton would be removed. All but one of these would be deciduous trees (48 cottonwoods, 1 red alder, and 1 willow). One coniferous tree (a 6-inch-diameter Douglas-fir within the clearing area for the proposed pedestrian bridge) would be removed. Twenty of the trees proposed for removal are between 6 inches and 10 inches in diameter. Eight trees are smaller than 6 inches, 13 trees would be between 10 and 16 inches, and 10 trees (all cottonwoods) are larger than 16 inches in diameter. Construction of the western portion of the trail corridor would remove 14 trees larger than 4 inches in diameter within riparian buffers in the City of Tukwila. The existing buffer functions are somewhat degraded, compared to fully forested conditions, and these functions are provided at a low or moderate level. The predominant cover type within the project footprint is urban, consisting primarily of the gravel surface of the existing maintenance road. Where the existing surface is not composed of gravel, a worn dirt trail exists and is largely free of trees and shrubs. Clearing for trail construction would affect approximately 0.9 acre and is not expected to reduce species diversity or result in a substantial reduction in plant cover in the study area. Some low-growing plants would be replaced with hard surfaces, however, and the overhead canopy would be reduced in some places. Based on the nature and location of buffer impacts, no substantial degradation of riparian functions (e.g., fish and wildlife habitat, food chain support, water temperature maintenance) or process (e.g., water flow; erosion and accretion; infiltration; groundwater recharge and discharge; sediment delivery, transport, and storage; large woody debris recruitment; organic matter input; nutrient and pathogen removal; stream channel formation/maintenance) would result from permanent project-related clearing and no substantial effects on stream habitat or fish resources in any of the project area streams are anticipated. Temporary Effects Temporary impacts to stream buffers would occur from minor clearing and grading during project construction, as well as from potential erosion, sedimentation, and noise disturbance during construction. As previously discussed, there is some overlap between stream buffers and wetland buffers. The total amount of riparian buffer that would be subjected to temporary impacts would be 0.11 acre (5,312 square feet) (see Figures 4-2 through 4-5). Approximately 0.01 acre of this area (857 square feet) also falls within wetland buffers and are identified as wetland buffer impacts for regulatory purposes. For this analysis, therefore, the project would result in 0.10 acre (4,455 square feet) of temporary impacts to riparian buffers. Further details on these impacts are provided in the project’s Critical Area Study (Parametrix 2015b). Temporary riparian buffer impacts would occur primarily within the Black River riparian buffer; approximately 560 square feet of the temporary impacts would be within the Green River riparian buffer. Because the portions of the affected buffer are degraded (as discussed above) and these riparian areas would be replanted once construction is complete, temporary clearing is not expected to have a substantial effect on stream habitat or fish resources in any of the project area streams. Construction activities occurring directly adjacent to project area streams could increase turbidity and total suspended solid levels. However, no earthwork or riparian clearing would occur within 25 feet of the OHWM of the Green River or below the OHWM of the Black River. Along most of the proposed trail corridor, no ground-disturbing work would take place within 40 feet of any streams. Furthermore, potential effects would be avoided through the development and implementation of best management practices (BMPs), including temporary erosion and sediment control (TESC) and spill prevention control and countermeasures plans. Operational Effects The primary potential for operational effects would be from increased stormwater runoff, which can negatively affect stream flows. Although the project would add some non-pollution generating impervious surface to the project area in the form of the paved trail, the wide buffer distance between the trail and the Black and Green Rivers would allow ample opportunity for stormwater runoff be infiltrated or intercepted before entering the waterbodies. Also, no inter-basin transfers of stormwater would occur (all stormwater would remain in the basin it originated in). Therefore, no impact to the hydrology of these streams, including base flow and peak flow, would result from operation of the project. The proposed project would not add any pollution-generatin g impervious surface within the project area; heavy metals, polycyclic aromatic hydrocarbons, and other contaminants commonly associated with roadway runoff would not be generated on the pedestrian and bike trail and, therefore, no changes in water quality of the project area streams would result. The new pedestrian bridge over the Black River would be 109 feet long and 12 feet wide. The portion of the bridge spanning the OHWM of the river would be approximately 44 feet long, meaning approximately 528 square feet of the river would be affected by shading from the bridge. Shade from overwater structures such as bridges can be a migration barrier for fish. Juvenile salmonids avoid dark, shaded areas under structures, resulting in loss of access to habitat, blockage of movement, and potentially increased exposure to predators. In addition, shade from overwater structures can provide hiding cover for some non-native species, such as smallmouth bass, that prey on native fish. The Black River is not considered to be an important migratory corridor for salmonids because the Black River pump station immediately upstream of the study area presents a substantial barrier to upstream and downstream migration. In addition, reaches of the Black River and Springbrook Creek upstream of the project action area are unlikely to provide suitable spawning or rearing habitat for Chinook salmon or high-quality spawning or rearing habitat for steelhead. Moreover, the narrow footprint and north-south orientation of the bridge (minimizing the amount of time that any given point receives shade over the course of a day) would further diminish the potential for the structure to cast shade that presents a migration barrier for any juvenile salmonids that may pass through the project action area. All bridge components spanning the Black River would be designed and installed in accordance with the provisions of the HPA and other permits issued for the project. Per WAC 220-660-030, the HPA would include provisions designed to ensure no net loss of habitat functions necessary to sustain fish life. Compliance with the provisions of the HPA and other permits would be expected to avoid or minimize the potential for adverse effects resulting from bridge construction. Any unavoidable impacts would be addressed through compensatory mitigation. Figure 4-1. Stream Buffer Impacts Figure 4-2. Stream Buffer Impacts Figure 4-3. Stream Buffer Impacts Figure 4-4. Stream Buffer Impacts Figure 4-5. Stream Buffer Impacts MITIGATION The Lake to Sound Trail—Segment A project would avoid and minimize impacts to streams by proceeding in accordance with the mitigation sequencing requirements established by the NEPA, the CWA, and other aquatic area protection programs. According to NEPA (40 CFR paragraphs 1508.20), the definition of mitigation is as follows: Avoiding the impact all together by not taking a certain action or parts of an action. Minimizing impacts by limiting the degree or magnitude of the action and its implementation. Rectifying the impact by repairing, rehabilitating, or restoring the affected environment. Reducing or eliminating the impact over time by preservation and maintenance operations during the life of the action. Compensating for the impact by replacing or providing substitute resources or environments. Avoidance and Minimization Measures Consistent with the above sequencing requirements, a high priority was placed on designing the project to include measures and features that avoid and minimize adverse effects on streams and stream buffers. The streams in the study area have been avoided to the greatest extent feasible and no permanent filling of streams is anticipated. King County would apply the following strategies to minimize stream and buffer impacts during the design, permitting, and construction phases: Use a retaining wall to narrow the trail footprint in the vicinity of some riparian buffers. Near streams and wetlands, limit earthwork to the dry season to reduce the potential for sediment runoff. Construct the trail on an existing gravel maintenance road to minimize impacts to functioning riparian buffers. Where feasible, widen the trail on the north side of the existing corridor to minimize impacts to riparian buffers and wildlife habitat. Use appropriate sediment and erosion control BMPs (e.g., mulching, matting, and netting; filter fabric fencing; sediment traps) to reduce the risk of erosion and reduce or minimize the chance of sediments entering project waterbodies. Prepare and implement a TESC plan for clearing or removing vegetation, grading, ditching, filling, excavating, and conducting embankment compaction to minimize and control pollution and erosion from all vegetation or ground-disturbing activities. Restoration of Temporary Effects All temporarily affected areas would be restored to pre-construction conditions or better through re-planting or seeding and would support a level of riparian function that is the same, or greater, than under existing conditions. Compensatory Mitigation King County has developed plans for habitat improvement and restoration to mitigate for project-related effects on stream buffers. All unavoidable impacts to stream buffers would be mitigated in accordance with the provisions of the City of Renton Shoreline Master Program (RMC 4-3-090) and City of Tukwila critical areas regulations (TMC 18.44 and 18.45). Specific mitigation plans would be included in permit applications for construction of the project. The mitigation plans would focus on providing riparian buffer and wetland buffer mitigation that would provide equal or greater functions than were impacted. The mitigation site would be planted at a ratio of at least 1:1 to offset project impacts. Since the riparian buffer and wetland buffer impacts have some overlap, further details on the overall mitigation plan are provided in the Lake to Sound Trail—Segment A Critical Area Study (Parametrix 2015b). Broadly, the riparian buffer component of the overall mitigation plan consists of planting native trees and shrubs within the regulated riparian buffer of a fish-bearing stream (the Black River). On-site mitigation (within the project area and regulated buffer of the Black River) was selected as the preferred option. Riparian mitigation would consist of planting, or underplanting, in an area where existing riparian conditions are degraded. This type of mitigation would offset the project’s impacts on stream resources by maintaining or enhancing those riparian functions that support water quality and fish habitat. The riparian functions that would benefit from mitigation include LWD recruitment, stream temperature regulation, bank stability, leaf litter recruitment, and water quality functions. In addition to the riparian buffer impact mitigation described above, additional mitigation would be provided for tree removal where the proposed trail alignment runs adjacent to the Black River Riparian Forest in the City of Renton. In that area, all trees larger than 6 inches in diameter would be replaced by new trees at a ratio of 1:1 or greater. Planting for visual screening between the trail and the Black River heron nesting colony could result in the planting of more trees than would be needed to meet this commitment (Parametrix 2015a). In addition to mitigation requirements for displacement of buffers, enhancement of buffers is required by the provisions of RMC 4-10-095.F. Shoreline Master Program Nonconforming Uses, Activities, Structures, and Sties. The proposed trail is categorized as a Major Alteration: Expansion of impervious surface by more than 25%. This provision requires the project to install site improvements that protect the ecological functions and processes of the shoreline, consisting of either: Full compliance with Vegetation Conservation provisions of RMC 4-3-090F1, Vegetation Conservation, consisting of revegetation of a native community of the full required* buffer, or 100% of the area between an existing building and the water’s edge if the full buffer cannot be planted, or at least 10 ft., or An alternate mitigation proposal prepared by a qualified professional and approved by the Administrator of the Department of Community and Economic Development or designee that would provide at least equal protection of ecological functions and processes as the full required* setback and buffer. This requirement is met by a revegetation plan for areas between the trail and OHWM where the trail is within the 100 foot Vegetation Conservation Area of the Black River. REFERENCES Bax, N. J., E.O. Salo, and B.P. Snyder. 1979. Salmonid outmigration studies in Hood Canal. Final report, phase VI. FRI-UW-7921, 89 p. Fish. Res. Inst., Univ. Wash., Seattle. Blomberg, G., C. Simenstad, and P. Hickey. 1988. Changes in Duwamish River estuary habitat over the past 125 years. Pages 437-454 in Proceedings. First annual meeting on Puget Sound research. Volume 2. Prepared by the Puget Sound water quality authority. Seattle, Washington. Ecology (Washington State Department of Ecology). 2015. 2012 Washington State Water Quality Assessment (305[b] report and 303[d] list). Available at http://www.ecy.wa.gov/programs/wq/303d/currentasse ssmt.html. Accessed February 3, 2015. Ecology (Washington State Department of Ecology). 2015. 2012 Washington State Water Quality Assessment (305[b] report and 303(d) list). Available at: < http://www.ecy.wa.gov/programs/wq/303d/currenta ssessmt.html>. Accessed on February 3, 2011. Foerster, R.E. 1972. The sockeye salmon. Bulletin 162. Ottawa, Canada: Fisheries Research Board of Canada. 422 p. Harza. 1995. Comprehensive fisheries assessment of the Springbrook, Mill, and Garrison Creek watershed. Bellevue, Washington: prepared for City of Kent, Washington. Parametrix. 2011. Lake to Sound Trail—Segment A: Wetland Discipline Report. October 2011. Prepared for King County, Seattle, Washington. Parametrix. 2015a. Lake to Sound Trail—Segment A: Vegetation and Wildlife Discipline Report. April 2015. Prepared for King County, Seattle, Washington. Parametrix. 2015b. Lake to Sound Trail—Segment A: Critical Area Study. April 2015. Prepared for King County, Seattle, Washington. Rieman, B.E. and G.L. Chandler. 1999. Empirical evaluation of temperature effects on bull trout distribution in the Northwest. Final Report, Contract No. 12957242-01-0. U.S. Forest Service, Rocky Mountain Research Station, Boise, Idaho. Stober, Q.J, S.J. Walden, and D.T. Griggs. 1973. Juvenile salmonid migration through Skagit Bay, pp.35-70. In Ecological studies of proposed Kiket Island nuclear power site. Edited by Q.J. Stober and E.O. Salo. FRI-UW-7304. 537pp. Warner, E.J., and R.L. Fritz. 1995. The distribution and growth of Green River chinook salmon (Oncorhynchus tshawytscha) and chum salmon (Oncorhynchus keta) outmigrants in the Duwamish Estuary as a function of water quality and substrate. Muckleshoot Indian Tribe, Auburn, Washington. WDFW (Washington Department of Fish and Wildlife). 1998. 1998 Washington State salmonid stock inventory. Appendix: Bull trout and Dolly Varden. Washington Department of Fish and Wildlife, Olympia, Washington. 437 pp. WDFW (Washington Department of Fish and Wildlife). 2015a. PHS on the Web: An interactive map of WDFW priority habitats and species information for project review. Available online at http://wdfw.wa.gov/mapping/phs/. Accessed January 16, 2015. WDFW (Washington Department of Fish and Wildlife). 2015b. Salmonscape fish database and mapping application. Available online at https://fortress.wa.gov/dfw/salmonscape/. Accessed January 16, 2015. Williams et al. 1975. A catalog of Washington streams and salmon utilization. Volume 1, Puget Sound Region. Washington Department of Fisheries. Olympia, Washington. Kerwin, J. and T. S. Nelson.. 2000. Habitat Limiting Factors and Reconnaissance Assessment Report: Green/Duwamish and Central Puget Sound Watersheds (Water Resource Inventory Area 9 and Vashon Island) Washington State Conservation Commission and King County Department of Natural Resources. December 2000. Site Photographs