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Scup - 2q - 20.5'7 F( L � ' COPY Phase 1 Design Report ■ CA{,-qN -o3g Maplewood Creek Sedimentation Basin Reconstruction and Improvement Project 1 November 1994 City of Renton, Washington Prepared by NORTHWEST, INC. 1 Phase 1 Design Report i I i t Maplewood Creek Sedimentation Basin Reconstruction and Improvement Project November 1994 City of Renton, Washington i i Prepared by NORTHWEST, INC. i 1 i 1 O CERTIFICATE F ENGINEER C Maplewood Creek Sedimentation Basin Reconstruction and Improvement Project Phase I Design Report i The technical material and data contained in this report were prepared by, or iunder the supervision and direction of, the undersigned whose seal as professional engineer is affixed below. �RT Lj0 WAS x Albert Liou, P.E. V768 �O RFCIS-I�F�� ' SJONAL� EXPIRES i i i Phase I Design Report TABLE OF CONTENTS I. INTRODUCTION.......................................................................................... I A. Purpose of the Report.................................................................................................... 1 B. - Project Description........................................................................................................ 1 II. EXISTING CONDITIONS AND DESIGN CONSIDERATIONS............2 A. Site Description.............................................................................................................2 B. Geology......................................................................................................................... 3 C. Fish and Wildlife........................................................................................................... 3 1 D. Hydrology and Flood Flows.........................................................................................4 E. Sediment Load and Trap Efficiencies...........................................................................6 1 F. Future Fishway..............................................................................................................7 G. Evaluation of Alternatives ............................................................................................ 8 ' III. PROPOSED DESIGN....................................................................................9 A. Sedimentation Basin .....................................................................................................9 B. Main Spillway............................................................................................................. 11 C. Fishway Outlet and Maintenance Bypass................................................................... 11 D. Access Road........................................................................................... .. 12 E. Upper Dam Removal .................................................................................................. 12 F. Channel and Bank Stabilization.................................................................................. 13 G. Erosion and Sediment Control Plan............................................................................ 13 H. Construction Cost Estimate and Schedule.................................................................. 14 I. Construction Permits................................................................................................... 15 IV. CONCLUSIONS AND RECOMMENDATIONS..................................... 16 1 A. Conclusions................................................................................................................. 16 B. Recommendations....................................................................................................... 17 EXHIBITS APPENDIX A - Sediment Load and Geotechnical Evaluation Report APPENDIX B - Aquatic and Terrestrial Resources Report APPENDIX C - Preliminary Construction Plans ' Maplewood Creek Sedimentation Basin Reconstruction and Improvement Project Page i f..\'1134C'PH-1 REV J- I/'_IMJ 03 25 P%1 Phase 1 Design Report MAPLEWOOD CREEK PHASE 1 DESIGN REPORT 1 I. INTRODUCTION A. Purpose of the Report The City of Renton is proposing to reconstruct and improve the existing sedimentation basin located on Maplewood Creek above the Maplewood Golf Course in Renton, Washington (Exhibit 1). The improvements will help protect public and private property downstream of the basin from increased sediment deposition and potential flooding. iThe City has applied to the Federal Emergency Management Agency (FEMA) for Hazard Mitigation Grant Project funds for the project. Before FEMA can approve the grant request for 1 the construction phase of the project, it must address the potential impacts of the project in compliance with the National Environmental Policy Act (NEPA). The information included in this Phase 1 Design Report can be used by FEMA in preparation of its NEPA Environmental Assessment (EA), and approval for funding the construction of the project. The Design Report will also be used by the City to acquire all permits and approvals from various governmental ' agencies necessary for construction of the project. B. Project Description The Maplewood Creek Sedimentation Basin Project involves reconstructing and improving the existing sedimentation basin. The improvements include reconstructing the existing sedimentation basin to develop a larger storage volume for sediment and debris, ' removing the upper concrete dam and accumulated sediments, and stabilizing the upper creek channel to reduce the severe channel and bank erosion. The existing access road running along the west side of the basin and creek will be improved by placing a gravel road surface. ' The new sedimentation basin is designed based on the expected sediment load from the Maplewood Creek Basin and the minimum grain size desired for capture. The new sedimentation basin will have a sediment storage volume twice as large as the existing basin, In ' with the expansion occurring downstream of the existing basin. ' Maplewood Creek Sedimentation Basin Reconstruction and Improvement Project Page 1 F 71:4C KPH-I REV Jx:It/'_[/v:.0;:_5 P\f Phase I Design Report The toe of the south bank at the upper concrete dam is not stable and will be reinforced with riprap to prevent undermining after the dam is removed. A second section of the south bank, located just below the upper dam, will also be reinforced with riprap. ' A diversion structure will be installed in the sedimentation basin to direct water to a future low flow fish passage channel that will be constructed across through the golf course. The ' fish passage channel will be connected to a fish ladder and will allow migratory fish to travel up Maplewood Creek into the canyon. The low flow fish passage channel will be a separate project funded by the City. I II. EXISTING CONDITIONS AND DESIGN CONSIDERATIONS A. Site Description ' Maplewood Creek drains land areas lying both within the City of Renton and unincorporated King County. The creek drainage course travels from the plateau region north of the golf course into a steep ravine, through the Maplewood Golf Course, and discharges to the Cedar River on the south side of the Maple Valley Highway and the Milwaukee Railroad track. The natural course of the creek has been channelized on the golf course, and the last 1100 feet of ' the creek is confined in a culvert running under the highway and parallel to the railroad track prior to discharging into the Cedar River. The culvert entrance is above the normal water level in the river, and the culvert entrance and length act as a barrier to migratory fish passage. There are two existing ponds on Maplewood Creek within the golf course property. The lower pond located just north of the clubhouse parking lot was converted from an irrigation diversion pond to the existing sedimentation basin. However, the sedimentation basin acts as a ' barrier to fish passage and requires frequent sediment removal to maintain some efficiency. ' The embankment containing the existing sedimentation basin consists of a rock and earthen fill about 10 feet high and 50 feet long with a concrete weir located on the east side of the embankment. An overflow floodway is located in native soil against the east bank beyond the end of the constructed embankment. During a site visit in April 1994 the basin was filled with gravelly sand and at least two thin, discontinuous layers of clayey silt in the upper few inches of ' the deposit. Verbal communications with the golf course maintenance supervisor indicates that approximately 400 cubic yards of sediment is removed from the pond annually. ' Maplewood Creek Sedimentation Basin Reconstruction and Improvement Project Page 2 R\7134G,M I REV d�:l I/^_!04 Q1'5 P%1 Phase 1 Design Report ' The upper and is located approximately 500 feet north of the lower pond and was P PP Y 1 originally constructed as an irrigation facility in the 1920's, but was abandoned in the 1980's or earlier. The concrete dam which forms the upper pond was damaged by high storm flows which have undercut the toe of the south bank slopes. This pond also acts as a barrier to fish passage, ' and sediment has filled in behind it. The lower portion of the Maplewood Creek Basin has been prone to flooding from the runoff from the upper basin because of the unique geology and topography of the region. The I slopes connecting the upper basin plateau areas with the Cedar River valley are steep and highly susceptible to erosion. Most soils are shallow with only thin layers of vegetation overlaying deep deposits of glacial gravels and sands. As development has increased in the Maplewood Creek Basin, erosion and flooding have increased in intensity and frequency. Water quality problems have increased and fisheries and habitat areas in many parts of the creek have been substantially altered, and many eliminated. ' B. Geology An evaluation report involving geologic conditions and field sampling in the project area ris included as Appendix A to this Phase 1 Design Report. The following is a summary from the Appendix A report, pertaining to geology. The geologic environment of the canyon formed by Maplewood Creek consists of sub- horizontally bedded, glacial-derived sediments. Exposures within the canyon display sandy gravel, sand and clay beds varying in thickness from about one foot to several feet. All slopes observed in the canyon exhibit slope movement of varying degrees of severity. Near the creek, bank undercutting occurs on nearly every outside bed. Several rotational slope failures were identified. A rotational slope failure is located on the east bank immediately upstream of the upper concrete dam and a severely undercut slope is located about 100 feet downstream of the structure. Stabilization of the slope failures near the upper dam may be facilitated by installing a toe buttress for erosion protection and a toe surcharge to minimize slope movement by sliding. C. Fish and Wildlife An aquatic and terrestrial resource report was prepared and is included as Appendix B to this Phase 1 Design Report. The following is a summary from the Appendix B report. Maplewood Creek Sedimentation Basin Reconstruction and Improvement Project Page 3 F.`.;I:GU'H-I REV.II-11/'_1/9403.25 P%1 Phase 1 Design Report While the Cedar River has a large natural run of sockeye salmon, steelhead and a 1 moderately-sized run of river smelt, these fish appear to seldom use Maplewood Creek for spawning or rearing. The lower half-mile channel of Maplewood Creek through the golf course and the culvert system under SR-169 is largely barren of habitat and functions primarily as a drainage ditch. Erosion in the steep, lower reach of the east fork of Maplewood Creek has washed fine sediments into potential spawning gravels and significantly impacted fish habitat. In addition, the existing sedimentation basin and the upper abandoned concrete dam represent a fish passage barrier to the upper canyon. Resident trout have been observed in the lower reaches of Maplewood Creek, from the golf course area upstream into the steeper canyon reaches. The upper end of the project area is in a forested ravine. The forest canopy is fairly open, and a well-developed shrub and herbaceous layer is present. Vegetation immediately adjacent to the upper concrete dam and siltation pond is herbaceous ground cover. Trees and shrubs are dense to the edge of the exiting sedimentation basin. On the south ' and west sides of the basin, vegetation is predominantly herbaceous and includes mixed grasses and weedy forbs. The east bank of the creek at the lower end of the project area is forested almost to the waterline. The west bank is bordered by dense thickets of blackberry measuring approximately 10 feet in width and abutting the golf course parking lot. ' Residential development on the uplands above the ravine, and recreational development below the project area limits the diversity of wildlife occurring within the project area. Habitat 1 does not exist for large mammals requiring large territories, such as the black bear and mountain lion. However, forest and riparian-dwelling wildlife species with moderate to small home range requirements such as deer, birds, waterfowl, small mammals, reptiles and amphibians are likely abundant along the main stem of Maplewood Creek. No adverse effects to fish and wildlife are anticipated from project implementation, except short-term disturbance during construction and revegetation planting. More discussion of potential effects of the project and the revegetation plan , as well as monitoring and maintenance of project elements, is provided in the Appendix B report. No wetlands other than the existing basin and the upper dam siltation pond will be affected by the proposed project construction. D. Hydrology and Flood Flows Maplewood Creek has two major tributaries which begin by collecting storm water from ' residential areas in the upper plateau regions of the basin. The west tributary discharges into the ' Maplewood Creek Sedimentation Basin Reconstruction and Improvement Project Page 4 F:\7111<;\PH-I RFV.d,,II/_I/W0is'_5 PSI ' Phase I Design Report ' main channel in the middle of a steep ravine at the confluence with the east tributary. Below the 1 confluence the main channel of the creek continues for about 1500 feet down the steep ravine, then passes through the upper concrete dam and into the existing sedimentation basin. From the sedimentation basin it flows almost due south next to a maintenance road across the Maplewood ' Golf Course. At the south side of the golf course the stream passes under the Maple Valley Highway (SR 169) in a 42-inch culvert and is entirely contained in a 72-inch culvert which runs to the west parallel to the railroad tracks prior to discharging to the Cedar River. ' Maplewood Creek drains an area of approximately 1,099 acres (1.72 square miles). The drainage area above the proposed sedimentation basin is slightly smaller, approximately 1,032 acres (1.61 square miles). Runoff contribution from the area downstream of the basin is ' negligible. Average annual precipitation is approximately 43 inches as recorded in the City of Renton. Mean annual flow is 3.20 cfs for current basin land-use conditions, and is projected to be 3.72 cfs for future basin land-use conditions, based on King County's HSPF model simulations. (Ref: King County Department of Public Works, Surface Water Management Division. 1993. Cedar River Current and Future Conditions Report). A review of daily flow data resulting from the simulations indicates that flows exceed 20 cfs approximately 5 to 7 days annually on average, primarily during winter months. Peak flows selected for design of the proposed sedimentation basin are provided below. These flows were determined by simulating the rainfall and runoff process of Maplewood Creek using the HEC-1 computer model developed by the U.S. Army Corps of Engineers. Details of the peak flow simulations are described in the 1989 draft report entitled "City of Renton Comprehensive Stormwater Plan: Maplewood Creek Basin Plan" prepared by Parametrix, Inc. The peak flow for the 100-year, 24-hour storm corresponding to future land use conditions was estimated to be 392 cfs, and was selected as the design flow for the sedimentation basin spillway and dam. ' Maplewood Creek Sedimentation Basin Reconstruction and Improvement Project Page 5 F\7131G\PH-IREV do 11/2I/9463'.25 PSI 1 Phase I Design Report ' HEC-1 Model Runoff Characteristics at Maplewood Golf Course ' Existing Land Use Conditions Future Land Use Conditions Storm Total Precipitation Peak Flow Runoff Volume Peak Flow Runoff Volume Event (inches) (cfs) (acre-feet) (cfs) (acre-feet) (24- hour) 2-year 2.0 118 119 173 157 10-year 2.9 202 199 275 247 r25-year 3.4 251 247 1 333 298 100-year 3.9 300 297 392 351 I ' E. Sediment Load and Trap Efficiencies An evaluation of sediment load and trap efficiencies is included in the Appendix A report. The evaluation includes field sediment sampling and testing, estimates of sediment supply distribution, and trap efficiencies for both existing and proposed sedimentation basins. Tbe. following is a summary from the Appendix A report. A total of 17 samples from the existing sedimentation basin, upstream side slopes, and streambed were obtained for sieve analysis. The analysis results display an average distribution of sand, gravel, and silt and clay, as shown below. Sample Location Percent Gravel Percent Sand Percent silt/clay 1 Sedimentation Basin 41 55 3 Side Slopes 22 71 6 Streambed 28 64 6 The sieve results confirm that gravel to coarse sand is captured by the existing ' sedimentation basin along with a small portion of the fine sand. Most of the fine sand and practically all of the silt and clay are passed downstream. Actively sloughing slopes as observed ' contribute large quantities of fine material. ' Maplewood Creek Sedimentation Basin Reconstruction and Improvement Project Page 6 F-.\7!14GTH-IRF.V.'„::1:_I N1:03'._5 P%I 1 Phase 1 Design Report It is estimated that an average of 1 200 cubic yards of sediment is transported into or g � Y P ' through the existing sedimentation basin on an annual basis. An average of 250 to 300 cubic yards of gravel and sand have been trapped in the basin each year under recent flow conditions. The remaining 900 cubic yards of material consisting primarily of fine sand, silt and clay is transported through the basin to further downstream. The estimated size distribution of the total sediment load is provided below. Grain Size Estimated Percent of Total Load Volume (cu yd) Gravel 10 120 i Coarse Sand 5 60 Medium Sand 25 300 Fine Sand 25 300 Silt and Clay 35 420 Total 100 1,200 ' The existing sedimentation basin has a surface area of approximately 4,000 square feet(at pool El. 109) and a volume of 300-400 cubic yards when cleaned out. The current basin would retain particles coarser than 0.2 mm (fine to medium sand) during a 2-year flood event under ' ideal conditions. The trap efficiency, defined as the ratio of the quantity of deposited sediment to the total sediment inflow, is estimated to be 25 percent (300 cubic yards annually) for the present basin. F. Future Fishway The City of Renton is proposing to construct a fishway channel across the Maplewood ' Golf Course under a separately funded project. The fishway channel project will provide suitable stream habitat for salmon migration into the Maplewood Creek canyon. It will be connected downstream to a fish ladder currently under construction by Washington State Department of Transportation (WDOT) as a part of the WDOT project to widen SR 169. The upstream end of the fishway channel will be connected to a fishway outlet structure to be constructed as a part of the proposed sedimentation basin project. It is the City's current plan to construct both the new sedimentation basin and the fishway channel in 1996. The WDOT fish ladder has been designed for a hydraulic capacity of 40 cfs. However, a review of the design drawings indicates that a maximum flow of approximately 50 cfs is possible ' Maplewood Creek Sedimentation Basin Reconstruction and Improvement Project Page 7 F-\71:1GTH-',RLv,J-1I/21t9403.'5 P%1 Phase 1 Design Report ' for the fish ladder. The sedimentation basin fishwayoutlet structure should be designed for an g ' hydraulic capacity less than the fish ladder maximum flow, allowing additional flow contribution from the golf course into the fishway channel. Minimum flows should be maintained in the fishway channel at all times, even during removal of the sediment captured in the new sedimentation basin. A bypass flow pipe will be ' used to temporarily divert stream flow from above the sedimentation basin and discharge it to the downstream fishway channel when sediment removal takes place. Sediment will usually be removed once a year during the low-flow period in the summer. G. Evaluation of Alternatives The following design alternatives for the sedimentation basin were evaluated: Alternative A-1: The new dam was located approximately 100 feet downstream of the existing dam. A bathtub overflow concrete spillway with a 6-foot diameter pipe rand outlet was incorporated into the design (See Exhibit 2). Alternative A-2: New dam location was the same as that for Alternative A-1. An overflow concrete spillway and stilling basin as a part of the dam section was incorporated into the design. (See Exhibit 3) ' Alternative B-1: The new dam location was located at the existing dam. A bathtub overflow concrete spillway with a 6-foot-diameter pipe and outlet was incorporated into the design. (See Exhibit 4). Alternative B-2: New dam location was the same as that for Alternative B-l. An overflow concrete spillway and stilling basin as a part of the dam section was incorporated into the design. (See Exhibit 5) Alternatives A-1 and A-2 represent a substantial expansion, approximately 3 times the area and volume of the existing sedimentation basin. Alternatives B-1 and B-2 represent ' reconstruction of the existing basin without any significant expansion in size. It was estimated that the sediment trap efficiencies for Alternatives A-1 and A-2 will be approximately twice the ' efficiencies for Alternatives B-1 and B-2. Trap efficiencies between Alternatives A-1 and A-2, or between Alternatives B-1 and B-2 were estimated to be approximately the same. All ' alternatives include the same fishway outlet facility. Comparative construction cost estimates for the alternatives are provided in Exhibits 6, 7, 8, and 9. ' Maplewood Creek Sedimentation Basin Reconstruction and Improvement Project Page 8 F'.l71 34G\PH-1 REV d-11/21/94 01:5 PM .J Phase 1 Design Report ' The cost estimates indicate that the cost would increase by approximately a roximatel $10,000 from ' Alternative A-1 to Alternative A-2, or from Alternative B-1 to Alternative B-2. The cost increase is primarily due to more spillway concrete required for Alternatives A-2 and B-2. It was ' therefore determined that the bathtub spillway configuration used for Alternatives A-1 and B-1 is preferred over the spillway design configuration used for Alternatives A-2 and B-2. ' The cost comparison also indicate that expansion of the sedimentation basin as shown in Alternatives A-1 and A-2 would involve an additional cost of approximately $23,000, or 12 percent of the total construction cost, over the cost of rebuilding the existing basin as shown on Alternatives 13-1 and B-2. Since the trap efficiency of the expanded sedimentation basin would be double the efficiency of the rebuilt existing basin the 12 percent cost increase was considered to be economically justified. Alternative A-1 was reviewed by the City of Renton Surface Water Utility and Parks Department, and the embankment location was moved 20 feet to the north to allow for planned golf course redevelopment. The basin design then proceeded using the revised embankment location. ' III. PROPOSED DESIGN A. Sedimentation Basin The proposed sedimentation basin design is shown on drawing sheet 1 of Appendix C, Preliminary Construction Plans. The new basin will have a normal pool level at El. 108.5. The fishway outlet overflow weir crest is set at El. 107.5, and the spillway overflow weir crest at El. 109.0. The minimum pool during summer low flow months will approximately El. 108.0 and maximum pool during the 100-year storm event will be at El. 110.5. The dam crest will be ' constructed at El. 111.5 to provide a 1-foot freeboard during the 100-year storm event, and with a minimum width of 12 feet for maintenance vehicle access. 1 The new basin will have a pool surface area of approximately 12,000 square feet and a volume of 1,300 cubic yards at pool El. 109.0. The new basin is predicted to capture a larger ' portion of the fine sand than the existing basin, with particles larger than 0.1 mm captured during a 2-year storm event. It is estimated that the trap efficiency will increase from 25 percent for the ' existing basin to 40 or 50 percent (500 to 600 cubic yards annually) for the new basin. ' Maplewood Creek Sedimentation Basin Reconstruction and Improvement Project Page 9 F.M 3,4GTH-I REV.,7:1/'_1/93:03:15 PM Phase 1 Design Report ' Initiall the basin bottom will be constructed at El. 105.0. This will provide a sediment Y ' storage volume of approximately 600 cubic yards, assuming a minimum 2 feet of water depth for sediment settling during high flow events when the water level reaches the spillway crest El. 109.0. The new basin will operate at an increased trap efficiency and will require cleaning an average of once a year. If less frequent cleaning is desired, the bottom elevation could be lowered by one or two feet to provide additional sediment storage volume. Depending upon the storm frequency and intensity, the basin may need to be cleaned after a single large storm, or may not require cleaning for several years if there are no high flow events. ' A 75 foot long, 8-inch diameter underdrain pipe buried in a gravel-filled trench upstream of the proposed spillway will be provided to facilitate draining ponded water prior to cleaning the basin. A slide gate located on the discharging end of the pipe at the spillway structure will be installed to control draining operation. The new basin will be constructed as a compacted earthfill embankment. Offsite ' materials from an established borrow source will be used for the compacted embankment core. Local materials will be used at the outer edge of the embankment and for fill in other less critical ' areas since they could contain organic debris that would make compaction more difficult. It is recommended that bidding documents include specifications for borrow materials. Further technical discussion of the embankment design and construction is provided in Section 11.0 of ' the Appendix A report, Geotechnical Requirements for Proposed Embankment. A private landowner, southeast of the existing golf course club house, has a property line that appears to be described as the center of the creek. The land owner has expressed concern with the idea of water being diverted from Maplewood Creek for the majority of the year. To taddress those concerns a 8-inch bypass pipe and slide gate will be installed in the overflow spillway. The gate will be adjusted to allow a small amount of flow (0.5 to 1 cfs) to be directed ' down the main channel of Maplewood Creek at all times. The bypass pipe will also allow flow to be directed to the main channel if the future fishway should become inoperable, or if the water ' in the sedimentation basin needs to be lowered in an emergency. The private landowner appears to have a water right which allows a diversion of 0.02 cfs, or 1 acre-foot per year from Maplewood Creek. The landowner has a connection to an old irrigation line that goes from the existing sedimentation basin to a pump station that was ' previously used to irrigate the golf course. A new inlet will be constructed in the sedimentation basin and connected to the existing irrigation line to provide the same access to water that now exists for the private landowner. Maplewood Creek Sedimentation Basin Reconstruction and Improvement Project Page 10 F.\7I34GIPII-I REV J.,11/21 N403:25 PM ' Phase I Design Report ' B. Main Spillway p y A rectangular bathtub overflow spillway shown on drawing sheet 2 of Appendix C is proposed for the new sedimentation basin. It will be a 24-foot-long by 12-foot-wide (excluding concrete thickness) reinforced concrete structure, providing a total overflow crest length of 60 feet. The spillway crest will be at El. 109.0. For the 100-year storm event the peak flow into the basin is 392 cfs and the pool elevation will be El. 110.5. Approximately 347 cfs will flow over the main spillway and 45 cfs ' will flow through the fishway outlet. It is estimated that the frequency of water flowing over the main spillway will be approximately 7 days per year on average, primarily during the winter high ' flow months. The overflow spillway structure will be connected with a 30 foot long, 72-inch diameter ' concrete outlet pipe buried under the dam embankment. A small concrete outlet structure will be located at the downstream end of the pipe to discharge flow to Maplewood Creek. Excessive ' hydraulic energy of the flows will be dissipated within the spillway, pipe and outlet structural system. C. Fishway Outlet and Maintenance Bypass ' The proposed fishway outlet design is shown on drawing sheet 3 of Appendix C. The outlet will be located on the west side of the sedimentation basin embankment, anticipating that Ithe future fishway through the golf course will be connected with the outlet at this point. The fishway outlet will consist of two concrete weir structures connected by a 32 foot long, 42-inch diameter concrete pipe buried under the dam embankment. The design of the weirs is exactly the W same as that used for the DOT fish ladder weirs currently under construction. However, due to ' additional backwater effect created by the connecting pipe, the maximum hydraulic capacity through the fishway outlet will be approximately 45 cfs, slightly less than that of the WDOT fish ladder. The slight reduction in hydraulic capacity will provide a safety margin, allowing some ' flow contribution from the golf course area to the fishway during storm events. ' The upstream weir crest of the fishway outlet is set at El. 107.5. The downstream weir crest of the outlet will be 0.8 foot lower, at El. 106.7. Both weirs will be a trapezoidal shape with a one-foot weir crest width at the bottom and an 8-foot width at the top. The fishway channel bottom will be 3 feet below the weir opening. Flow discharge rating for the proposed fishway outlet and main spillway is estimated as follows: ' Maplewood Creek Sedimentation Basin Reconstruction and Improvement Project Page 11 F: 1',4G PIi-I REV-::_'1194.V3'2_5 P%1 ' Phase 1 Design Repon ' Water Elevation In Fishway Outlet Main Spillway Total Flow Sedimentation Basin Flow( cfs ) Flow (cfs ) ( cfs ) 107.5 0 0 0 108.0 2 0 2.0 108.5 7.7 0 7.7 ' 109.0 17 0 17 109.5 29 65 94 110.0 42 185 227 110.5 45 347 392 Fishway Outlet Weir at El. 107.5 Main Spillway Crest at El. 109.0 A 300 foot long, 12-inch diameter maintenance bypass pipe is proposed to be buried along the west side of the sedimentation basin and access road. The bypass pipe system includes ' a small inlet and gate structure located above the sedimentation basin, and a discharge point at the fishway outlet weir. The bypass pipe system will have an hydraulic capacity of ' approximately 5 cfs, which will be adequate to divert low flows during the summer for sediment removal. The diversion will require temporary sand bagging of Maplewood Creek at the bypass ' pipe inlet to stop flow from travelling into the basin. D. Access Road The existing access road along the west side of Maplewood Creek will be improved by ' placing crushed rock surfacing a minimum of 4-inches deep and 12 feet wide. The west embankment of the new sedimentation basin will be finished with the same crushed rock ' surfacing to serve as part of the access road. A new ramp with a maximum 12.5 percent slope will also be constructed at the south end of the basin. ' E. Upper Dam Removal The upper concrete dam located 500 feet upstream of the existing sedimentation basin will be removed to facilitate fish passage into the upper creek area. Removal may be partial or ' complete depending on the type and condition of the concrete and foundation. We recommend the use of a track-hoe mounted pneumatic pavement breaker for removal of the dam. ' At a minimum the concrete must be removed to a depth of one foot below stream grade (approximately El. 122.5) measured on the downstream side of the wall. The opening should be ' a minimum of 10 feet wide at the bottom and slope upward at 45 degrees to each bank. In the ' Maplewood Creek Sedimentation Basin Reconstruction and Improvement Project Page 12 F'M',4&PII-I REV J-11/21/94::)4:13,P%1 ' Phase 1 Design Report ' event that the dam does not have a foundation or that the opening extends the full height of the P g g ' wall, all of the concrete wall will be removed. ' F. Channel and Bank Stabilization Prior to the upper dam removal, the accumulated sediments in the 120 foot long section of the creek upstream of the dam will be excavated and removed from the site. After the sediments and upper dam are removed each bank will be armored using riprap (8-inch size rock) for a distance of at least 60 feet upstream. This distance should coincide with the east bank slope repair and existing armoring on the west bank. Two east bank slopes near the upper dam are proposed for repair, involving installation of a toe buttress for erosion protection and a toe surcharge to minimize slope movement by sliding. ' Details of the proposed repairs are shown on drawing sheet 1 of Appendix C. The Washington State Department of Fish and Wildlife suggests stream habitat ' enhancement by placing 2- to 3-foot size boulders along the creek bottom at about 8 to 10 foot spacing. The boulders will be placed from the upstream end of the new sedimentation basin to ' 100 feet upstream of the upper dam (for a total distance of approximately 400 feet). G. Erosion and Sediment Control Plan Project construction is planned to be started in July 1996 and completed in September. Construction will require approximately eight weeks and will involve primarily earth-moving of approximately 6,000 cubic yards of excavation and fill material. The control of erosion and ' sediment at the construction work areas is addressed below and will be incorporated into the construction contract to be issued for bid in the spring of 1996. In general, industrial standards ' of soil erosion control, the erosion control requirements of the King County Surface Water Design Manual, and Best Management Practices for erosion and sediment control will be used. rThe proposed contractor staging area will be the existing parking lot immediately south of the new sedimentation basin. Use of this area for staging will not require grading or removal ' of any vegetation. Soil erosion or sedimentation will not result from the use of this site as a staging area, so no special protection measures are proposed, other than routinely checking the ' parking lot drainage and maintaining it in appropriate working condition during construction. Access to the parking lot and sedimentation basin will be from the existing roads on the ' golf course. A new access road and ramp will be constructed on the west side of the new ' Maplewood Creek Sedimentation Basin Reconstruction and Improvement Project Page 13 F.',-:;=GPH-IRE''.i: '.'.'I,va.03-_5 PSI Phase 1 Design Report ' sedimentation basin embankment to the upper dam. Several short ramps may be constructed PP P Y ' from the west side access road to the bottom of the creek to reach other work areas, such as the upper dam and the slope stabilization areas. Silt fences constructed from filter fabric will be used at the edge of all areas where soil is disturbed to prevent sediment from reaching the creek. These areas include the slope stabilization areas, the new access road, and construction of the new sedimentation basin After construction is completed all accumulated sediment will be removed from the silt fences. The existing sedimentation basin will be kept in working condition as long as possible to act as a secondary sediment trap. ' Prior to work in the creek the contractor will need to divert all stream flow. The diversion method will probably involve sand-bagging the creek above the working area and ' diverting the creek past the working area in a temporary 12- to 18-inch pipe. In some areas a pump may be used during the workday instead of a pipe if equipment would need to cross the ' diversion pipe location. All diversion methods used by the contractor will be subject to approval by the City, and will be removed at the end of construction. All of the excavated material, approximately 3,000 cubic yards of silt, sand, gravel and top soil, will be backfilled or used in regrading ground contours in the finished work areas. ' Excavated soil will be stockpiled in the work area in small quantities, and silt fences will be used around the perimeter of the stockpile. Most of the 1,700 cubic yards of the embankment core fill and all of the 300 cubic yards of rock and rip rap will be imported and delivered directly to the work areas without stockpiling because of the small quantities involved. The 75 cubic yards of concrete will also be delivered directly to the site for placement without any on-site process or ' stockpiling. ' Following construction, exposed soils will be revegetated to control erosion. A discussion of the revegetation plan is provided in Appendix B. Detailed planting specifications, including size of stock, spacing, care and handling of plant materials, will be prepared as part of the construction plans and specifications. ' H. Construction Cost Estimate and Schedule The estimated construction cost for the proposed sedimentation basin reconstruction and improvement project is $ 196,117 and is shown in Exhibit 10. The costs were developed from the preliminary design details shown in Appendix C and are based on August 1994 prices. Maplewood Creek Sedimentation Basin Reconstruction and Improvement Project Page 14 F-\7114GTH IRE%'..i. I.i'1,914 is_5 PSI ' Phase I Design Report Quantity estimates were made of work items and materials for the main components of the Q Y P proposed design, and approximate unit prices were applied to arrive at the base costs. Allowances were made for taxes, engineering, permitting, and the City's administration. ' It should be noted that the estimated costs are preliminary only, and contingent upon approvals of the proposed design by FEMA and other agencies. The final project costs for the proposed design would also depend on final design details, price escalation, and actual bidding outcome. Because of these factors, the final project costs could vary from the estimates ' presented herein. The proposed schedule for design and construction of the proposed project is shown on ' Exhibit 11. On-site construction is expected to be started in July 1996 and to be completed in September 1996. The schedule is based on the Park Department's request that construction of the ' new sedimentation basin not begin until after the new golf course club house is in operation. The schedule also assumes that the Hydraulic Project Approval issued by the Washington ' Department of Fish and Wildlife will only allow instream construction during the summer low- flow months. ' L Construction Permits ' Permits and approvals which will be required for construction of this project include: Section 404 Permit - Section 404 of the Federal Clean Water Act (P.L. 92-500) requires ' that a U.S. Army Corps of Engineers permit (a Section 404 or Nationwide Permit) be applied for if the project will dredge or fill materials into or out of the waters of the United States or on their ' adjacent wetlands. ' CZM Consistency and Water Quality Certifications - The Corps may take care of obtaining the Water Quality Certification and approval from Washington Department of Ecology (WDOE) that the project is consistent with the Coastal Zone Management Act as part of its ' Section 404 Permit review. Many of the Corps' "nationwide" permits preclude the need for a separate Water Quality Certification or CZM Consistency Certification. ' Short-Term Water Quality Modification - This approval, obtained from the Department ' of Ecology, defines which water quality parameters will be exceeded during instream construction work. The City must define the parameters and the duration water quality may be degraded below state standards. ' Maplewood Creek Sedimentation Basin Reconstruction and Improvement Project Page 15 F\7131G`PI4-I REV,1i 1!:'1194-�3-'_5 PM Phase I Design Report Hydraulic Project Approval(HPA) - Pursuant to RCW 75.20.100, an HPA must be ' obtained from Washington Department of Fish and Wildlife for any hydraulic project involving waters of the State of Washington. The purpose of the approval is protection of fish resources, and the permit will define instream work windows and may include construction-related stipulations for the protection of aquatic life. Archaeological Approval- Executive Order 11593 requires consultation with and approval by the Washington State Office of Archaeology and Historic Preservation (OAHP) for ' federally-approved projects. This involves sending a letter to OAHP describing the location of the project, and requesting approval. If determined necessary by OAHP, an archaeological reconnaissance survey could be required. SEPA Compliance - Compliance with the State Environmental Policy Act of 1971 ' (SEPA) is required before state- and city-required permits and approvals can be issued. The City of Renton will assume lead agency role and initiate the SEPA process by completing the environmental checklist and making a threshold determination as to the need for an Environmental Impact Statement. The checklist and the preliminary threshold determination will be sent to all appropriate agencies for review. ' Gradang Permit- Access road excavation and grading will require approval from the Cit y ' of Renton. Shoreline Subtantial Development Permit - Maplewood Creek has a mean annual flow ' of less than 20 cfs, therefore a Shoreline Substantial Development Permit is not required. ' IV. CONCLUSIONS AND RECOAMENDATIONS ' A. Conclusions Based on the results of the Phase 1 preliminary design and analysis performed for the Maplewood Creek Sedimentation Basin Reconstruction and Improvement Project, it is concluded that: ' The most cost justifiable design for the new sedimentation basin is to provide an expanded basin with a pool surface area of approximately 12,000 square feet and a volume of 1,300 cubic yards, at pool El. 109.0. The proposed new basin size is approximately triple the existing basin size. ' Maplewood Creek Sedimentation Basin Reconstruction and Improvement Project Page 16 P.M14GIPI I-I REV.Ju 11/21194.03'.'_5 P%1 Phase 1 Design Report ' 0 The new basin will provide a sediment storage volume of approximately 600 cubic PP Y t yards assuming a 2-foot water depth for settling during high flow events. This is approximately twice the sediment storage volume of the existing basin. • The new basin is predicted to capture a larger portion of the fine sand than the existing basin, with particles larger than 0.1 mm captured during a 2-year flood event. In comparison, the existing basin would only retain particles larger than 0.2 mm under ideal conditions. The trap efficiency is estimated to increase from 25 percent (300 to 400 cubic yard annually) for the existing basin to 40 or 50 percent t (600 cubic yards annually) for the new basin. To maintain the improved trap efficiency, the new basin will need to be cleaned an average of once a year. ' 0 The cost difference to construct the expanded basin is approximately $26,000 (15 percent) more than to rebuild the existing basin. In view of approximately doubling the trap efficiency, the cost increase for the basin expansion is considered to be economically justified. • Construction of the proposed project will also provide opportunities for stream bank slope stabilization and habitat improvements on Maplewood Creek. It will ' also provide access to the upper section of Maplewood Creek for adult salmon spawning by removing the upper concrete dam and providing a fishway passage at the new basin. B. Recommendations It is recommended that the new expanded sedimentation basin and associated stream bank and habitat improvements be constructed as proposed. The proposed basin reconstruction and improvements are shown on the three preliminary design drawings in Appendix C, with all configurations and major dimensions outlined. The estimated total construction cost for the proposed works is $196,117 based on August 1994 price levels. It is recommended that the schedule for the project design and construction as shown on Exhibit 11 be carried out for the project to be completed in September 1996. ' Maplewood Creek Sedimentation Basin Reconstruction and Improvement Project Page 17 F\7134GTH-I REV.d-11/21!91.03'.15 PM E"+ MH F+� FBI w � � � � r � � � � i � � � �■ � � � � � E"+ MM�1 w H 406 •• ' 1 11 - Il West Branch • 4p0 57 A - : •..• .• 1 East Branch / \ Maplewood Creek ••• •. Upper Dam / •- • ;�.•, Existing Sedimentation ,•• .• •••• - • i�'• Basin ,�� • .• �� �00 _ •'• CO ` ,":36IN p 0 • •• • • •• / 11 �� C �� t _ \14- 41P N ' SOURCE: U.S.G.S. RENTON SHEET, 1:24,000 1000, City of Renton Maplewood Sedimentation Basin Reconstruction and Improvement Project ' — LOCATION MAP NORTHWEST, INC. 1 ConS. . nqC nee S 6f Sc!en`.. . PRC-ECT NC. i C)ATE Exhibit ' 7134G NOV., 1994 /I i '•� r / ` r/ ' fir'/7;' fo 1:" HEMLOCK (2) ' 1 4" HEM rIfJ I B � / I If AW / / 20" HE IL nil COTI 50' 4'0 FISHWAY L PIPE S�i lr l l/ll r l/ll�ll=i_ SPILLWAY ' CREST it / EL. 107 '/'�!1/, os/ _ R Q / \ —� FISHWAY Y /� /i• �/ / �'o CHANNEL c� (FUTURE) DAM CREST L. 110 ' � 60 PIPE OUTLET EXBIT 2 HI,�,:i It =\ Ni ,, -;' i /-� / �,' I ' � ,� `•'`�\,",, SCALE IN FEET DATE: 5-25-94 Al TP-P NI ATII/r' A- 1 f I j it_ cc 20" HEML 30" MAP PLCJAB 7o d ,� 1 � i Q � / o/ 1 rr i/r• 4'0 FISHWAY PIPE r SPILLWAY r CREST // / �� , � �,f//"�j/'/%ii;� \ _ EL. 107/ oa�� /� ,/j +b• // fig'/' \\ '°2 —T DAM CREST EL. 110 FISHWAY CHANNEL (FUTURE) N ��Y / STILLING — BASIN EXHIBIT 3 SCALE IN FEET DATE: 5-25-94 Al TP'RKIATI\/C* A _7 4'0 FISHWAY �' '✓ 1 PIPE " HEM' oo ' 4 SPILLWAY nk / CREST ^a �� EL. 109 01 it 20" HEML 30" MA co IV / I aPLE \ PIPEIla j . .Y DAM CREST EL. 112 ' OUTLET 104 SHWAY CHANNEL (FUTURE) R ,� C 4.I i t PC',vt= E If / t EXHIBIT 4 cK\24" MAPLE' 1 2" yl ',�•�% � 'y SCALE IN FEET DATE: 5-25-94 �- Al TFRNIATIvP' R— I co 14" HEMLOCK (2) V / ' � 4'0 FISHWAY 5 / `°` PIPE 14" HEM / � Jt co i 20" HEML ;ti / / ? SPILLWAY—7 / 30" MA \o // �� \ CREST ,IAPLE 0. M /' DAM CREST—J104 EL. 112 =l Jar ,^ STILLING / BASIN I ; Fl HAY CHANNEL (FUTURE) / ��/� %�/'` cc �\\ I0 �/f IF X. , r , EXHIBIT 5 M,2,P�E\,12" MaPL ol MHS i ' i �\'\•����`;�;\ SCALE IN FEET � Yi J �� DATE: 5-25-94 , r p \�� V `�_�. Al TP-QNIATIvP- R- ') ' CONSTRUCTION COST ESTIMATE - ALTERNATIVE A-1 MAPLEWOOD CREEK SEDIMENTATION BASIN PROJECT ' CITY OF RENTON, WASHINGTON Item Quantity Unit Unit Price Amount ------------------------- -------- ---- ---------- -------- Clearing & Grubbing lump sum LS ----- $4,000 Basin/Dam Embankment excavation 1500 CY $6.00 $9,000 ' core fill 1250 CY $12.00 $15,000 shell fill 900 CY $6.00 $5,400 Overflow Spillway excavation 120 CY $6.00 $720 ' reinforced concrete 50 CY $450�00 $22,500 6' -dia. concrete pipe lump sum LS $1,500 backfill 80 CY $6.00 $480 riprap 15 CY $30.00 $450 ' Fishway Outlet excavation 60 CY $6.00 $360 reinforced concrete 10 CY $450.00 $4,500 ' 4' -dia. concrete pipe lump sum LS =____ $800 backfill 40 CY $6.00 $240 4'x4 ' slide gate lump sum LS $1, 600 Upper Dam Removal ' sediment removal 700 CY $6�00 $4,200 concrete removal lump sum LS $1,500 Bank Slopes Repair excavation 250 CY $6.00 $1,500 rockery rock 100 EA $56.00 $5, 600 riprap 45 CY $30.00 $1,350 crushed rock 30 CY $12.00 $360 Access Road Upgrade lump sum LS ----- $3,000 Stream Habitat Improvements lump sum LS =____ $3,500 Mobilization & Misc. lump sum LS $33,273 Total Direct Construction Cost $120,833 Sales Tax 8% $9, 667 Engineering/Permitting $52,200 Administration $10,440 ' TOTAL CONSTRUCTION COST $193, 139 (June 1994 Dollars) ' EXHIBIT 6 ' CONSTRUCTION COST ESTIMATE - ALTERNATIVE A-2 MAPLEWOOD CREEK SEDIMENTATION BASIN PROJECT CITY OF RENTON, WASHINGTON Item Quantity Unit Unit Price Amount ------------------------- -------- ---- ---------- -------- Clearing & Grubbing lump sum LS ----- $4,000 Basin/Dam Embankment excavation 1500 CY $6.00 $9,000 core fill 900 CY $12.00 $10,800 shell fill 650 CY $6.00 $3,900 Overflow Spillway excavation 150 CY $6.00 $900 ' reinforced concrete 75 CY $450.00 $33,750 backfill 90 CY $6.00 $540 riprap 15 CY $30.00 $450 Fishway Outlet ' excavation 60 CY $6.00 $360 reinforced concrete 10 CY $450.00 $4,500 4'-dia. concrete pipe lump sum LS ----- $800 backfill 40 CY $6.00 $240 4'x4' slide gate lump sum LS ----- $1,600 Upper Dam Removal sediment removal 700 CY $6.00 $4,200 ' concrete removal lump sum LS ----- $1,500 Bank Slopes Repair excavation 250 CY $6.00 $1,500 rockery rock 100 EA $56.00 $5,600 riprap 45 CY $30.00 $1,350 crushed rock 30 CY $12.00 $360 Access Road Upgrade lump sum LS ----- $3,000 Stream Habitat Improvements lump sum LS ----- $3,500 ' Mobilization & Misc. lump sum LS ----- -$34,903- Total Direct Construction Cost $126,753 Sales Tax 8% $10, 140 ' Engineering/Permitting $54,757 Administration $10,951 ' TOTAL CONSTRUCTION COST $202,602 (June 1994 Dollars) ' EXHIBIT 7 CONSTRUCTION COST ESTIMATE - ALTERNATIVE B-1 MAPLEWOOD CREEK SEDIMENTATION BASIN PROJECT CITY OF RENTON, WASHINGTON Item Quantity Unit Unit Price Amount ------------------------- -------- ---- ---------- -------- Clearing & Grubbing lump sum LS ----- $2,000 Basin/Dam Embankment excavation 900 CY $6.00 $5,400 ' core fill 750 CY $12.00 $9,000 shell fill 600 CY $6.00 $3,600 Overflow Spillway excavation 120 CY $6.00 $720 ' reinforced concrete 50 CY $450�00 $22,500 6' -dia. concrete pipe lump sum LS $1,500 backfill 80 CY $6.00 $480 riprap 15 CY $30.00 $450 ' Fishway Outlet excavation 60 CY $6.00 $360 reinforced concrete 10 CY $450.00 $4,500 ' 4' -dia. concrete pipe lump sum LS =____ $800 backfill 40 CY $6.00 $240 4'x4' slide gate lump sum LS $1,600 Upper Dam Removal ' sediment removal 700 CY $6_00 $4,200 concrete removal lump sum LS $1,500 Bank Slopes Repair excavation 250 CY $6.00 $1,500 ' rockery rock 100 EA $56.00 $5,600 riprap 45 CY $30.00 $1,350 crushed rock 30 CY $12.00 $360 Access Road Upgrade lump sum LS ----- $3,000 ' Stream Habitat Improvements lump sum LS =____ $3,500 Mobilization & Misc. lump sum LS $28,181 Total Direct Construction Cost $102,341 Sales Tax 8% $8, 187 Engineering/Permitting $49,738 Administration $9,948 ' TOTAL CONSTRUCTION COST $170,213 (June 1994 Dollars) ' EXHIBIT 8 ' CONSTRUCTION COST ESTIMATE - ALTERNATI -ALTERNATIVE B 2 MAPLEWOOD CREEK SEDIMENTATION BASIN PROJECT ' CITY OF RENTON, WASHINGTON Item Quantity Unit Unit Price Amount ------------------------- -------- ---- ---------- -------- Clearing & Grubbing lump sum LS ----- $2,000 Basin/Dam Embankment excavation 900 CY $6.00 $5,400 ' core fill 400 CY $12.00 $4,800 shell fill 350 CY $6.00 $2, 100 Overflow Spillway excavation 150 CY $6.00 $900 ' reinforced concrete 75 CY $450.00 $33,750 backfill 90 CY $6.00 $540 riprap 15 CY $30.00 $450 Fishway Outlet ' excavation 60 CY $6.00 $360 reinforced concrete 10 CY $450.00 $4,500 4' -dia. concrete pipe lump sum LS ----- $800 ' backfill 40 CY $6_00 $240 4'x4 ' slide gate lump sum LS $1,600 Upper Dam Removal sediment removal 700 CY $6.00 $4,200 ' concrete removal lump sum LS ----- $1,500 Bank Slopes Repair excavation 250 CY $6.00 $1,500 rockery rock 100 EA $56.00 $5,600 ' riprap 45 CY $30.00 $1,350 crushed rock 30 CY $12.00 $360 Access Road Upgrade lump sum LS ----- $3,000 Stream Habitat Improvements lump sum LS ----- $3,500 ' Mobilization & Misc. lump sum LS ----- -$29,811- Total Direct Construction Cost $108,261 ' Sales Tax 8% $8,661 Engineering/Permitting $52,615 Administration $10,523 ' TOTAL CONSTRUCTION COST $180,060 (June 1994 Dollars) EXHIBIT 9 CONSTRUCTION COST ESTIMATE - PROPOSED DESIGN MAPLEWOOD CREEK SEDIMENTATION BASIN PROJECT ' CITY OF RENTON, WASHINGTON Item Quantity Unit Unit Price Amount ------------------------- -------- ---- ---------- -------- Clearing & Grubbing lump sum LS ----- $4,000 Basin & Dam Embankment excavation 1800 CY $6.00 $10,800 core fill 1700 CY $10.00 $17,000 shell fill 900 CY $6_00 $5,400 8"-dia drain system lump sum LS $2,000 Overflow Spillway & Outlet t excavation 150 CY $6.00 $900 reinforced concrete 53 CY $400.00 $21,200 6' -dia. concrete pipe lump sum LS ----- $1,500 backfill 80 CY $6.00 $480 ' riprap 15 CY $30.00 $450 Fishway Outlet & Flow Bypass excavation 60 CY $6.00 $360 reinforced concrete 21 CY $400.00 $8,400 ' 42"-dia. concrete pipe lump sum LS ----- $700 backfill 60 CY $6.00 $360 12"-dia. bypass system lump sum LS ----- $8,000 Upper Dam Removal sediment removal 700 CY $6�00 $4,200 concrete removal lump sum LS $1,500 Bank Slopes Repair 1 excavation. 250 CY $6.00 $1,500 rockery rock 100 EA $56.00 $5,600 riprap 45 CY $30.00 $1,350 crushed rock 30 CY $12.00 $360 ' Access Road Upgrade lump sum LS =____ $3,000 Stream Habitat Improvements lump sum LS $3,500 Mobilization & Misc. lump sum LS ----- $27,178 ' Total Direct Construction Cost $129,738 Sales Tax 8% $10,379 Engineering/Permitting $50,000 ' Administration --$6,000- TOTAL CONSTRUCTION COST $196,117 (August 1994 Dollars) 150 g� 25� I'bb 3 bo 2920 ' EXHIBIT 10 Maplewood Creek Sedimentation Basin Project Proposed Design and Construction Schedule Task Name Duration Start End - - - -- - - -- —1995 1996 _ --— - — - - e Jan el�Ma Apr a Jun Jul u eprOct ovDe Jane Ma Air a Jun J_ul T u_ - _ _. A AGENCY CONSULTATION 16.00 m Dec/01/94 Apr/23/96 uur m1t[�:umt lli[ fill 11tu[ u[u1[ [utm [t I[ ilumfi[lntu u1[>II1 utuu lntn- - . - - - 1.FEMA Review/Approval 6.00 m Dec/01/94 Jun/08/95 2.Construction Permits 10_00 m _Jun/09/95 Apr/23/96 _ -- - -- B.CONTRACT DRAWINGS&SPECS 1.00 m Feb/26/96 Mar/26/96 2.Design Drawings 1.00 m Feb/26/96 Mar/26/96 r 3,Specifications_.-- _ l,00 m Feb/26/96 Mar/26/96 C.CONTRACT BID/AWARD 3.00 m Mar/27/96 Jun/27/96 D.CONSTRUCTION --_-_ 8,00 u1/15/96 _Sep/09/96 _1.Mobllization 1.00 w Jul/15/96 J_ui/19/96 _-2.Basin- &Dam Embankment 6.00 w Jul/22/96'Aug%30/96 _ _ 3.Overflow Spillway&Outlet 6.00 w Jul/22[96 Aug%30/96 ishway&Flow Bypass 6.00-.w--- Jul/22/96 Aug%30/96 0� - 5.Upper Dam Removal 1.00_w Aug/19%96 Aug/23/96 -6._Bank Slopes Repair— 1.00 w Aug/26/96 Aug/30/96 7,Access Road Upgrade 1.00 w Aug/12/96 Aug%16/96 8.S_tream_H_abitat Improvements 1.00 w Au /26/96 Au /30/96 9.Demobolization 1,00 w Sep/03/96 Se /09/96 Harza NW, Nov/21/94 Milestone A Summary M1 1.1 Fixed Delay - - - 1 APPENDIX A ' Sediment Load and Geotechnical Evaluation Report 1 APPENDIX A Sediment Load and Geotechnical Evaluation Report 1 1 1 Appendix A, Phase 1 Design Report TABLE OF CONTENTS 1 ' 1.0 Introduction.................................................................................................. 1 2.0 Geologic Conditions ..................................................................................... 1 3.0 Slope Stabilization........................................................................................ 2 ' 4.0 Field Sampling and Testing.........................................................................4 ' 5.0 Sediment Size Distribution.......................................................................... 4 6.0 Sediment Supply...........................................................................................6 7.0 Size of Sediment............................................................................................7 8.0 Sedimentation Basin Dynamics................................................................... 8 9.0 Sedimentation Basin Efficiency................................................................. 10 10.0 Removal of Deposited Sediments.............................................................. 10 ' 11. 0 Geotechmcal Requirements for Proposed Embankment....................... 10 12.0 Concrete Dam Remdval and Channel Modification............................... 12 ' References ............................................................................................................. 14 Figure ' Figure 1 - Landslide and Sample Site Locations ' Attachment A - Sieve Analyses Results ' Maplewood Creek Sedimentation Basin Reconstruction and Improvement Project Page i F:\7134G\Geo-REV.doc:11/21/94:03:33 PM Appendix A Phase 1 pp Design Report APPENDIX A ' SEDIMENT LOAD AND GEOTECHNICAL EVALUATION REPORT 1 ' 1.0 Introduction This Sediment Load and Geotechnical Evaluation Report was prepared for use in ' analyzing options for reconstructing and improving the Maplewood Creek Sedimentation Basin. A complete description of the project being proposed by the City of Renton is provided in the "Phase 1 Design Report" to which this report is an appendix. ' 2.0 Geologic Conditions Maplewood Creek watershed is 1,099 acres in area. The watershed area includes part of ' the golf course, the wooded ravine that Maplewood Creek flows through and residential and commercial areas on the plateau above the ravine. For determination of sediment yield an ' acreage of 1,032 has been used which encompasses only the area upstream of the proposed sedimentation basin. The deep part of the canyon containing the creek represents approximately ' 200 acres of this area. Slopes observed in the canyon are marginally stable to unstable. They are heavily vegetated with numerous mature fir and alder trees. Approximately 10 significant landslides were observed on the canyon slopes (some of which are located on the accompanying ' Figure 1) during our field traverse on April 26, 1994. These unstable areas include raveling slopes undercut by stream action, rotational failures, slope creep and debris flows. ' The stream channel is remarkably free of debris derived from these slides. The channel ' floor is covered by a thick blanket of sand and gravel possibly up to 10 feet thick. Organic debris, such as logs, bridge the creek but intermittent stream flows must have been sufficiently high to strip most fine organic debris from the channel. Two minor canyon debris jams were ' found, but these do not impede the normal stream flow. ' The geologic environment of the canyon formed by Maplewood Creek consists of subhorizontally bedded, glacially-derived sediments. Exposures within the canyon display sandy ' gravel, sand and clay beds varying in thickness from about one foot to several feet. Near the ' Maplewood Creek Sedimentation Basin Reconstruction and Improvement Project Page i F:\713dG\Geo-REV.doc:11/21/94:03:33 PM c ' Appendix A, Phase 1 Design Report ' mouth of the canyon the left (east) bank` consists of a massive clay apparently bed a arentl greater than ' 10 to 15 feet thick. Up slope on the right bank and vertically in the geologic section is a thick layer of sandy gravel with a trace of silt and clay in the matrix. These layers alternate with clean sand beds upward to the top of the canyon. Most exposures of bedded sediments are covered by a steeply sloping mantle of gravelly sandy clay that includes an abundance of organic material. All slopes observed in the canyon exhibit slope movement of varying degrees of severity. Near the creek, bank undercutting occurs ' on nearly every outside bend. Several rotational slope failures were identified. One was located high on the left bank about two thousand feet upstream of the golf course and the second about one thousand feet upstream on the right bank. Soil creep is visible under the vegetation cover on ' nearly every slope. The mature trees in many cases reflect a long term exposure to soil creep. ' The canyon is mapped as a large Holocene landslide in the Generalized Geologic Map of Seattle and Suburban areas (Galster and Laprade, 1991). This slide mass is carved into the ' recessional glacial deposits left by the retreat of glaciers about 10,000 years ago. The layering of these clastic recessional deposits is conducive to the formation of complex slides. Descending groundwater seeps laterally along the top of clay layers and discharges on the slope, undercutting ' overlying bedding which fails by toppling or slumping. Clay layers may allow internal hydrostatic pressures to increase where confinement is attained until rotational failure results. ' The poorly consolidated sand beds are readily eroded by stream activity during floods and sloughing of the creek banks occurs. The canyon bottom sloughing destabilizes the upper slopes and keeps the whole complex slide system active. ' 3.0 Slope Stabilization Evaluation of the canyon slopes identified two large landslides and about ten sloughing ' slopes where creek undercutting was apparent. These two large slides appear to be in a thicker till unit of the geologic section. The slides are marginally stable and do not appear to have moved in recent years. Seepage was visible along the upper margin and sides of these slides. Slope creep may be active on the upstream, east bank slide that is moving into the East Tributary ' of Maplewood Creek. The undercut stream banks could be repaired at significant cost and disturbance to the stream. In most localities the stream is narrow and toe stabilization measures would take up a ' Nomenclature used in this report: Site is viewed looking down canyon,the left bank is the east side;right bank- is the west side. ' Maplewood Creek Sedimentation Basin Reconstruction and Improvement Project Page 2 F:\7134G\Geo-REV.doc:l1/21/94:03:33 PM ' Appendix A, Phase I Design Report ' sizable portion of the stream bed. While the amount of sediment produced from the existing p p fo s g failing slopes may be excessive, repairs are likely to only transfer the focus of erosion to adjacent banks. ' Stabilization'of the canyon slopes would alter the natural character of the stream. The stream channel is at a relatively uniform gradient from the upstream tributary confluence located ' 2,000 feet above the golf course. Dead falls, rock debris and gravel bars have effectively stabilized the stream gradient and may tend to reduce flood velocities as water levels rise. There ' are few large rock fragments in the stream channel. Most rock is gravel size and less than two inches nominal diameter. There is no evidence that the large slope failures will develop at an ' increasing rate since most of the present vegetation is mature and most failures, except the undercut streambanks, appear to be quite old. It is our opinion that the sediments presently found in the stream channel are representative of that which will be transported over the next ' several years. A rotational slope failure is located on the left bank immediately upstream of the upper concrete dam, and a severely undercut slope is located about 100 feet downstream of the dam. These two unstable areas are possibly the result of changes in stream energy resulting from the construction of the upper concrete dam. A longitudinal profile along the creek (see Appendix C, sheet 1, Section A) shows a significant scour zone below the dam. ' Dam removal may reactivate slope erosion upstream of the structure. Protection laced at Y P P P the toe of the upper slipping slope will enhance the stability of the rotational failure area that has developed (see Appendix C, sheet 1, Sections B and Q. Upon removal of the dam the ' downstream scour zone is likely to fill, reducing the risk of slope failure on the left bank. Slope protection is warranted until stability of the channel is attained. We recommend no action be taken to stabilize the upper canyon slope failures and to allow the stream and adjacent slopes to attain their own level of stability. Stabilization of the slope failures near the upper dam may be facilitated by installing a toe buttress for erosion protection and a toe surcharge to minimize slope movement by sliding (see Appendix C, sheet 1, ' Sections B and Q. No additional repairs are recommended on other slopes in the canyon unless additional significant movement is observed. At that time, selective remedial measures can be employed. 1 Maplewood Creek Sedimentation Basin Reconstruction and Improvement Project Page 3 F:\7134G\Geo-REV.doc:11/21/94:03:33 PNT ' Appendix A, Phase I Design Report 4.0 Field Sampling Testing P g an n g ' Five soil samples were collected and field classified using Unified Soil Classification System descriptions (Table 1). Only descriptive parameters were obtained; Plasticity Index (PI) ' or Liquid Limit (LL) were not measured. The soil samples were obtained from slope soils near the site of the proposed sedimentation basin and from two sites upstream. ' Table 1 Unified Soil Classification System Soil Descriptions (Field Classification Only) ' Site A. Clay; CL-CH, dark brown, moist, organic rich, high plasticity, medium to low dilatancy, high toughness, medium dry strength, trace of silt. ' Site B. Clay; CH-CL, dark brown, moist, organic rich, high plasticity, medium to low dilatancy, high toughness, medium dry strength, trace of silt. Site C. Silty clay; NIL-CL, dark gray brown, moist, low to medium ' plasticity, medium dilatancy, low toughness, medium dry strength. Site D. Silty clay; MI-CL, yellow brown, moist, medium to low ' plasticity, no dilatancy, low toughness, high dry strength, till - looks like claystone. Site E. Clay; CL, dark brown, moist, low plasticity, medium ' toughness, medium to low dry strength. 5.0 Sediment Size Distribution ' A total of 17 soil samples were obtained from the sedimentation basin, stream bed, canyon sidewalls and tributary streams in order to determine the bedload size distribution and the ' potential volume of fines transported through the canyon. Sampling locations are shown on Figure 1. The collected sediments were sieved on four screens which bracket the grain-size range of interest. Results of the sieving are displayed in Attachment A at the end of this report, ' and summarized in Table 2. ' Maplewood Creek Sedimentation Basin Reconstruction and Improvement Project Page 4 F:\7134G\Geo-REV.doc:11/21/94:03:33 PM Appendix A, Phase I Design Report ' Table 2 Sediment Sampling Results ' Sample Percent Percent Percent Silt Number Gravel Sand and Clay Sample Location ' Sedimentation Basin 1 52 46.5 1.0 In sedimentation basin,upstream right side. ' 2 52.5 45.7 1.6 In sedimentation basin,downstream right side. 3 4.3 86.5 9.1 In sedimentation basin,downstream left side. 4 56 43.0 0.9 In sedimentation basin,upstream left side. ' Average 41 55 3 Side Slopes ' 5 22.5 68.1 9.3 75 feet upstream of dam, left slope, 30 feet from pond. 6 6.6 82.2 11.2 East(left) of dam, left slope, 10 feet above top of ' dam. 7 34.5 60.6 3.5 30 feet upstream of dam, 5 feet above road ' elevation, right slope. 9 24.7 67.9 6.6 Sloughed area, left bank, 100 feet below concrete dam. 10 4.6 90.9 4.4 Sloughed area, left bank stream terrace, 100 feet below concrete dam. 13 15.7 78.2 5.1 Left streambank 200 yards upstream of concrete ' dam. 14 48 49.0 1.2 100 feet upstream of access trail, right bank, 6 feet above streambed. Average 1 22 71 6 Streambed ' 8 27 64.9 7.2 Stream deposits 250 feet upstream of sedimentation pond. 11 27 66.8 3.1 Side stream from right bank below concrete dam. ' 12 49 48.6 0.6 Stream sample, 50 feet upstream of concrete dam. ' 15 39 56.3 2.2 Left(East Tributary) streambed sample, at confluence. 16 19.9 75.6 4.0 Right(West Tributary) streambed sample, at ' confluence. 17 4.9 74.3 20.8 Streambed sample below large active slide. ' Average 28 64 6 Sedimentation Basin: Three of the four samples (1, 2, 4) obtained in the basin contained less than two percent silt and clay and had nearly equal amounts of gravel and sand. The fourth ' Maplewood Creek Sedimentation Basin Reconstruction and Improvement Project Page 5 FA7134G\Geo-REV.doc:11/21/94:03:33 PM ' Appendix A, Phase I Design Report ' sample (3) obtained from the left eddy zone upstream of the outlet channel contained 9 percent ' silt and clay deposited in the last two highwater episodes and over 85 percent sand with half of the sand component in the fine sand category. ' Streambed Samples: The streambed sediments were sampled in the lower creek, upstream of the sedimentation basin (samples 8, 11, and 12) and in the main channel and east and west forks approximately 2,000 feet upstream of the basin (samples 17, 15 and 16). No apparent coarsening upstream patterns were seen in the sampled sediments. Rather, sediments appeared to ' reflect upstream source areas, particularly sample 17, which contains an abundance of silt and clay (21 percent) and over 40 percent fine sand. The source of this high volume of fine material is sloughing from the adjacent active slide. The streambed samples contain an average of 28 percent gravel, 64 percent sand, and 6 percent silt and clay. ' Side Slope Samples: Samples of the canyon side slopes display an average of 6 percent silt and clay, 71 percent sand, and 22 percent gravel. ' These sieve results confirm that gravel to coarse sand is captured by the existing sedimentation basin along with a small portion of the fine sand. Most of the fine sand and ' practically all of the silt and clay are passed downstream. Actively sloughing slopes contribute large quantities of fine material. Approximately ten actively eroding zones were observed on the ' slopes between the sedimentation basin and the confluence of the East and West Tributaries. ' 6.0 Sediment Supply The volume of sediment supplied to the existing and proposed sedimentation basins on Maplewood Creek varies greatly from year to year. The amount of sediment transported into the basin is a function of the amount eroded from mass movements, surface erosion, soil creep, and ' bank erosion upstream of the basin, and the capacity of the stream to transport those sediments downstream. Transport capacity is dependent upon the flow of water in the creek. The majority of sediment is transported during high flows, with bedload transport generally being initiated when flows exceed bankfull flow, roughly equivalent to the 1.5-year recurrence interval flood flow. Since there have been n direct o d rec measurements of sediment supply or transport in the ' Maplewood Creek basin, several different methods were used to estimate the volume of sediment supplied to the stream. Direct measurements of suspended sediment transport were made in the ' nearby Snoqualmie River basin by Nelson (1971). He calculated average annual suspended Maplewood Creek Sedimentation Basin Reconstruction and Improvement Project Page 6 F:\7134G\Geo-REV.doc:11/21/94:03:33 PM ' Appendix A, Phase 1 Design Report ' transport rates of 300 to 980 cubic yards/square mile in different subbasins. Assuming bedload t transport rates of 10 percent of the suspended load, Nelson's rates for total transport would be 330 to 1080 cubic yards/square mile/year. ' Estimates of sediment transport and deposition rates in the lower Cedar River and delta area were made by Harza NW (1992). They estimated suspended sediment transport rates of 165 cubic yards/square mile/year and 50 cubic yards/square mile/year of bedload transport. These rates correspond to sediment supply averaged over the entire lower Cedar River basin; sediment ' supply from the actively eroding Maplewood Creek basin would be expected to be several times higher. ' The golf course maintenance supervisor reported that the existing sedimentation basin has been cleaned out every year except 2 during the last 9 years. It also required cleaning following the November 1990 flood event. Assuming 300 to 400 cubic yards of sediment (the total volume of the basin) was removed from the basin 7 out of the last 9 years, an average of 230 to 300 cubic yards is trapped by the basin each year. This is the equivalent of 145 to 185 cubic yards/square mile. The material trapped in the sedimentation basin consists of gravel and sand. These materials are carried as bedload in streams the size of Maplewood Creek. The estimates of ' sediment supply rates from the sedimentation basin correspond to the bedload portion of the total sediment supply in Maplewood Creek. Bedload is generally 5 to 20 percent of the total load of a ' stream. Assuming 10 percent bedload, the total sediment supply rates based on these estimates are 1,400 to 1,800 cubic yards/square mile. Based on the above information and the actively eroding Maplewood Creek basin, it is estimated that an average of 1,200 cubic yards of sediment is transported into the existing sedimentation basin on an average annual basis. An average of 250 to 300 cubic yards of gravel and sand have been trapped in the basin each year under recent flow conditions. The remaining ' 900 cubic yards of material consisting primarily of fine sand, silt, and clay is transported through the basin and is deposited in the channel upstream of the highway culvert or is transported into ' the Cedar River. 7.0 Size of Sediment The grain size distribution of the total sediment load in Maplewood Creek is not known. ' Sediment samples taken from the bed and sedimentation basin are representative of only the coarsest fraction of the total load moving in the creek. Fine sand, silt, and clay particles that ' make up the majority of the sediment load in most river systems are carried as suspended load ' Maplewood Creek Sedimentation Basin Reconstruction and Improvement Project Page 7 F:\7134G\Geo-REV.doc:11/21/94:03:33 PM Appendix A, Phase 1 Design Report and are not retained in the streambed or in the existing sedimentation basin. The grains size distribution of the total load can be estimated based on measured streambed size gradations and measurements of suspended load from other systems. IAssuming the sedimentation basin traps all of the gravel and coarse sand transported into it, a total of 120 cubic yards of gravel and 60 cubic yards of coarse sand is trapped on an annual ' basis. These numbers correspond to 10 and 5 percent of the total load, respectively. Using these numbers as end points and assuming the total sediment load curve follows a slope similar to the ' grain size curves of measured samples from the creek and banks, an estimated grain size distribution was constructed (Table 3). Table 3 Estimated Size Distribution of Total Sediment Load Grain Size Estimated Percent of Total Load Volume (cu yd) Gravel 10 120 Coarse sand 5 60 ' Medium sand 25 300 Fine sand 25 300 Silt and clay 35 420 Total 100 1,200 This distribution shows that an average of 300 cubic yards each of medium and fine sand are transported annually, along with 420 cubic yards of silt and clay. It should be noted that no direct measurements of the silt and clay portion of the load have been made; accurate estimates ' of suspended sediment transport rates and sizes require several years of sampling during varying flow conditions. 8.0 Sedimentation Basin Dynamics ' The basic principle governing the behavior of sedimentation basins is that by slowing the velocity of sediment-laden water, the water will lose the energy necessary to transport the particles in suspension or as bedload and the particles will settle out of the water column and be deposited in the basin. In order for a particle to be trapped in the basin, the residence time of the particle in the basin must be long enough to allow it to fall to the bottom before it is transported out of the basin. Goldman et al. (1986) have derived the following formula for determining ' sedimentation basin size: As = 1.2QVs where As = Surface area of sedimentation basin ' Maplewood Creek Sedimentation Basin Reconstruction and Improvement Project Page 8 F:\7134G\Geo-REV.doc:11/21/94:03:33 PM Appendix A, Phase I Design Report ' Q = Discharge of water Vs = Settling velocity of particle The existing sedimentation basin has a surface area of 4,000 square feet assuming a pool at El. 109 and a volume of 300-400 cubic yards when cleaned out. The proposed dimensions of the new sedimentation basin would give it a surface area of 12,000 square feet and a volume of 1,300 cubic yards. Assuming each basin were in a cleaned out state, the size of particles trapped ' in each under different flow conditions was calculated. The results are shown in Table 4. ' Table 4 Size of Particles Retained in Existing and Proposed Settling Basins. ExistingBasin Proposed Basin Settling Velocity of Particle Size Settling Velocity Particle Size Flood Discharge Particles Retained Retained of Particles Retained Frequency (cfs) (ft/s) (MM) 1 Retained (ft/s) (MM) 1 ' 2 years 173 0.052 0.18 0.017 0.09 10 years 275 0.083 1 0.23 0.028 0.11 25 years 333 0.100 0.28 0.033 0.14 ' 1 100 years 392 0.118 0.31 0.039 0.15 1 Grain size determined from empirical graph of settling velocities versus grain size(Goldman et al. 1986)at water temperature of 10°C(50°F�. These calculations indicate that the current sedimentation basin would retain particles coarser than 0.2 mm(fine to medium sand) under ideal conditions. Based on the size of particles ' sampled from the main body of the basin (not the backwater area), 97 percent of the particles are larger than 0.2 mm. Based on the grain size of sediments from streambed samples, with an average of 15 to 20 percent finer than 0.2 mm, only a portion of this sized particle available for transport in the creek is trapped in the basin. This indicates that the basin is not as efficient as the calculations predict, likely due to turbulent eddies and resuspension of sediment as the basin tfills and water depths are reduced. ' The proposed new pool is predicted to capture a larger portion of the fine sand than the existing pool, with particles larger than about 0.1 mm captured during a 2-year flood event. As ' with the existing pool, trap efficiencies will decrease as the pool fills with sediment. However, the larger area and volume of the proposed pool will allow a greater volume of sediment to be ' trapped before efficiencies are lowered, and will allow the water to slow and spread over a greater area, reducing turbulence. 1 Maplewood Creek Sedimentation Basin Reconstniction and Improvement Project Page 9 F:\7134G\Geo-REV.doc:11/21/94:03:33 PM ' Appendix A, Phase 1 Design Report ' 9.0 Sedimentation Basin Efficiency ' Reservoir efficiency is defined as the ratio of the quantity of deposited sediment to the total sediment inflow. This efficiency is dependent primarily on the sediment settling velocity ' and the flow velocity through the reservoir. The present basin has an estimated trap efficiency of 25 percent (300 cubic yards). By increasing the size of the pool,the trap efficiency will increase. Assuming the new basin will trap particles coarser than about 0.1 to 0.2 mm diameter, it is ' estimated that trap efficiency will increase to 40 or 50 percent (500 to 600 cubic yards annually). ' 10.0 Removal of Deposited Sediments Based on the proposed new basin configuration, the trapped sediments should consist primarily of gravel and sand which will be readily dewatered and small amounts of coarse silt and clay representing less than 10 percent which should have no real effect on large-scale dewatering but may result in extra weight hence higher hauling costs. ' Removal of the debris should be initiated by the preliminary excavation of a bypass channel through the basin to facilitate dewatering or utilization of the bypass pipe installed for ' the pu Yose. A dewatering trench could be excavated a few days prior to clean out and may significantly reduce the total tonnage of material removed. 1 In order to retain the optimum settling characteristics in the basin, at least 2 feet of water depth should be provided for settling during high flow events when the basin pool level reaching the proposed spillway crest at El. 109. This means that the basin floor should be deeper than 107 feet at all times. If the basin is designed with a bottom elevation of 105 feet, this will allow 600 ' cubic yards of the total 1,300 cubic yards to act as sediment storage volume and will require cleaning on an average of once a year. If less frequent cleaning is desired, the bottom elevation could be cleaned to 104 feet to provide a total of 900 cubic yards of storage. As with the present basin, depending upon the storm frequency and intensity, the basin may need to be cleaned after a single large storm, or may not require cleaning for several years if there are no high flow ' events. 11.0 Geotechnical Requirements for Proposed Embankment The proposed embankment is planned as a compacted earthfill embankment. The embankment will be penetrated by a fishway and a spillway. Compacted fill will be required to form the embankment and foundation for the fishway and the spillway. While the local materials 1 ' Maplewood Creek Sedimentation Basin Reconstruction and Improvement Project Page 10 F:\7134G\Geo-REV.doc:11/21/94:03:33 PM ' Appendix A, Phase 1 Design Report ' may be suitable, excessive organic debris may make use of this material an unattractive option over importation of soils from an established borrow area. No subsurface investigation of the site has been conducted. The local published geology ' indicates that highly competent pre-Vashon glacial and nonglacial sediments may underlie the embankment zone. These sediments, as well as the Vashon till and recessional sand and gravel, can form a satisfactory foundation for the embankment. Minimal stripping may be necessary to establish the base of the dam. Well logs obtained from the City indicate sand and gravel strata ' approximately 10 feet below existing grade at the well sites about 500 feet south. We expect that sand and gravel may be encountered at a similar depth along the embankment axis. ' We recommend that bidding documents include specifications for borrow materials. Prior to construction, samples will be collected and tested by Modified Proctor Tests to ' determine optimum moisture content and maximum dry density. General specifications for the compacted embankment will call for compaction to 98 percent of maximum dry density at no ' more than 2 percent over optimum moisture content. No rock over six inches will be allowed in the embankment. Additional soil parameters will be provided prior to construction. The fill material should attain the following general specifications: ' 0 Well graded sand and gravel, g ' 0 Less than 5 percent silt and clay, • No rock 6 inches or greater, in size, ' 0 Organic content less than 2 percent, • Maximum dry density range of 120 - 130 pcf, • Moisture content 8 to 12 percent optimum. ' Prior to bidding for construction, a geotechnical investigation should be performed on the site. We recommend that the embankment and structure foundations be stripped to sound ' bearing soils and inspected by the geotechnical engineer prior to construction (see Appendix C, sheet 1, Typical Dam Section). All soft spots in the foundation must be overexcavated and backfilled with compacted fill. If locally derived soils are used in the embankment, we recommend that they be used to fill out the outer slopes of the embankment. The core section of the embankment should consist of imported fill conforming to the general specification. This core with uniform slopes of 1:1 could be raised concurrently with the upstream and downstream shell using locally derived organic-free sediments. All imported and local fill materials must ' Maplewood Creek Sedimentation Basin Reconstruction and Improvement Project Page 11 FA7134G\Geo-REV.doc:11/21/94:03:33 PM ' Appendix A, Phase 1 Design Report attain a compacted density of 98 percent of maximum dry density, and the moisture content must lie within optimum moisture content or up to 2 percent above the optimum moisture content. ' This latter requirement may be difficult to attain without substantial effort. Because of the low height of the structures, field borings to verify subsurface conditions may need to extend only a few feet below the ground surface. Borings within 500 feet indicate ' sand and gravel approximately 10 feet below the surface. Overexcavation of soft materials and replacement with imported compacted fill will provide a satisfactory embankment. Locally ' derived fill material conforming to the general specifications identified above and compacted to specification will readily hold at slopes of 2:1 (H:V) upslope and 2.5:1 downstream. The total height of the embankment from top to downstream toe is about 8 feet. This height of ' embankment, soil type, required compaction and low permeability should attain a satisfactory factor of safety. ' Seepage is not expected to be a problem if the embankment is constructed from well- ' compacted glacial till. Normal pool water level is El. 108.5 feet and the base of the embankment is about El. 103. This low head and wide embankment, as well as construction on a native soil of glacial till, is expected to form a competent impermeable structure. 12.0 Concrete Dam Removal and Channel Modification The upper concrete dam located 500 feet upstream of the existing sedimentation basin will be removed to facilitate fish passage into the upper creek area. Removal may be partial or ' complete depending on the type and condition of the concrete and foundation. We recommend the use of a track-hoe mounted pneumatic pavement breaker for removal. ' At a minimum the concrete must be removed to a dep th of one foot below stream grade ' (approximately El. 122.5) measured on the downstream side of the wall. The acquired opening should be at minimum 10 feet in width at the bottom and slope outward at 45 degrees toward each bank. In the event that the dam does not have a foundation or that the opening extends the full height of the wall, all of the concrete wall shall be removed. ' After removal of the dam and accumulated sediments each bank must be armored using riprap (8-inch size rock for a distance of at least 60 feet upstream). This distance should be ' coincide with the left bank slope repair and pre-existing armoring on the right bank. ' Maplewood Creed Sedimentation Basin Reconstruction and Improvement Project Page 12 F:\71 34G\Geo-REV.doc:11/22/94:11:14 AM Appendix A, Phase 1 Design Report Stream habitat enhancement calls for the placing of 2- to 3-foot size boulders along the creek bottom with about 8 to 10 feet spacing. This method should extend from about 100 feet ' upstream of the upper dam to the upstream end of the reconstructed sedimentation basin. Maplewood Creek Sedimentation Basin Reconstruction and Improvement Project Page 13 F:\7134G\Geo-REV.doc:11/21/94:03:33 PM Appendix A, Phase I Design Report References Galster, R.W., Editor. 1989. Engineering Geology in Washington. Washington Division of ' Geology and Earth Resources, Bulletin 78. Goldman, S.J, K. Jackson, and T.A. Bursztnsky, 1986. Erosion and Sediment Control ' Handbook. McGraw-Hill:New York. Harza Northwest. 1992. Reconnaissance Sediment Transport Report for the Cedar River Delta ' Project Renton, Washington. Unpublished report prepared for the City of Renton. March 1992. Nelson, L.M.. 1971. Sediment Transport by Streams in the Snohomish River Basin, ' Washington: October 1967 - June 1969. USGS Open-File Report 71-213. ' Maplewood Creek Sedimentation Basin Reconstruction and Improvement Project Paoe 14 F:\7134G\Geo-REV.doc:11/21/94:03:33 PM I • . Trader •.....•� — • ° � • 1 9 .. . ••• . . • .•.•. • -l • ° i tt. .' • . u 3 na i -. _ ---- f� c's 1 - M .• .. N •' .•' •• '. ; •• • eve / I.. g o Riv •. '• •• ,• ' GENERALIZED GEOLOGIC MAP OF SEATTLE AND SUBURBAN AREAS SIEVE ANALYSIS GALSTER AND LAPRADE, 1991 14 SAMPLE LOCATION BULLETIN OF AEG, VOL 28, NO. 3 1 OBSERVED 850' SLOPE FAILURES ' City of Renton Maplewood Sedimentation Basin Reconstruction and Improvement Project LANDSLIDE AND ' NORTHWEST, INC. SAMPLE SITE LOCATIONS �OrSUiLfI� -E-z�ree-s & Sc'e- Sts NO. GA-E Figure 1 ' 7134G AUG., 11994 ' Appendix A ATTACHMENT A ' SIEVE ANALYSES RESULTS ' Description ' Sieve analyses were performed on 17 samples obtained from the creek channel, sedimentation pond and side slopes within the drainage area of Maplewood Creek. These ' samples were obtained in order to characterize the type of materials transported through the system. ' Testing was done on the samples without regard to moisture loss or minor losses in weighing. Errors by weight may be as much as 2-3 percent. The results of the sieve analyses are shown on Figures Al through A 17 and Table A-1. Table A-1 ' Results of Sieve Analyses Retained on Sieve Size Total Sample pan Sample# Wei ht(gm) 16 mm 2 mm 0.5 mm 0.0625 mm Silt & Clay 1 968.9 236. 466.5 197.5 56.2 3.7 2 676.70 140.6 369.8 108.6 51.9 5.8 3 647.70 0 47.8 234.9 336.8 28.2 4 967.8 271.7 464.1 155.5 74.5 2. ' 5 469.8 50.3 95.9 77.7 222.5 23.4 6 401.6 0 45.4 58. 278.7 19.4 7 692.8 63.9 317.1 157.4 143.5 10.9 ' 8 742.10 97.3 188.1 125.7 305.9 25.1 9 472.90 17.5 185. 175.8 75.5 23.9 ' 10 638.4 0 50.2 360.4 219.7 8.1 11 695.3 120.7 151.3 212.7 208. 2.6 12 751.10 184.4 336.8 196.2 32.5 1.2 ' 13 840.2 26. 196.2 267.4 338.5 12.1 14 766.6 203. 307.1 181.6 72.7 2.2 15 677.2 129.7 259.2 193.3 87.9 7.1 ' 16 719.4 12.4 229.9 179.2 295.8 2.1 17 305.5 0 25.7 84.4 144.9 50.5 ' Maplewood Creek Project Pale A-1 FA71340(;,tech.do I1/_l-A 33 PNt ixwariiin aun�iinn A � pllll 11���11 �11�� a�-IIIpIIIIII�, �Ie111�lYlA�llllllp�ll�l�v �; Ai�ldl � I�YNIIIII��IIIII�■ u In■m�� �Y u� mnuiu �Iv119��1YI1S�I��N11��Y111�1�� 0 ��I r�� ��IINII���M�IYIIII� n n on YHI�IYIYIYIYIIVI �IWIIIV011 �■ � psi u� i °� ■ 1 ns n ■ u nn u� IE ennui un� I40 N I m� llmmiiiiiilmmiiiiiiimLlillillismillI IY.IUWY��flll ■III�IIN�11� II�IIIIS i SILT OR CIAY Sampled upstream left side, pond area AGRADATION CURVES, ASTM D-422 I�Iaplewood Creek Sedimentation Study Renton, Washington NORTHWEST, INC. ■ r� I�AdY �dlAvll�1� � III � pus u�� nA m �mm� i nee rs i � 1��I r �yfalilYIIINYW�IIY■�IIIII�■ II��OI�l�fi It �IIIII�■ 11�11 W��Idl I 1��11111�■ �°i�■uuu�ioini �uiiiu III Id 1�11��1�■u�lAlll� �111p1�pg1�1��1�■O�IAIII� II�YI� ��llnl� ��O���ei�■iiem��iiiniin�■ e �I���If1YYYIIIIIpYY, �Iui ■imm 11 Iv��11111��A� 111� IAll9� p II��I � p IIIII�� A Y 1 vllll III �����11=iI���u11 i � � ■ � ro io�er���i ips�m� emu■ u�i��wi�i �u■i i�m�i�uoiiiiii� i mull 1111111111111111 �lallslll ����un aim nuuAnrs� �u� � INN 7N 111IM11111 I M IY NIEMEN MENEM Sampled sloughed area 100 feet below concrete wier left bank, slope sample GRADATION CURVES, ASTM D-422 RTEIWFSr. C. Consulting Engineers & Scientists nsiuunww� �u��im NO 11in WIMP Sampled sloughed area 100 feet below concrete wier on left bank stream terrace below slough GRADATION CURVES, ASTM D-422 NORTHWEST, INC. I 'AIM# ConsWfing Engineers & Scientists i n ��ii ��■oIn� ��iiii Ia�I1R1��11 I ��IIII�I@llly I � �� �w�u■� � � �m �inui uve ��r■o�� i m �n m Ii �innn �ruu iw �m II�IIYIII� IIIIII�II �MIII�� �INYII��IIII RY�IIII �IIIIII� �mnumm in��m �innm■ ■ i Y��NIIIY�IIIYIY �WIII YR�111� �IIIII � u i n� �u n ism u� 10 lir YBWI�IIIV�I fWNlls��llll N�INw ��' u■IIN �W IY�I i A MIN I � �IIIII� ��smn�Y IIN I ■ " a �� III ii lli illinismillil iiiiinm lifilloomillN ism iiiiismiiiii s Hills 11 UNMOVED in mismi nolillinsiLlillilli 111=111 RHINE m I In M IN M EM1111111111 NMI Ul Hilinswililitt MINIMUM MEMOIR HIM SENIOR IIIII ■ HIM INN HOME 111011111111 M illinisol 1111,111 goil YI IN llmmiiilmmmiiii ME HIM 11111111111111 Mill ism i �NINE MUM ll�If� WYIWIN �{AYI NIW ■ I �1191 � wu in soul ■ ■IIIR IIYI M11111 INN ME "0 IIII mom liiiimmiiiiiilmmiiiiilimmillillin ne 0111111111111111111111111 1101110 11011111 Sampled streambed sediments coming from left branch of Maplewood Creek about mile upstream of existing pond �&plewood Creek Sedimentation Study Renton, Washington NORTHWEST, INC. Consulting Engineers & Scientists m IIVNMsns�� � �n a�n4� .INIII� � lam iuin N Milifilin smiuliii lilloollinismilillin IN I HIM momplilin 11 NINE 1111 no INIIIIS1 N R 111111 � n Millillom lismill Ism nowlifillin M 11 NOUN ii Iu Y Mill HI E ; MINI NONE lsmiiiliiimm smiiiiiiimmiii mlliiilk,§M :B iiimmiii Millilll= 11111111111 no lmmiiiiiilmmiiii lmmmiiilmmiiliiilmmiiiii Ismnilmiii W ll n � n�oniue�i� $0 i11 HINERiiiiiismIII IW n ON ENRON OEM 0 F IMMUNE HIM III N 1111 INS HIM 10111111 IN BEEN lmmmiiiiiiim ME 11111111101 lismililill i m �11 lsmi 111111 lillomillillism 11 �S A Itl�Y�lllll� 11� 11110 11110 1110 Sampled stream sediments below large active slide GRADATION CURVES, ASTM D-422 Alaplewood Creek Seditnentation Study Renton, Washington NORTHWEST, INC. ConsuIting Engineers & Scientists ' APPENDIX B ' Aquatic and Terrestrial Resources Report APPENDIX B Aquatic and Terrestrial Resources Report Appendix B, Phase 1 Design Report TABLE OF CONTENTS 1 1.0 Introduction.................................................................................................... 1 2.0 Existing Habitat Conditions.......................................................................... I 2.1 Aquatic Habitat............................................................................................................. 1 2.2 Terrestrial Habitat......................................................................................................... 2 2.2.1 Vegetation............................................................................................................2 2.2.2 Threatened, Endangered and Sensitive Plants ....................................................4 2.2.3 Wildlife................................................................................................................4 2.2.4 Threatened, Endangered and Sensitive Animals ................................................ 5 3.0 Potential Effects.............................................................................................. 5 4.0 Revegetation Plan........................................................................................... 6 5.0 Monitoring and Maintenance........................................................................7 6.0 References .......................................................................................................8 rMaplewood Creek Sedimentation Basin Reconstruction and Improvement Project Page i F'\7134G\Aq,-REV.J-1 li_1/71.03.37 PNt Appendix B, Phase 1 Design Report APPENDIX B AQUATIC AND TERRESTRIAL RESOURCES REPORT 1.0 Introduction This Aquatic and Terrestrial Resources Report was prepared for use in determining impacts associated with the Maplewood Creek Sedimentation Basin Reconstruction and ' Improvement Project. A complete description of the proposed project is provided in the "Phase 1 Design Report" to which this report is an appendix. t 2.0 Existing Habitat Conditions ' Harza biologists conducted a site visit on April 26, 1994, during which current terrestrial habitat within the Project Area and vicinity were assessed. Potential project effects, mitigation ' measures, and revegetation strategies were evaluated. Recently compiled aquatic habitat literature and observations documented during the site visit were used for the aquatic habitat section of this report. We also reviewed the 1989 Draft Maplewood Creek Basin Plan, the April ' 1993 Cedar River Current and Future Conditions Report and associated correspondence, and we requested and received U.S. Fish and Wildlife Service (USFWS), Washington Department of ' Fish and Wildlife (WDFW) and Washington Department of Natural Resources (DNR) database searches. 2.1 Aquatic Habitat ' While the Cedar River has a large natural run of sockeye salmon, steelhead and a moderately-sized run of river smelt, these migratory fish appear to seldom use Maplewood Creek ' for spawning or rearing. Resident trout have been observed in the lower reaches of Maplewood Creek, from the golf course area upstream into the steeper canyon reaches. This section of ' stream has been restocked by citizens a number of years ago with trout provided by the State Department of Game (Draft Maplewood Creek Basin Plan 1989; Cedar River Current and Future ' Conditions Report 1993). Erosion in the steep, lower reach of the east fork of Maplewood Creek has washed fine ' sediments into potential spawning gravels and significantly impacted fish habitat. In addition, the two ponds originally constructed for golf course irrigation represent a passage barrier. The ' upper concrete dam structure is severely damaged and has been undermined, severely eroding the Maplewood Creek Sedimentation Basin Reconstruction and Improvement Project Page 1 frA713g6bkq.-r-d-1 1;_1;1)4 03,37 PM 1 Appendix B, Phase 1 Design Report channel bottom. The lower dam has been maintained as a sediment/debris dam; however, it lacks adequate fish passage. As described in the Maplewood Creek Sediment Load and Geotechnical Evaluation ' Report (Appendix A to Phase 1 Design Report), the stream channel is remarkably free of organic debris despite approximately 10 significant landslides observed on the canyon slopes during the ' site visit. Some logs bridge the creek but intermittent stream flows must be sufficiently high to strip most fine organic fragments from the channel. Two minor canyon debris jams were found, 1 but these do not impede the normal stream flow. The channel floor is covered by a thick blanket of sand and gravel possibly up to 10 feet thick. The lower half-mile of Maplewood Creek is greatly affected by the Maplewood Golf Course, the existing culvert systems under SR-169, and the railroad grade. The creek was placed in a 72-inch diameter culvert for its lowermost 1,000 feet from the Cedar River, past the railroad embankment, and under SR-169. This probably occurred during the construction of the railroad or state highway. Through the golf course, the channel is largely barren of habitat and functions ' primarily as a drainage ditch. Although coho salmon have been reported to migrate through the culvert and into the golf course reach in recent years (Draft Maplewood Creek Basin Plan 1989), the existing culvert system appears not ideal for adult fish migration. Therefore WDOT is presently constructing a fish ladder immediately adjacent to the culvert outlet to the Cedar River to be connected to a future fishway channel through the golf course to the reconstructed sedimentation basin. Little information is available on the quality of water in Maplewood Creek. The continued presence of resident trout indicates that generally water quality within the creek is adequate. During high stream flows, however, turbidity levels get very high from erosion in the upper channel segments. These turbidity levels along with habitat changes may be limiting the ' population of the resident trout fishery (Draft Maplewood Creek Basin Plan 1989). 2.2 Terrestrial Habitat ' 2.2.1 Vegetation The upper end of the project area is in a forested ravine with moderate to steep slopes up ' to the Renton Plateau. The topography flattens out at the golf course parking lot. Slopes on the west side of the Maplewood Creek ravine are somewhat wetter than those on the east side, and ' numerous groundwater seeps were observed during the site visit. The predominant plant ' Maplewood Creek Sedimentation Basin Reconstruction and Improvement Project Pale 2 FA7114G1Aqu-Tm-"1 i/'I/94?3 37 PM ' Appendix B, Phase 1 Design Report association is western hemlock (Tsuga menziesii)lswordfem (Polystichum munitum)-salal ' (Gaultheria shallon). Western redcedar(Thuja plicata) is common on moister sites, and large cedar stumps, indicating timber harvest several decades ago, are scattered throughout the stands. Douglas fir (Pseudotsuga menziesii) is more common on the drier sites. The overstory also ' contains a minor component of red alder (Alnus rubra), cottonwood (Populus trichocarpa) and bigleaf maple (Acer macrophyllum) trees. The forest canopy is fairly open, and a well-developed shrub and herbaceous layer is ' present. Along the riparian zone, salmonberry (Rubus spectabilis) and Himalayan blackberry (R. discolor) are dominant. Snowberry (Symphoricarpos alba), red elderberry (Sambucus racemosa), vine maple (Acer circinatum), devil's club (Oplopanax horridum), and currant (Ribes ' spp.) were also observed. ' The banks around the upper concrete dam are steep and have been reinforced with rip- rap. A gravel/cobble bar is located upstream of the dam. Water depth averages approximately 1 ' foot. Vegetation immediately adjacent to the pond is herbaceous ground cover including smartweed (Polygonum spp.), mixed grasses, Robert's geranium (Geranium robertianum), and horsetail (Equisetum arvense, E. telmateia). The lower sediment basin is located just above the golf course parking lot.g p b The bottom of the basin consists of a layer of fine sediments in its lower end and gravel substrate just below its inlet. Water depths average 1-2 feet. ' An old access road parallels the north shoreline of the creek. The south shoreline and adjacent upland slope is steep. Trees and shrubs are dense to the edge of the pond. On the south and west sides, vegetation is predominantly herbaceous, and includes mixed grasses and weedy forbs such as dandelion (Taraxacum officinale), lance-leaved and common plantain (Plantago ' lanceolata and P. major), hairy cat's ear(Hypochaeris radicata) and clovers (Trifolium repens, T. pratense), with creeping buttercup (Ranunculus repens) and western bittercress (Cardamine occidentalis) also common. Small amounts of reed canarygrass (Phalaris arundinacea), an ' aggressive exotic species, are also present. The creek reach at the southern end of the project area is confined to a narrow channel. The east bank is forested almost to the waterline. The shrub layer is diverse and includes snowberry, salmonberry, elderberry and vine maple. The west bank is bordered by dense thickets of blackberry measuring approximately 10 feet in width. The golf course parking lot and residential property abut the shoreline vegetation on the west. ' Maplewood Creek Sedimentation Basin Reconstruction and Improvement Project Page 3 F:N7134GUq,-Ten J� 11i'1/403�37 PN1 ' Appendix B, Phase 1 Design Report 2.2.2 Threatened, Endangered and Sensitive Plants ' A search of the Washington Department of Natural resources (DNR) Natural Heritage Information System (June 8, 1994) indicates that no records of rare plants, high quality native wetlands, or high quality native plant communities exist for the project vicinity. Two threatened ' plant species and 14 sensitive plant species are thought to occur in King County. Of these plants, only the four noted below would be likely to occur in habitat types that will be affected by ' construction of the new sedimentation basin, i.e., low elevation riparian and pond habitat. ' Water lobelia(Lobelia dortmanna) is listed as threatened in Washington. Water lobelia is an aquatic plant that grows in shallow water along lake or pond margins. No aquatic vegetation was noted in either of the ponds on Maplewood Creek. Bristly sedge (Carex comosa), on the state sensitive list, also grows along the shores of ' lakes and ponds and other wet places. Bristly sedge is best identified from May through August by its cylindrical, 2-7 cm, pedunculate spikes, similar to bottle-brushes. The only sedge noted on 1 the Project site during the survey was Dewey's sedge (Carex deweyana). Since Dewey's sedge is a much smaller plant that produces sessile spikes only 7-20 mm in length, it is easily distinguished from bristly sedge. ' Bo clubmoss L co odiella 'n g ( y p t undata) occurs most often in the cold, acidic soils of sphagnum bogs, but may also be found in other wet habitats. No clubmosses were noted in areas that would be affected by construction. ' Lance-leaved grape-fern (Botrychium lanceolatum) has been documented to occur in various habitat types, usually in forested situations. No grape-fern species were noted in the ' project area. ' 2.2.3 Wildlife Residential development on the uplands above the ravine and recreational development ' below the project area limits the diversity of wildlife occurring within the project area. For example, habitat does not exist for large mammals requiring large territories, such as the black ' bear and mountain lion. However, forest and riparian-dwelling wildlife species with moderate to small home range requirements such as deer, birds, waterfowl, small mammals, reptiles, and ' amphibians are likely abundant along the mainstem of Maplewood Creek. ' Maplewood Creek Sedimentation Basin Reconstruction and Improvement Project Paoe 4 F 1I/21/' v337 P%I ' Appendix B, Phase 1 Design Report ' During the site visit conducted on April 26, deer sign, a mallard pair, and rodent carcasses were observed. In addition, many bird species were heard and observed. Cavities evident in the scattered snags and large, live coniferous and deciduous trees indicate that habitat exists for cavity-nesting birds and mammals. Species requiring cavities for nesting or foraging likely present within the Project Area include the common flicker (Colaptes auratus), winter wren (Troglodytes troglodytes), black-capped chickadee (Parus atricapillus), and the western gray squirrel (Sciurus griseus). Gravel substrate and sandbars, observed within the shallow waters of the lower sediment pond, likely provides foraging platforms suitable for great blue heron (Ardea herodius). Although raccoon (Procyon lotor) sign was not observed, habitat is present, making it probable that this species is also present within the project area. ' Results from the WDFW Priority Habitat and Species database search, received on May 17, 1994, indicate that there are no records of species of concern occurring within the project ' area. ' 2.2.4 Threatened, Endangered and Sensitive Animals A search of the U.S. Fish and Wildlife Service database (June 17, 1994) for the occurrence of threatened, endangered and sensitive species indicated that bald eagles could be present in the project area during the winter. However, the WDFW's PHS data contained no ' records of bald eagle nesting, roosting or concentrations in the vicinity. Construction is planned for the low-flow period in late summer, and would therefore not disturb any eagles that might fly near the area during the winter. No potential habitat will be removed. Enhancement of fish passage in Maplewood Creek is intended to improve conditions for resident trout, which do not represent an important forage resource for bald eagles. The project is not expected to have adverse or beneficial effects on bald eagles. ' 3.0 Potential Effects No adverse effects to fish and wildlife are anticipated from project implementation, except short-term disturbance during construction and revegetation planting. Aquatic habitat is currently low-quality due to high sediment loads and barriers to fish passage. Terrestrial habitat ' that will be directly affected by construction includes riparian shrubs along approximately 80 feet of the creek and mixed grasses and weedy herbaceous species growing along the sedimentation basin, dike and golf course parking lot. A 30" cottonwood and a few trees measuring less than 10 inches in diameter at breast height (d.b.h.) will be removed from the east ' Maplewood Creek Sedimentation Basin Reconstruction and Improvement Project Page 5 F-k'I;JGU ar yu-T .d. ;/'_1i`1-J,37 RM ' Appendix B, Phase 1 Design Report ' side of the sedimentation basin. The Revegetation Plan presented below is designed to minimize construction-related impacts to terrestrial habitat. ' Implementation of engineered elements of the Project are expected to provide benefits to P g J P ' aquatic habitat. The expanded sedimentation basin will reduce flooding and control erosion. Subsequently, sedimentation is reduced, improving downstream water quality. In addition, the ' proposed bank stabilization work will help minimize erosion. The removal of the upper concrete dam will restore access to the upper ravine and aquatic 1 habitat, and will help restore the channel to a more natural state. Stream habitat enhancement calls for the placing of 2- to 3-foot size boulders along the creek bottom with about 8 to 10 feet spacing. This method should extend from about 100 feet upstream of the upper dam to the upstream end of the reconstructed sedimentation basin. Channel reconstruction and bank ' stabilization will help to re-establish pools and riffles, provide areas for rearing and escapement, and increase production of food organisms. The elimination of the pond behind the upper concrete dam will be balance by the expansion of the sedimentation basin and restoration of the ' channel. In addition, the fish passage structure proposed as part of the basin reconstruction and improvement project, as well as the low flow fish passage channel proposed by the City in a ' separate project, will improve access to the upper ravine by migratory fish species. ' 4.0 Revegetation Plan Following construction, revegetation of exposed soils will be needed to control erosion. Selection of native shrub and herbaceous species for revegetation will promote diversity in areas that are currently dominated by grasses and weedy forbs. Plantings of shrubs along the new ' pond margin will provide cover and increase forage opportunities for many species of reptiles, amphibians, small mammals and birds. Planting of sedges, rushes and bulrushes in shallow ' water areas of the pond will add another element of habitat diversity that is not currently present. Plants for revegetation in areas affected by construction were selected based on their ' capacity to 1) tolerate site conditions; 2) stabilize slopes and exposed soils; 3) provide shading cover along streambanks and pond margins; 4) increase the structural complexity of the habitat, ' providing additional forage and cover opportunities for wildlife; and 5) increase diversity in the native plant community. ' Tree species selected for planting include western redcedar, western hemlock and Oregon ash (Fraxinus latifolia). Shrub species include willow (Salix species) and dogwood (Corpus ' Maplewood Creek Sedimentation Basin Reconstruction and Improvement Project Pace 6 F.M34C�Aqu-T< J. 11/'_1 NW 03,37 Phi ' Appendix B, Phase 1 Design Report ' stolonifera) as cuttings, Pacific ninebark (Physocarpus capitatus), and Nootka rose (Rosa nutkana). ' Gradual contouringof the slopes around the new and will allow for planting of P P P b ' emergent species in shallow water and saturated soils. Small-fruited bulrush (Scirpus microcarpus), broad-fruited burreed (Sparganium eurycarpum), beaked sedge (Carex rostrata), ' Baltic rush (Juncus balticus) and dagger-leaf rush (J. ensifolius) will be considered for planting at appropriate water depths. ' A grass/forb seed mix will be applied to exposed soils to ensure erosion control during the period of time when trees, shrubs and emergents are becoming established. The mix will include colonial bentgrass (Agrostis tenuis), foxtail (Alopecurus pratense), red fescue (Festuca rubra) and water smartweed (Polygonum hydropiperoides). ' Strategically planting the trees and shrubs in suitable spots will enhance future growth. Trees will be planted in small clumps for naturalizing purposes, while shrubs and emergents will ' be placed to provide adequate soil coverage. Detailed planting specifications, including size of stock, spacing, care and handling of plant materials, will be prepared as part of the construction ' plans and specifications. Seed mix can be applied and rooted stock can be planted immediately following ' construction. Willow and dogwood cuttings are best planted during the period when they are dormant (fall and winter). 5.0 Monitoring and Maintenance Elements of the project that are designed to improve fish habitat and fish passage will be maintained by the City. It is recommended that monitoring of the aquatic habitat, including ' aquatic invertebrates and fish populations, be conducted within the Cedar River Management Plan. The stream channel and bank stabilization work will be inspected by the City ' approximately two times per year during the rainy season, particularly following heavy rainfall events. Evidence of sloughing and/or erosion will be recorded, and appropriate mitigative ' measures will be taken, if necessary. Vegetation should be monitored at quarterly intervals during the first year after planting, ' and then annually for the following two years, to ensure adequate survival and density of ' Maplewood Creek Sedimentation Basin Reconstruction and Improvement Project Page 7 FA7131GWq,-TertdJ 11/21/94,33 37 PM ' Appendix B, Phase 1 Design Report ' plantings. Monitoring and maintenance could be performed by the City Stormwater Utility or by golf course personnel. 1 6.0 References Ingles, Lloyd G. 1965. Mammals of the Pacific States: California, Oregon, Washington. Standford University Press, Stanford, California. ' King County Department of Public Works, Surface Water Management Division. 1993. Cedar River Current and Future Conditions Report. Parametrix, Inc. 1989. City of Renton Comprehensive Stormwater Plan: Maplewood Creek Basin Plan. Prepared for the City of Renton Public Works Department, Storm Water Utility Division. ' Robbins, Chandler S., B. Bruun, and H.S. Zim. 1983. Birds of North America: A Guide to Field Identification. Golden Press, New York. Western Publishing Company, Inc. Racine, Wisconsin. ' USDA Forest Service. 1977. Cavity-NestingBirds of North American Forests. Agriculture Handbook No. 511. Washington, D.C. ' Maplewood Creek Sedimentation Basin Reconstruction and Improvement Project Page 8 g ; i APPENDIX C ' Preliminary Construction Plans APPENDIX C Preliminary Construction Plans 1 a x BYPASS PIPE INLET / SEE DWG. 2 CENTER NOTCH SECTION OF UPPER ' \ 12'MIN- - DAM CREST ,/ / 120' LG SEDIMENTATION ZONE M1 EL 111.5 / ♦♦S CONCRETE DAM TO BE REMOVED AT REMOVE ACCUMULATED SEDIMENT ELEVATION LEAST TO EL 122.5 OR ONE FOOT PRIOR TO DAM REMOVAL 3 = 4> /'l� BELOW DOWNSTREAM GRADE OF CREEK DOWNSTREAM / _21 UPSTREAM q ACCESS ROAD AND 12*0-- / / L/t SCOUR ZONE -Z 130 SIDE F1F-// II E 11 ��\ M SIDE ADS N-12 BYPASS PIPE (MIN. PIPE SLOPE 1%) - 0 / \ / \ / 120 ALL FILL COMPACTED TO 98X y --"-7 j A — A MAXIMUM DRY DENSITY AND EXISTING ACCESS ROAD TO / / / FROM OPTIMUM MOISTURE VARIES © FLLPOFF-SITE BE IMPROVED SEE NOTE 1 ' / LONGITUDINAL PROFILE AT MAPLEW000 CONTENT TO PLUS 2X. MATERIALS / CREEK ACROSS UPPER CONCRETE DAM / SCALE: 1" - 20' H 110 OO LOCALLY DERIVED / / / 1' 10' V TYPICAL DAM SECTION FILL ' SCALE: 1' = 10'(HORIZ. AND VERT.) A 4 MAN ROCK 24'-30' DIA. /�4" OCK 8 2 MAN ROCK 12'-18'DIM. (C I STREAM / I• LENGTH OF REPAIR / I SECTION - 70®� / FEET CHANNEL • LENGTH OF REPAIR SE1:110N - 60 FEET \ / • TOE OF SLIDE WILL ' REQUIRE- 60 4 D TY X FO LG ADS HEAVY N ti� �y ♦0 TOE OF SLOUGH WALL REQUIRE 40 DUTY PERFORATED DRAIN o / / , /� / 40" MAPLE 'BEDDING GRAVEL— \ / MAN ROCK, 30 PIPE SEE DETAIL 2 DWG. 3 ♦� B - B 2 MAN ROL'K; 10 CUBIC YARDS OF / CUBIC YARDS OF 20 CRUSHED ROCK(2-W(H). // CUBIC OS EXISTING 91 WOOD SCALE: 1' - 10• 1 OF 14" HEMLOCK 2 / / CRUSHED ROCK ' ( ) ♦k / n PIPE TO BE REMOVED • MINOR RESHAPING AL UPPER �� b ^/ / ^♦ / SLOPE AND DISPOSAL OF WIDTH �/ • (2-INCH). SLOPE TO BE REVEGETATED ♦ ♦,LO E145TING 8'� VEGETATION AND SURFACE �� SLOPE CONTROL GRASSES AND -� WITH A MIX OF EROSION 1 w SOIL a 6 ' / METAL PIPE TO _ WALL REQUIRE - - ION NATIVE SHRUBS (TYP.) 14' HEMLO // /08 I - REMOVED C - C DDIISPOSAL OF 25 CUBIC YARDS OF END OF EXISTING ACCESS - VEGETATION AND EXISTING MO PVC PIPE ROAD TO BE IMPROVED, SCALE: 1' - 10' SURFACE SOLS/ In BE REMOVED ♦,1,a / / / SEE �� i � O- 4 MAN ROCK 24'-30' DIA. g .ry /?• EL 108 / 55 C)- 2 MAN ROCK 12'-18'DIA. ♦'L 'V / !/ SILT TO BE REMOVED BEFORE �� P (C)-RESHAPE SLOPE ♦♦� /// J / r / a, J - 3Cl COTTONWOOD REMOVING CONCRETE DAMS - O (p)- REMOVE ACCUMULATED / SECTION / b ry �� � SEDIMENTS �FlSHWAY OUTLET ♦♦ / � / / ry A 2 SEE DWG. 3 ,♦a ! / CENTER NOTCH SECTION OF .�✓17> ♦5 .� 20" HEMLOC ♦`L / / o EXISTING CONCRETE DAM TO i8 -I - �� 12". ADS N-12 - ^ / EL 105 / BE REMOVED. NOTCH SECTION BYPASS PIPE 0" MAPLES t ♦� ,�1 / / REMOVE EXISTING MIN. 10' BOTTOM WIDTH AT o Lc QUANTITIES STATED ARE 00 EL IRRIGATION INLET 45•CUT BOTH SIDES / ll FOR ENGINEERING ESTIMATE N EL 1 CREEK BOTTOM AT 8' 5 / AND PIPE UPSTREAM CONTRACTORS MUST ONLY Y DOING PURPOSES.AND NOTTO BE USED OF NEW INLET / 18' MAPLE �� _Zt o / / BOULDERS OF 2' TO 3'- // / '/ PREPARE INDEPENDENT /9~'tC SIZE TO BE PLACED ONTITY 118 I / DAM CREST EL 111.5 SEE TYPICAL DAM SECTION :) / / TO 10' SPACING (TYP.) // 4" CEDAR 30• FROM UPSTREAM END OF / OF 00S11NG / / THE SEDIMENTATION BASIN / A E FUTURE Fl MpN SHWAY / pAyET t, / TO 100' UPSTREAM OF THE / / 0. HEMLOCK CHANNEL ♦ UPPER DAM SPILLWAY CREST M \ � - v EL 1 'os / EL.. 111.5 11.5 / / � / EDGE OF EXISTING // � / ♦b bry 50" MAPLE /♦ /\ / 10 ACCESS ROAD (TYP.) • � ro b EG CONCRETE / j 12" MAPLE CEDAR WEIRT WEIR TO BE REMOVED EXISTING RIPRAP TO BE REMOVED // / `.°b REMOVE ,y /^\ ..� / / i. ♦ry � NEW INLET 7D/ / / ♦♦� / a' CED SEWER MHO, PIPE AND TRENCH / A� / om ♦^� IRRIGAIXXN// / // �� � � LE STING PAVEME) 0 9y �� 70 MATERIAL FROM BASIN AND / / o PIPE / � NDER DAM. CUT AND CAP PIPE / i. ACCESS ROAD SURFACE TO BE 4' DEEP fC_ 10 /? 7/8' CRUSHED ROCK ROLLED ON A 2 o / / �OV44EDR EARTH AD WI SURFACE FOR A -EDGE OF EXISTING PA T(TYP. / b / p \\ /�0? ti� / 0 AR 2, ® EXCAVATE TO RESHAPE "_ / o•V ,�,0 / / N m / ry THE SLOPE. SLOPE TO BE OVER & GUY AN / / // % HEMLOCK I � REPLACE WITH ROCKERYAAND• RIPRAP WITH GRAVEL DRAIN. r SPILLWAY / CITY OF RENTON R// SEE DWG. 2 / 10 20 DEPARTMENT OF PUBLIC WORKS APPROXIMATE LOCATION OF EX NORTHWEST, INC.ISTING IRRIGATION • SCALE IN FEET MAPLEWOOD CREEK SEDIMENTATION BASIN / PIPE `o)f, Engi— rs and s�+e�csts RECONSTRUCTION AND IMPROVEMENT PROJECT 1' 20' Beuewe, Washington SITE pIAN AND SECTIONS zi 4" MAPLE 12" MAR I - EDGE OF EXISTIN, BUILDING (TYP) / E-TI 11-22-y4 FIIE NAME: .. AS NNTED- �F,U BIXN: PM£ 1 CHECKED-A L. NW NO. RM;iON BY APPR. DATE APPROVED: "MEET: 1 OF:3 Wd a 8'EMERGENCY y o', DRAW GATE JOINT TO MATCH -� 72'0 PIPE END D M D Lo -------- ----------- -------- I I o • I I n a _ _ _ 1 SPILLWAY _ _ I _ 72'0 OUTLET PFE I o - --------- --------- 0 1'-0' SLOT T7 0 8' SUBDRAIN ! GATE PLM F _ 26*-0' 5'-0' L tY-0' 9•-_0: 1 8'FLAT BACK LIGHT DUTY SLUICE GATE PROVIDE TEE 14'-0' HANDLE FOR GATE OPERATION ' EL tits E DAM CREST EL. 111.5 100 YR. FLOOD MAX _X. DAM CREST EL 111 111.5 0 POOL EL 110.5 2.5 SPILLWAY CREST EL 109.0 1 PPLANE1t CUTTING 1 2 _ t EL 107.0 EL 107.0 INV. EL 106.0 MATCH 410404� X BASIN BOTTOM EL 105.0 � • - ------------------- 2 -� 11L 9&5 0 INV.EL 102.0 I EL 9&5 - 72'0 X 30'LG CONgtETE pPE of I AS7M-C-76 CL q \� I I I I I i EL 97.5 � E ' 8'0 PERFORATED DRAIN m D D PIPE IN GRAVEL FILLED 1'-0' *6 E - E TRENCH MIN. PIPE SLOPE 1 OUL 1X SEE DETAIL 1 TYP. a—a' 5'-0' ' FILTER FABRIC TO BE USED AS A MARKER DURING POND CLEAN OUT AS S-0'(MIN) WELL AS A FILTER. BASIN BOTTOM EL 105.0 - z o c BACKFlLL AROUND 8'0 PIPE USING 1 1/2 INCH NOMINAL DIAMETER WASHED GRAVEL PERFORATIONS SHOULD BE ON _ �i LOWER PART OF PIPE. I CITY OF RENTON 0 2 4 a + DEPARTMENT OF PUBLIC WORKS ' NORTHWEST, INC. MAPLEWOOD CREEK SEDIMENTATION BASIN SEDIMENTATION POND SUBDRAIN SCALE W FEET Engi—,. -d Scientists RECONSTRUCTION AND IMPROVEMENT PROJECT DETAIL 1 1'- 4' 3e11ewe, Washington SPILLWAY AND OUTLET PLAN, SECTIONS dt DETAIL N.T.S. DESIGNED:A.L.HNW *DATE: 11-22-94 FILE NAME: DRAWN: C.L.C.HNW CHECKED: A.L.MNWLE: AS NOTED n[Lo xow. vAc[-. NO REVISION D1' APPR. DATE pPPROK O: SMEET: 2 OF:3 1 • fL 12F BYPASS PIPE H 1 II G I G 1 L ----------- i—� - - - - _ .42' CONCRETE I I ' I ----------- J-FUTURE FISHWAY ---------------------- I 1 CHANNEL I I I b PLAN H b FlSHWAY OUTLET i STAFF GAUGE TO 1 DAM CREST BE INSTALLED 12'0 BYPASS 6'-0' 4'-0' PIPE 8-0' V-01 B'-O' 3,-6' 6' I 1 DAM CREST EL 111.5 - 42'0 PIPE El. 111.5 SEE DETAL 3 100 YR. FLOOD MAX EL 105.7 f --u-jO9.5 110.5 �/ � EL_109�_ INV. EL 107.0 1 EL 107.5 = NORMAL POOL EL 108.5 EL 106.7 J 1 142'i_ 32'LG CONCRETE PIPE - I SEE DETAIL 3 I ! LEL 104.5 I 6'FILLET TYP. I - - - - - I BASIN 80TTOM EL 105 0 BASIN BOTTOM EL 105.0 I --- EL 104.5 MATCH BOTTOM OF EL 103 7 , FUTURE FlSHWAY CHANNEL -cr i-0. SECTION CUTTING PLANE 1 TIP. TYP. H — H --_ - 6'1 COVER MIN. I ROADWAY--- 0. _ c = BACKFILL AROUND 12'0 ADS N-12 PIPE T� +32" USING 1/4-INCH CRUSHED ROCK.A MINIMUM OF 36-MCHES OF COVER 8' STAINLESS STEEL WITH LOCALLY DERIVED FlLL REWIRED �I p woe, OVER PIPE WITHIN ROADWAY ALIGNMENT. ATES W/BEVELS 5'-0' WHERE COVER BACKFILL WITH(LEAN MIX-50 LB S LESS THAN INCHES, PLAN u �r� a CEMENT 350 LB FLYASH PER YARD �X-6- BYPASS PIPE INLET °e (WITHIN ROADWAY ALIGNMENT ONLY). 1 e� eo FINISHED GRADE TYPICAL_ FlSHWAY TYPICAL TOP OF WEIR ELEVATION FlSHWAY WEIR 1 17Y BYPASS PIPE FOR GA TEE HANDLE BYPASS PIPE 6' BED MIN. SCALE: 1- MIN. SLOPE 1% FOR GATE OPERATION TYPICAL DETAIL 2 _ EL 116.5 N.T.S. DETAIL 3 EXISTING GRADE 1 12"UG FLAT BACK" - INV. EL 113.5 LIGHT DUTY SLUICE GATE 113.0 CITY OF RENTON fr 0 2 4 6 DEPARTMENT OF PUBLIC: WORKS g 3'-0' 1'-0- SCALE IN FEET NORTTiVrES T,ieINCS MAPLEWOOD CREEK SEDIMENTATION BASIN 1 1' — 4' B.Ilawa, Washington RECONSTRUCTION AND IMPROVEMENT PROJECT o FISHWAY OUTLET PLANS, SECTIONS & DETAILS Tr S 1-0' DESIGNED:A.L.HNW DATE: 11-22-94 FILE NAME: 1 J — J DRAWN: C.L.C.HNW CHECKED AL.HIM AS NOTED DRo Boa r x N0. REVISION BY APPk.I DATE A T'ROVEO: SHEET: 3 -I