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Home My WebLink AboutRS_Drainage memo_181018_v1Drainage Memorandum K:\project\32900\32978\ProjectDocs\Drainage Memo\May Creek Trail Extension Drainage Memo.docx Technical Memorandum To: Lori McFarland From: Greg Laird, PE Copies: Tasha Wang Date: October 18, 2018 Subject: May Creek Trail Extension Stormwater Management Project No.: 32978 The City of Renton (City) is proposing the May Creek Trail Extension Project (the Project) - a pedestrian trail extension along the north side of May Creek from Jones Avenue NE to the existing May Creek Trail west of Interstate 405 (I-405). Otak, Inc. (Otak) is scoped to prepare a drainage memorandum to describe the stormwater management facilities and Best Management Practices (BMPs) that will be required for the trail based on the 2017 City of Renton Surface Water Design Manual. It is assumed that the Project will have a Targeted Drainage Review since it is located in or adjacent to a flood hazard area. The following sections describe the Project in accordance with standard Technical Information Report sections. 1. Project Overview The May Creek Trail Extension Project (the Project) is a soft surface pedestrian trail that extends from Jones Avenue NE to the existing May Creek Trail west of Interstate 405 (I-405) (Figure 1). The Project will be constructed by Washington State Department of Transportation (WSDOT) as a component of their I- 405 widening project. The trail will be approximately 6-feet wide and will be composed of a fine bark mulch atop a compacted gravel borrow layer. Approximately 100-feet to either side of the newly constructed trail will be cleared of invasives and will be enhanced and restored with native vegetation. The project is located entirely within the City of Renton, King County, Washington. The project follows the north side of May Creek from Jones Avenue NE to the May Creek Trail west of I-405. A portion of the project is within WSDOT right of way (Figure 1). The project is in Section 32, Township 24, Range 05 East of the Public Land Survey System. The trail extension will be approximately 815 feet long, and approximately 270 feet of it will be underneath I-405. The existing condition has been described in the critical areas report (Otak, 2018) as forested with a dense understory of Himalayan blackberry, Japanese knotweed and reed canarygrass. Tree species within the project area include black locust, red alder, big leaf maple, and black cottonwood. An informal dirt trail connects the existing May Creek Trail to Jones Avenue NE (Photo 1). The informal trail follows the north side of May Creek, beneath I-405 and extends through a large Himalayan blackberry and reed canarygrass field before connecting with Jones Avenue NE. The riparian buffer of May Creek is dominated by invasive species. Field samples of the soil along the trail alignment have classified the native soils as loamy sands. The Project is located within the floodplain of May Creek and within the stream buffer and within the buffer of an adjacent wetland. The trail will be 6 feet wide, except where it is underneath I-405 where it Page 2 May Creek Trail Extension Drainage Review October 18, 2018 K:\project\32900\32978\ProjectDocs\Drainage Memo\May Creek Trail Extension Drainage Memo.docx will be 8 feet wide. The trail will be constructed of 3 inches of fine bark mulch over 6 inches of gravel borrow. A geotextile will separate the trail from the native soils. No alteration or additional fill materials will be placed other than the minimum fill needed to construct the trail to meet established safety standards. 2. Conditions and Requirements Summary The trail extension will be approximately 815 feet long, and approximately 270 feet of it will be underneath I-405. Stormwater for the portion of trail underneath I-405 will be managed by existing facilities serving I- 405 or by new facilities designed to serve the widening of I-405. An informal dirt trail connects the existing May Creek Trail to Jones Avenue NE. The Project replaces the informal dirt trail with a soft surface trail designed to City standards. The trail will be 6 feet wide, except where it is underneath I-405 where it will be 8 feet wide. The trail will be constructed of 3 inches of fine bark mulch over 6 inches of gravel borrow. A geotextile will separate the trail from the native soils. From the stormwater management requirements, the Project represents 3,660 square feet of new pervious surface. The design of the soft surface trail is intended to not increase the rate of flow or the quantities of runoff compared to the flow present under natural conditions prior to the Project. There are no underdrains planned for the trail that would collect stormwater runoff that would require the consideration of the pervious surface as impervious for the purposes of stormwater management. There are no stormwater facilities within the Project limits (along May Creek and excluding I-405 bridge over May Creek). Stormwater currently infiltrates or is dispersed as sheet flow towards May Creek. The Project will not change how or where stormwater is discharged. 3. Offsite Analysis The Project will not have significant adverse impact on the downstream and /or upstream drainage system. Field reconnaissance of the Project area and May Creek above and below the Project limits did not identify significant bank erosion (Photo 2), or other water quality concerns that should be considered for stormwater management in the design of the Project. 4. Flow Control, Low Impact Development and Water Quality Facility Analysis and Design The Project is exempt from the flow control requirements. Stormwater from the Project will infiltrate to the native soils through the 3 inches of fine bark mulch and the 6 inches of gravel borrow. Any water that does not infiltrate will be fully dispersed as sheet flow through a minimum of 40 feet of the native vegetated area. Low Impact Development features are provided by infiltration and full dispersion. Water Quality Facilities are not required as the soft surface trail is not considered a pollution generating impervious or pervious surface. 5. Conveyance System Analysis and Design The stormwater from the Project will infiltrate through the bark mulch and gravel borrow. Any runoff from the trail that does not infiltrate will be fully dispersed through native vegetated area. There are no conveyance systems required for the Project. Page 3 May Creek Trail Extension Drainage Review October 18, 2018 K:\project\32900\32978\ProjectDocs\Drainage Memo\May Creek Trail Extension Drainage Memo.docx 6. Special Reports and Studies The Project appears that it could be located in the May Creek floodplain as delineated by Federal Emergency Management Agency (FEMA). A portion of FEMA’s Flood Insurance Rate Map is shown as Figure 2 and the base flood elevations (BFEs) shown are in the NAVD 29 vertical datum. However, converting those BFEs to the project vertical datum (NAVD 88) by adding 3.57 feet to the BFE’s on FEMA’s map, it appears that the proposed trail may be above the 100-year flood elevations. No alteration or additional fill materials will be placed other than the minimum fill needed to construct the trail to meet established safety standards. 7. Other Permits The Project appears to be located in the floodplain of May Creek and within the stream buffer and avoids the wetland buffer. The Project will have to submit applications to receive permits from the City for the grading and construction of the trail extension. The permits anticipated include Shoreline Substantial Development Permit, Environmental Checklist (for State Environmental Policy Act (SEPA) compliance), and a Biological Assessment. 8. Construction Stormwater Pollution Prevention Analysis and Design The preliminary temporary erosion and sediment controls (TESC) for the Project are shown in the 30- percent plans and as Figure 3 attached. The project will be built by WSDOT in conjunction with the widening of I-405. The finalization of the TESC plans and details, and the inclusion of the stormwater pollution prevention and spill control plan will be the responsibility of WSDOT and their contractor. 9. Bond Quantities, Facility Summaries, and Declaration of Covenant The City’s Bond Quantity Work Sheet is included in the Appendix. 10. Operations and Maintenance Manual There are no stormwater facilities proposed for the Project. The only maintenance anticipated would include trail maintenance activities such as pruning vegetation and replenishing the bark mulch as needed. 11. Special Requirement #2: Flood Hazard Area Delineation The FEMA delineation of the flood hazard area is shown as Figure 2. This flood boundary is shown on City of Renton’s GIS (Figure 4), and it appears that the trail may be within the flood hazard boundary. However, based on the proposed elevations of the trail and the base flood elevations from the FEMA map (Figure 2) converted to NAVD 88 by adding 3.57 feet to the BFE’s on FEMA’s map, it appears that the proposed trail may be above the 100-year flood elevations. Page 4 May Creek Trail Extension Drainage Review October 18, 2018 K:\project\32900\32978\ProjectDocs\Drainage Memo\May Creek Trail Extension Drainage Memo.docx Site Photographs 1. Informal trail leading to large open Himalayan blackberry field. 2. Riparian vegetation, view west. Banks are dominated by Japanese knotweed and Himalayan blackberry. Page 5 May Creek Trail Extension Drainage Review October 18, 2018 K:\project\32900\32978\ProjectDocs\Drainage Memo\May Creek Trail Extension Drainage Memo.docx References City of Renton, 2017. 2017 City of Renton Surface W ater Design Manual, December 12, 1016. Federal Emergency Management Agency, Flood Insurance Rate Map, Panel 53033C0664, effective date May 16, 1995 King County iMap. 2018. Available at http://gismaps.kingcounty.gov/iMap/ . Accessed August 16, 2018. Otak, 2018. Critical Areas Report Appendix Renton Bond Quantity Worksheet. Page 6 May Creek Trail Extension Drainage Review October 18, 2018 K:\project\32900\32978\ProjectDocs\Drainage Memo\May Creek Trail Extension Drainage Memo.docx Figure 1 Page 7 May Creek Trail Extension Drainage Review October 18, 2018 K:\project\32900\32978\ProjectDocs\Drainage Memo\May Creek Trail Extension Drainage Memo.docx Figure 2 Page 8 May Creek Trail Extension Drainage Review October 18, 2018 K:\project\32900\32978\ProjectDocs\Drainage Memo\May Creek Trail Extension Drainage Memo.docx Figure 3 Page 9 May Creek Trail Extension Drainage Review October 18, 2018 K:\project\32900\32978\ProjectDocs\Drainage Memo\May Creek Trail Extension Drainage Memo.docx Figure 4 Appendix Planning Division |1055 South Grady Way – 6 th Floor | Renton, WA 98057 (425) 430-7200 Date Prepared: Name: PE Registration No: Firm Name: Firm Address: Phone No. Email Address: Project Name: Project Owner: CED Plan # (LUA):Phone: CED Permit # (U):Address: Site Address: Street Intersection:Addt'l Project Owner: Parcel #(s):Phone: Address: Clearing and grading greater than or equal to 5,000 board feet of timber? Yes/No:Water Service Provided by: If Yes, Provide Forest Practice Permit #:Sewer Service Provided by: AddressAbbreviated Legal Description: Abbreviated Legal City, State, Zip N/A 1055 S. Grady Way Additional Project OwnerJones Ave. NE and May Creek ######## 425.430.6400 8/17/2018 Prepared by: FOR APPROVALProject Phase 1 greg.laird@otak.com Greg Laird 25758 Otak 11241 Willows Road, NE, Redmond, WA 98052 425.739.4204 SITE IMPROVEMENT BOND QUANTITY WORKSHEET PROJECT INFORMATION CITY OF RENTON CITY OF RENTON 1 Select the current project status/phase from the following options: For Approval - Preliminary Data Enclosed, pending approval from the City; For Construction - Estimated Data Enclosed, Plans have been approved for contruction by the City; Project Closeout - Final Costs and Quantities Enclosed for Project Close-out Submittal Phone Engineer Stamp Required (all cost estimates must have original wet stamp and signature) Clearing and Grading Utility Providers N/A Project Location and Description Project Owner Information May Creek Trail Extension Renton, WA 98057 32240 59010, 32240 59109 City of Renton ##-###### Page 1 of 1 Ref 8-H Bond Quantity Worksheet SECTION I PROJECT INFORMATION Unit Prices Updated: 06/14/2016 Version: 04/26/2017 Printed 8/27/2018 CED Permit #:######## Unit Reference #Price Unit Quantity Cost Backfill & compaction-embankment ESC-1 6.50$ CY Check dams, 4" minus rock ESC-2 SWDM 5.4.6.3 80.00$ Each Catch Basin Protection ESC-3 35.50$ Each Crushed surfacing 1 1/4" minus ESC-4 WSDOT 9-03.9(3)95.00$ CY Ditching ESC-5 9.00$ CY Excavation-bulk ESC-6 2.00$ CY Fence, silt ESC-7 SWDM 5.4.3.1 1.50$ LF Fence, Temporary (NGPE)ESC-8 1.50$ LF Geotextile Fabric ESC-9 2.50$ SY Hay Bale Silt Trap ESC-10 0.50$ Each Hydroseeding ESC-11 SWDM 5.4.2.4 0.80$ SY Interceptor Swale / Dike ESC-12 1.00$ LF Jute Mesh ESC-13 SWDM 5.4.2.2 3.50$ SY Level Spreader ESC-14 1.75$ LF Mulch, by hand, straw, 3" deep ESC-15 SWDM 5.4.2.1 2.50$ SY Mulch, by machine, straw, 2" deep ESC-16 SWDM 5.4.2.1 2.00$ SY Piping, temporary, CPP, 6"ESC-17 12.00$ LF Piping, temporary, CPP, 8"ESC-18 14.00$ LF Piping, temporary, CPP, 12"ESC-19 18.00$ LF Plastic covering, 6mm thick, sandbagged ESC-20 SWDM 5.4.2.3 4.00$ SY Rip Rap, machine placed; slopes ESC-21 WSDOT 9-13.1(2)45.00$ CY Rock Construction Entrance, 50'x15'x1'ESC-22 SWDM 5.4.4.1 1,800.00$ Each Rock Construction Entrance, 100'x15'x1'ESC-23 SWDM 5.4.4.1 3,200.00$ Each Sediment pond riser assembly ESC-24 SWDM 5.4.5.2 2,200.00$ Each Sediment trap, 5' high berm ESC-25 SWDM 5.4.5.1 19.00$ LF Sed. trap, 5' high, riprapped spillway berm section ESC-26 SWDM 5.4.5.1 70.00$ LF Seeding, by hand ESC-27 SWDM 5.4.2.4 1.00$ SY Sodding, 1" deep, level ground ESC-28 SWDM 5.4.2.5 8.00$ SY Sodding, 1" deep, sloped ground ESC-29 SWDM 5.4.2.5 10.00$ SY TESC Supervisor ESC-30 110.00$ HR Water truck, dust control ESC-31 SWDM 5.4.7 140.00$ HR Unit Reference #Price Unit Quantity Cost EROSION/SEDIMENT SUBTOTAL: SALES TAX @ 10% EROSION/SEDIMENT TOTAL: (A) SITE IMPROVEMENT BOND QUANTITY WORKSHEET FOR EROSION & SEDIMENT CONTROL Description No. (A) WRITE-IN-ITEMS Page 1 of 1 Ref 8-H Bond Quantity Worksheet SECTION II.a EROSION_CONTROL Unit Prices Updated: 06/14/2016 Version: 04/26/2017 Printed 8/27/2018