The URL can be used to link to this page

Home My WebLink AboutSWP272255(9) Raymond Center West Surface Water Technical Information Report Prepared for: City of Renton, Washington Site Plan Approval Prepared by: KPFF Consulting Engineers ¢�o�WAsylticd 1201 Third Avenue, Suite 900 �� o Seattle, WA 98101 y A 24711 ' �� RFGia AL August August 1996 17.1VF, EXPtAES J L 9 1996 ' DEVELUI-Im-N{ PLANNING CITY OF RENTON Page 1 of 2 King County Building and Land Development Division TECHNICAL INFORMATION REPORT (TIR) WORKSHEET PART 1 PROJECT OWNER AND PART 2 PROJECT LOCATION PROJECT ENGINEER AND DESCRIPTION Project Owner Project Name Address F) l�r)! 'F4- -, !r NP =� ;! i I Location Phone - �= _ Township Range 4 Project Engineer 2, t i Section ' Company r r.: i I =I _ Project Size AC , Address Phone 2 Upstream Dra Wage Basin Size AC ' PART 3 TYPE OF • OTHER Subdivision ! DOF/G HPA Shoreline Management Short Subdivision !_^ COE 404 Rockery ' Grading DOE Dam Safety Structural Vaults j Commercial i7FEMA Floodplain Other Other c i_ COE Wetlands HPA PARTS SITE COMMUNITY AND DRAINAGE BASIN Community Drainage Basin r River Floodplain g Stream ; r ;r r Wetlands j Critical Stream Reach Seeps/Springs Depressions/Swales _ High Groundwater Table — Lake _ Groundwater Recharge - Steep Slopes _ Other Lakeside/Erosion Hazard 1 • Soil Type Slopes _ Erosion Potential Erosive Velocities T Additional Sheets Attatched — 1/90 Page 2 of 2 King County Building and Land Cevelopment Division TECHNICAL INFORMATION REPORT (TIR) WORKSHEET PART 8 DEVELOPMENT LIMITATIONS REFERENCE LIMITATION/SITE CONSTRAINT Ch.4-Downstream Analysis r i 1 r� I Additional Sheets Attatched PART 9 ESC REQUIREMENTS MINIMUM ESC REQUIREMENTS MINIMUM ESC REQUIREMENTS DURING CONSTRUCTION FOLLOWING CONSTRUCTION J Sedimentation Facilities Stabilize Exposed Surface Stabilized Construction Entrance Remove and Restore Temporary ESC Facilities Perimeter Runoff Control g Clean and Remove All Silt and Debris Clearing and Grading Restrictions Ensure Operation of Permanent Facilities Cover Practices _ Flag Limits of NGPES Construction Sequence Other Other PART 10 SURFACE WATER SYSTEM Grass Lined Channel Tank Infiltration Method of Analysis Pipe System i Vault Depression Open Channel Z Energy Dissapator i Flow Dispersal Compensation/Mitigaticn Dry Pond C Wetland Waiver of Eliminated Site Storage i Wet Pond Stream Regional Detention ' I Brief Description of System Operation Furl Al; f ^. , POND Z d/ Facility Related Site Limitations Additional Sheets Attatched Reference Facility Limitation PART 11 STRUCTURAL ANALYSIS (May requim special structural review) i �,. Drainage Easement Cast in Place Vault Other Access Easement Retaining Wall Native Growth Protection Easement Rockery>4'High Tract Structural on Steep Slope Other PART'14 SIGNATURE OF PROFESSIONAL ENGINEER I or a civil engineer under my supervision have visited the site. Actual site conditions as observed were incorporated into this worksheet and the ' attatchments. To the best of my knowledge the information provided here is accurate. SgnidOiri 1/90 ' TABLE OF CONTENTS ' Page No. SECTION I - PROJECT OVERVIEW Technical Information Report Worksheet Project Description 1 Existing Drainage System and Problems 1 Proposed Drainage System 1 ' Variances 1 SECTION II - PRELIMINARY CONDITIONS SUMMARY ' Core Requirements 2 Special Requirements 3 SECTION III - OFF-SITE ANALYSIS Upstream Analysis 5 Downstream Analysis 5 Mitigation 5 SECTION IV- RETENTION/DETENTION ANALYSIS AND DESIGN Existing Site Hydrology 6 Developed Site Hydrology 6 Water Quality Control 6 SECTION V-CONVEYANCE SYSTEM ANALYSIS AND DESIGN Off-Site Conveyance 7 SECTION VI - EROSION/SEDIMENTATION CONTROL DESIGN 8 APPENDICES Appendix A On-Site Conveyance Calculations Appendix B Detention Sizing Calculations Appendix C Springbrook Creek, HEC-2 Model Appendix D Floodplain Letter FIGURES Figure 1 Vicinity Map Figure 2 Existing Site Basin Map -> (These figures will be completed after ' Figure 3 Proposed Site Basin Map - the site plan review. See site plan review drawings for most current site layout.) ' Figure 4 Pond Section ' SECTION I ' PROJECT OVERVIEW Project Description ' The Technical Information Report (TIR) provides stormwater requirements and design details for the Raymond Center West project. The project is located in Renton, Washington. The site ' is situated in the SE 1/4, Section 24, Township 23, Range 4 in King County (see Figure 1). The site is bordered by the Group Health Facility to the north, the City of Seattle Cedar River Pipe Line #4 right-of-way to the south, Springbrook Creek to the east, and the Boeing ' Company to the west. A majority of the site is relatively flat, sloping down gently to the south and east. There is a moderately steep bank at the east end of the site which slopes down to Springbrook Creek. Existing Drainage System and Problems The existing drainage system consists of overland flow east to Springbrook Creek and south to the existing wetland. Proposed Drainage System The proposed drainage system will consist of pipes, catch basins and a combined wetpond/detention pond, with controlled discharge to Springbrook Creek. Variances and Exceptions No variances from the 1990 Surface Water Drainage Manual or from the Sensitive Areas Ordinance 9614, dated 1990, are needed. ' 1 i � 11 � z cn •p�c, i —+ m �To,�, N C (� m H PACIFIC A E S. J � �--i THOMAS AV W. 91 z B RAYMOND AVEW. C wh D 0 LIND AV . �O —T7 -A cn STATE SIGN ROUTE 167 SECTION 11 ' PRELIMINARY CONDITIONS SUMMARY The intent of this section is to address the core and special requirements set forth by the King ' County Surface Water Management Design Manual and the requirements of the most recent Sensitive Areas Ordinance (SAO) that pertain to the project. Each requirement will be listed with a brief statement explaining how the design addresses or conforms to the conditions. ' Core Requirements 1 .2.1 Discharge at the Natural Location Flow from the site currently flows to the east and discharges into Springbrook Creek, or south and discharges to the existing wetland. 1 .2.2 Off-site Analysis Runoff from the developed site is limited to at or below existing runoff rates and, therefore, will not negatively impact downstream conveyance. The City of Renton is currently analyzing existing and future flows in Springbrook Creek and has ' indicated a downstream analysis will not be required for this project. 1 .2.3 Runoff Control ' Runoff control is achieved by the construction of a detention facility that controls release rates. Runoff control has been designed to limit the developed condition peak runoff rates according to Washington State Department of Ecology (DOE) requirements. The release rates will be at or below the existing one-half the 2- year, the 10-year and the 100-year, 24-hour design storm events. This criteria exceeds King County requirements. I1 .2.4 Conveyance Facilities Closed pipe systems used to convey on-site runoff will be designed to carry the 25- ' year event flow and provide a minimum of 0.5 feet of freeboard between the hydraulic grade line and the top of the structure. 1 .2.5 Erosion/Sedimentation Control Plan Erosion control measures are outlined in Section IV. Special Requirements These "Special Requirements" are in addition to the seven core requirements and their ' requirements must be met when the "threshold" applies to this project. 1 .3.1 Critical Drainage Areas There are no critical basins within this project indicated on the Critical Drainage Area Maps. ' 2 ' 1 .3.2 Compliance with an Existing Master Drainage Plan ' There are no master drainage plans covering the project site. 1 .3.3 Conditions Requiring a Master Drainage Plan ' The project does not require a master drainage plan. ' 1 .3.4 Adopted basin plan or community plan. This project lies within the jurisdiction of the City of Renton. There is no adopted basin plan at this time. 1 .3.5 Special Water Quality Controls The project will increase impervious area subject to vehicular use by more than 5,000 sf; therefore, a wetpond or water quality swale is required. The current ' design proposal for the site will include a wetpond designed to Department of Ecology Standards. These standards will provide a facility that will double the King County volume requirements. This project will seek a code alteration modification to get credit for providing more wetpond volume than King County would require. This would alleviate the need for a biofiltration swale. 1 .3.6 Coalescing Plate Oil/Water Separators The project will not increase impervious area subject to vehicular use by 5 acres or more within the drainage basin. Therefore, no coalescing oil/water separators are required. 1 .3.7 Closed Depressions ' The project is not tributary to any closed depressions. 1 .3.8 Use of Lakes, Wetlands or Closed Depressions for Peak Runoff Control The project will not use a lake, wetland or closed depression for peak runoff control. ' 1 .3.9 Delineation of 100-Year Floodplain See Appendix "D." 1 .3.10 Flood Protection Facilities for Class 1 and 2 Streams There are no existing or proposed flood protection facilities for Class 1 or 2 streams within the project. ' 1 .3.1 1 Geotechnical Analysis and Report A geotechnical analysis was completed for this project. See Geotechnical Engineering Study, dated August 19, 1996, prepared by Earth Consultants. 1 .3.12 Soils Analysis and Report Soils in the area were described in the Geotechnical Engineering Study, but were not classified per SCS Classification. See the complete Geotechnical Engineering Study. 3 SECTION 111 OFF-SITE ANALYSIS This section identifies the tributary basin areas upstream of the project site, and evaluates ' upstream and downstream drainage system problems. The intent of this section is to demonstrate the proposed project will neither aggravate existing problems or create new drainage problems. ' Upstream Analysis ' Minor flow is discharged to the on-site wetlands from the Longacres training track located west of the site. The flow is discharged to Springbrook Creek through an existing 36-inch culvert. This drainage will be maintained as the development will not encroach on the wetland. ' Downstream Analysis The downstream drainage system consists of Springbrook Creek. The City of Renton is ' currently analyzing existing and future flows in Springbrook Creek and has indicated a downstream analysis will not be required for this project. Springbrook Creek has been modeled with a HEC-2 analysis. A recent update of this analysis, that includes modifications for this project, is included in the appendix. Mitigation tOn-Site Mitigation Mitigation to offset the increased runoff from the building and paved parking area will be accomplished by a detention facility. Runoff will be released at or below the existing one- half the 2-year, 10- and 100-year flow rates. ' An additional mitigation measure incudes the incorporation of a wetpond facility with the detention facility. 4 SECTION IV ' RETENTION/DETENTION ANALYSIS AND DESIGN Existing Site Hydrology The existing site hydrology includes currently undeveloped land sloping from the northwest corner of the site east to Springbrook Creek and south to the existing wetland. ' Developed Site Hydrology ' The developed site hydrology includes the construction of a paved parking area for a 124,300- square foot building. The roof area is 2.85 acres and the paved area subject to vehicular use is 3.4 acres. The total impervious area is 6.25 acres. The new drainage system will collect ' surface runoff in catch basins and convey the water via a pipe system to a 2-cell water quality/detention pond. The facility will discharge controlled flows to Springbrook Creek. Water Quality Control ' Water quality control will be provided by a wetpond. It is located in the same facility as the detention pond. Water quality will be achieved by providing 26,300 cubic feet of inactive (dead) runoff storage underneath 50,800 cubic feet of detention pond storage. Figure 4 is a cross-section of the facility. Due to the volume provided by the water quality pond (double the King County requirements), the project will seek a code alteration modification to excuse the bioswale requirements. ' 5 T` 9"Ot no. Drof.ct ND C • Consulting Engineers wcmwn aat. 1201 Third Avenue, Suite 900 IM no. Seattle, Washington 98101 cll.nt (206)622-5822 Fax(206)622-8130 c I&U R E f d-' ►n 2 a wo LL u 0 0 d In O I n, I 2 d co �sr 0 r 1� ' SECTION V ' CONVEYANCE SYSTEM ANALYSIS AND DESIGN In accordance with King County Core Requirement #4, pipe systems and culverts will be designed to convey and contain at least the peak runoff rate for the 25-year design storm. Off-Site Conveyance ' There is no off-site conveyance. ' On-Site Conveyance The on-site conveyance system will be designed to convey the peak flow for the 25-year event. ' As recommended in the King County Surface Water Manual, the Rational Method will be used to calculate on-site peak flow rates. Peak flows developed for impervious surface using the Rational Formula, with times of concentration less than 30 minutes, are more conservative than those using the SBUH Method because that method uses rainfall information developed on hourly averages. ' 6 SECTION VI EROSION/SEDIMENTATION CONTROL DESIGN Erosion control measures will include silt fences, straw check dams, catch basin inlet ' protection and ground cover practices. Silt fences will be placed at the downstream edges of all disturbed areas. The plans will include details and notes for the use and maintenance of straw check dams, catch basin protection and ground cover practices. v J �LO co O W Q ' APPENDIX A ON-SITE CONVEYANCE CALCULATIONS (WILL BE COMPLETED AFTER SITE PLAN REVIEW) 9 ' APPENDIX B DETENTION SIZING CALCULATIONS ' 10 8/16/96 2 : 12 : 5 pm KPFF Inc. page 1 ' Site Plan Review RAYMOND WEST --------------------------------------------------------------------- --------------------------------------------------------------------- BASIN SUMMARY ' BASIN ID: Al - NAME: 2 YEAR EXISTING SCS METHODOLOGY TOTAL AREA. . . . . . . . 6 .80 Acres BASEFLOWS : 0 . 00 cfs RAINFALL TYPE. . . . : KC24HR PERV IMP ' PRECIPITATION. . . . : 2 .00 inches AREA. . : 6 .80 Acres 0 . 00 Acres TIME INTERVAL. . . . : 10 .00 min CN. . . . : 84 .00 98 . 00 TC. . . . : 76 . 13 min 0.00 min ' ABSTRACTION COEFF: 0 . 20 TcReach - Sheet L: 300.00 ns:0. 2200 p2yr: 2 .00 s:0 .0050 TcReach - Shallow L: 250 . 00 ks: 9 . 00 s:0 . 0070 ' PEAK RATE: 0 . 62 cfs VOL: 0 . 41 Ac-ft TIME: 510 min BASIN ID: A2 NAME: 10 YEAR EXISTING SCS METHODOLOGY TOTAL AREA. . . . . . . : 6 .80 Acres BASEFLOWS : 0 . 00 cfs RAINFALL TYPE. . . . : KC24HR PERV IMP PRECIPITATION. . . . : 2 . 90 inches AREA. . : 6. 80 Acres 0 . 00 Acres TIME INTERVAL. . . . : 10. 00 min CN. . . . : 84 . 00 98 . 00 TC. . . . : 76. 13 min 0 . 00 min ABSTRACTION COEFF: 0 . 20 ' TcReach - Sheet L: 300 .00 ns:0 .2200 p2yr: 2 . 00 s:0.0050 TcReach - Shallow L: 250.00 ks: 9 . 00 s : 0. 0070 PEAK RATE: 1 . 40 cfs VOL: 0 . 79 Ac-ft TIME: 510 min ' BASIN ID: A3 NAME: 100 YEAR EXISTING SCS METHODOLOGY TOTAL AREA. . . . . . . : 6 . 80 Acres BASEFLOWS : 0 . 00 cfs ' RAINFALL TYPE. . . . : KC24HR PERV IMP PRECIPITATION. . . . : 3. 90 inches AREA. . : 6 . 80 Acres 0 . 00 Acres TIME INTERVAL. . . . : 10.00 min CN. . . . : 84 . 00 98. 00 - TC. . . . : 76. 13 min 0 . 00 min ABSTRACTION COEFF: 0 . 20 TcReach Sheet L: 300.00 ns: 0 .2200 p2yr. 2 .00 s: 0 .0050 TcReach - Shallow L: 250.00 ks: 9 .00 s: 0 . 0070 ' PEAK RATE: 2 . 37 cfs VOL: 1 .26 Ac-ft TIME: 510 min BASIN ID: A4 NAME: 2 YEAR DEVELOPED ' SCS METHODOLOGY TOTAL AREA. . . . . • 6 .80 Acres BASEFLOWS : 0 . 00 cfs RAINFALL TYPE. . . . : KC24HR PERV IMP PRECIPITATION. . . . : 2 .00 inches AREA. . : 0 . 55 Acres 6 . 25 Acres ' TIME INTERVAL. . . . : 10.00 min CN. . . . : 88 .00 98 . 00 TC. . . . : 5.95 min 8 .29 min ABSTRACTION COEFF: 0 . 20 TcReach - Sheet L: 20. 00 ns:0. 1500 p2yr: 2 .00 s:0 .0050 impTcReach - Sheet L: 200. 00 ns : 0 . 0110 p2yr: 2 . 00 s:0 . 0050 impTcReach - Channel L: 650 .00 kc:42 . 00 s: 0 .0050 PEAK RATE: 3 . 83 cfs VOL: 0 . 95 Ac-ft TIME: 470 min ' 8/16/96 2 : 12 :5 pm KPFF Inc. page 2 RAYMOND WEST Site Plan Review BASIN SUMMARY BASIN ID: A5 NAME: 10 YEAR DEVELOPED SCS METHODOLOGY TOTAL AREA. . . . . . . : 6 . 80 Acres BASEFLOWS: 0 .00 cfs RAINFALL TYPE. . . • KC24HR PERV IMP PRECIPITATION. . . . . 2.90 inches AREA. . . 0 .55 Acres 6 .25 Acres TIME INTERVAL. . . . : 10.00 min CN. . . . : 88.00 98 .00 r ABSTRACTION COEFF: 0 . 20 TC. . . . : 5 .95 min 8.29 min TcReach - Sheet L: 20 .00 ns: 0 . 1500 p2yr: 2.00 s:0.0050 impTcReach - Sheet L: 200 .00 ns: 0 . 0110 p2yr: 2 .00 s: 0.0050 impTcReach - Channel L: 650 .00 kc:42 .00 s:0.0050 PEAK RATE: 5 . 75 cfs VOL: 1 . 44 Ac-ft TIME: 470 min ' BASIN ID: A6 NAME: 100 YEAR DEVELOPED SCS METHODOLOGY TOTAL AREA. . . . . . . : 6 .80 Acres BASEFLOWS : 0 .00 cfs RAINFALL TYPE. . . . : KC24HR PERV IMP PRECIPITATION. . . . : 3 . 90 inches AREA. . : 0 .55 Acres 6 .25 Acres TIME INTERVAL. . . . : 10 . 00 min CN. . . . : 88. 00 98 . 00 TC. . . . . 5 . 95 min 8 .29 min ABSTRACTION COEFF: 0 . 20 TcReach - Sheet L: 20 .00 ns:0 . 1500 p2yr: 2.00 s:0 .0050 impTcReach - Sheet L: 200 .00 ns : 0 . 0110 p2yr: 2 . 00 s:0 .0050 ' impTcReach - Channel L: 650 . 00 kc: 42 . 00 s:0 . 0050 PEAK RATE: 7.88 cfs VOL: 1 . 99 Ac-ft TIME: 470 min r BASIN ID: A7 NAME: 6-MONTH DEVELOPED SCS METHODOLOGY TOTAL AREA. . . . . . . : 3 . 95 Acres BASEFLOWS : 0.00 cfs r RAINFALL TYPE. . . . : KC24HR PERV IMP PRECIPITATION. . . . : 1 . 32 inches AREA. . : 0. 55 Acres 3.40 Acres TIME INTERVAL. . . . : 10.00 min CN. . . . : 88 . 00 98 . 00 TC. . . . . 8.29 min 0 . 00 min ABSTRACTION COEFF: 0 . 20 TcReach - Sheet L: 200.00 ns: 0 .0110 p2yr: 2 .00 s:0.0050 TcReach - Channel L: 650 . 00 kc: 42 . 00 s:0. 0050 ' PEAK RATE: 0. 06 cfs VOL: 0.02 Ac-ft TIME: 470 min 1 1 1 r 1 8/16/96 2: 12:5 pm KPFF Inc. page 3 RAYMOND WEST Site Plan Review HYDROGRAPH SUMMARY PEAK TIME VOLUME ' HYD RUNOFF OF OF Contrib NUM RATE PEAK HYDRO Area cfs min. cf\AcFt Acres 1 0 . 621 510 17811 cf 6. 80 2 1 . 397 510 34402 cf 6. 80 3 2 . 372 510 54813 cf 6 .80 4 3.826 470 41241 cf 6 .80 5 5 . 750 470 62580 cf 6 . 80 6 7.880 470 86469 cf 6.80 ' 7 0 . 062 470 885 cf 0. 55 11 0. 301 1440 38770 cf 6. 80 12 0. 856 660 58129 cf 6. 80 1 13 2 . 365 510 81923 cf 6. 80 8/16/96 2 : 17:27 pm KPFF Inc. page 1 RAYMOND WEST Site Plan Review --------------------------------------------------------------------- STAGE STORAGE TABLE CUSTOM STORAGE ID No. 31 Description: Detention Area (w/o F.S. ) STAGE <----STORAGE----> STAGE <----STORAGE----> STAGE <----STORAGE----> STAGE <----STORAGE----> ' (ft)-==_cfAc-Ft- - _(ft)----cf=-_ __Ac-Ft=- --(ft) ---cf=-=-_=Ac-Ft_----(ft)----cf--- ==Ac-Ft- -- 13.00 0.0000 0.0000 14.10 8200 0.1883 15.20 17032 0.3910 16.30 28160 0.6465 13.10 634,90 0.0146 14.20 8957 0.2056 15.30 18044 0.4142 16.40 29171 0.6697 ' 13.20 1391 0.0319 14.30 9714 0.2230 15.40 19056 0.4375 16.50 30183 0.6929 13.30 2148 0,0493 14.40 10470 0.2404 15.50 20067 0.4607 16.60 31194 0.7161 13.40 2905 0.0667 14.50 11227 0.2577 15.60 21079 0.4839 16.70 32206 0.7393 ' 13.50 3661 0.0840 14.60 11983 0.2751 15.70 22090 0.5071 16.80 33217 0.7626 13.60 4418 0.1014 14.70 12740 0.2925 15.80 23102 0.5303 16.90 34229 0.7858 13.70 5174 0.1188 14.80 13496 0.3098 15.90 24113 0.5536 17,00 35240 0.8090 ' 13.80 5931 0.1362 14.90 14253 0.3272 16.00 25125 0.5768 13.90 6687 0.1535 15.00 15009 0.3446 16.10 26136 0.6000 14.00 7444 0.1709 15.10 16021 0.3678 16.20 27148 0.6232 8/16/96 2: 17:27 pm KPFF Inc. page 2 RAYMOND WEST Site Plan Review STAGE DISCHARGE TABLE MULTIPLE ORIFICE ID No. 40 Description: OUTLET STRUCTURE Outlet Elev: 13 . 00 ' Elev: 13.00 ft Orifice Diameter: 2 . 6000 in. STAGE <--DISCHARGE---> STAGE <--DISCHARGE---> STAGE <--DISCHARGE---> STAGE <--DISCHARGE---> (ft) ---cfs-- ------- (ft) ---cfs-- ------- (ft) ---cfs-- ------- (ft) ---cfs-- ------- -------------------------------------------------------------------------------------------------------- -------------------------------------------------------------------------------------------------------- 13.00 0.0000 14.10 0.1924 15.20 0.2721 16.30 0.3332 13.10 0.0580 14.20 0.2010 15.30 0.2782 16.40 0.3383 13.20 0.0820 14.30 0.2092 15.40 0.2842 16.50 0.3432 13.30 0.1005 14.40 0.2171 15.50 0.2901 16.60 0.3481 13.40 0.1160 14.50 0.2247 15.60 0.2958 16.70 0.3529 13.50 0.1297 14.60 0.2320 15.70 0.3014 16.80 0.3576 13.60 0.1421 14.70 0.2392 15.80 0.3070 16.90 0.3623 13.70 0.1535 14.60 0.2461 15.90 0.3124 17.00 0.3669 13.80 0.1641 14.90 0.2529 16.00 0.3177 13.90 0.1740 15.00 0.2594 16.10 0.3230 14.00 0.1834 15.10 0.2658 16.20 0.3282 8/16/96 2: 17: 27 pm KPFF Inc. page 3 RAYMOND WEST ' Site_Plan-Review _____________________________________________________ STAGE DISCHARGE TABLE RISER DISCHARGE ID No. 41 Description: OVERFLOW WEIR Riser Diameter (in) : 12 .00 elev: 16 . 15 ft Weir Coefficient. . . : 9 . 739 height: 17. 00 ft Orif Coefficient. . . : 3 . 782 increm: 0. 10 ft STAGE <--DISCHARGE---> STAGE <--DISCHARGE---> STAGE <--DISCHARGE---> STAGE <--DISCHARGE---> ' (ft) ---cfs-- ------- (ft) ---cfs-- ------- (ft) ---cfs-- ------- (ft) ---cfs-- ------- 16.15 0.0000 16.40 1.2174 16.70 2.8048 17.00 3.4868 ' 16.20 0.1089 16.50 2.0166 16.80 3.0491 16.30 0.5658 16.60 2.5370 16.90 3.2753 1 i i t i 1 1 1 8/16/96 2 : 17:27 pm KPFF Inc. page 4 RAYMOND WEST ' Site Plan Review STAGE DISCHARGE TABLE COMBINATION DISCHARGE ID No. 45 Description: 1-ORIFICE W/riser Structure: 40 Structure: Structure: 41 Structure: Structure: STAGE <--DISCHARGE---> STAGE <--DISCHARGE---> STAGE <--DISCHARGE---> STAGE <--DISCHARGE---> (ft) ---cfs-- ------- (ft) ---cfs-- ------- (ft) ---cfs-- ------- (ft) ---cfs-- ------- 13.00 0.0000 14.10 0.1924 15.20 0.2721 16.30 0.8990 13.10 0.0580 14.20 0.2010 15.30 0.2782 16.40 1.5556 13.20 0.0820 14.30 0.2092 15.40 0.2842 16.50 2.3598 13.30 0.1005 14.40 0.2171 15.50 0.2901 16.60 2.8851 13.40 0.1160 14.50 0.2247 15.60 0.2958 16.70 3.1577 ' 13.50 0.1297 14.60 0.2320 15.70 0.3014 16.80 3.4067 13.60 0.1421 14.70 0.2392 15.80 0.3070 16.90 3.6376 13.70 0.1535 14.80 0.2461 15.90 0.3124 17.00 3.8537 ' 13.80 0.1641 14.90 0.2529 16.00 0.3177 13.90 0.1740 15.00 0.2594 16.10 0.3230 14.00 0.1834 15.10 0.2658 16.20 0.4370 r r r 8/16/96 2: 12 : 8 pm KPFF Inc. page 6 RAYMOND WEST Site Plan Review LEVEL POOL TABLE SUMMARY ?MATCH INFLOW -STO- -DIS- <-PEAK-> STORAGE <--------DESCRIPTION---------> (cfs) (cfs) --id- --id- <-STAGE> A VOL (cf) ----------------------------------------------------------------------------- ----------------------------------------------------------------------------- ' 2 YEAR ....................... 0.31 3.83 31 45 15.70 11 22058.83 cf 10 YEAR ..................... 1.40 5.75 31 45 16.29 12 28064.53 cf 100 YEAR ..................... 2.37 7.88 31 45 16.50 13 30192.11 cf 1 1 C4EC u 4YD Wr MPN rSure fov,* f02 ' DV_rCL0W RAX 9VA10'i RarE. 1 t 1 r r r r r 1 r r 1 STORMWATER MANAGEMENT MANUAL FOR THE PUGET SOUND BASIN ' FIGURE III-1.1 Volume Correction Factor to be Applied to Streambank Erosion Control BMPs ' Based on Site Impervious Cover 1 so 45 1 40 � I 1 Q 3s G Q ' LL 30 ' O r U W 25 r Q cc 1 v 20 i i 15 10 1 0 20 40 60 80 �j100 SITE �,VEPVV ICUS COVER [%-, 96/ i 1 ia R Q Ec Tool/ AA- LY0,2, /% y REC�v//I EO ✓oe- 571v ,E 1 ✓pLv/h� / 2ov/,pE� �Q, (gbo G� 1 III-1-3 FEBRUARY, 1992 t APPENDIX C ' SPRINGBROOK CREEK, HEC-2 MODEL 1 1 1 1 1 northwest hydraulic consultants inc. tsacramento - 16300 Christensen road,suite 350 vancouver tukwila,washington 98188-3418 r,U j 1`I - ' (206)241- edmonton 0-phone (206)439-2422420-fax seattle ' y August 20, 1996 b W ' KPFF Consulting Engineers — Attn: Mr. Tom Jones 1201 Third Avenue, Suite 900 Seattle, WA 98101 ' RE: HEC-2 modeling of proposed Springbrook Creek road crossing for Winmar project. Dear Mr. Jones: ' Northwest Hydraulic Consultants (NHC) has completed its hydraulic impact analysis of the proposed road crossing over Springbrook Creek for the Winmar development. You had retained us to determine, using the HEC-2 backwater model program, the potential water level increases due to constructing a bridge over Springbrook Creek. The proposed bridge site is in south Renton, Washington,just upstream of SW 19th Street (extended). We are pleased to summarize herein our analysis and present our results. ' Baseline Modeling (no bridge) Using an existing HEC-2 model developed by NHC for the City of Renton, we ran the following ' baseline scenarios: • Existing channel topography, future land-use 100-yr discharge, and no Winmar bridge crossing; • Alternative 2 channel improvement proposed under the East Side Green River Watershed Project (ESGRWP), future land-use 100-yr discharge, and no Winmar bridge crossing. The proposed channel widening improvements under the ESGRWP extend from SW 16th Street ' to about SW 23rd Street, which includes the reach through the Winmar project. The existing condition HEC-2 model had already been modified by HNTB Corporation to reflect the Alternative 2 channel improvements. We utilized their baseline model to simulate this condition. The discharges used for the respective baseline model runs were taken from Table 1 of a letter ' dated February 2, 1996, from Scott Woodbury of the City of Renton to Tim Puryear of the Winmar Company. The following table presents these flows, extending from the Black River ' Pump Station (BRPS) upstream through the channel improvement reach (to SW 23rd). These ' RIVER ENGINEERING HYDRAULIC MODEL TESTING / HYDRAULIC ANALYSIS AND DESIGN COASTAL ENGINEERING HYDROLOGY / SEDIMENTATION ENGINEERING NUMERICAL MODELING / APPLIED RESEARCH FORENSIC ENGINEERING ' Tom Jones 2 August 20, 1996 ' flows represent the ESGRWP conveyance event, which assumes no pumping restrictions at the BRPS. The table also compares water surface elevations from the ESGRWP (using the FEQ ' unsteady model) to the water surface elevations we computed with the baseline HEC-2 models described above. The HEC-2 model results are shown to compare reasonably well to the FEQ results from the ESGRWP. ' Existing channel, future 100-yr Alt. 2 channel, future 100-yr flow: flow: ESGRWP HEC-2 ESGRWP HEC-2 Location/ Flow water water Flow water water description (cfs) level (ft) level (ft) (cfs) level (ft) level (ft) ' BRPS inflow 1223 4.7 4.7 1747 5.4 5.4 Grady Way u/s 1110 7.6 T6 1498 8.8 8.7 ' SW 16th u/s 1106 8.2 8.0 1488 9.1 9.1 SW 19th extend 1088 11.6 11.9 1441 11.0 10.5 ' SW 23rd extend 989 12.6 13.3 1344 11.9 11.7 ' The existing HEC-2 model, as well as the ESGRWP, reference elevations to the NGVD 1929 datum. Therefore, all results herein (including the above table) are referenced to this datum. To convert to the NAVD 1988 datum, one should add 3.57 feet to these elevations. With-bridge Modeling The baseline HEC-2 models were modified to reflect the proposed bridge crossing over Springbrook Creek, resulting in the following baseline scenarios: ' Existing channel topography, future land-use 100-yr discharge, and Winmar bridge alternative 4 (from KPFF); ' Alternative 2 channel improvement proposed under the East Side Green River Watershed Project, future land-use 100-yr discharge, and Winmar bridge alternative 4. The respective "with-bridge" models were run using the same discharges as used for the baseline conditions (see above table). Winmar bridge alternative 4a consists of a clear-span bridge, 72 ft long between abutments and 37 ft wide. The proposed bridge deck is 3 ft above the approximate water surface of the 100-yr ' storage event (assumes BRPS pumping restrictions), as per City of Renton clearance tnorthwest hydraulic consultants inc. ' Tom Jones 3 August 20, 1996 requirements. For the 100-yr conveyance event, the abutments of the proposed structure may encroach somewhat into the channel. Please find attached a cross-section plot from the HEC-2 ' model, showing the Winmar bridge crossing over the proposed ESGRWP alternative 2 flood control channel. ' Results For each of the respective channel conditions (existing and ESGRWP improvement), the ' baseline results were compared to the results with the proposed Winmar bridge. We also investigated the potential further impacts due to shortening the bridge span by 6, 12, and 18 ft (i.e. moving the abutments in towards the channel). The following table summarizes the impacts due to the bridge, in terms of upstream water level increases (given in feet). ' Existing channel, future 100-yr Alt. 2 channel, future 100-yr flow: flow: Bridge alternative Just u/s of At u/s Winmar Just u/s of At u/s Winmar (span length) proposed bridge property line proposed bridge property line Bridge 4a (72 ft) 0.01 0.00 0.01 0.01 ' Bridge 4b (66 ft) 0.02 0.01 0.03 0.02 ' Bridge 4c (60 ft) 0.03 0.02 0.05 0.04 Bridge 4d (54 ft) 0.03 0.03 0.09 0.06 The results show that the primary bridge design (bridge alternative 4a) will have minimal impact ' on Springbrook Creek 100-yr conveyance event water levels. The computed results from HEC-2 indicate the water surface elevation just upstream of the bridge would increase from 12.26 ft to 12.27 ft (NGVD 1929), given the existing channel. At the upstream property line, there is no ' impact shown. For the proposed ESGRWP alternative 2 channel widening, the abutments cause a minor increase in water level, from 10.74 ft to 10.75 ft at the bridge. Shorter bridge lengths (bridges 4b through 4d) result in measurable, although still small, increases in water level. Conclusions ' The analysis described herein indicates the proposed Winmar bridge design (alternative 4a) would have negligible hydraulic impact on water levels in Springbrook Creek, given both the existing channel and the ESGRWP improved channel geometry. Furthermore, the proposed clear-span bridge design calls for no piers; therefore local pier scour does not need to be investigated. ' northwest hydraulic consultants inc. ' Tom Jones 4 August 20, 1996 The input and output files for the HEC-2 models are included on the enclosed diskette. Please call me should you have any questions. I look forward to working with you again soon. ' Yours very truly, ' NORTHWEST HYDRAULIC CONSULTANTS z� Ed�� ' Robert C. Elliot, P.E. northwest hydraulic consultants inc. Springbrook Futr Brdge4a Cross —section 7755 . 000 30 rn N 25 > z Bridge Deck + 20 v ------------------------------- C Q �i� '� i� ------- I W I I � j I W ' I � 10 I , I I 10.75 5 Proposed ESGRWP Channel 0 400 420 440 460 480 500 520 540 560 Distance (feet) APPENDIX D t FLOODPLA/N LETTER 1 1 1 1 1 1 1 1 ' 1z neer3 August 23, 1996 Mr. Gregg Zimmerman, P.E. Administrator City of Renton 200 Mill Avenue S. Renton, WA 98055 Subject: Raymond Center West Compensatory Storage Dear Mr. Zimmerman: The Raymond Center West project involves the construction of a 124,300-square foot building, with surface parking on a site adjacent to Springbrook Creek. The site will be filled to elevate the finished floor 1 foot or more above the FEMA 100-year flood elevation. Through discussions with Scott Woodbury, we understand the City has performed extensive hydraulic modeling of Springbrook Creek to estimate peak flows and water surface elevations ' during extreme rainfall events. This modeling projects a 100-year flood elevation at our site of 16.9, which is 2.7 feet lower than the FEMA elevation of 19.6 (NAVD 88). We understand the City's model results have compared favorably with field observations and that a FEMA ' letter of map revision will soon be applied for by the City. Based on the above, we request an administrative revision that allows this project to use the ' 100-year storage elevation generated by the City's model for determining the volume of compensatory storage required. We appreciate your consideration of the above. ' Sincerely, Tom Jones ' Project Engineer MAV:cjs t cc: Mark Miller, Mark Miller Consultants Mark Veldee, KPFF ' 65700 _22_,a_ Seattle Portland San Francisco Los Angeles Phoenix San Diego Cairo