Loading...
HomeMy WebLinkAbout203562.1 ■ RE '. iVED �04 ■ TACOMA S EATTLE O dcal Information Report PREPARED FOR : Renton School District 1220 North 4th Street Renton, WA 98055-1539 ff MVA LIM ff h PROJECT: Nelsen Middle School Access and Parking Reconfiguration 203562.10 PREPARED BY. Carol M. Hurst, P.E. Project Engineer REVIEWED BY: Douglas G. Tapp, P.E. Project Manager Doreen S. Gavin, P.E. Principal December 8, 2004 Civil Engineers Structural Engineers Landscape Architects Community Planners • Land Surveyors • Neighbors Technical Information Report PREPARED FOR : Renton School District 1220 North 4th Street Renton, WA 98055-1539 ti PROJECT.- '� r'�"" �` ` Nelsen Middle School Access and Parking Reconfiguration 203562.10 1 � �ts'►���` ���°° PREPARED BY. �z-7 u Carol M. Hurst P.E. �-7 ---— Project Engineer REVIEWED BY. I hereby state that this Technical Information Report for Nelsen Middle School has been prepared by me or under my supervision and Douglas G. Tapp, P.E. meets the standard of care and expertise that is Project Manager usual and customary in this community for professional engineers. I understand that the City of Renton does not and will not assume Doreen S. Gavin, P.E. liability for the sufficiency,suitability,or performances of drainage facilities prepared by Principal me. December 8th, 2004 TABLE OF CONTENTS SECTION PAGE 1.0 Project Overview....................................................................................................... 1 1.1 Purpose and Scope........................................................................................... 1 1.2 Existing Conditions............................................................................................ 1 1.3 Post-Development Conditions........................................................................... 1 2.0 Conditions and Requirements Summary.................................................................. 1 2.1 Core Requirements........................................................................................... 1 2.1.1 C.R. #1 - Discharge at the Natural Location....................................... 1 2.1.2 C.R. #2 - Off-site Analysis .............................................................. 2.1.3 C.R. #3 - Flow Control................................................................... 2 2.1.4 C.R. #4 - Conveyance System ........................................................ 2 2.1.5 C.R. #5 - Erosion and Sediment Control ........................................... 2 2.1.6 C.R. #6 - Maintenance and Operations............................................. 2 2.1.7 C.R. #7 - Financial Guarantees and Liability ...................................... 2 3.0 Off-site analysis ........................................................................................................ 2 4.0 Detention Analysis and Design................................................................................. 2 4.1 Existing Site Hydrology ..................................................................................... 2 4.2 Developed Site Hydrology................................................................................. 3 4.3 Flow Control System ......................................................................................... 3 4.4 Water Quality System........................................................................................ 3 5.0 Conveyance System Analysis and Design............................................................... 3 6.0 Special Reports And Studies.................................................................................... 3 7.0 TESC Analysis and Design....................................................................................... 3 8.0 Operations and Maintenance Plan ........................................................................... 4 9.0 Conclusion................................................................................................................ 4 APPENDICES Appendix A............ Existing Survey Appendix B............Sub-Basin Maps (Existing and Developed) Appendix C...........Storm Calculations and Analysis 1.0 PROJECT OVERVIEW 1.1 Purpose and Scope The site, which is currently used by the existing Nelsen Middle School, will have its access reconfigured to separate parent and bus drop off areas. This report describes the analysis and design of proposed stormwater facilities and demonstrates that the project is exempt from providing flow control BMPs in accordance with Section 1.2.3 of the 1990 KCSWDM. 1.2 Existing Conditions The project site currently has a one-way access from Jones Ave. for bus, parent and service vehicles, and a one-way exit to 27th Street. Some staff parking is located in the northeast corner with the main parking lot located west of the school building. Surrounding uses consist mainly of single-family residential. The site currently has a storm drainage system which discharges to the northwest. The site is located in the Rolling Hills Drainage basin. There is little to no off-site drainage tributary to the project site. There are no wetlands located on the site or adjacent to the site. 1.3 Post-Development Conditions The project proposes to widen the access on Jones Ave. to accommodate two-way traffic and an 8' sidewalk. This will become the bus and staff entrance. A bus drop loop will be created along the east side of the building by displacing some of the staff parking. A new staff parking lot will be constructed to replace the lost stalls. The access off of 271h will be widened to allow for two-way traffic and a 5' walking path. This will become the parent and service access. A raised concrete plaza will be constructed to separate the bus and parent drop areas. Asphalt and catch basin repair work will also be accomplished under this project. Improvements for this project increase the impervious area on-site, but meet criteria for the "Peak Flow Exemption;"therefore, runoff control is not required for the project. The project does, however, provide opportunities for water quality improvements. A bioswale will be used to provide treatment to runoff from the parent access road. 2.0 CONDITIONS AND REQUIREMENTS SUMMARY 2.1 Core Requirements 2.1.1 C.R. #1 - Discharge at the Natural Location The existing storm system discharges to the northwest of the site. This project will maintain the existing storm system. 1 a© 2.1.2 C.R. #2 - Off-site Analysis As no changes to the existing storm system are proposed no off-site analysis has been completed. 2.1.3 C.R. #3 - Flow Control As the increase in calculated peak flow from each "Threshold Discharge Area" during the 100-year storm is less than 0.5 cfs to each basin, the site is exempt from providing flow control per 1990 KCSWDM Section 1.2.3. A bioswale will be provided for water quality. 2.1.4 C.R. #4 - Conveyance System The new pipe systems will be designed to convey and contain the 25-year peak flow for the proposed development, per the 1990 KCSWDM, Section 4.3. In addition, the 100-year peak flow will be conveyed and contained within the proposed system. 2.1.5 C.R. #5 - Erosion and Sediment Control Erosion and sediment control will be provided by catch basin inserts and hydroseeding. Work under this project will be limited to the school's summer break between mid-June and late-August. 2.1.6 C.R. #6 - Maintenance and Operations The maintenance and operations will be the responsibility of the owner. 2.1.7 C.R. #7 - Financial Guarantees and Liability This project will provide for a Drainage Facilities Restoration and Site Stabilization Financial Guarantee. 3.0 OFF-SITE ANALYSIS 4.0 DETENTION ANALYSIS AND DESIGN 4.1 Existing Site Hydrology The existing developed site collects stormwater in a series of catch basins and pipes. Pervious Area Impervious Area Total Area 100-yr Peak Flow Existing 1.78 ac 2.16 ac 3.94 ac 3.01 cfs 2 ODOM 4.2 Developed Site Hydrology The developed site will maintain the existing storm system and runoff will continue to flow to the same Natural Discharge Locations. Pervious Area Impervious Area Total Area 100-yr Peak Flow Developed 1.50 ac 2.44 ac 3.94 ac 3.10 cfs Since the developed condition for the "Threshold Discharge Area" does not increase the 100-yr peak flow by 0.50 cfs, the project will be exempt from providing flow control. Therefore, no detention or retention facilities will be provided on-site. Runoff will be routed through the existing conveyance systems into the same Natural Discharge Locations. 4.3 Flow Control System In accordance with the 1990 KCSWDM, the project is exempt from the requirement to provide a formal flow control facility as the increase in the post developed 100-year storm is less than 0.5 cfs. 4.4 Water Quality System Stormwater runoff from the parent access road will be treated for water quality via a bioswale. In accordance with the 1990 KCSWDM, the bioswale will be designed to treat the 2-year peak flow rate from the tributary areas. See Appendix C for water quality calculations. 5.0 CONVEYANCE SYSTEM ANALYSIS AND DESIGN The existing on-site stormwater network consists of underground pipes, catch basins, and grass-lined conveyance ditches. Runoff will be tightlined to the existing system. Runoff from the parent access drive will be sheet flow the aforementioned bioswale. 6.0 SPECIAL REPORTS AND STUDIES 7.0 TESC ANALYSIS AND DESIGN The proposed development shall comply with guidelines set in the 1990 KCSWDM. The plan will include erosion/sedimentation control features designed to prevent sediment- laden runoff from leaving the site or adversely affecting critical water resources during construction. The erosion potential of the site is influenced by four major factors: soil characteristics, vegetative cover, topography, and climate. Erosion/sedimentation control is achieved by a combination of structural measures, cover measures, and construction practices that are tailored to fit the specific site. 3 101000 The following measures will be used to control sedimentation/erosion processes: • Clearing limits— only small areas require any site clearing or grading. • Cover measures - disturbed areas shall be covered as required in the 1990 KCSWDM. • Storm drain inlet protection -filter fabric protection will be provided on all new and existing catch basins downstream of construction activities. • Dust control - dust control measures will be implemented when exposed soils are dry to the point that wind transport is possible and roadways, drainage ways, or surface waters are likely to be impacted. 8.0 OPERATIONS AND MAINTENANCE PLAN Operations and maintenance will be the responsibility of the owner. All drainage facilities shall be maintained and operated in compliance with the City of Renton maintenance standards. 9.0 CONCLUSION This site has been designed to meet 1990 King County Surface Water Design Manual guidelines for stormwater management. The site incorporates water quality facilities for on-site generated stormwater flows. The biofiltration swale is designed to treat stormwater runoff from pollution-generating impervious surfaces. Flow calculations/modeling will utilize the King County standards for sizing stormwater conveyance networks and treatment facilities. This report demonstrates that the "Threshold Discharge Areas" are exempt from providing runoff control facilities for this redevelopment project. This analysis is based on data and records either supplied to, or obtained by, AHBL. These documents are referenced within the text of the analysis. The analysis has been prepared utilizing procedures and practices within the standard accepted practices of the industry. We conclude that this project, as proposed, will not create any new problems within the existing downstream drainage system. This project will not noticeably aggravate any existing downstream problems due to either water quality or quantity. AH1BL, Inc. Carol M. Hurst, P.E. Project Engineer CMH/lak December 2004 562T1 rep041207.doc 4 0©0 is APPENDIX A Existing Survey APPENDIX B Sub-Basin Maps (Existing and Developed) APPENDIX C Storm Calculations and Analysis Peak Flow (100-yr) Calculations pre Event Summary: BasinlD Peak Q Peak T Peak Vol Area Method Raintype Event (cfs) (hrs) (ac-ft) ac /Loss pre 3.01 8.00 1.0554 3.94 SBUH/SCS TYPEIA 100 yr Drainage Area: pre Hyd Method: SBUH Hyd Loss Method: SCS CN Number Peak Factor: 484.00 SCS Abs: 0.20 Storm Dur: 24.00 hrs Intv: 10.00 min Area CN TC Pervious 1.7800 ac 86.00 0.17 hrs Impervious 2.1600 ac 98.00 0.08 hrs Total 3.9400 ac Supporting Data: Pervious CN Data: None Entered 86.00 1.7800 ac Impervious CN Data: None Entered 98.00 2.1600 ac Pervious TC Data: Flow type: Description: Length: Slope: Coeff: Travel Time Fixed None Entered 0.00 ft 0.00% 10.0000 10.00 min Impervious TC Data: Flow type: Description: Length: Slope: Coeff: Travel Time Fixed None Entered 0.00 ft 0.00% 5.0000 5.00 min post Event Summary: BasinlD Peak Q Peak T Peak Vol Area Method Raintype Event (cfs) (hrs) (ac-ft) ac /Loss post 1.32 8.00 0.4669 3.94 SBUH/SCS TYPE1A 2 yr post 3.10 8.00 1.0838 3.94 SBUH/SCS TYPEIA 100 yr Drainage Area: post Hyd Method: SBUH Hyd Loss Method: SCS CN Number Peak Factor: 484.00 SCS Abs: 0.20 Storm Dur: 24.00 hrs Intv: 10.00 min Area CN TC Pervious 1.5000 ac 86.00 0.17 hrs Impervious 2.4400 ac 98.00 0.08 hrs Total 3.9400 ac Supporting Data: Pervious CN Data: None Entered 86.00 1.5000 ac Impervious CN Data: None Entered 98.00 2.4400 ac Pervious TC Data: Flow type: Description: Length: Slope: Coeff: Travel Time Fixed None Entered 0.00 ft 0.00% 10.0000 10.00 min Impervious TC Data: Flow type: Description: Length: Slope: Coeff: Travel Time Fixed None Entered 0.00 ft 0.00% 5.0000 5.00 min Water Quality Calculations and Design tmp#l.txt channel calculator Given Input Data: shape Trapezoidal solving for . . . . . . . . . . . . . . . . . . . . . Depth of Flow Flowrate . . . . . . . . . . . . . . . . . . . . . . . . 0.0948 cfs slope 0.0125 ft/ft Manning' s n . . . . . . . . . . . . . . . . . . . . . 0. 3500 Height . . . . . . . . . . . . . . . . . . . . . . 2.0000 ft Bottom width . . . . . . . . . . . . . . . . . . . . 2.2500 ft Left slope . . . . . . . . . . . . . . . . . . . . . . 3.0000 ft/ft (v/H) Right slope . . . . . . . . . . . . . . . . . . . . . 3.0000 ft/ft (v/H) computed Results: Depth . . . . . . . . . . . . . . . . . . . . . . . . . . 0.2451 ft velocity . . . . . . . . . . . . . . . . . . . . . . . . 0.1659 fps Full Flowrate . . . . . . . . . . . . . . . . . . . 2.5852 cfs Flow area . . . . . . . . . . . . . . . . . . . . . . . 0. 5715 ft2 Flow perimeter . . . . . . . . . . . . . . . . . . 2.7667 ft Hydraulic radius . . . . . . . . . . . . . . . . 0.2066 ft Top width . . . . . . . . . . . . . . . . . . . . . . . 2.4134 ft Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.8333 ft2 Perimeter . . . . . . . . . . . . . . . . . . . . 6.4664 ft Percent full . . . . . . . . . . . . . . . . . . . . 12.2553 critical Information critical depth . . . . . . . . . . . . . . . . . . 0.0380 ft critical slope . . . . . . . . . . . . . . . . . 5.4903 ft/ft critical velocity . . . . . . . . . . . . . . . 1.1026 fps critical area . . . . . . . . . . . . . . . . . . . 0.0860 ft2 critical perimeter . . . . . . . . . . . . . . 2.3301 ft critical hydraulic radius . . . . . . . 0.0369 ft critical top width . . . . . . . . . . . . . . 2.2753 ft specific energy . . . . . . . . . . . . . . . . . 0.2455 ft Minimum energy . . . . . . . . . . . . . . . . . . 0.0570 ft Froude number . . . . . . . . . . . . . . . . . . . 0.0601 Flow condition . . . . . . . . . . . . . . . . . . subcritical Page 1 i 10 Q AOVA � TACOMA SEATTLE www.ahbl.com 2215 North 30th She 316 Occidental Avenue South Suite 300 Suite 320 Tacoma,WA 98403-3350 Seattle,WA 98104-4421 253.383.2422 TEL 206.267.2425 TEL 253.3a3.2572 Fax 206.267.2429 FAx