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02944 - Technical Information Report - Drainage
SURFACE WATER DRAIt�AGE REPORT AND ANALYSIS FOR - , , � .Sc�//� Z7_ JIM'S AUTOMOTIVE Z� `�� Renton, Washington �,.��r�����-:��� � R��� ���,�R�'� JUL 0 9 2001 BUILDING DI'JlSION p.•'�H ESF �j oF wAsy � �� � ' ��d,Iol �_; 2 �%r 26606 �'o R�c,s�EO � ���� S�ONAL� EXPIRES 3�'2� OI � Job No.: 01-019 SEGA Engineers� Struct ral & Civil Consulting Engineers 22928 SE 312m ST (360)886-1017 Black Diamond,WA 98010 Copyright 2001,SEGA Engineers 21�l�� SUMMARY OF DRAINAGE ANALYSIS FOR � JIM'S AUTOMOTIVE SECTION 19, TOWNSHIP 23 NORTH, RANGE 5 EAST, W.M. RENTON, WASHINGTON May 31, 2001 Introduction This portion of the analysis is included to give a brief overview of the project and a description of the existing storm drainage system on and off the site. For this analysis one site visit was made to note the condition of the existing drainage system. Field observations were completed on May 31, 2001. The proposed project involves the construction of a new retail building, revised parking facilities, and roadside improvements. Existing site topographic maps, U.S.G.S. maps, City of Renton Storm Drainage maps, and a field investigation were used to determine the existing drainage configuration. Proposed Site The project is located on the south side of Southwest 12�' Street midway between Seneca Avenue SW and Lind Avenue SW, in Renton, Washington (see attached vicinity map). The site is approximately 0.33 acres and is currently developed with existing asphalt parking used for automobile storage. A new retail building with a floor area of about 1,750 square feet will be located at the east central portion of the site adjacent to the existing parking area. The existing residence on the east side of the site has been previously demolished and removed. Approximately 700 sf of asphalt parking will be removed for the new building and modified entrance and about 690 sf of paved parking will be constructed on the north and south side of the new building. Existing Drainage Conditions Surface runoff from the existing paved area is conveyed to a storm drain system beginning on the west side of the parking area. Surface runoff from the parking lot is � � Jirri s Automotive. Drainage Analysis. collected in a catch basin and conveyed via 8" ADS pipe to a catch basin on the south side of SW 12th Street. Flows are then conveyed to the north side of SW 12�' Street and west to Seneca Avenue SW. Conveyance continues in the public system west to Raymond Avenue SW and then north to SW Grady Way. Method of Analysis Drainage calculations were performed using methods described in Chapter 3 -- Hydrologic Analysis, of the King County SurFace Water Drainage Manual. Peak runoff rates for the pre-developed and post developed conditions were calculated using the Santa Barbara Urban Hydrograph Method. The Water Works design program by Engenious Systems was used to develop peak runoff rates for the various hydrographs. DRAINAGE DESIGN CRITERIA The calculations for analyzing the surface water discharge are based on the following criteria: Design Storm Rainfall: 2 yr, 24 hour = 2.00 in. 10 yr, 24 hour = 2.90 in. 100 yr, 24 hour = 3.90 in Existing Conditions: Pervious area = 0.197 Acres Impervious area = 0.137 Acres SCS Curve Number: Pervious C�: 81 (Existing Conditions) If11pe1vlOUS C�: 98 Proposed Conditions: Pervious area = 0.193 Acres Impervious area = 0.142 Acres SCS Curve Number: Pervious C�: 90 (Developed Conditions) Impetvious C�: 98 Soil Type: Puget Silty Clay Loam (Pu) SCS Group D . .; 2 • , Juri s Automotive. Drainage Analysis. King County Drainage Manual -- Core Requirements Core Requirement# 1. Discharge at the Natural Location: The proposed development will in no way divert nor change the natural drainage flow of the property and the discharge of all site drainage will continue to be at its natural location. Downstream drainage continues as sheet flow across the site to the north and enters the public conveyance system. Core Requirement#2. Off Site Analysis: A Level 1 analysis was conducted. We visited the site and found no signs of erosion or other drainage problems at or around the proposed areas of construction. There was no evidence of past flooding or slides. The Level 1 analysis indicated that the downstream conveyance system appeared adequate and no drainage problems are predicted after development. Core Requirement#3. Runoff Control: The proposed project site post-developed peak runoff rate for the 100-year, 24- hour duration design storm event is calculated to be less than 0.5 cfs more than the pre-developed peak runoff rate for the site. This is conside�ed to be a negligible peak runoff rate increase. Therefore, on-site peak rate runoff control will not be required for the proposed project. Core Requirement#4. Conveyance System: The existing on-site conveyance system which consist of a parking lot catch basin and underground storm sewer will carry flows to the public conveyance system. A roof collection system will be added and connected to the existing catch basin. Core Requirement#5. Erosion £�Sedimentation Contrvl Plan: Standard erosion/sedimentation control measures should be adequate since the area to be developed is relatively small and has minimal slope. We recommend catch basin filters at two locations and these are shown on the design drawings. We have also provided information on mulching and erosion control seeding and plantings. We also recommend mulching disturbed areas which are to be left uncovered for more that 24 hours during the months September through May. Core Requirement#6. Maintenance and Operation: A maintenance and operation requirement for private facilities will be provided per the King County SWM. Core Requirement#7. Bonds and Liability: Bonding will be provided per the King County SWM. 3 _ ,.�n � : � jim's Automotive. Drainage Analysis. � Summary Our Level I investigation indicates that there is no record of any drainage problem within 1/4 mile downstream of the site nor are any drainage problems predicted after development. The proposed development will not divert runoff from the natural existing location. The increased rate of surface water discharge is negligible and no on-site detention system is required. 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' (•� �f � �.��t"'t •• . � .1', ,.�1,+�` i'�x ' " r ,; �� •.�' �� �� .�,�� � . � �,•�� , ,� .� � �r` ` .,,� •.�A.. _ kt' ^5 �'�1; �y � e "� �'�� �� � � .r�_+. �.a3�'�..rw � ,4�� `'T ! .�� � a "��� aw. _...+...,. . ,_ ♦ �1 °"� «, JE Z . . . r,��`,�4�� ' , � :; y � . ,�4�+1' �` t �, _"" �.�,...... . : •a..� � �.�, "M +���'.�. %�� �'Y •.��'t'A''�A��Ir�'�•�,lt'il.�,,�Y'.�4�• '��r��;��j.�y,►�'�''�GS t 4' .�' �1�''� /'' —��/ ��;�'`�n _;•17` ��� � y \ ` . � ., � -.,{ .f(' ��s�'�«a►� .r^'",9k�G I��J''���-ri3�.�.����r� SEGA Engineers Project Jim's Automotive Structural&Civil Consulting Engineers Job No. 01-019 By: GAT 22928 SE 312th ST (360)886-1017 Black Diamond,WA 98010 Checked Date: 05/31/01 Sht � Drainage Analysis Summary Topic Pre-Developed Post-Developed Land Use Landscape, Brush, Parking Grass, Building, Drives/Parking A pervious (Acres) 0.197 0.193 C„ pervi0us 81 90 A impervious (Acres) 0.137 0.142 C„impervious gg gg T� (min.) 29.65 �6 Precipitation (in.) (24 hour) 2 yr. 2.00 2.00 10 yr. 2.90 2.90 100 yr. 3.90 3.90 Peak Q (cfs) Q Q (cfs) 2 yr. 0.08 0.12 0.04 10 yr. 0.13 0.19 0.06 100 yr. 0.20 0.27 0.07 COPYRIGHT 2001,SEGA ENGINEERS 6/1/Ol 8 :44 :20 am SEGA Engineers page � JIM' S AUTOMOTIVE EXISTING CONDTIONS BASIN SUMMARY BASIN ID: A10 NAME : 10 YR PRE DEV SBUH METHODOLOGY TOTAL AREA. . . . . . . : 0 .33 Acres BASEFLOWS : 0 . 00 cfs RAINFALL TYPE. . . . : KC24HR PERV IMP PRECIPITATION. . . . : 2 . 90 inches AREA. . : 0 .20 Acres 0 . 14 Acre� TIME INTERVAL. . . . : 10 . 00 min CN. . . . : 81 . 00 98 . 00 TC. . . . . 29 . 65 min 5 . 00 min ABSTRACTION COEFF: 0 . 20 TcReach - Sheet L: 110 . 00 ns : 0 . 2400 p2yr: 2 . 00 s : 0 . 0070 PEAK RATE: 0 . 13 cfs VOL: 0 . 05 Ac-ft TIME : 480 min BASIN ID: A100 NAME: 100 YR PRE DEV SBUH METHODOLOGY TOTAL AREA. . . . . . . : 0 . 33 Acres BASEFLOWS : 0 . 00 cfs RAINFALL TYPE . . . . : KC24HR PERV IMP PRECIPITATION. . . . : 3 . 90 inches AREA. . : 0 .20 Acres 0 . 14 Acres TIME INTERVAL. . . . : 10 . 00 min CN. . . . : 81 . 00 98 . 00 TC. . . . : 29 . 65 min 5 . 00 min ABSTRACTION COEFF: 0 .20 TcReach - Sheet L: 110 . 00 ns : 0 .2400 p2yr: 2 . 00 s : 0 . 0070 PEAK RATE: 0 .20 cfs VOL: 0 . 08 Ac-ft TIME : 480 min BASIN ID: A2 NAME: 2 YR PRE DEV SBUH METHODOLOGY TOTAL AREA. . . . . . . : 0 . 33 Acres BASEFLOWS : 0 . 00 cfs RAINFALL TYPE. . . . : KC24HR PERV IMP PRECIPITATION. . . . : 2 . 00 inches AREA. . : 0 .20 Acres 0 . 14 Acres TIME INTERVAL. . . . : 10 . 00 min CN. . . . : 81 . 00 98 . 00 TC. . . . . 29 . 65 min 5 . 00 min ABSTRACTION COEFF: 0 .20 TcReach - Sheet L: 110 . 00 ns : 0 .2400 p2yr: 2 . 00 s : 0 . 0070 PEAK RATE : 0 . 08 cfs VOL: 0 . 03 Ac-ft TIME: 470 min 6/1/O1 8 :45 : 1 am SEGA Engineers page ,� JIM' S AUTOMOTIVE PROPOSED CONDTIONS BASIN SUMMARY BASIN ID: B10 NAME: 10 YR POST DEV SBUH METHODOLOGY TOTAL AREA. . . . . . . : 0 .33 Acres BASEFLOWS : 0 . 00 cfs � RAINFALL TYPE. . . . : KC24HR PERV IMP PRECIPITATION. . . . : 2 . 90 inches AREA. . : 0 . 19 Acres 0 . 14 Acres TIME INTERVAL. . . . : 10 . 00 min CN. . . . : 90 . 00 98 . 00 TC. . . . . 18 . 86 min 2 . 33 min ABSTRACTION COEFF: 0 .20 TcReach - Sheet L: 100 . 00 ns : 0 . 1500 p2yr: 2 . 00 s : 0 . 0070 impTcReach - Sheet L: 100 . 00 ns : 0 . 0110 p2yr: 2 . 00 s : 0 . 0070 PEAK RATE : 0 . 19 cfs VOL: 0 . 06 Ac-ft TIME: 470 min BASIN ID: B100 NAME: 100 YR POST DEV SBUH METHODOLOGY TOTAL AREA. . . . . . . : 0 .33 Acres BASEFLOWS : 0 . 00 cfs RAINFALL TYPE. . . . : KC24HR PERV IMP PRECIPITATION. . . . : 3 . 90 inches AREA. . : 0 . 19 Acres 0 . 14 Acres I TIME INTERVAL. . . . : 10 . 00 min CN. . . . : 90 . 00 98 . 00 TC. . . . . 18 . 86 min 2 . 33 min ABSTRACTION COEFF: 0 .20 TcReach - Sheet L: 100 . 00 ns : 0 . 1500 p2yr: 2 . 00 s : 0 . 0070 impTcReach - Sheet L: 100 . 00 ns : 0 . 0110 p2yr: 2 . 00 s : 0 . 0070 PEAK RATE: 0 .27 cfs VOL: 0 . 09 Ac-ft TIME: 470 min I BASIN ID: B2 NAME: 2 YR POST DEV SBUH METHODOLOGY TOTAL AREA. . . . . . . : 0 . 33 Acres BASEFLOWS : 0 . 00 cfs RAINFALL TYPE. . . . : KC24HR PERV IMP PRECIPITATION. . . . : 2 . 00 inches AREA. . : 0 . 19 Acres 0 . 14 Acres TIME INTERVAL. . . . : 10 . 00 min CN. . . . : 90 . 00 98 . 00 TC. . . . : 18 . 86 min 2 . 33 min ABSTRACTION COEFF: 0 .20 TcReach - Sheet L: 100 . 00 ns : 0 . 1500 p2yr: 2 . 00 s : 0 . 0070 impTcReach - Sheet L: 100 . 00 ns : 0 . 0110 p2yr: 2 . 00 s : 0 . 0070 PEAK RATE: 0 . 12 cfs VOL: 0 . 04 Ac-ft TIME: 470 min 6/1/O1 8 :45 : 58 am SEGA Engineers page �.. JIM' S AUTOMOTIVE HYDROGR.APH SUMMARY PEAK TIME VOLUME HYD RUNOFF OF OF Contrib NLJM R.ATE PEAK HYDRO Area cfs min. cf\AcFt Acres --------------------------------------------- --------------------------------------------- 1 0 . 079 470 1315 cf 0 . 33 2 0 . 132 480 2212 cf 0 . 33 3 0 . 197 480 3280 cf 0 . 33 4 0 . 117 470 1677 cf 0 . 33 5 0 . 187 470 2695 cf 0 . 33 6 0 . 266 470 3858 cf 0 . 33 11 0 . 020 900 1878 cf 0 . 33 12 0 . 099 530 4085 cf 0 . 33 13 0 . 099 530 4086 cf 0 . 33