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Ccivil&structural <br /> ENGINEERING engineering&planning <br /> MEMORANDUM <br /> To: Thad Newport(City of Everett Permit Services) <br /> 3200 Cedar St, 2nd Floor. <br /> Everett,WA 98201 <br /> Permit#: PWW1811-001 <br /> Date: May 17,2023 <br /> Subject: WCS Properties LLC Frontage Drainage <br /> Purpose <br /> This memo has been provided for the WCS Properties LLC development, on 232 103Fd St SW, which is currently under <br /> construction. Per sheet C3.1 of the approved civil plans, approximately 124 LF of 18" DIP storm pipe is shown running east to <br /> west along the north frontage.This storm pipe is not taking on runoff from the site, and only a small area from the ROW.The <br /> project proposes to revise this frontage pipe from 18"to 12"diameter.The following section provides calculations to justify this <br /> change. <br /> Research&Calculations <br /> Rational method calculations were performed to determine 25-year peaks flows from the catchment areas of each pipe. <br /> Catchment areas to each catch basin are shown in the figure below: <br /> I I <br /> 1 <br /> I I <br /> I I <br /> I I <br /> I <br /> N 88'21'05" W 1 128.72' <br /> 103RD ST SW <br /> TYPE I CATCH BASIN I I <br /> RIM=100.90` I <br /> IF IN(:B'F)=198.7/ I I RIM-201.152 <br /> IF OUI(18"WI-198.0/ I I IF IN(12'E)=198.76 <br /> - ----_____-__ I I IE IN(4'S)=198,76 <br /> _____1F QS21118_WJ=198,66 <br /> TOC _ _ ____ _______, <br /> __________ __________________ <br /> 201.60 <br /> sf— <br /> gf99 LF^18"DIP 0.5% � <br /> --T C 201.67 209 <br /> 201.12 4-_ 201.17 TOE - <br /> �— <br /> .6 ° 4' 4 ° - 201.68 TOC <br /> d 4 101.65 <br /> BSW 261.22 201.35 ° <br /> M 88'21,05" W 99. ,'' of BSW <br /> 01-75 <br /> 201.394 -201.52 J <br /> 4 ° 4 <br /> \ 201.43 201.36 a CONCRLI� I <br /> ' PAVING , <br /> \ 201.29 a <br /> a <br /> °4 201.16 201.20 <br /> e 4 <br /> ' d - 201.15 I <br /> 20113 ° d a <br /> GRAVEL <br /> a <br /> �. <br /> 70'05'.e ENTRY <br /> 201.251� 1 `�. 201.25 <br /> Figure I:Catchment areas map. <br /> 250 4th Avenue South,Suite 200 <br /> Edmonds,WA 98020 <br /> ph.425.778.8500 I f.425.778.5536 <br /> www.cgengineering.com <br />