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, �y1 <br />�� � ���c� <br />l <br />� <br />Reid, Middlecon & <br />. <br />Associates, Inc. <br />Engineers • Surveyors • Plonners <br />Sept 19, 1986 <br />File No. 02-86-119 <br />SNI3�E�TER DEt�S]TION CALCULATIpNS FOR <br />MALT�"1E.�iT C�7."�,R <br />P7N. N.�. 1/4 SflCPION 24, T. 28 N., R. 4 E., W.M. <br />Lots 61, 60 and So. 70 Ft. of Lots 54 & 58, Plat of Broad:�ay Crest <br />EVEF2�,'1'P. WASFIING'iC)N <br />a !L _ �, .� <br />The existing property is urdeveloped except for a storm sewer culvert whici: <br />traverses to property from north to south from Everekt Mall Way. Tfie existiag <br />culvert is being Civerted by City of Ebezett LID 714 A to lst. P1. W, ard is <br />utderconstruction at this date. <br />Area of property = 46,045.37 sq.ft. or 1.06 acres. <br />Fxisting Runoff ccefficient = 0.15 for S�iarce Trees and Grourd Cover <br />�= 240/(1.6)(60) + 10 min- = 12.5 min. <br />Intensity i= 1.65 in/hr @ 10 Yeaz Return Storm �erett Rainfall Curve <br />4 allowable = ci1� = 0.15 (1.65) 1.06 = 0.26 c.f.s. <br />Using the Yrjanianen ard Warren Method for si�le detention system design the <br />following calculations are to determine the detention volume for this project: <br />Pror.ating future runoff ccefficient <br />Paved att] building areas = 40,849.72 sq.ft. = 0.94 Ac C� 0.9 <br />Landscaped areas = 5,195.00 sq.ft. = 0.12 A7 @ p.2 <br />�• �• � � <br />Qo = 0.26 <br />0.82 (1.06) = 0.30 <br />City require�rent for 25 year storm detention <br />T - -25 + .�� <br />� 0.30 = 69.97 min. <br />0.82 = Fut C <br />Vs = 4329 (69.97) <br />25 + 69.97 - 40 (0.30) 69.97 = 3189.43 - 839.64 <br />= 2349.79 Cu.Ft./Ac C <br />121 Sth Avenue North, Suice 200, Edmonds, Woshinqcon 98020 (206) 775•�4�4 <br />