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� �, <br />Reid, Middlt�ton � Associates, Inc. <br />ENGINEERS • SURVEYORS • PLANNERS <br />�24 Main Street, Edmonds. Woshington 98020 <br />,, l . . -,. <br />'` ' ' '., - <br />� �'' �' , � . 4 �' � � <br />, . I ^ � �I `r <br />• (206) 775-�4a4 <br />Revised <br />OcCober 12, 1979 <br />September 14, 1979 <br />File No. %9-157 <br />' �';�� STOR11 WATER DETENTION CALCULATIOMS <br />� , � : ,� . ,,�� <br />..',, � � + <br />� .;r _i ;:�. � �� FOR <br />=�4-•��.i� G�i��'-�:�� <br />�"""'�� f,qSCADE VILLAGE PAP,K <br />Exisling Site InPormation <br />P�L�' _ _'` � <br />''� <br />OCT 1� 1979 <br />................................... ... ...... <br />CITY OF EVERFTi <br />Puplic VJorks U_r,,, <br />Area = �i.88 acres <br />Existin9 topography - Rollinq 3- a'; <br />Site condition - Partially �!evelo�ed resideneial and opr,n snsce, <br />runoff coefficient = 0.25 <br />Using Che Yrjanainen and Warren method for simple retenCion/ <br />deCention basin design, the follotaing calculations are to determine the <br />required volume oF detention for this development. <br />LongesC distance to point of discharye from site on each, property <br />line = 365 + 285 = 650 I.f. <br />1'ime to concentraCion = Tc = 10 min. + 650/(l.l)60 = 19.8 min. <br />Intensity = i= 1.5� in/hr @ 25 year storm frequency - Everett Curvc <br />Q existing = ciA =(0.25)�1.58)(4.88) = 1.93 c.f.s. <br />2 allowable = 1:.93 c.f.s. <br />�, , <br />Developed Site <br />Frorate future runoff coe(ficient - Cfut <br />Bldg. area = 1.82 ac. � 0.90 c. <br />l�spha I t area = 1.65 ac. (�; 0:85 c <br />Environmental roadway = 4.-08 ac. � 0.60 c <br />La�•m & landscaped arez = 1.27 ac. (' 0.40 c. <br />IloCe: Poot area to drain to san, sewer = 0.06 ac, excluded from <br />slr�rm calculations. <br />Cfut = (1.87)(0.9)�(1.65)(0.85)�i�.0")(o.Gh;l.z7 io.ho) = 0.75 <br />—!� .82 — <br />2� _ Q allowable _ 1.93 = p.53 c.f.s/AcC <br />Ac x CFut - 4.8$ x 0.75 <br />�ssume orifice condiCions exist <br />r=-25 + 27o6/Qo =-25+ 2706/0.53 = h6.h5 �,���,. <br />vs = 1iz791 _ t�oQoT = �+329(46.45) - 40(0.53)(46.45 <br />�+25 . 5 + z5 <br />28i4.3o - 984.74 = i829.5, �c.�/ncC <br />U total = (Vs)(Ac)(Cfut) _ (1829.5�1(4.88)(0.75) _ �c,�r�.�� rc.3 <br />Volnrnc of dcLcnti�m reqiiirrd =(G�6.19 ft.� <br />