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� 3 p g �'„e�� �e �., <br />• <br />Reid, Middleton � Associates, Inc. <br />Engineers • Surveyors • Plonners <br />March 20, 1981 <br />File No. SO-157A <br />STORM 41ATER DETENTiON SYSTEM CALCULATIONS <br />FOR <br />COMMERCIAL DESIGN ASSOCIATES <br />PROPOSFD EVERETT III BUILDING <br />EVERETT, WASHINGTON <br />Existing Site Condition <br />Area = 0.63 Ac. <br />Slope = 0.3% Northerly <br />CC�(���d�� <br />MAR 2� 19�1 <br />.... .................................. ..... . ...... ........ <br />CITY OF EVEREii <br />Pubiic �1�crks Dep;. <br />Site Condition - Westly 11D feet of property behind the curb was used <br />as gravel used car parking lot and the remaining easterly portion is <br />grass. <br />Prarated existing runoff coefficint =(0.04)(0.9)+(0.34)(�;63)+(0.7.5)(0.15) = n.5? <br />Existing runoff coefficient = 0.52 <br />Tc = L/(V)60 + 10 min. lA0/(1.75)60 + 10 = 11.7 min. <br />Intensity = i= 1.71 in/hr @ 10 year storm frequency (Everett c�rve) <br />Q existing = ciA = (0.52)(1.71)(0.63) _ �.56 c.f.s. <br />Q allowable = 0.56 c.f.s. <br />Using the Yrjanainen-4larren method for simple retention/detention system design, <br />the following calculations are to determine the required volume of detention <br />for this development. <br />121 Sth Avenue sJorth, Sui[e 200, Edmonds, Woshington 98020 (206) 775-�4�4 <br />