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�o � % �(JC�y�ecn <br />• <br />Reid, Middleton & Associates, Inc. <br />Engineers � Surveyors • Planners <br />January 29, 1981 <br />File No. 80-157A <br />Site Information <br />Area = 0.63 Ac.'" <br />Slope - 3% Northerly <br />STORM WATER DETENTION CALCULATIGNS <br />OF <br />PROPOSED EVERETT 3 BUiLD <br />FOR COMMERCIAL DESIGN ASSO @�TE'$ ����� D <br />IN EVERETT, WASHINGTON Fr� C 1J8) <br />....................................... . .... <br />CITY OF [VERETT <br />Public Works Dept, <br />Existing site is nearly bare of vege`tation on the west half and grass on east <br />half <br />Existing runoff coefficient -- O�qO' �J• �-�'� <br />/ <br />Tc = L/V + 10 min = 1&0/(1.75)(60) + 70 min = 11.7 min � <br />Intensit / � �� + �� <br />Y= i= 1.71 in/hr @ u0��yr storm freq (Evere � Curve) Area�l� �r� l �� or.�rk'� i <br />Using q= CiA Qallowable =�)(1,7�)(0.63) = 0� Dc.f.s. �� <br />design,ttheYfollowing caWculationsharefto determinetethe�nrequired�volumenof <br />detention for this development: <br />Prorated Future runoff coefficient = Cr <br />Duildiny and concrete area = 0.18 Ac @ 0.90 <br />Asphalt Area = 0.39 Ac (� Q.90 <br />Planter Area = 0.06 Ac @ 0.20 <br />(0.1£3)(0.9) •f (0.39)(0.9) -� (0.06)(0.2) = 0.78 = Cf <br />0.67 <br />Qo = allowable +�_�^ = 0.8II c.f.s./Ac. Cfut <br />A Cfuture 0.63 0.78 <br />121 Sth Avenue North, Sulte 200, Edmonds, Woshington 98020 (206) 775-�4�4 <br />