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Revised <br />Octeoer 12, 1979 <br />Septerrbcr 14, 1979 <br />File t�o. 79-�57 <br />Page 2 <br />STORM WATER DETENTION CALCULATIONS FOR CASCADE VILLAGE PARK (cont.) <br />OPf-site Drainage Basin (see attached) <br />Area = 2.33 ac. � " <br />S1. = Roll(ng 3 - 8� <br />L = 450' <br />Tc = 450/(l.l) (60) + 10 min. = 16.82 min. <br />Intensity = 1.71 in/hr C Z5 year storm frequency - EvereLC Curve <br />RunoFf coefficinet existing = 0.25 <br />Assume no increase in storm drainage because of Cit:y ordinance <br />Q max = ciA =(0.25)�1.71)(2.33) = 0.996 c.f.s. <br />Sizing Bypass Culvert System <br />Slope of system - 0.50q Q/S I/2 = 1/0.0707 = 14.14 <br />Conveyance factor = 14.14 required <br />Conveyance factor 12" hel. 16 ga. _�!6 <br />Use 12" as min. size <br />Qmax for 12" � 0.507; = 3.25 e.f.s., Cherefore, o.l<. <br />Sizing the Orifice <br />Q alloo-�able = 1.93 c.f.s. <br />Q off-site bypass = 1.0 c.F.s. <br />Q alloo-iable project = 2.93 c.�.s. <br />Using the orifice equation Q= cdA }�2gli <br />Solving for A= �� Q 9� Assume I� = 5•23' <br />2.93 = �•z575 or 6.87" orifice <br />o. 2 i. 5.23 <br />If 6-7/8" orifice is used = 0.257a h will change <br />Q // 2,93 Z <br />Solving for h= (cdA /2g -( 0. 2, 0.257 �4.h - 5.22 <br />\ <br />Sizing the DetenCion System <br />Required volume of storage = 6696.19 (t.3 <br />CO MN No. 7 Type II 5.27. v.i. x 15.9 fc.3/v.f. = a3,0 ft.3 <br />cs r�n No. 7 co 6 72 I.f. 48�� cuiv. @ 0.5�� 72 x Iz,57 fi.3/I.f. = 905.04 fc,3 <br />CB MFI No. 6 Type II 4.82 v.f. x 15.9 ft. /v.f. = 76.96 ft. <br />NoCe v.f. = Vertical fleignt above flowline to max. �va:er surPace <br />CB IIII No. 5 Type <br />CB 11H 5-4 34 I. f. <br />CB MH 5[o C� 5A <br />II 3•83 v.f. x 15.9 f�•3/ v•f• = 60,90 ft.3 <br />36" culv. @ G.50<; f� 7.069 I"�,3/i.f, = 268.62 ft.3 <br />I9z l.f. 36�� cui�. r o.50� 172' futi <br />20' full - 1.20 ft.3 <br />192x7.o 9 f�3/I.F. = 1357.z5 <br />- l.zo <br />1356.05 ft.3 <br />