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I <br />City Building inspection Department <br />September 12, 1979 <br />page 3 <br />Design Storm <br />Pre Development frequency 1 in 10 years <br />1 in 25 years <br />Poet Development frequency 20 minutes <br />Duration intensity Pre Development 1.3 in./hr.1.6 in./hr. <br />Intensity Post Development <br />Pre Development Design Runoff <br />(,71)(133)(1/12)(20,210) _ .71(730) - 518 CFT <br />post Development Design Runoff <br />(.79) (1.66) ( 1) (20,210) a .79(898) - 709 CFT <br />Runoff Differential - 191 CFT <br />Orifice Opening <br />Diameter = 2-3/4" 20 21C = <br />`f Dischbrge = .71(1.3)(a) .43 CFS <br />IHead = 4.5 Ft. <br />_ .43 = .43 .040 Ft.2 <br />A = (.63) (64.4)(4.5) (.63)(17.02) <br />D = 2 F= (2).113 - .226' or 2.71" r use 2-3/4 <br />Outlet Pipe <br />Diameter 6" <br />Slope 1" in 100' = 1% <br />Capacity = .463 (.5)8/3 (.01)1/2 = .61 <br />20 210 = .596 CFS � .61 <br />poet Development capacity = (.79)(1.6)(�) <br />Capacity of Outlet Pipe O.K <br />Retention/Detention SYstem 1F2 <br />i�AA 24" Die. Conc. pipe Btwn Now & Existing C.H. @ 42'-0" o.c. <br />_ <br />CPf of% �n V - (3.1416) (38) = 119 CFT 24" 16 conc. pipe38'-0" long <br />,i5 pl V = (12.57)(4.66) = 59 CFT Catch Basin )#3 <br />SjC ` V - (12.57) 2.75 = 213 CFT 191Existing C.B. <br />V Total <br />