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25yr -- 24 hr = 0.65 inches <br />5. Determine peak discharge of runoff CN85 (pp 18 - FIG. S-lA, SCS) <br />2Syr -- 24hr = 14.5 cfs/inch of runoff <br /><- 0.65 inches <br />= 9.4 cfs <br />Design from Drawi <br />1. Pond volume <br />Principal Spillway = 0.77 acre ft <br />Emergency Spillway = 0.96 acre ft <br />2. Peak flow capacity of Emergency Spillway <br />12.67' <br />Q= A 1-_5 R2/3 S Z ~ I <br />n <br />• ~ 2/3 <br />Q = (4' x 7.67') (0,017)((4'x2 2.67 ) <br />Q = (10.68ft2) (88.235)(0.05) (1.09) (0.22) <br />Q = 229.68 cfs <br />3. Freeboard <br />H = (30 2/3 (3 4ft)3/S)2/3 = 0.85 ft <br />Summary <br />1. Pond volume <br />Needs 0.34 acre ft water volume <br />Needs 0.25 acre ft = 0.035 acre ft/acre x 7.21 acre <br />Needs 0.59 acre ft total volume <br />Designed for 0.77 acre ft <br />• <br />