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s <br />CRDA N0. 2 AND M0. 3 COLLECTION DI7CN DESI611 <br />~~ • <br />Ditch Design {JJ Exhibit 51 and 52) <br />Q = (1.49/N) AR2(3 S1(2 Manning's Equation <br />N = 0.040 <br />R = (bd + zdz)/(b + 2d zz +1) b = 3' <br />A = bd + zdz for 1h:1V side slopes z=2 <br />S 0.33 max.. 0.03 min. <br />Flow Related to Slope and Depth <br />S = 0.33 <br />@d = 6" Q 22.5 CFS <br />@d = 7" Q 29.7 CFS <br />@d 8" Q 38.1 CFS <br />S = 0.03 <br />@d = 12" Q 24.7 <br />^. ~ @d 13" Q 28:8 <br />@d 14" Q = 33.3 <br />@d = 15" Q = 38:2 <br />Ditch Design for CRDA No. 2 <br />Peak Flow: East Ditch 28.6 CFS <br />Mest Ditch 27.6 CFS <br />@S 0.33 use d = 7" + 4" freeboard I1" min. depth <br />@S = 0.03 use d = 13" + 4" freeboard = 17" min. depth <br />D50 = (VS0.17/7.58)z x 12 = rip-rap in inches (minimum size of 50x of <br />the rip-rap) <br />Y Velocity = 28.6 CFS/5.6 ftz = 5.1 fps <br />D50 = [5.1(0.330.17)/7.58]z x 12 3.7" min. <br />• <br />(New 10-31-90) <br />CRDA3-9 <br />