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i <br />;,, • CRDA N0. 2 AND NO. 3 COLLECTION DITCH DESIGN <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 + zd2)/(b + 2d z2 +1) b = 3' <br />A bd + zd2 for 1h:iY side s]opes 2=2 <br />S = 0.33 max., 0.03 min. <br />Flow Related to STope and Depth <br />S = 0.33 <br />@d = 6" Q = 22.5 CFS <br />@d = 7" Q = 24.7 CFS <br />@d=8" Q=38.1CF5 <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 />West Ditch 27.6 CFS <br />@S = 0.33 use d = 7" + 4" freeboard = 11" min. depth <br />@S = 0.03 use d = 13" + 4" freeboard = 17" min. depth <br />D50 = (V50.17/7.58)2 x 12 = rip-rap in inches (minimum size of SOZ of <br />the rip-rap) <br />Y = Velocity = 28.6 CFS/5.6 ft2 = 5.1 fps <br />D50 = [5.1(0.330'17)/7.58]2 x 12 = 3.7" min. <br />~- • <br />- (New 10-31-90) <br />CRDA2-6 <br />