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3 <br />1;• <br />Ditch Design (E-E Exhibit 98) <br />Q = (1.49/N) AR 2/3 S 1/2; Manning's Equation <br />N = 0.040 <br />R = zd/2 z2 + 1 z = e/d <br />A = zd2 for 2h:1V side slopes z = 2 <br />S = 0.037 " <br />@d= 12" Q= 9.9 cfs <br />@d = 18" Q = 29.3 cfs <br />@d 17" Q=25.2 cfs <br />Ditch Required = 17" + 4" freeboard = 21" <br />Existing ditch varies from 22 to 30" deep. <br />Velocity = Q/A = 25.2/4.0 = 6.3 fpm <br />050 = (VS 0.17 /7.58)2 x 12 <br />050 = ((6.3) 0.037 0.17/7.58)2 x 12 = 2.7" Rip-Rap <br />~.• <br />~, Ditch Design (fr6 Exhibit 9B) <br />Q = (1.49/N) AR 2/3 S I/2; Manning's Equation <br />N = 0.04 <br />R = (bd + zd2)/(b + 2d z2 + 1) b=2' <br />A = bd + zd2 z=e/d <br />for lh:ly side slopes z=1 <br />S = 0.25 max., 0.05 min. <br />@d.25 = 10" Q = Z9.2 CFS <br />@d.25 = 9" Q = 24.2 CFS <br />@d.05 = 14" Q 24.2 CFS <br />Ditch required for 0.25 slope = 9" + 4" Freeboard = 13" <br />V.25 = 24.2/2.1 = 11.5 fpm <br />050 = ((11.5) 0.25 0.17/7.58)2 x 12 = 17.2" Rip-Rap <br />Ditch required for 0.05 slope 14" + 4" Freeboard = 18"8 <br />V.05 = 24.2/3.7 = 6.5 fpm <br />050 = ({6.5) 0.05 0.17/7.58)2 x 12 = 3.2" Rip-Rap <br />~: • <br />CRDA~-~~ 2/4 LMR NEW 10-23-87 <br />