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DIVERSION DITCH DESIGNS <br />(Cont'd) <br />Basin shape factor (hydraulic length 2,350 ft., equivalent area 57 ac.) = 34/7/57 = <br />0.609 <br />Corrected peak flow = 6.5 cfs x 0.925 x 0.6^9 = 3.7 cfs <br />Design: trapezoidal ditch, 2.0 ft. deep, bottom width = 1.0 ft., side slopes 2:1, <br />' gradient = O.OL ft/ft, n = 0.03 <br />Flow conditions: depth = 0.63 ft., velocitry = 2.57 fps, area = 1.44 sq. ft. <br />Check calculation: Q = VA = 2.57 x 1.44 = 3.7 cfs <br />Ditch E-3 <br />Tributary area = 16.5 ac. reclaimed <br />' Weighted CN = 70 <br />Total runoff @ CN(70) = 0.17 (in) / 12 in/ft x 16.5 ac. = 0.23 ac-ft <br />Peak flow (flat slope) 9.4 cfs/in. runoff x 0.17 in runoff = 1.6 cfs uncorrected <br />Basin slope factor (actual slope 1.2%) = 1.120 <br />Basin shape factor (hydraulic length 2,450 ft., equivalent area 62 ac.) = 16.5/62 = <br />' 0.226 <br />Corrected peak flow = 1.6 cfs x 1.120 x 0.266 = 0.48 cfs <br />Design: trapezoidal ditch, 1.5 ft. deep, bottom width = 1.0 ft., side slopes 2:1, <br />gradient = 0.01 ft/ft, n = 0.03 <br />' Flow conditions: depth = 0.22 ft., velocitry = 1.52 fps, area = 0.32 sq. ft. <br />Check calculation: Q = VA = 1.52 x 0.32 = 0.48 cfs <br />Ditch E-4 <br />' Tributary area = 12.6 ac. watershed <br />Weighted CN = 70 <br />Total runoff @ CN(70) = 0.17 (in) / 12 in/ft x 12.6 ac. = 0.18 ac-ft <br />Peak flow (steep slope) 17.7 (cfs/in. runoff) x 0.17 (in runoff) = 1.6 cfs uncorrected <br />Basin slope factor (actual slope 2696) = 1.07 <br />' Basin shape factor (hydraulic length 760 ft., equivalent area 8.5 ac.) = 12.6/8.5 = <br />1.48 <br />' Corrected peak flow = 3.0 cfs x 1.07 x 1.48 = 4.75 cfs <br /> 9 <br /> <br /> <br />