Laserfiche WebLink
<br />MINE 3 <br />DIVERSION DttCH DESIGNS <br />Assumptions: <br />10-yr, 24-hr precipitation event: 1.8 inches (NOAH) <br />Antecedent moisture condition (AMC): II <br />' Disturbed land curve number (dirt road, soil group C): 87 <br />Undisturbed/reclaimed land curve number (contoured rangeland, good <br />' condition, soil group C): 70 <br />Manning open channel flow equation: Q = 1.49/n R0.67 S0.5q <br />' Mannings "n" for earthen channel = 0.03 <br />' Ditch E-1 <br />Tributary area = 19.5 ac. disturbed, 15.5 undisturbed <br />Weighted CN = 19.5 (87) = 15.5 (70) = 80 <br />35.0 <br />Total runoff @ CN(80) = 0.44 (in) / 12 in/ft x 35 ac. = 1.28 ac-ft <br />Peak flow @ CN(80), 35.0 ac, Type II storm, western Colorado, steep slope) = 43 <br />cfs/in. runoff x 0.44 in runoff = 18.9 cfs uncorrected <br />Basin slope factor (actual slope 11%) = 0.925 <br />Basin shape factor (hydraulic lengt 2,200 t., equivalent area 52 ac.) = 35/52 = <br />' 0.673 <br />Corrected peak flow = 18.9 cfs x 0.925 x 0.673 = 11.8 cfs <br />Design: trapezoidal ditch, 2.5 ft. deep, bottom width = 1.0 ft., side slopes 2:1, <br />gradient = 0.01 ft/ft, n = 0.03 <br />Flow conditions: depth = 1.08 ft., velocitry = 3.48 fps, area = 3.39 sq. ft. ' <br />Check calculation: Q = VA = 3.48 x 3.39 = 11.8 cfs <br />Ditch E-2 <br />Tributary area = 34.7 ac. reclaimed <br />' Weighted CN = 70 <br />Total runoff @ CN(70) = 0.17 (in) / 12 in/ft x 34.7 ac. = 0.49 ac-ft <br />' Peak flow (steep slope) 38 cfs/in. runoff x 0.17 in runoff = 6.5 cfs uncorrected <br />Basin slope factor (actual slope 11%) = 0.925 <br />' 8 <br />r <br />