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is <br />Riprap Sizing - Drainage Ditch D -1-11 1% Slope Reach <br />D50 = Size of Riprap <br />D50 = ((V X S ^.17)/7.58)) ^2 <br />D50 = Diameter in feet <br />V = Velocity <br />S = Slope <br />D50 = 0.02 feet 0.3 inches <br />None Required <br />Concrete Ditch <br />Flow From 1 -1 and J 4 - 10 Year Event <br />Manning's Equation <br />Flow In a Trapezoidal Channel <br />DEPTH <br />D <br />0.130 <br />FEET <br />WIDTH <br />W <br />2.000 <br />FEET <br />Slope <br />S <br />0.010 <br />EXPRESS AS DECIMAL <br />Mannings "N" <br />N <br />0.015 <br />EXPRESS AS DECIMAL <br />SIDE SLOPE <br />X <br />1.000 <br />SLOPE = X:1 <br />AREA= (W *D) +(X *D ^2)= <br />0.28 <br />FEET ^2 <br />WETTED PERIMETER= (W) +2 *[((X <br />*D) ^2 +D ^2) ^0.5] <br />2.37 <br />FEET <br />R= AREANVETTED PERIMETER <br />0.12 <br />V= (1.49/N) *(R ^.667) *(S ^.5) = <br />2.38 <br />FT /SEC <br />Q =AXV= <br />0.66 <br />CFS <br />Q REQUIRED - Peak Discharge <br />0.60 <br />CFS <br />TR -91 <br />Volume XI, App. B -9 <br />12/14 <br />