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DITCH 18 <br />Manning's Equation <br />Flow In a Trapezoidal Channel <br />DEPTH <br />D <br />0.75 <br />FEET <br />WIDTH <br />W <br />3 <br />FEET <br />Slope <br />S <br />0.2 <br />EXPRESS AS DECIMAL <br />Mannings "N" <br />N <br />0.04 <br />EXPRESS AS DECIMAL <br />SIDE SLOPE <br />X <br />1.5 <br />SLOPE = X:1 <br />AREA=(W*D)+(X*D2)= <br />WETTED PERIMETER=(W)+2*[((X*D)2+D2)112] <br />R=AREA/ WETTED PERIMETER <br />V=(1.49/N)*(R2'3)*(S "2)= <br />Q=AXV= <br />Q REQUIRED - Peak Discharge <br />Riprap Sizing - Dtich 18 <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 = 1.24 feet 14.8 inches <br />TR -16 17 <br />3.09 Feet2 <br />5.70 Feet <br />0.54 <br />11.08 Ft/Sec <br />34.28 CFS <br />34.23 CFS <br />05/08 <br />