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WA's Collection Ditches <br />Collection Ditch CD-3E will be a triangular channel 0.800 <br />feet deep with 2h:ly side slopes. With a freeboard of 0.3' <br />the total depth of the collection ditch is 1.100 feet. <br />The flow velocity is slow enough that erosion will not be a <br />problem. <br />Collection Ditch CD-1W <br />Flow In a Triangular Channel <br />DEPTH D 0.900 FEET <br />SLOPE S 0.020 EXPRESS AS DECIMAL <br />Mannings "N" N 0.035 EXPRESS AS DECIMAL <br />SIDE SLOPE X 2.000 SLOPE = X:1 <br />AREA=(W*D)+(X*D^2)= 1.62 FEET^2 <br />WETTED PERIMETER=(W)+2((XD^2+D^2))^.5 4.02 FEET <br />R=AREA/WETTED PERMITER 0.40 <br />V=(1.49/N)*(R^.667)*(S^.5)= 3.28 FEET/SEC <br />Q = A X V = 5.32 CFS <br />Q REQUIRED 4.93 <br />Collection Ditch CD-1W will be a triangular channel 0.900 <br />__ feet deep with 2h:ly side slopes. With a freeboard of 0.3' <br />the total depth of the collection ditch is 1.200 feet. <br />~ The flow velocity is slow enough that erosion will not be a <br />problem. <br />The ditches will be vegetated with the seed mix <br />that will be used on the topsoil stockpiles. According to <br />Table 4-8 - Maximum Permissible Velocities in Vegetal-lined <br />Channels - in the Handbook of Steel Drainage & Highway <br />Construction Products - the allowable flow velocity for <br />a grass mixture lined channel is 4 to 5 feet per second. <br />Collection ditch CD-lE has a calculated velocity which is <br />slightly over the allowable veloctiy so the ditch will be <br />monitored for erosion an maintenance will be performed as <br />necessary. <br />Summary of Ditch Sizes: <br />Ditches are all V-Ditches with 2H:1V Side Slopes <br />Depth Freeboard Total Depth <br />Ditch CD-3E 0.80 0.30 1.10 <br />Ditch CD-2E 1.00 0.30 1.30 <br />Ditch CD-lE 1.40 0.30 1.70 <br />Ditch CD-1W 0.90 0.30 1.20 <br /> <br />9-32 July 1992 <br />