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Asc-5 <br />• II. SEDIMENTATION RESERVOIR EMERGENCY SPILLWAY DESIGN <br />Determine the hydraulic data of a trapezoidal outlet ditch, <br />depth of flow for the design storm, and high waterline <br />elevation of the reservoir, <br />q25 = 8.90 cfs (from peak discharge calculations) <br />n = 0.03 (Manning coefficient for riprap) <br />Sidesolpe = 4:1 (horizontal to vertical) <br />Slope = O.OI Ft/Ft <br />w = 6.0 ft <br />Manning Equation: q25 <br />Hydraulic data: Q25 = 8.85 <br />D = 0.45 <br />A = 3.5] <br />R = 0.26 <br />s = 0.01 <br />n = 0.03 <br />V = 2.52 <br />=(1.49 / n) A R2/3 S1/2 <br />cfs <br />ft <br />ft2 <br />ft <br />ft/ft <br />fps <br />Assume that the reservoir high waterline at the design storm is <br />equal to the spillway invert elevation plus the depth of flow <br />in the outlet channel: <br />• H. W. L. 25 year = 5231.00' + 0.45' = 523!.45' <br />To provide one foot of freeboard, the top of the embankment <br />shall be at an elevation of 5233.00 ft. <br />III. TOTAL RESERVOIR VOLUME: <br />Liquid Volume = 1.95 Ac-Ft = 84.942 cubic feet <br />Sediment Volume = 1.90 Ac-Ft = 82.764 cubic feet <br />Minimum Reservoir Volume Required = 3.85 acre feet <br />Design Reservoir For a Volume of 3.95 acre- feet <br />Dimensions: Bottom length = 150 feet <br />Width = 80 feet <br />Depth = 10 feet <br />Side s 1 opes = 2^i <br />Total Designed Volume = 4.00 acre-feet <br />See Capacity Table <br />A cleanout marker will be installed at the level at which <br />sufficient storage capacity remains for both the runoff and <br />sediment generated by the ten-year, 24 hour storm event. The <br />. level will be calculated and the marker installed after the <br />reservoir is constructed. Analysis will be included in the <br />sediment pond certification document. <br />2/16/89 <br />