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1 <br />SEDIMENT POND E DESIGN CALCULATIONS <br />(Cont'd) <br />t i/ <br />Required Sediment Volume. 0.26 ac-ft x (100/40) = 0.64 ac. ft. <br />' ri <br />Required Sediment Cleanout: When pond is 60% full of sediment. <br />RUNOFF VOLUME: <br />1.8 in. rainfall and curve No. 82 = 0.52 in. runoff <br />' 35 ac watershed x 0.52 (in runoff) ' 12 (in/ft) = 1.52 ac-ft of runoff volume <br />' TOTAL VOLUME: <br />0.64 ac-ft of sediment volume + 1.52 ac-ft of runoff volume = 2.16 ac-ft of total <br />volume <br />EMERGENCY SPILLWAY: <br />-Design for 25-yr, 24-hr event = 2.2 in rainfall <br />-35 ac watershed <br />' -AMC [I Curve No. 82 <br />-Average slope of runoff area is 6% <br />' -Slope correction factor = 1.1 l <br />2.2 in rainfall @ curve No. 82 = 0.83 in. runoff <br />' PEAK FLOW: <br /> 31 cfs/in runoff (1) x 0.83 in runoff x 1.11 = 28.6 cfs <br />1 <br /> SPILLWAY DESIGN SUMMARY: <br />-Depth of flow is 0.5 ft. <br />-Velocity of flow is 5.2 fps <br />' -Bottom of spillway is 1.5 ft below top of dam <br />-Width of spillway is l0 ft across bottom <br />' -Side slopes are lv:2h <br />-Gradient of spillway is 3% <br />' (1) taken from graphs -Peak Flows in Colorado, SCS, March, 1977 <br />' _' 4 <br /> <br />