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<br />channel design and construction as previously described, and design and <br />construction of a sedimentation pond. The sedimentation pond is the <br />primary element in prevention of contributions of sediment to streamflow <br />or runoff outside the permit boundary. Criteria used in the design of the <br />sedimentation pond follow: <br />Volume <br />(a) 10-year, 24-hour event volume <br />(b) 0.1 acre-feet per acre of disturbed area <br />Surface Area <br />1 square foot per 50 gallons per day inflow from a 10-year, <br />24-hour precipitation event <br />Primary Spillway <br />(a) To provide 24-hour detention time for the 10-year, <br />• 24- hour precipitation event. <br />(b) Discharge only permissible effluent by not allowing <br />surface film to discharge. <br />(c) Maximum distance possible from inlet to outlet. <br />Emergency Spillway <br />(a) Set at an elevation so that no flow will occur from <br />events less than the 10-year, 24-hour event. <br />(b) Must safely pass the peak flow resulting from a 25-year, <br />24-hour event. <br />Embankment <br />(a) <br />(b) <br />(c) <br />• (d) <br />Elevation of primary spillway outlet set at the <br />sediment storage volume level. <br />Emergency spillway crest set at a minimum of one vertical <br />foot above principle spillway crest. <br />Dam crest minimum of one vertical foot above the design <br />flow level of the emergency spillway. <br />Minimum top width of W~(H+35)/5 <br />23-162R Revised - August, 1990 <br />