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Sedimentation Pond Volume Calculation <br />(a) Drainage area 7.445 acres <br />10-year, 24-hour event 1.6 loch storm <br />Runoff - Curve #90 0.76 inches <br />(0.76 in/12 in per ft) x 7.445 acres = 0.47 acre/feet <br />(b) Drainage area <br />volume required <br />7.445 acres <br />0.1 acre-foot per acre <br />(0.1 acre-feet/per acre) x 7.445 acres = 0.74 acre-feet <br />TOTAL VOLUME 1.21 acre-feet <br />Surface Area Calculation <br />Drainage area 1.445 acres <br />10-year, 24-hour event 1.6 inch storm <br />Runoff - Curve N90 0.16 inches <br />Volume in gallons: <br />(0.76 inches/12 inches per ft) x 7.445 acres z 43,560 <br />sq ft per acre x 7.5 gallons per cubic ft ~ 154,045 gal, <br />154,045 gal. per day/50 gal. per day x 1 sq ft = 3,081 sq ft <br />sinimum <br />Actual Pond Surface 18.660 sq ft <br />Primary Spillway Design <br />(a) The primary spillway was designed to provide the 24-hour <br />detention time for the 10-year, 24-hour event. A 2-inch <br />discharge riser pipe which discharges Into a 6-loch <br />conduit through the embanlanent is used. Figure 23-25, <br />Rating Curve for Principe Spillway. shows the rating <br />curve for this riser pipe and Figure 23-26. <br />' Inflow-Outflow Hydrographs, compares the inflow and <br />outflow hydrographs. Theoretical detention time for the <br />23-163 <br />