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2. Runoff <br />Return Period: <br />Rainfall, P: <br />Runoff, Q: <br />Runoff Volume: <br />10 -Year <br />2.00 in <br />0.3498 in <br />4.5316 Acre -Ft <br />The pond volume below the emergency spillway will be comprised of three design needs: <br />1) 10 year storm inflow of 4.5 acre feet, as described above <br />2) 3 year sediment delivery of 0.02 acre feet, as based on the calculations shown below. <br />Therefore, the total design volume below the emergency spillway is 4.5 + 0.02 ac -ft which is <br />4.52 acre feet. As is shown in the SEDCAD details, the bottom of the emergency spillway is <br />5616.0', which has a volume of 12.3 acre -ft at this elevation. <br />Pond Volume Calculation based on Universal Soil Loss Equation (SurvCAD) <br />Input Data <br />Landuse Area <br />Rainfall <br />Erod- <br />Length <br />Slope Ls Cf Pf <br />(ft ^2) <br />Factor <br />ability <br />(ft) <br />M <br />Pasture 6770530.8 <br />50.0 <br />0.37 <br />2121.0 <br />4.1 1.39 0.04 1.00 <br />Runoff = 1.000 inch. <br />Sediment Density = 175.000 <br />Time = 1.0 years <br />Drainage Ratio = 0.37 <br />Total Area = 155.430 acres <br />Gross Erosion = 159.846 tons /yr. <br />Total Yield = 59.143 tons /yr. <br />Runoff Volume = 12.953 acre -ft <br />Sediment Volume = 0.016 acre -ft (3 -year total) <br />Total Volume = 12.968 acre -ft <br />The Cf factor is determined from the chart on the following page, shown in Design Hydrology <br />Revised February 2010 (PR06) Attachment 2.05.3(3) -22 -4 <br />