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Run -off Volume <br />Pond 015 excavation has been designed to contain the 100 -year 24 -hour event with no <br />discharge. The pond is completely incised, so there is no embankment that could fail. The <br />excavated side slopes are 2H:1 V. The run -off volume for the worst case drainage area is 0.68 <br />acre -ft. This was determined using a combined curve number from the weighted average of the <br />curve numbers of the undisturbed areas as well as the area ahead of the pit which has just had <br />its topsoil stripped. <br />Runoff Curve Number and Runoff <br />Project: Pond015 <br />1. Runoff Curve Number (CN) <br />By: B. Langenfeld Date: 05/11/09 <br />Cover description <br />CN <br />Area(Acre) <br />Topsoil stripped <br />89 <br />2.745 <br />Grasses <br />78 <br />2.794 <br />CN (weighted): <br />83.5 <br />Total Area: <br />5.539 Acre <br />2. Runoff <br />Return Period: <br />100 -Year <br />Rainfall, P: <br />3.00 in <br />Runoff, Q: <br />1.4778 in <br />Runoff Volume: <br />0.6821 Acre -Ft <br />Sediment Volume <br />Sediment build up within the pond was determined using the Revised Universal Soil Loss <br />Equation (RUSLE): <br />A= RxKxLSxCxP <br />A = soil loss in tons /year per acre <br />R = rainfall factor (from standard chart of area) <br />Revised May 2010 (PR06) Attachment 2.05.3(3) -20 -3 <br />