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K = soil erodibility factor (function of site specific soil) <br />LS = length slope factor (from contour map & chart) <br />C = management factor dependent upon vegetation & mulch <br />P = erosion control practice factor <br />For the worst case drainage area that drains to Pond 015, the sediment load was determined to <br />be 0.04 acre -ft over 3 years. The calculations of this volume follow. <br />N;�- <br />The rainfall factor is the product of rainfall energy times the maximum 30- minute <br />intensity for a given rainstorm. It is considered as the erosive power of the rain for that <br />particular area. A chart of "R" values for Colorado developed by the Transportation <br />Research Board in 1980 shows that the "R" value for the entire Nucla area is 26. <br />K = 0.39 (N RCS soil type #14) <br />LS = 0.39 <br />The effects of topography on soil erosion are determined by the dimensionless "L" and <br />"S" factors, which account for both rill and interrill erosion. These factors have been <br />considerably revised since the initial Universal Soil Loss Equation. The new RUSLE <br />computer database for the combined "LS" factor is based on the soil's ratio of rill to <br />interrill erosion. For most western rangeland soils, the equations for low rill to interrill <br />ratio are used. Table 1 (from Predicting Soil Erosion by Water: A Guide to <br />Conservation Planning With the Revised Universal Soil Loss Equation - US <br />Department of Agriculture 1997) shows a chart based on these equations. From this <br />chart (attached on page 6) the LS value was interpolated from between the 2.0% and <br />3.0% slopes at 1000 feet of horizontal distance. <br />C = 1.0 <br />Since the topsoil- stripped area in advance of the pit has no cover, a 0% appreciable <br />cover with no canopy was used for this factor. This is very conservative since roughly <br />half of the drainage area is undisturbed ground that does have cover. The factor comes <br />Revised May 2010 (PR06) Attachment 2.05.3(3) -22 -3 <br />