Laserfiche WebLink
Length Slope Factor "LS" <br />The effects of topography on soil erosion are determined by the dimensionless "L" and "S" <br />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 Conservation <br />Planning With the Revised Universal Soil Loss Equation - US Department of Agriculture <br />1997) shows a chart based on these equations. The average slope of the release areas in <br />both pre-mine and post-mine is determined with an algorithm in SurvCAD, using a 3D grid <br />of the topography in both cases. The slope length will be 1000 feet, as this is the limit of <br />the "LS" table. <br /> Calculated Avg. Land LS Factor <br /> Slope <br />Pre-Mine Irrigated 4.74 1.02 <br />Pasture <br />Post-Mine Irrigated 3.06 0.57 <br />Pasture <br />From Table 2, it is seen that the pre-mine "LS" factor for Irrigated Pasture is 1.02 based <br />on a length of 1000 feet and a grade of 4.74%. Post-mine "LS" factor is 0.57 for irrigated <br />pasture based on 3.06% average slope. These average slopes are calculated for both the <br />pre-mine and post-mine conditions based on topography from pre-mine and post-mine <br />surveys that are then run through a Carlson software algorithm. The "LS" factors are then <br />interpolated from the values in Table 2. <br />SL-12 CURRENT 11MARll.wpd 20