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• value decreases to 0.04 while the other values remain the same. The <br />soil loss from the bench then becomes 0.32 tons/acre/year. <br />Under existing natural conditions the soil erosion <br />21.5 tons/acre/year. This number was derived using <br />and dividing the area into two different sections. <br />based on percent slope. The upper section of the <br />long with a slope of 40 percent. The lower section <br />with a slope of 20 percent. <br />is an average of <br />the USLE equation <br />The sections were <br />hill is 150 feet <br />~ is 150 feet long <br />For the upper section, the R and K values remain the same, 40 and 0.25 <br />respectively. The LS value is 16 based on the measurements given <br />above. C value is 0.2 based on a ground cover of 30 percent. Thirty <br />percent was chosen by using a description of natural conditions in the <br />permit application. A P value of 1.0 is used since there are no <br />terraces. Using these values in the USLE equation, the soil loss is A <br />_ (40) (.25) (16) (.2) (1.0) = 32.0 tons/acre/year. On the lower sec- <br />• tion, the R, K, and C values remain the same 40, 0.25, and 0.2 respec- <br />tively. The LS value is 5.5 and again no P value. The resulting soil <br />loss is A = (40) (.25) (5.5) (.2) = 11.0 tons/acre/year. Averaging <br />the upper and lower sections, the soil loss under existing natural <br />conditions is 21.5 tons/acre/year. <br />The soil loss under natural conditions is so high because of the long <br />uninterrupted slope length. The long slopes enable runoff velocities <br />to increase and remove soil. The use of terraces decreases the length <br />of slope, lowers runoff velocities, and reduces soil loss. The use of <br />terraces on the refuse pile will aid in the establishment of <br />vegetation. <br /> <br />4-53 <br />