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<br />U <br />Universal Soil Loss Ecruatton <br />The Universal Soil Loss Equation (LISLE) is the best available means <br />of estimating soil loss and evaluating control measures on a quantitative <br />basis. It was developed primarily for use in predicting sheet and rill ero- <br />sion on non-irrigated croplands. It does not account forgully eros ion <br />and does not calculate sediment yield. <br />The soil loss equation is: <br />A = RKLSCP <br />where A is the soil loss (Tons/Acre/Year) <br />R = rainfall factor <br />K = soil erodibility factor <br />L = length of slope) <br />S = percent slope ) <br />Combined into an LS factor <br />C = cropping management factor <br />P = erosion control practice factor <br />Each of the five factors mentioned above are multiplied together to <br />give the answer "A, Soil Loss" in terms of Tons/Acre/Year. Therefore, <br />the smaller the factors, the smaller the amount of soil loss from water <br />erosion. <br />It must be recognized that the USLE is an empirical formula; based <br />on research, experience and observation. Good judgment must be exer- <br />cised in deriving values for each of the factors. <br />R (rainfall) factors are assigned by geographical regions.based on <br />weather data furnished by the U. S. Weather Service. R values are based <br />on rainfall amount, time, and intensity. In the mountains, R values were <br />computed primarily for valley areas and have been increased to account <br />for runoff from snow melt. <br />• An iso-erodent map, "R" factor map, has been developed for the <br />entire state. In the mountain regions it was necessary to generalize to <br />a large extent because of the wide variation in rainfall patterns. See <br />Figure 9 _ <br />-63-