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<br />Estimating Soil Losses from Water Erosion <br /> <br />The Universal Soil-Loss equation can be used as a <br />planning tool for estimating soil loss and evaluating <br />alternative land treatment measures. The procedure <br />has been used for many years by the Soil Conservation <br />Service in developing conservation plans on fannland. <br />Recent developments have expanded its use as a means <br />of estimating soilloss on various types of project areas. <br /> <br />THE UNIVERSAL SOIL-LOSS EQUATION <br />(Modified for project sites) <br /> <br />A = R (or EI) X K X LS X C <br /> <br />A - The computed soil loss expressed as tons per acre <br />per year. <br /> <br />R - The average annual erosion index for a specific <br />geographic region, considering amount, time and <br />duration or the rainfall. <br /> <br />EI -The erosion index for only a portion of the year. <br />Determine the percentage of the total erosion <br />index and multiply times the total annual "R" <br />factor shown on Figure 7. See Figure 8 to deter- <br />mine the percent of E.!. <br /> <br />K - The soil erodibility factor based on particle size <br />distribution, organic matter content, structure <br />and permeability. Contact the Soil Conservation <br />Service for factor values. <br /> <br />LS- The factor that accounts for the length and per- <br />cent slope. See Figure 9. <br /> <br />C - The soil cover factor. This factor accounts for the <br />soil protection provided by various kinds, and <br />amounts of soil cover. See Figure 10 or II. <br /> <br />Example Situation: <br /> <br />An urban development project is planned in Arapahoe <br />County. To predict annual soil loss, determine the ap- <br />plicable R, K, LS, and C factors. The product of these <br />factors is an estimate of tons of soil loss per acre per <br /> <br />Segment I <br /> <br />50 x <br />R <br />50 x <br /> <br />4.0 x <br />LS <br />1.4 x <br /> <br />.32 x <br />K <br />.28 x <br /> <br />Segment 2 <br /> <br />To predict soil loss for a portion of the year, factor "R" <br />wiD need to be adjusted by the percentage of the erosion <br />index occurring during that portion of the year. For <br />example to determine the E.!. for August, September <br />and October, refer to Figure 8. Multiply the percentage <br /> <br />year. It may be necessary to divide the area into seg- <br />ments to account for variation in factor values. In this <br />example, notice the "C" factor is 1.0, which indicates <br />that the soil will be essentially void of protective cover. <br /> <br />1.0 <br />C <br />1.0 = <br /> <br />256.0 tons <br /> <br />64 tonsx4Ac= <br /> <br />19.6 tons X 6 Ac - <br />Total TonslYr <br /> <br />117.6 tons <br />373.6 tons <br /> <br />from Figure 8 times the "R" value for that geographical <br />region. The result is the E.!. for that period of the year. <br />Therefore, an "R" factor of 50 would be adjusted to <br />13.5 (50 x 27%). <br /> <br />Segment I <br /> <br />.32 x <br />K <br />.28 x <br /> <br />4.0 x 1.0 = 17.2 x 4 Ac <br />LS C <br />1.4 x 1.0 5.2 x 6 Ac <br />Total tons during Aug-Oct <br /> <br />= 68.8 <br /> <br />= 31.2 <br />100.0 tons <br /> <br />13.5 x <br />E.!. <br />13.5 x <br /> <br />Segment 2 <br /> <br />26 <br />