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Estimating Sall Losses from Water Erosion <br />'fhe 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 t'or many years by the Soil Conservation <br />Service in developing conservation plans on farmland, <br />Recent developments have expanded its use as a means <br />of estimating soil loss on various types of project areas. <br />THE UNIVERSAL SOIL-I-OSS EQUATION <br />(Modified for project sites) <br />A= R(orLl)x KxLSxC <br />A -The computed soil loss expressed as tons peracre <br />per year. <br />R -The average annual erosion index for a specific <br />geogrttphic region, considering amount, lime and <br />duration or the rainfall. <br />Example Situation: <br />An urban development project is planned in Arapahoe <br />County. 1'o predict annual soil loss, determine the aP• <br />plicable R, K, LS, and C factors. The product of these <br />factors is nn estimate of tons of soil loss per acre per <br />Segment 1 30 x ,32 x 4.0 x 1.0 <br />R K LS C <br />Segment 2 SO x ,2H x 1.4 x 1.0 = <br />To predict soil loss for a portion of the year, tactor"R" <br />will need to he adjusted by the percentage of the erosion <br />index occurring during that portion of the year. For <br />example to determine thu E.1. for August, September <br />and October, refer' to Figure 8. Multiply the pcrecmage <br />EI-The erosion index Cur only a portion of the year. <br />Determine the ptrcemage of the toad erosion <br />index and multiply times the total annual "R" <br />factor shown on Figure 7. See Figure 8 to de[cr- <br />mine the percent of E.1. <br />K -The soil credibility factor based on particle size <br />dis[ribution, organic matter content, strucwre <br />and permeability. Convect the Suil Conservation <br />Service for factor values. <br />LS-The factor that accounts tier the length and per- <br />cent slope. See Figure 9. <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 I1. <br />year. It may be necessary to divide the area into scg• <br />menu to account fur variation in factor values. In this <br />example, notice the "C" fnctor is I.O, which indicates <br />that the soil will he essentially vuidufprotectivecover. <br />64 Wns x 4 Ac ~ 23G.0 tons <br />19.6 tons x G Ac - 117.6 tons <br />7'otai TonslYr 373.6 tuns <br />from Figure 8 times the "R" value: for that geogruphicul <br />region. The result is the E.I. for that period of the yter. <br />Therefore, an "R" factor of SU would be adjusted to <br />13.3 (SO x 27%). <br />Segment 1 13.3 x ,.12 x 4,0 x 1.0 = 17.2 x 4 Ac <br />P..1. K LS C <br />Segment 2 13.5 x ,28 x 1.4 x 1.0 5.2 x ti Ac <br />Total tons during Aug-Oct <br />`': ~ 26 <br />,. )1 <br />= Gs.s <br />= 31.2 <br />IOO.U tons <br />1 <br />