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' • Practical Approa~far Effective E & S Control - 81 <br />' hydraulic mulch or dry straw mulch) from the total volume of water applied, <br /> one can determine the amount of water which has infiltrated the soil, and is <br /> thereby available for plant use. In grid climates the percentage of water <br /> available for plant use may be in fact the most critical variable in the long term <br /> erosion control effectiveness of a system. A surface applied or incorporated <br />' mulch may reduce runoff by absorption or adsorption, but the retained moisture <br /> serves has no benefit to plants unless that water is in proximity to plant roots or <br /> held at tensions where it can be available to plane. <br />1 <br /> Y Sediment Yield, given in tons/acre or as a percentage of a control <br /> The Universal Soil Loss Equation (LISLE) provides a method to estimate the <br /> amount of erosion occurring on a plot of soil on an annual basis. It is expressed <br />' as: <br />' A=RxKzLSxCxP <br />' where: <br /> A =Annual amount of erosion(tons/acrelyeaz) <br /> R =Rainfall factor <br /> K = Soil erodibility factor <br />' LS = Slope length and steepness factor <br /> C =Cover factor <br />' P =Conservation practice factor <br /> One limitation of the LISLE is that it predicts annual erosion, not storm or event <br /> generated soil loss. Also, while we aze naturally concerned about the amount of <br /> erosion occurring on a site, today we are most commonly concerned about the <br /> amount of sediment which is delivered off the site by runoff water, pazdculazIy <br /> in light of recent stotmwater management regulations. The variable "Y" in this <br />' discussion is used to evaluate a practice based on its ability to retain sediment on <br /> site, either through reducing the erosion potential of the soil or by retaining <br />' sediment generated from any erosion that does occur. <br /> "Y" for most erosion control materials is best determined utilizing rainfall <br /> simulation and comparing sediment yield from a bare soil control plot to that <br /> delivered from a similaz plot treated with an erosion control practice. A <br />' dominant number of erosion control practices and materials on the mazket today <br />have been evaluated in such a manner on test flumes at Purdue University, the <br /> Utah State Water Resources Laboratory, Colorado State and other reseazch <br />' facilities. A relative ranking of dissimilar technologies on their effectiveness to <br />' O 1995 IECA <br />