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Practical Approacha for Effe:tive E do 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 rue 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 rite retained moisture <br />serves has no benefit to plants unless that water is in pmxim,ity to plant roots or <br />held at tensions where it can be available to plants. <br />Y Sediment Yield, given in toss/acre or as a percentage of a control <br />The Universal Soil Loss Equation (USL~ 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=RxKxLSxCzP <br />where: <br />A =Annual amount of erosion(tons/acre/yeaz) • <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 USLE is that it predicu annual erosion, not storm or event <br />generated soil loss. Also, while we are naturally concernod 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, particulazly <br />in light of recent stormwater 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 utiliring rainfall <br />simulation and comparing sediment yield from a bare soil control plot to that <br />delivered from a similar plot treated with an erosion conm~l practice. A <br />dominant number of erosion control practices and materials on the market today <br />have been evaluated in such a manner on test flumes at Purdue University, the <br />Utah State Water Resources Laboratory, Colorado Stare alyd other reseazch <br />facilities. A retative ranking of dissimilar technologies on their effectiveness to <br />O 1995 IECA <br />