Runoff dependent erosivity and slope length factors suitable for modelling annual erosion using the Universal Soil Loss Equation
2007
Kinnell, P.I.A.
Despite revisions and refinements, the Revised Universal Soil Loss Equation (RUSLE), which is the revised version of the Universal Soil Loss Equation (USLE), over predicts small annual soil losses and under predicts large annual soil losses. To some large extent, this results from the equation over estimating small event soil losses and under estimating large event soil losses. Replacing the USLE/RUSLE event erosivity index (EI₃₀) by the product of EI₃₀ and the runoff ratio (QR) significantly reduces the errors in estimating event erosion when runoff is measured, but the USLE-M, the USLE variant that uses the QREI₃₀ index, requires crop and support practice factors that differ from those used in the RUSLE. The theory which enables the QREI₃₀ index to be used in association with the RUSLE crop and support practice factors is presented. In addition, the USLE/RUSLE approach was developed for conditions where runoff is produced uniformly over a hill slope. A runoff dependent slope length factor that takes account of runoff variations over a hill slope is presented and demonstrated for the situation where runoff from a low runoff producing area passes onto an area where runoff is produced more readily.
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