| Modelling erosion for prediction purposes started with the development of the Universal Soil
Loss Equation the focus of which was the prediction of long term (~20) average
annul soil loss from field sized areas. That purpose has been maintained in the
subsequent revision RUSLE, the most widely used erosion prediction model in the world.
The lack of ability to predict short term soil loss saw the development of so-called
process based models like WEPP and EUROSEM which focussed on predicting event
erosion but failed to improve the prediction of long term erosion where the RUSLE
worked well. One of the features of erosion recognised in the so-called process
based modes is the fact that runoff is a primary factor in rainfall erosion and some
modifications of USLE/RUSLE model have been proposed have included runoff as in
independent factor in determining event erosivity. However, these models have ignored
fundamental mathematical rules. The USLE-M which replaces the EI30 index by
the product of the runoff ratio and EI30 was developed from the concept that soil
loss is the product of runoff and sediment concentration and operates in a way that
obeys the mathematical rules upon which the USLE/RUSLE model was based. In
accounts for event soil loss better that the EI30 index where runoff values are known or
predicted adequately. RUSLE2 now includes a capacity to model runoff driven erosion. |