『Summary
The Universal Soil Loss Equation (USLE) is the most widely used
and misused prediction equation in the world. although it was
designed to predict long-term average annual soil loss, it has
the capacity to predict event soil losses reasonably well at some
geographic locations and not well at others. Its lack of capacity
to predict event erosion is highly influenced by the fact the
event rainfall-runoff factor used in the USLE and its revisions
(RUSLE, RUSLE2) does not consider runoff explicitly. While including
direct consideration of runoff in the event rainfall-runoff factor
improves the capacity to predict event erosion when runoff is
measured, that capacity is reduced by inaccurate runoff prediction
methods. Even so, the predictions may be better than when the
traditional event rainfall-runoff factor is used if the rainfall-runoff
model used to predict runoff works reasonably well. Direct consideration
of runoff in the rainfall-runoff factor may improve the ability
of the model to account for seasonal effects. It also enhances
the ability of the model to account for the spatial variations
in soil loss on hillslopes which result from spatial variations
in soil and vegetation. However, the USLE model will not provide
a capacity to account for deposition taking place on concave hillslopes
unless it is coupled with an appropriate sediment transport model,
as in done in RUSLE2. Changing the basis of the event rainfall-runoff
factor has consequences on a number of the other factors used
in the model, in particular new values of the soil erodibility
factor need to be determined. Using runoff values from cropped
areas is necessary to account for differences in infiltration
capacities between vegetated and tilled bare fallow areas, but
requires re-evaluation of the crop factors.
Keywords: Rainfall erosion; Hillslopes; Spatial and temporal variation』
Contents
Introduction
Runoff and event erosivity
The impact of erosivity indices on other factors in the USLE
model
The K factor
The C factor
The P factor
The L and S factors
Non uniform runoff production
Hillslope form
Event erosion and the unit plot approach
Model predictive capacity
Determining EI30 and the R factor
Accuracy of runoff predictions
Accuracy of predictions of soil loss by more process-based models
Conclusion
References