A GIS procedure for automatically calculating the USLE LS factor on topographically complex landscape units

ABSTRACT: A computer algorithm to calculate the USLE and RUSLE LS-factors over a two-dimensional landscape is presented. When compared to a manual method, both methods yield broadly similar results in terms of relative erosion risk mapping. However, there appear to be important differences in absolute values. Although both methods yield similar slope values, the use of the manual method leads to an underestimation of the erosion risk because the effect of flow convergence is not accounted for. The computer procedure has the obvious advantage that it can easily be linked to GIS software. If data on land use and soils are available, specific K, C and P-values can be assigned to each land unit so that predicted soil losses can then be calculated using a simple overlay procedure. The algorithm leaves the user the choice to consider land units as being hydrologically isolated or continuous. A comparison with soil data showed a reasonably good agreement between the predicted erosion risk and the intensity of soil truncation observed in the test area.