Length slope factors for applying the Revised Universal Soil Loss Equation at basin scale in southern Italy

In this paper, for a basin divided into morphological units, a distributed model based on the Revised Universal Soil Loss Equation (RUSLE), with different expressions for the topographic factors, and on the sediment delivery ratio of each morphological unit is used. At first, the caesium-137 data available from a Sicilian basin are calibrated with two different models [the Proportional Method (PM), the Simplified Mass Balance (SMB) model] to provide net soil loss data for each morphological unit. Then, for a selected expression of the topographic factor, the slope length exponent is calculated for each morphological unit, equating the calculated sediment yield with the net soil loss. The analysis showed that the median value of the slope length exponent is dependent on the mesh size of the Digital Elevation Model used for calculating the slope of each morphological unit. The analysis also showed that the slope of the linear relationship between slope length exponent and mesh size is independent of the calibration method used for the caesium-137 measurements. Finally, the sediment yield measurements carried out in three small Calabrian basins and a Monte Carlo technique are used for evaluating the effect of the knowledge uncertainty and the stochastic variability of the model parameters on calculated sediment yield. (C) 2000 Silsoe Research Institute.