Because eroded sediments are produced from different sources throughout a basin, it is often advantageous to model sediment delivery processes at basin scale using a spatially distributed approach. In this paper, a sediment delivery distributed (SEDD) model applicable at morphological unit scale, into which a basin is divided, is initially proposed. The model is based on the Universal Soil Loss Equation (USLE), in which different expressions of the erosivity and topographic factors are considered, coupled with a relationship for evaluating the sediment delivery ratio of each morphological unit. Then the SEDD model is calibrated by sediment yield and rainfall and runoff measurements carried out, at annual and event scales, in three small Calabrian experimental basis. At event scale, the analysis showed that a good agreement between measured and calculated basin sediment yields can be obtained using the simple rainfall erosivity factor; the agreement is independent of the selected equations for estimating the topographic factors. The analysis developed at annual scale showed that the model reliability increases from the event scale to the annual scale. Finally, a Monte Carlo technique was used for evaluating the effects of the uncertainty of the model parameters on calculated sediment yield.

In this paper, using Sicilian and Australian rainfall intensity data, a comparison between different estimators (modified Fournier index F, F_F index) of the rainfall erosivity factor in the USLE was made. The relationship between the modified Fournier index and the mean annual rainfall, P, was theoretically derived. The K constant, linking the F_F index and P, and its cumulative distribution function (CDF) were used to establish hydrological similitude among different geographical regions of southern Italy and southeastern Australia. To predict the erosion risk for an event of given average recurrence interval, the probability distribution of the annual value F _a.j of the Arnoldus index was studied. In order to establish the theoretical CDF to use as a regional parent distribution, the descriptive ability of LN2 and EV1 distributions was studied by both an at-site analysis and a hierarchical regional procedure. The analysis showed that for each sub-region of southern Italy and southeastern Australia, characterized by a constant coefficient of variation, the erosion risk index is constant.