Identifying areas of a basin that are most sensitive to erosion have stimulated the study of within-basin variability of the sediment-delivery processes and the use of spatially distributed models. To verify the reliability of a sediment-delivery distributed model applicable at the morphological unit scale (i.e., the area of clearly defined aspect, length, and steepness), experiments were carried out at mean annual and event scales in a small Sicilian basin. A Geographical Information System is briefly presented into which the measurements carried out at the basin outlet (runoff sediment yield, etc.) and other point and areal information (soil erodibility, digital terrain model, etc.) were entered. For validating the model at mean annual temporal scale, the sediment yield spatial distribution calculated by the model was compared with the net soil erosion spatial distribution obtained by cesium-137 activity measurements. At morphological unit scale, the agreement between measured and calculated sediment yield values showed a good predictive ability of the model at mean annual temporal scale. Finally, the model was calibrated and tested using five rainfall-runoff events measured at the outlet of the experimental basin. The analysis showed that -the coefficient β, appearing in the expression of the sediment delivery ratio of each morphological unit, is independent of subdivision criterion and can be estimated by the hydrological characteristics of the rainfall-runoff event. The comparison between measured and calculated sediment yield values showed that the sediment delivery distributed approach has a good predictive ability at event scale, too.
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