Use of Caesium-137 Measurements and Long-Term Records of Sediment Load to Calibrate the Sediment Delivery Component of the SEDD Model and Explore Scale Effect: Examples from Southern Italy

Soil erosion has become a serious environmental problem in southern Italy, where annual soil loss associated with extreme rainfall events can reach 100-150tha-1. In order to predict rates of soil loss and sediment yields, to inform the development of effective erosion and sediment control strategies in these areas, several prediction models have been utilized in recent years. Most of these models are based on the universal soil loss equation (USLE) or revised universal soil loss equation (RUSLE). However, they require calibration and validation if they are to be used to provide reliable estimates of soil erosion and sediment yield. The use of fallout Cs-137 measurements affords a useful means of assembling spatially distributed information on soil redistribution rates, which can be used to calibrate and validate sediment yield models. This paper reports a study in which Cs-137 measurements have been used to calibrate the sediment delivery component of the sediment delivery distributed (SEDD) model for four catchments of contrasting size, slope, and land use, located in southern Italy. The estimates of net soil loss for the individual catchments and subcatchments derived from the Cs-137 measurements have been used to calibrate the model specific parameter, beta, which showed a strong dependence on the sediment delivery ratio (SDR) values for individual subcatchments. The SEDD model was then successfully validated at the annual timescale using values of annual specific sediment yield derived from measurements of the suspended sediment loads at the catchment outlets.