CALIBRATING AND VALIDATING THE SEDIMENT DELIVERY DISTRIBUTED (SEDD) MODEL USING 137CS MEASUREMENTS

Soil erosion has become a serious environmental problem in the agricultural and forest lands of southern Italy, where annual soil loss associated with extreme rainfall events can reach 100 t ha-1. There is a need to use numerical models to predict soil erosion and sediment delivery under different physiographic and land use conditions, in order to assess erosion risk and develop effective erosion and sediment control strategies. However, model validation and calibration is a key requirement for the successful use of such models. The use of fallout 137Cs measurements affords a useful means of assembling spatially distributed information on soil redistribution rates, which can be used to calibrate and validate sediment delivery models. In this paper, 137Cs measurements are used to calibrate and validate the SEDD model for the 31.61 km2 Trionto catchment located in Calabria (southern Italy), where high values of soil erosion in mountain areas are balanced by deposition and sediment storage in lowland areas, resulting in a relatively low sediment delivery ratio for the catchment. The sediment delivery ratios estimated using the 137Cs measurements made within the catchment have been used to calibrate the model specific parameter ?, which showed a strong dependence on the SDR values for individual subcatchments. The SEDD model was then validated at the annual timescale using the specific sediment yield derived from measurements of the suspended sediment flux at the catchment outlet.