Modeling soil erosion and sediment load at different time scales in a medium-sized watershed

A monitoring station for suspended sediment transport is in operation in the Carapelle torrent since 2007. Continuous data are registered to investigate the relationships between suspended sediment concentration and water discharge in flood flows and to model soil erosion and sediment load at the watershed scale. The Carapelle is one of the main streams of Apulia region (Southern Italy); the rainfall regime is typically Mediterranean and the land use is largely represented by winter wheat, with a lower fraction of deciduous oaks, hardwoods, pasture and other land uses. The AnnAGNPS model was calibrated and validated at the event scale. Thirty-six events were used to estimate the performance of the model during the period 2007-2011. The model performed well in predicting runoff; the prediction capability of sediment load was also good. On the monthly and annual scale, the model showed a good prediction capability for runoff and satisfactory results for sediment load. Based on the current conditions of the watershed as a baseline scenario, the effectiveness of alternative management practices was also evaluated, with a focus on reduced tillage and conversion of cropland to forest. To identify feasible strategies, the latter was targeted only at the most erosion-prone areas, as detected by the model. The effect of vegetated streams and riparian buffers as natural traps increasing the in-situ sediment deposition was also considered.