Evaluation of the WEPP model and digital elevation grid size, for simulation of streamflow and sediment yield in a heterogeneous catchment

The Water Erosion Prediction Project (WEPP) model was tested using data from a detailed study conducted on experimental plots in the Apennines Mountain Range, northern Italy. Runoff, soil water and sediment data, together with weather information, were collected on an hourly basis at the study site. WEPP was first applied to simulate transient surface runoff, soil water and erosion. Two important input parameters, the biomass energy ratio for crop and the effective hydraulic conductivity of surface soil, were calibrated using field-observed runoff, soil water, erosion and plant biomass data. The calibrated model was then used to simulate the hydrologic and erosion impacts of three typical crop rotations, thereby to evaluate their abilities in reducing surface runoff and sediment yield. Results indicated that, with the definition of a restrictive layer at the bottom of the soil profile and the calibration of the two crucial model parameters, WEPP could adequately account for the water balance for the modeled experimental plot. For the study area, continuous corn with a conservation practice that delayed primary and secondary tillages produced low surface runoff and soil erosion, from both field observation and WEPP modeling. However, this mono-cultural practice may lead to accelerated soil-quality degradation. On the other hand, a four-year-rotation, corn–wheat–alfalfa–alfalfa, was predicted to substantially reduce soil erosion and has potential to become a sustainable cropping system under the pedo-climatic settings of the study area.