Evaluating the MEFIDIS model for runoff and soil erosion prediction during rainfall events

MEFIDIS-short for Physically Based Distributed Erosion Model-was developed to simulate the consequences of climate and land-use changes for surface runoff and erosion patterns during extreme rainfall events. The model relies on physically based runoff and soil detachment equations, dividing the simulation area into spatial homogeneous units and using a dynamic approach for runoff and suspended sediment distribution. It was evaluated with measured runoff and net erosion data for 16 events in the Lucky Hills 103 (USA) and Ganspoel (Belgium) catchments, using a single parameter set for each catchment and simple assumptions (wet or dry) on pre-storm soil moisture. The model was applied with a resolution of 5 × 5 m and 1-s time-steps. Observed soil erosion patterns in Ganspoel were also used in the evaluation exercise. Overall, simulation results have a good correlation with measured data (ranging from 0.85 to 0.96). Model precision was less satisfactory (average unsigned error ranging from 37% to 47%), but it still fell well below the variability of the events (two orders of magnitude for runoff and net erosion). Part of the simulation errors appear to be linked with variability in runoff and erosion measurements. The calibrated model for Ganspoel required two parameter sets for crusted and non-crusted conditions for half of the analyzed land-use classes; better calibration of parameters associated with crusting significantly improved model performance for this catchment. Despite this problem, MEFIDIS was shown to perform well for the range of selected events. Within-watershed simulated runoff in Lucky Hills 103 compared well with measured results. In Ganspoel, the simulated erosion patterns did not compare well with observed patterns; however, simulated erosion sources were located inside the fields where erosion features were observed, and within a distance of 65 m. The model has therefore the potential to predict sediment sources inside a catchment, but the high resolution results should be used only as an indicator