Evaluating a multiclass net deposition equation in overland flow conditions

Abstract

The movement of sediment and related pollutants in overland flow from the point of erosion to a stream normally occurs through a series of deposition zones. Here we present the evaluation of a new multiclass model of sediment transport through these zones. This model simulates size-selective net deposition as a result of simultaneous deposition by settling and nonselective reentrainment of previously deposited sediment [Hairsine et al., 2002; Sander et al., 2002]. Multiclass sediment deposition models provide a useful basis for simulating off-site effects of soil erosion, but information on the grain-size composition of deposited and exported sediment is crucial for calibrating and evaluating such models. Therefore the multiclass sediment deposition model was tested using detailed experimental data. Information on the amount of sediment deposition, on the grain-size distribution of the deposited and exported sediment, and on the spatial pattern of the deposits was collected during sediment deposition experiments. Calibration of the multiclass model, using one part of these data, was performed by adjusting the function of stream power available for sediment reentrainment by minimizing errors between both simulated and observed total outflow sediment concentration and grain-size distribution of the exported sediment. Evaluation was conducted, using the other part of the data, over a wide range of conditions. The evaluation shows that the deposition equation is capable of reasonably simulating the observed size selectivity of the deposition process. However, the model is not capable of simulating correctly the spatial pattern of the deposited sediment because of simplifications used in the hydraulic model.