Sediment Transport by Overland Flow on Irregular Hillslope Surfaces
Athol Abrahams Principal Investigator
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Soil erosion models have become an essential tool for soil conservation planning and design and for a variety of other land management and assessment tasks. Modern soil erosion models are process based, and virtually all of them contain a formula for predicting sediment transport capacity, as transport capacity controls both rate of erosion and rate of deposition. Although all hillslopes have irregular surfaces, no existing formula is capable of accurately predicting the transport capacity of overland flow on such surfaces. There is an urgent need for development of such a formula. This project will develop sediment transport formulas for stone covered and grass covered surfaces as a first step toward development of a more general formula for all irregular surfaces. The research will be based on two sets of flume experiments in the laboratory. Cylinders will be used to simulate stones and nails will simulate grass. Experiments will be performed in a six meter long flume using a variety of water discharges, gradients, grain sizes, and cylinder and nail concentrations. The analysis will establish empirical relations between transport capacity and appropriate hydraulic variables that reflect the energy dissipated near the bed and available to transport sediment. The ability of process-based soil erosion models to provide accurate predictions of soil erosion is dependent on the accuracy of the transport capacity equation they employ. This research should produce formulas for stone and grass covered surfaces which can be incorporated immediately into existing soil erosion models. Use of these formulas should lead to more accurate estimates of sediment transport capacity and thus better predictions of soil erosion rates on irregular surfaces.