Sediment transport capacity and erosion processes: Model concepts and reality

Sediment transport capacity, T-c, defined as the maximum amount of sediment that a flow can carry, is the basic concept in determining detachment and deposition processes in current process-based erosion models. Although defi ned conceptually and used extensively in modelling erosion, T-c was rarely measured. Recently, a series of laboratory studies designed to quantify eff ects of surface hydrologic conditions on erosion processes produced data se ts feasible to evaluate the concept of T-c. A dual-box system, consisting o f a 1.8 m long sediment feeder box and a 5 m long test box, was used. Depen ding on the relative magnitudes of sediment delivery from feeder and test b oxes, five scenarios are proposed ranging from deposition-dominated to tran sport-dominated sediment regimes. Results showed that at 5 per cent slope u nder seepage or 10 per cent slope under drainage conditions, the runoff fro m the feeder box caused additional sediment transport in the test box, indi cating a transport-dominated sediment regime. At 5 pet cent slope under dra inage conditions, deposition occurred at low rainfall intensities. Increase s in slope steepness, rainfall intensity and soil erodibility shifted the d ominant erosion process from deposition to transport. Erosion process conce pts from the Meyer-Wischmeier, Foster-Meyer and Rose models were compared w ith the experimental data, and the Rose model was found to best describe pr ocesses occurring during rain. A process-based erosion model needs to have components that can represent surface conditions and physical processes and their dynamic interactions. Copyright (C) 1999 John Wiley & Sons, Ltd.