Submitted to: Earth Surface Processes and Landforms
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/30/1998
Publication Date: N/A
Interpretive Summary: More than 50 years ago, between 1944 and 47, Ellison published a series of papers on water erosion and proposed the mechanistic approach to separate erosion processes to detachment and transport by raindrop splash and surface flow. Ellison's work built the foundation and led to the development of current process-based erosion prediction models. Nevertheless, experimental procedures to test some of the model concepts were not developed, making them hypothetical in nature. A dual-box system, consisting of a 1.8 m sediment feeder box positioned upslope to a 5 m test box, was designed to evaluate sediment mass balance relationships and erosion process scenarios. The test box can be set to seepage or drainage conditions, thus enabling us to study the surface hydrologic effects on erosion. Results showed that at 5% slope under seepage or 10% slope under drainage condition, the runoff from the feeder box caused additional sediment transport in the test box, indicating a transport-dominated sediment regime. At 5% slope under drainage condition, deposition occurred at low rainfall intensities. Increases in slope steepness, rainfall intensity and soil erodibility shifted the dominant erosion process from deposition to transport. These findings further the understanding of erosion processes and their dynamic interactions with changing soil surface conditions. These results can be used to improve the predictive capability of process-based erosion models.
Technical Abstract: Sediment transport capacity, Tc, defined as the maximum amount of sediment that a flow can carry, is the basic concept in determining detachment and deposition processes in the current process-based erosion model framework. Although defined conceptually and used extensively in modeling erosion, Tc was rarely measured. Recently, a series of laboratory studies designed to quantify effects of surface hydrologic conditions on erosion processes produced data sets feasible to evaluate the concept of Tc. A dual-box system, consisting of a 1.8-m long sediment feeder box and a 5-m long test box was used. Depending on the relative values of sediment delivery from the feeder and test boxes, five scenarios are proposed ranging from deposition-dominated to transport-dominated sediment regimes. Results showed that at 5 percent slope under seepage or 10 percent slope under drainage condition, the runoff from the feeder box caused additional sediment transport in the test box, indicating a transport-dominated sediment regime. At 5 percent slope under drainage condition, deposition occurred at low rainfall intensities. Increases in slope steepness, rainfall intensity and soil erodibility shifted the dominant erosion process from deposition to transport. Erosion process concepts from the Meyer-Wischmeier (1969), Foster-Meyer (1972) and Rose (1985) models were compared with the experimental data and the Rose model was found to best describe processes occurring during rain. A process-based erosion model needs to have components that can represent surface conditions and physical processes and their dynamic interactions.