Effects of transport capacity and erodibility on rill erosion processes: A model study using the Finite Element method

Soil erosion prediction models are of great significance for soil and water conservation management. Rill erosion is the most important component of hillslope soil erosion processes. Therefore, predicting hillslope erosion requires that rill erosion is well understood and predictable. In this study, a physical process-based model for rill erosion was developed. A series of mathematical models were advanced to simulate rill hydrodynamics, soil detachment, and transport capacity for well-defined rill channels. The Finite Element method and a Visual C++ program were used to numerically solve the hydrodynamic and sediment continuity model equations. Model parameters, estimated by a different method, were used in simulation case studies to determine the impacts of their values on rill sedimentation processes, as compared with the experimental data. The comparison of experimental results with simulation outputs of the model validated the model equations and the computer program. The model is capable of simulating the dynamics of rill erosion processes. Comparisons of the simulated results with different model parameters indicated that: (i) the developed model can well simulate the rill erosion processes, provided that the model parameters were correctly estimated; (ii) the transport capacity limits the sedimentation process and the maximum possible sediment concentration at the rill outlet; (iii) rill erodibility determines the rate at which sediment concentration approaches its allowed value; and (iv) rill erodibility and transport capacity combined determine the distribution of soil erosion along a rill. Therefore, this study not only supplies a tool for further development of dynamic soil erosion prediction models but also verifies the importance of correctly estimating model parameters.