A gravity-driven runoff and erosion model for sediment transfers at the catchment scale

Abstract

The aim of this work is to simulate hydraulic transfers and upstream erosion sources in steep and erodible mountain watersheds with a physicallybased hydraulic model. In such environments, immature debris flows and shallow landslides can be the largest sources of sediments transported at the outlet. To simulate these phenomena, a gravity-driven erosion model and a 1D vertical infiltration model have been developed in the TELEMAC 2D numerical code. In this new erosion model, the motion of the granular flow is described with a fully dynamic system and a Coulomb-like bottom friction treatment, more adapted to the properties of the flow. The new model is first qualitatively evaluated on a theoretical test case: a steep plot with a slope break is used to evaluate the erosion and deposition dynamics of a single immature debris flow. Then, the model is confronted to field data on a real catchment (Draix, in the Southern French Alps). First, the infiltration model is successfully calibrated in order to simulate two different rain events. Then, the new erosion model is applied at the catchment scale. The numerical results show a very realistic behavior compared to the field observation, providing erosion in the upper parts of the hillslopes and deposition in the hydraulic network. This work opens promising perspectives, for example by coupling this new model with a classical and complementary velocity-driven model for the erosion, deposition and transfers in the hydraulic network.