Fine sediment deposits in gravel bed rivers: Sensitivity analysis to particle properties using a 2D hydrodynamic and sediment model

Fine sediment dynamics in mountainous rivers are poorly understood. However, high suspended sediment concentrations during natural events or reservoir flushing are known to be an issue further downstream. Numerical models are frequently used to predict sediment behavior, but measurements of cohesive sediment properties are rarely available. This study investigates the sensitivity of a numerical model to parameters describing cohesive sediment behavior. The study case is a 3-km reach of the Isère River in the Alps with alternate gravel bars. The simulated outputs are the surfaces and volumes of fine sediment deposits over control areas. These outputs are analyzed to assess the sensitivity to the parameters describing erosion and sedimentation in order to identify on which measurements and in which areas measurements efforts should be focused. For two simulated flushing events, disparities between various deposition areas are observed, depending on their locations on the gravel bar and the local hydraulic conditions.