Modelling sediment transport over partially non-erodible bottoms

In depth- and cross section-averaged morphodynamic models, based on explicit time integration, it may happen that the computed bed level becomes lower than the top level of a non-erodible layer (e.g. concrete, bedrock or armoured layer). This is a standard pitfall which has been addressed in different ways. In this paper, we present an original approach for avoiding computation of non-physical bed levels, using an iterative procedure to correct the outward sediment fluxes. The procedure is shown to be computationally efficient while it achieves a high accuracy in terms of mass conservation. We compare our original approach with the existing Struiksma’s method and with a reformulation of the problem in terms of mathematical optimization of a linear or non-linear objective function under linear constraints.
The new procedure has been incorporated into an existing finite volume morphodynamic model. It has been validated with several 1D benchmarks leading to configurations with sediment transport over non-erodible bottom. The computation time has been verified not to increase by more than 15% compared to runs without non-erodible bottom.