ABSTRACT
Gravel replenishment by artificial deposits is a potential measure to address sediment deficit in rivers. The main goals of gravel addition are preventing further erosion, reestablishment of natural river morphology, and restoration of spawning grounds for fish. Over the last decade, this technique has gained popularity and is applied in a number of Swiss gravel-bed rivers, such as the Aare, Reuss, Rhine and Limmat Rivers. However, the erosion process of artificial gravel deposits and the corresponding impact on river morphology are not yet fully understood. To improve the understanding of the erosion process of gravel deposits, a composite modeling approach was used. Physical experiments of the erosion of gravel deposits were performed for conditions typically found in Swiss lowland gravel-bed rivers (Friedl et al. 2016). Based on these data, we evaluated the capability of the 2D depth-averaged morphodynamic model BASEMENT to reproduce gravel deposit erosion. The included transport model is based on the Hirano-Exner approach for non-uniform sediment, and considers reduction of the critical Shields parameter due to local slope, correction of bed load transport direction due to lateral bed slope, and bank collapse. In the present paper, we investigated different configurations with regard to the geometry of the gravel deposit, discharge, and grain size distribution by numerical experiments. The results of the numerical model are in good agreement with the temporal evolution of cross-sectional geometry and erosion rates found in the laboratory experiments. The promising results indicate the potential use of the numerical model as a planning and decision-making tool for sediment replenishment projects applied on reach-scales.
