Numerical study of the effect of vegetation on alternate-bar morphodynamics

Abstract:

The presence of riparian vegetation on rivers has attracted increasing attention from both the scientific community and the river managers. Vegetation modifies flow structure, increases local hydraulic roughness and sediment deposition contributing to bed and bank accretion and flood risk. A variety of numerical models have been developed to consider the effects of vegetation on river morphodynamics. The common way for accounting the effects of vegetation in numerical models is to define a specific roughness for vegetated beds or to add a drag force as a friction source term in the momentum equation. However, studies suggest that using a global roughness for vegetated beds leads to incorrect estimations of the sediment transport rate and, the drag force exerted by the plants does not affect directly sediment transport. In this study, we propose to model the direct effect of vegetation on morphodynamics. Based on the original way by adding a drag force, Einstein’s flow intensity parameter ψ has also been modified by adding a correction factor including plant characteristics as proposed by Armanini & Cavedon (2019). A 2D-H model has been constructed and calibrated based on the flume experiments of these authors using the open TELEMAC-MASCARET system. A second numerical model is constructed and calibrated from experiments of Vargas-Luna et al., (2019) to validate this numerical implementation and will be used to study the effect of vegetation on alternate-bar morphodynamics.