Author(s): Lieke Lokin; Jord Warmink; Anouk Bomers; Suzanne Hulscher

Linked Author(s): Lieke Lokin, Jord Warmink, Anouk Bomers

Keywords: River dunes; Modelling; Low flow; High flow

Abstract: River dunes are dynamic bed forms on the river bed, which are formed by the constant interaction between the governing flow and the sandy bed. The river dunes increase water levels during flood events because they increase roughness, but they can also limit navigable depths during low flows specifically when dunes propagate over already shallow areas in the river. To improve river management, related to these bed forms, accurate models that are able to simulate these river dunes are needed. Currently a wide variety of river dune models do exist, ranging from idealized models to study processes in dune formation to complex numerical models that solve flow, sediment transport and bed elevation changes in a 3D grid. As complexity increases, computation time increases as well. To be applicable for predictions on where dunes may cause problems for example for navigability or what roughness, a dune model is needed that is able to accurately simulate dune dynamics in real rivers, including the range of discharge regimes possible, but with relatively small computation times. Therefore, we improved a dune simulation model, which has previously been used to model dune dynamics for high flows and which is now able to also accurately mode dune dynamics during low flows. The model solves the flow field in a 2DV grid using a constant eddy viscosity. The flow field is then used to calculate sediment transport and update the bed. The domain of the model is one dune length long and with cyclic boundary conditions. The domain length and therefore the dune length is determined through a linear stability analysis which is updated when flow properties change. This model has been calibrated based on dune data from the main distributary of the Rhine River in the Netherlands. Specifically on the year 2018 which first started with a flood wave after which the discharge was relatively constant around the long term median discharge and the year ended with a period of extreme low discharges. Therefore we present a physics based dune simulation model, which can fairly fast and accurately simulate dune dynamic throughout discharge regimes ranging from extreme low flows to high flood waves. Which in the future can be used to make predictions on the height and location of river dunes, for making estimations on navigability, planning dredging operations and evaluation of river management policy.

DOI: https://doi.org/10.3850/IAHR-39WC2521711920221514

Year: 2022