ABSTRACT
Dunes are major bed forms in waterways and significantly influence the local water depth which can affect the shipping capacity. The prediction of dune dimensions such as height and length is therefore of high interest for the Federal Waterways Engineering and Research Institute, Karlsruhe, Germany (BAW). An existing three dimensional hydro-morphodynamic numerical model was used to simulate the movement of bed forms in a 4 km long section of the River Elbe during constant discharge conditions. The model consists of 13 million elements with a maximum horizontal node distance of 2 m. This resolution is needed to directly represent bed forms (50-140 m length, 0.5-1.2 m height) in the mesh. The statistical dune parameters for a constant low water discharge could not be forecast precisely but the simulations show the correct trends for all parameters. An eight day segment from the subsiding part of a flood wave event was simulated and the dune parameters were compared to the measured ones. The correct trends for dune height, skewness and kurtosis could be simulated but highly overestimated the measured values so the prediction was not satisfying.
In principle, dune prediction with three-dimensional numerical RANS (Reynolds-Averaged Navier- Stokes) models and a proper turbulence model such as the k-epsilon model seems possible. However, more experience is needed to achieve this ambitious goal, firstly in the analysis of measurements and secondly in the numerical simulation of different discharge situations.
