The Prediction of Dunes and Their Related Roughness in Estuarine Morphological Models

The prediction of dune characteristics in coastal waterways is of great importance for at least two reasons. On the one hand the crests impose a lot of dredging problems and on the other hand dunes contribute to the hydraulic resistance of the system and to the damping of the tidal wave. Therefore it is a major research aim to simulate the development of dunes in morphological numerical models. In this paper an algorithm is developed to simulate the evolution of dune heights and lengths. In the first step the dune parameters are calculated using empirical relations (i.e. here van Rijn) for every hydrodynamical time step. The values obtained in that way are not the actual dune heights and lengths because they would grow during ebb and flood tide and they would disappear during slack water. Instead of this they are regarded as asymptotical values reached theoretically after a certain time. The actual dune height and length are calculated applying a relaxation method using the empirical values as asymptotical values. This algorithm gives good results for the location of dunes in the Weser estuary at the North sea coast of Germany. The predictions for the dune heights and lenghts are reasonable.