The Influence of Waves on the Sediment Composition in a Tidal Bay

Following paper contains a presentation of an integrated model approach combining tidal current and wave impact on a graded sediment transport model. The tidal currents are modelled by using a two-dimensional hydrodynamic numerical model. A coupled wave climate model calculates directional frequency-spectra. In order to describe hydrodynamic and wave influenced sediment transport developments, a graded sediment model is used. The following paper will show that the graded sediment transport model allows a site-specific description of sediment distribution in a bay. The development of different tidal flats, e.g. mud flat and sand flat, can be reproduced. It will be shown that this integrated model approach is capable of simulating the accumulation of fine sediments in shallow areas and bed coarsening in the deeper channels due to tidal currents. Combined impact of tidal currents and waves leads to resuspension of Fine sediments in shallow areas. A part of the resuspended sediments are brought back into the deeper areas of the bay. Tidal current transports fine sediments from deep water regions with high bed shear stress to shallow areas in a bay. In the shallow regions the sediment accumulates based on low bottom shear stress induced by tidal current. Waves have a converse effect in shallow regions in comparison to tidal currents. The combined bottom shear stress can become higher than the current induced bottom shear stress, so that the accumulated sediment is mobilized again. This correlation points out the necessity for simultaneously consideration of both effects.