Abstract
Sediment transport rates subject to varying wind conditions ware evaluated with current-wave fields derived from a coupled numerical model. The study area is the Sylt-Rømø bight, an enclosed back barrier tidal basin located in the North Sea. The bight has an area of some 400 km2 in which sandy flats prevail. This work provides numerical estimates of the sediment transport rates and shear velocities applying existing current-wave fields derived from a coupled numerical model to both the Bagnold and the Soulsby-van Rijn formula. Water levels, vertically averaged two-dimensional current velocities and wave spectra were used as input from validated numerical model calculations. Four days covering a full storm period in April 1997 were selected for the calculations of total bed shear velocities and sediment transport rates. The simulation shows that during moderate wave conditions sediment transport mainly takes place in the tidal channels. However, with high wave energy present, sediment transport becomes more important in shallow areas. The general distribution of shear velocities and suspended sediment concentrations over the basin suggests a large erosion and resuspension of sediment in shallow areas by wave action which may not be so evident in the sediment transport rates because of the low current velocities there. This suggests that storms will continue to erode shallow areas, increase the tidal prism and probably the tidal currents and the continuing exportation of sediment.
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