Modelling impact of northerly wind-generated waves on sediments resuspensions in the Dover Strait and adjacent waters
Résumé
The present study investigates the effect of a storm on the resuspensions of heterogeneous sediments in the eastern English Channel. The numerical approach is based on the coupling of the wave propagation module SWAN (Simulating WAves Nearshore) with the three-dimensional circulation module COHERENS (COupled Hydrodynamical-Ecological model for RegioNal and Shelf seas). Suspended sediment transport is computed for the four grain-size classes of silts (d 1 = 25 µm), very fine sands (d 2 = 75 µm), fine sands (d 3 = 150 µm) and medium sands (d 4 = 350 µm). The application focuses on a storm in October 1998. Predicted times histories of waves variables and the near-bottom mean current and total suspended sediment concentration (SSC) are compared with field data collected off Merlimont Beach, in the south of Boulogne-sur-Mer. Map-pings of the increases of the near-bottom total SSC during the storm are produced. The total SSC increases by four at the Merlimont site. The multiplying factor reaches 40 along the exposed northern French coastline revealing the Flandres bed features. This increase is limited to five in deep waters of the southern Dover Strait with local strengthening on the top of the Vergoyer and the Bassure de Baas sandbanks. The storm modifies the gran-ulometric composition of suspended materials by increasing the contribution of medium sands. Main modifications appear at the southwestern entrance of the Dover Strait and in the exposed southern North Sea. The near-bottom resuspensions remain elsewhere dominated by the local resuspensions of fine sands added to remote resuspended silts advected by currents.
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