Seasonal Evolution of Shoreface and Beach System Morphology in a Macrotidal Environment, Dunkerque Area, Northern France
Keywords:Morphology, shoreline evolution, shoreface, beach, macrotidal regime, cell segmentation, cross- and long-shore transport, erosion, accretion.
Differential maps have been digitalized and compared from successive bathymetric and topographic surveys performed under different meteorological conditions from May 1992 to December 1994 in the shoreface-to-beach system of the 30 km long coastal area extending from Gravelines to the French-Belgian border in southernmost North Sea. The data, which concern a low-relief sandy coastal system exposed to a macrotidal regime with flood-driven eastward sediment transport, have been interpreted according to meteorological, hydrodynamical and aerodynamical characteristics.
A balanced sediment budget was observed, which contradicts previous data suggesting a progressive long-term erosional trend. This result indirectly underlines the key-role on the sedimentary budget of exceptional events such as severe storms. The two types of erosion identified comprise the action of frontal waves and the combined interaction of tidal currents and wind.
Five hydrodynamical cells have been recognized along the shoreface. The corresponding segmentation is attributed to the specific distribution of the wave energy along the coast due to the presence of submarine banks responsible for the deformation of the wave propagation.
The morphological changes of the beach depend on the tide and swell action responsible for the construction/migration/destruction of the ridge and runnel system.