Influence of high water levels on aeolian sand transport: upper beach/dune evolution on a macrotidal coast, Wissant Bay, northern France
Résumé
Aeolian sand transport measurements and detailed topographic surveys were carried out during 1 year along a macrotidal upper beach/dune system experiencing rapid coastal retreat. Aeolian transport measurements, coupled with wind records, showed extreme spatial and temporal variability along a spatially limited upper beach sector. Analysis of wind velocity, rainfall, and water level showed that aeolian sand transport may occur all year long on the upper beach with the most energetic conditions occurring during winter and spring. Analysis of volume change revealed that aeolian sedimentation on the upper beach occurred only during the summer period, while the rest of the year was characterised by upper beach and dune scarp erosion. This erosion, due to storm events combined with high water levels, completely eliminated summer aeolian sand accumulation. Our results show that aeolian transport and upper beach/dune evolution on this macrotidal beach is strongly controlled by the magnitude and frequency of occurrence of high water levels. This study illustrates the fact that upper beach/dune evolution cannot be completely understood and satisfactorily modelled if only potential aeolian sand transport is considered.