Haut de plage et front dunaire : enregistrement morphologique de la dynamique éolienne et marine dans un système macrotidal (Upper beach and foredune profile : morphological registration of aeolian and marine dynamics in a macrotidal environment)

摘要

The sandy beaches and associated coastal dunes of the côte d'Opale (North of France) belong to macrotidal coastal systems. In this context, the instantaneous shoreline periodically migrates across the beach profile according to the "tidal translation rate". It determines where and how long the different nearshore processes act upon the beach profile. These processes depend upon the marine dynamics (linked with the dissipation of incident wave energy in the shoaling, surf and swash zones) and wind dynamics. During a lunar tidal cycle, and all along the year, the respective duration of both dynamics and their spatial impact vary considerably upon the beach profile. Swash processes affect the upper shoreface during only a relatively short time. It explains that storms are really efficient upon the upper beach profile only when they occur during a high spring tide. The combined marine-aeolian dynamics is registered in the morphology of the upper shoreface and foredune profile. Landforms, which formed in different dynamics environments can survive and lay side by side, despite contrasted morphodynamics significance. The jumbling juxtaposition of marine or aeolian process-induced landforms has to be considered when sensing aerial photographs or topographic profiles. These data have no real significance if they are not spatially and timely related to the regional context. Although spectacular, the storm morphological effects may rapidly disappear in case of abundant sediment supply.