Morphodynamics of beach/dune systems: examples from the coast of France

Four representative sectors encapsulating the morphological and hydrodynamic diversity of the French coast are used to illustrate the morphodynamics of beach/dune systems at various timescales. These beach/dune systems cover the four shoreline sectors composing the French coast, i.e., the southern North Sea, the English Channel, the Atlantic Ocean, and the Mediterranean, and range from storm-dominated short-fetch to swell settings, and from micro- to macrotidal. The short-term processes affecting the beach/dune systems are strongly hinged on wind incidence and storm intensity, while sediment supply, modulated by marine processes, notably storms and tides, and by the regional wind directions, constitutes the primary control on long-term patterns of development. Beach morphology, notably the presence of bar/berm-trough systems, and water levels attained during storms, constitute key elements in the process of sand supply to the dune systems, which vary from low, poorly developed forms in the Mediterranean, to the well developed, but largely presently stable to erosive systems characterising the other three sectors. The comparative study of these systems shows that there is no linear relationship between storm intensity and the rate of dune erosion (except on Vougot site, English Channel), because of the influence of various parameters, notably the antecedent beach state.