Evolution et mobilité des sédiments superficiels de l'estran occidental de la baie du Mont Saint-Michel

The western part of the Mont Saint-Michel Bay is characterized by very extended mud- to sand-flats, predominantly subject to tidal currents, episodically to wave action. In order to define and quantify the rhythm and amplitude of the processes of erosion and sedimentation on such broad tidal flats, measurements of sediment elevation have been performed along three cross-shore profiles. Each profile, few kilometers long, is representative of the different sedimentary environments of the western bay. Monthly measurements, realized during high spring tides, evidence that the amplitude of reworking is generally low (< ± 5 cm), and variable from west to east : relatively high at Cancale and Vilde-Hirel, it is much lower at Cherrueix. During storm events, especially during winter season, the whole flat experiences severe erosion of decimetric scale, which is however