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International audienceIn marine coastal environments, storms have a major morphological impact on sand beaches. This study, part of the French Programme National d'Environnement Côtier, consisted in developing and applying hydrodynamic and sedimentary models to simulate the major processes that modify sand beaches. In order to study sediment dynamics, we developed three models to simulate waves, currents and sediment transport associated with a storm event. The wave model was a Mild Slope Equation model based on the parabolic approximation of the refraction-diffraction equation of Berkoff. The hydrodynamic model was obtained by the depth-average of Navier Stockes' equations forced by the terms of radiation stresses induced by waves. The sedimentary model SEDSIM developed by Martinez and Harbaugh computed, by using empirical formulations, the transport, sorting, erosion and deposit of sediment. The numerical simulations computed the impact of a realistic storm event on a relatively realistic microtidal beach with wave-formed sand bars. The results show that after 15 h of storm, the beach receded on more than 20 m. Two sedimentary bars and an orthogonal sand structure were removed and levelled. A tendency towards a single bar was observed

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