Modélisation morphodynamique d'une embouchure tidale : Application aux Passes d'entrée du Bassin d'Arcachon

The Arcachon tidal inlet exhibits a particularly active morphology due to strong tidal currents and rough wave conditions. During the past 300 years, maximum and minimum extents of the Cap Ferret sand spit have resulted in a difference of 8 km while two channels have alternatively allowed circulation between the lagoon and the ocean. A bidimensional horizontal morphodynarnic model was developed in order to simulate the system evolution under tidal forcing alone or under combined tide and wave action. Modelling at a scale of decades requires the definition of mean annual wave and tide conditions which are representative with respect to sediment transport. Medium term results thus give general trends of evolution. Driven by these average conditions and starting from a hypothetical initial topography where the tidal inlet is of constant depth, the model allows the reproduction of a channel and bar system comparable to actual observations. Morphological evolutions simulated from the 1993 bathymetry are less convincing given the restrictive assumptions imposed by the model development and by the lack of representation of extreme events that play a major role in reshaping the tidal inlet.