Co-oscillating tide controls long-term sedimentation in the Gironde Estuary, France

Abstract

Study of the sedimentation of the Gironde Estuary in France over the last three centuries has revealed that there are areas where the volume of the river under the lowest water level has varied greatly and others where it has remained remarkably stable. The processes of erosion and sedimentation thus, do not take place uniformly throughout the estuary. The distribution of stable and unstable areas along the estuary, moreover, is in no way due to change. The unstable areas are 25–26 km and 18–20 km long and regularly alternate with <5 km long stable areas. Spectral analysis of tidal currents shows the presence of short-period currents linked to waves whose length is double that of the unstable areas. These wavelengths correspond to those of the semidiurnal co-oscillating tide within the estuary, and the antinodes of oscillation coincide with the positions of the unstable areas. These facts make it possible to show that the co-oscillating tide controls long-term sedimentation in the Gironde Estuary.