HYDROSEDIMENTARY STUDIES TO RESTORE THE MARITIME CHARACTER OF MONT-SAINT-MICHEL

The monastery of Mont-Saint-Michel, listed by UNESCO as a World Heritage Site, is situated on a small rocky island in the bay of the same name at the mouth of the River Couesnon in Normandy, France. There is a considerable tidal range of up to 15 m in the bay, and the sediment deposition that has been occurring for centuries has been accelerated over the past 200 years by human activity, to the extent that this now seriously threatens the Mount itself. This article describes the hydrosedimentary studies carried out between 1995 and 2002 on a combination of two numerical and two physical models with a view to predicting the future morphodynamic behaviour of the intertidal areas and salt marshes around the Mount and finding solutions to avoid local sediment deposition. Solutions aimed at improving the flushing effect of ebb currents leaving the Couesnon while at the same time enabling the river to meander on both sides of the Mount were devised and tested on a movable-bed scale model capable of predicting the future of the sea bed in 45 years' time.