Mont Saint-Michel - Tidal Island

Tidal Island

Mont Saint-Michel was previously connected to the mainland via a tidal causeway, i.e. a trackway covered at high tide and revealed at low tide. This connection has been altered over the centuries. The coastal flats have been polderised to create pasture, thus the distance between the shore and the south coast of Mont-Saint-Michel has decreased, and the Couesnon River has been canalised, reducing the flow of water and thereby encouraging a silting-up of the bay. In 1879, the tidal causeway was converted into a raised or dry causeway. This prevented the tide from scouring the silt around the mount.

On 16 June 2006, the French prime minister and regional authorities announced a €164 million project (Projet Mont-Saint-Michel) to build a hydraulic dam using the waters of the river Couesnon and of tides to help remove the accumulated silt deposited by the rising tides, and to make Mont-Saint-Michel an island again. It was projected to be completed by 2015.

The construction of the dam began in 2009 and is now complete. The project also included the removal of the causeway and its visitors car-park. It will be replaced by a light bridge, allowing the waters to flow freely around the island, which will improve the efficiency of the now operational dam, and a replacement car-park on the mainland. Visitors will use small shuttles to cross the future bridge which will still be open to pedestrians and unmotorised vehicles.