France, 2006 - 2015
After twenty years of studies and works, the Mont Saint-Michel has finally regained its former and authentic maritime character. Over the centuries and as a result of human activities, sedimentation built up around the Mont-Saint-Michel. Gradually, the sea receded – while the earth advanced. If nothing were done, by 2040 the site would have been completely surrounded by salt marshes with no possible way to turn back the clock. Begun in 1995, the operation to give back Mont Saint-Michel’s unique maritime character became a vital necessity.
The operation’s keystone: the new Caserne dam. Entirely automated, the 170-m long dam enabled incoming sea water upstream of the works to be stored temporarily, then released twice a day downstream by a "flushing" effect. In addition, hydraulic work on the Couesnon downstream of the dam consisted in realizing the "watershed line" – a line separating waters into two flows from the dam flushing process, either side of the Rock, in order to harmonize the erosion of the bay’s seafloor. Other dedicated works (deflecting and spreading groynes) complemented amenities to help currents flow and thereby carry sediment out to sea.