The Couesnon Barrage is situated at the bottom centre of the picture to the left. It is situated at the Northern end of the accommodation and tourism centre for Mont Saint Michel. There are no private vehicles allowed past here.New car parks and a bridge have been built in 2014, people can now reach the Mont Saint Michel either on foot or with the free shuttles that operate from 7.30am to 12.00am.

The dam’s operating stages

Stage 1.
The valves close 1.5 hrs before high tide. The first flow hits the dam and the sediment is deposited downstream from the dam; this is the decantation process. Once decanted of its sediment, the water will limit the silting upstream in the Couesnon.

Stage 2.
The valves are opened between 1 hour and 10 minutes before high tide and the tide fills the Couesnon by over-flow (over the top of the valves) with the water that contains the least sediment. The tide enters the Couesnon. In some cases there is no filling, a highly visual stage in the dam’s operation:

Stage 3.
The valves close as the tide starts to fall. Between 70,000 and 1,700,000 m3 of water is stored depending on the seasons and the tides. The higher the volume of water stored, the longer it will take for the water to be released.

Stage 4.
The valves are opened gradually 6 hours after high tide (by the bottom of the valves), creating a progressive water release without waves or breakers lasting 30 minutes to 3 hours. The longer the water release the more effective it is in transporting sediment.  

The dam is a fabulous viewing platform at all hours of the day and night.