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: Filling is generally river-maritime. Filling is exclusively river for tides whose coefficient is lower than 50 or for the Couesnon’s natural flow between 30 and 40m3/sec. No water is released beyond 40m3/sec.
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.
Couesnon dam water release times
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Today (26/04/2024)
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The new dam over the Couesnon will release water at the following times:
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Forecasts for tomorrow (27/04/2024)
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The new dam over the Couesnon will release water at the following times:
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