A major project got under way to stop sand building up around the bay, make Mont-Saint-Michel an island again and restore the Wonder’s unique beauty. Waterworks, new roads and engineering structures: the mammoth project is still one of the most original landscaping operations in Europe.
Mont Saint-Michel was listed twice as UNESCO World Heritage in 1979. But there was some bad news too. Sand was slowly burying the Wonder… The work of mankind since the 19th century had fast-tracked natural sediment build-up: channelling the Couesnon, dam, road, car parks outside the ramparts etc. Models in the late 90s showed that if nothing was done, Mont-Saint-Michel would no longer be an island in 2040…
The local authorities (Normandy Region, Brittany, Manche Département, Ille-et-Vilaine, councils) joined forces as the Syndicat Mixte Baie du Mont Saint-Michel and launched a major project to make Mont-Saint-Michel an island again in 2005. Big ideas to match a big attraction: restore the landscape for the long term and provide visitor facilities worthy of the world heritage site and its symbolism.
A new dam, the cornerstone of the operation
The Couesnon tidal barrage was replaced by a reversible dam with eight sluice gates. Building work began on the cornerstone of the operation in 2006. It works on a “closed loop” principle: it fills the river at high tide and empties at low tide. It has been discharging 70,000-1.2 million m3 of water every day since 2009. Enough of a surge to give the river the power it needs to take sediment out to sea… Aside from its hydraulic function, the structure was designed to showcase the site’s unique features. Its footbridge takes visitors from one bank to the other whilst its sea platform and terraces provide a unique place to relax and drink in views of the bay.
The dam was the first part of the mammoth project. Its technical features and appearance made it a tricky task. Its unique measurements and heavy sluice gates required significant logistical and lifting equipment. All on hard-to-handle pit sand…
Upstream, the project focused on rebuilding a reservoir. The old dam had silted over the Couesnon riverbed, so 4.7km of it was cleared out. The banks were cleaned and the reed beds were flattened. A little further away, a former meander called Anse de Moidrey was restored: an 8km network of main channels was formed to store up to 300,000m3 of water. A total of 1.5 million m3 of pit sand was extracted during the operations.
New structures for a new horizon
Visitor structures for the Mont have been completely overhauled to stop restricting water circulation. A new car park with 4000 spaces has been built on the mainland. Visitors who want to reach Mont-Saint-Michel, on foot or by boat, now use the new 1085 road further east. It includes a 760m bridge. Like a tightrope above the water, the bridge stands on 134 piles on footings 20m below sea level.
The bridge comes out onto an esplanade topped by a ford to cover the last 120m up to the Mont. About twenty times a year during exceptional tidal coefficients, the ford is under water. That’s when the mammoth project fulfils its objective: Mont-Saint-Michel is an island once again in the middle of the sea.
This iconic project put us in the spotlight with a focus on meeting exemplary expectations and our deadlines. The stakes were very high, especially in terms of the environment.
Tangible results
Last but by no means least, the final symbolic stage of the project to make Mont-Saint-Michel an island again was demolishing the car parks outside the Mont and dismantling the dyke road in 2015. The currents could flow freely once again. The first topographical surveys since then have found that a large area has been reclaimed by the sea within a kilometre of the Mont (20 hectares more in 2014 compared to 2009).
It’s also boosted tourism and the local economy. More and more visitors flock here to see Mont-Saint-Michel surrounded by water. Something that hadn’t happened since the first dyke road was built in 1879. The Wonder has made its mark as a major attraction and seen visitor numbers rise to 3 million a year. It’s the most popular destination in France after Paris.
Thematics
