Dam busters: Tearing down concrete walls to save Atlantic salmon

Issued on: 15/04/2022 - 12:54

3 min

Since the 20th century, European rivers have been dammed and diverted for the sake of generating renewable energy. But the concrete walls have left an indelible mark, upending entire ecosystems. Migratory fish species in particular are paying the price. Atlantic salmon can no longer find they way back to their home streams to spawn, pushing the species to the brink of extinction. Should dams be torn down in the name of biodiversity? We take a closer look in this edition of Down to Earth.

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In France’s western Normandy region, the Selune River flows into the famed Mont-Saint-Michel bay. This is where Jean-Marc Roussel and his team of scientists are carrying out a series of experiments to check the river's vital signs.

"We're like river doctors," he explains.

In 2019, a 35-metre-tall dam was removed from the Selune, while the demolition of a second dam is also underway. It’s the largest dam removal project of its kind in Europe, and a unique opportunity to investigate what happens once nature has reclaimed its territory.

The team of scientists from France’s National Institute for Agricultural Research (INRAE) capture migratory fish and insects to count them, measure them and find out how quickly ecosystems are being restored.

The results have exceeded their expectations.

"The way the river has been reborn is such an important message, a message of hope," says Roussel. "Just when you think that everything is going wrong with the environment, sometimes you can get a sign, a concrete example of nature reclaiming its territory. And I think that’s really comforting."

Nearly half a million obsolete dams in Europe

Are dams really worth it? And what happens once they’re no longer in use?

Roberto Epple has been grappling with those questions for more than a decade. As president and founder of the non-profit European Rivers Network, he is a fervent advocate of free-flowing rivers.

He takes us to one of the many dams that have been abandoned in Europe. The Chavanon dam was built more a century ago but never completed and has been obstructing the river ever since. There could be more than 500,000 dams like this one, says Epple – obsolete and forgotten.

At the time they were built, their end of life was never factored in. But now, energy producers are having to rethink how the massive structures fit into the landscape.

Dams, made to measure

Can hydropower production ever be compatible with healthy ecosystems? In central France, on the Allier River, one dam has had a major facelift. The Poutes dam was once almost 20 metres high. Now it’s less than 7 metres tall and a large part of the concrete structure has been taken apart. Two main gates have also been installed. Opening them allows the river to follow its natural course during the salmon migration season. Production is now completely shut down twice a year. Overall, the plant has been running at 85 percent capacity.

A last-ditch effort to save an iconic species

Redesigning dams only solves part of the problem. It will take more than that to save the Atlantic salmon. That's why France’s Wild Salmon Conservancy, also located on the Allier River, has been overseeing a reproduction programme spanning several years. The fish are captured, bred in conditions nearly identical to their natural habitat and released back into the wild.

Céline Bérard, the centre’s director, is hopeful that the work done at the Poutes dam will bear fruit. In the meantime, the situation remains critical.

"They’re really holding on by a thread," she says.