New map shows 20% of French coasts are threatened by erosion

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Nearly 20% of France’s coastline is threatened by erosion and sea level rise, a new interactive map shows, as the COP26 climate change conference opens in Glasgow today (Sunday, October 31 ).

The interactive map, compiled by FranceInfo, shows exactly how this will affect the French coastal landscape.

Using data from the Center for Studies and Expertise on Risks, the Environment, Mobility and Planning (Cerema), the experts compared aerial images dating from the 1930s to 1950s with more recent photos.

It shows that nearly 20% (18.6%) of the French coastline, or 900 km, is “retreating”. To date, a total of 523 municipalities will have “at least one affected area”.

And the 59 most affected municipalities can suffer up to 1.5 meters of erosion per year on average.

Advanced erosion on sandy coasts

The regions with a sandy coast (41% of the coast) are the most affected by a modification of the coastline: 37% are experiencing a decline, 23% an increase.

In areas of cliffs and rocky coasts (54% of the coastline), 6% of the coastline is affected by a retreat.

The scenarios are pessimistic: by 2100, between 5,000 and 47,300 homes could be victims of erosion according to Cerema, and the cost would reach 8 billion euros.

The Gironde, Manche and Charente-Maritime, which have long sandy beaches, are the departments most affected. Erosion will cause a loss of 30 km2 in 50 years in Gironde, and the south of the island of Oléron, in Charente-Maritime.

Certain specific municipalities are also particularly affected: this is the case of La Tremblade (Charente-Maritime), where some dunes retreated by 7.9 meters per year between 1945 and 2010.

But if no housing is yet threatened in La Tremblade, this is not the case in municipalities like Soulac-sur-Mer (Gironde), where a residential building built 200 meters from the sea in the 1970s was evacuated in 2014 due to erosion. and storms.

The coastline declined 4.3 meters per year between 1957 and 2013, and more than 30 meters suddenly during the winter of 2013-2014.

In 2016, the Observatoire du littoral aquitain l’Observatoire de la côte Aquitaine predicted that the coast would be eroded by 50 meters by 2050. In some places, such as the Gâvres peninsula, near Lorient (Morbihan) , erosion threatens vital infrastructure – in this case, the only access route to the city.

Near Béziers, concern is growing in Valras-Plage (Hérault). Its barrier, built in 1995 to contain the sand, no longer plays its role.

Philippe Barbet, director of the water cycle for the Béziers-Méditerranée agglomeration, says Midi Libre October 29: “It aggravates the erosion of the beach in this zone of marine submersion.

Solutions are being considered to stop the process, as the range is narrowing day by day.

A new project in Normandy

In Quiberville, in Seine-Maritime, the authorities are choosing another approach, and are embarking on an unprecedented project, supported by the European Union and the government, to “let the sea enter the city”.

Instead of erecting walls and fences, the municipality allows the ocean to enter the land, with the beach and coastline “redeveloped” accordingly.

Since 2017, other similar projects, called “flexible coastal management”, have been carried out in France, initiated by the coastal group, the Conservatoire du littoral.

Professor Stéphane Costa, researcher at the CNRS, has been studying the decline of the Normandy coast for thirty years and believes that global warming will worsen the problem.

He told France 24 October 28: “The village is already threatened with submersion by the sea and flooding from the Saâne on the land side. In the heights, we must also face the problem of erosion.

Concerns for archaeological sites

In certain regions of France, climate change can even threaten certain archaeological sites on the coast, reported Le Figaro October 22.

The most sensitive sectors are located on the sandy Atlantic coast, and in the French overseas departments and territories.

Discussions on how to prevent this damage took place earlier this month, during an event organized by the National Institute of Preventive Archeology (Inrap), at the Quai Branly Museum in Paris on October 20 and 21.

The advancement of the coast in certain regions

On the other hand, in certain places, the coastline “advances”, as at Grau-du-Roi in the Gard.

In parts of the area, the coastline rose by more than 15 meters per year between 1937 and 2011, due to the construction of a port and a dam, which favored the accumulation of sand.

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