Coastal municipalities in search of solutions to the decline of the coastline

In the Basque Country, which has 35 kilometers of sandy and rocky coast, more than 500 individual and collective homes and around forty businesses are threatened within 20 years by rising water levels and its consequences, estimates the Urban Community.

With eight coastal municipalities which concentrate 40% of the population, it plans 242 million euros of investments to adapt the management of the places. “These are quite difficult trade-offs, between the issues for people and economic activity,” comments Matthias Delpey, research and development manager at Rivages Pro Tech.

This center of expertise specializing in the management of aquatic environments, a subsidiary of Suez, was created in 2014 in the Basque Country to "anticipate crisis management" and study the impact of storms and coastal floods.

That year, winter storms caused 500.000 euros of damage in Biarritz (Pyrénées-Atlantiques), recalls Michel Laborde, deputy mayor responsible for coastal development. Since then, the City has developed a strategy on several fronts.

Helped by Rivages Pro Tech, it has set up six alert thresholds for the risk of submersion. “We do not necessarily observe an increase in frequency but stronger phenomena,” says the elected official. “What we know is that the water level is rising and that if the trend continues, the frequency of episodes will intensify,” adds Matthias Delpey.

Vulnerability

The City, launched into massive work to strengthen its cliffs, also deployed large sandbags, then a system of removable dikes developed by the company "Wave Bumper".

Tested for the first time in Biarritz in 2016, this solution has since attracted several towns on the Atlantic coast such as La Rochelle (Charente-Maritime), Capbreton (Landes) or La Tranche-sur-Mer (Vendée), as well as Mediterranean towns such as Saint-Cyprien (Pyrénées-Orientales) or Vallauris (Alpes-Maritimes).

“We are working on the impact of waves on given areas, depending on their vulnerability,” explains the inventor, Romain Chapron.

La Tranche-sur-Mer invested, at the end of 2022, around 150.000 euros to deploy this system over 80 linear meters of Rocher beach, the most exposed to marine erosion.

At the end of 2023, the Vendée coastline was hit by numerous storms. With a year's hindsight, the mayor notes that "the sand level has risen on the beach and that the dune, above the blocks, has reconstituted itself".

Pipe

The Kostarisk cross-border laboratory, between France and Spain, works on science-based solutions, directing research subjects towards issues in the field. “The current state of knowledge does not allow these risks to be properly managed or understood,” explains Matthias Delpey, also co-director of this laboratory.

Another tool, aerial monitoring of the retreat of the coastline, near Labenne and Capbreton in the Landes, was undertaken by the company Evotech. Thanks to microlight flights, she assembled thousands of photos to measure the impact of the storms of fall 2023.

“We see that a lot of sand is moving, that the storms have broken the edges and rounded the crests,” notes Anthony Gavend, founder of Evotech. The company also offers a “Flood simulator” to model in 3D a flood or a wave-submersion episode in an area.

Capbreton has also opted, for several years, for a transfer of sand between its northern beaches, more abundant thanks to the sedimentary drift of the currents, and those to the south. “We transfer it by hydraulic pipe, it’s a technique that comes from Australia but we are the only ones to use it in Europe,” underlines the elected official in charge of the coast, Jean-Luc Aschard.

At the same time, the municipality, which will devote 13 million euros over the next 5 years to the maintenance of its coastline, is collaborating with the University of Bordeaux to model sedimentary drift and the impact of the Capbreton gouf, which vast underwater canyon which extends up to 3 kilometers deep off the port.