Withdrawn thus a few tens of meters from the coast, under an azure blue sky, the Atlantic Ocean seems harmless. It is almost noon and at the very end of June, La Rochelle is sinking gently into summer torpor. The strong winds and mighty tides of winter are a long way off. Near the two majestic towers framing the entrance to the port, a promenade is full of onlookers. Among them, rare are those to distinguish, on the trunks of the trees, the now faded blue bands painted in 2017 to symbolize the water level reached on the night of February 27 to 28, 2010, during the passage of the storm Xynthia. A little less than 12 years after the disaster that devastated the Atlantic coast, the trauma is still tenacious in Charente-Maritime.
But memory is not enough. A few hundred meters away, in the Port-Neuf district, the urban community erected, between 2019 and 2021 and over more than a kilometer, a powerful dyke on the coast which stands up against the swell and waves. Solid riprap, anti-submersion walls and an infiltration system to capture water which cost the community 11 million euros. “The idea is to have a level of protection that allows us to be 20 centimeters above the submersion threshold reached during Xynthia,” explains Didier Roblin, community adviser in charge of protection against marine submersion for the agglomeration.
Damage threatens
This is the cost to stay the course facing the ocean. With Xynthia, the department became aware of its vulnerability to marine flooding and the erosion of its coastline. A necessary catalyst, because the damage is threatening “With the expansion of the ocean and the melting of continental ice linked to global warming, the rise in water levels is inexorable”, explains Eric Chaumillon, university professor, specialist in marine geology at the Rochelle University (1). A rise in sea level which, “with the same hazard, namely the same tide or the same bad weather, results in a much greater risk of submersion for the city”, he estimates.
Fearsome, the Atlantic is just as much about fifty kilometers further south, on the coastal town of Port-des-Barques, faced with the erosion of its coasts. “Between the pounding ocean and the runoff, the rock has become completely spongy,” notes Lydie Demené, mayor of the town. Over the years, the city councilor could only lament, powerless, the meters of cliff returned to the sea and see Île-Madame, a treasure of biodiversity accessible at low tide, shrink inexorably. “We don’t challenge nature, we deal with it,” she says, disillusioned, in front of a piece of beach closed to the public because of trees threatening to fall. Port-des-Barques is one of the communes of the department identified in the Climate and Resilience law as vulnerable to the erosion of their coasts. This list paves the way for public aid, which is essential for this small town.
Money, sinews of war always. In Charente alone, the reinforcement works carried out under the Flood Prevention Action Program (Papi) on the 500 kilometers of coastline (including the islands of Ré and Oléron) amount to 250 million euros from Xynthia, figures Sébastien Pueyo, engineer in the department in charge of coastal risks for the county council. A strategy that alternates hard defense, as in La Rochelle, but also prevention and alert programs, individual type protection or even beach re-silting operations. “The strategy is to focus on dense urban areas with dwellings. We arbitrate, in order to balance the value of the property we protect against the cost of defenses,” he explains. A reasoning that sometimes leads to a retreat. Throughout the department, almost 300 houses have been deconstructed since 2010.
Adapt and mitigate
Others will inevitably be added to this total in the coming years. A reality for the moment inaudible for a good part of the inhabitants of this very popular coast. In La Rochelle, accommodation facing the Atlantic has not been discounted following the threat of rising waters. “We must raise awareness of the culture of risk but also raise awareness that these defense strategies have a cost for the community”, explains Gérard Blanchard, vice-president of the urban community. A bill which, in La Rochelle, has been partly passed on to residents since this year via a local tax. This will increase further if the trajectory of global warming does not decline rapidly. “In 2100, it is not unthinkable that we could have even more brutal increases in sea level if nothing is done to fight against greenhouse gas emissions”, indicates Eric Chaumillon.
Also, the city intends to play its part in mitigating climate change. The agglomeration aims to become the first French urban coastal territory to achieve carbon neutrality by 2040. “The first milestone is to reduce our greenhouse gas emissions by 30%, our energy consumption by 20% and to increase the share of renewable energies from 10% to 33% in the energy mix by the end of the decade”, figures Gérard Blanchard, in charge of steering this project. Ambitious efforts, carried out in a consortium bringing together no less than 130 local players for a project with a budget of 80 million euros.
Enough to carry out a range of actions (about 70) broken down into a series of major axes (mobility, circular economy, renewable energy production, agriculture). On energy renovation, for example, the agglomeration has created a one-stop shop system and offers to manage its residents’ files from A to Z, from the financing of projects to the list of craftsmen that it labels to carry out the works. “The start is very lively. We are aiming for more than 45,000 renovations by 2040”, explains Gérard Blanchard. History of not initiating this transition against its population, La Rochelle also relies on a participatory approach. A citizens’ committee takes part in project management. Will this be enough to defuse the outcry over the future installation of 25 wind turbines and four biogas units in the territory by 2030? “For the moment, we are satisfied with the start of the consultations. The energy crisis is accelerating the awareness that we must bring production and consumption closer together and do without fossils”, wants to believe the elected official.
The decisive role of the Charente marshes
A whole range of solutions also available for companies or local authorities. This is, among other things, the role of the Carbon Cooperative. This collective interest cooperative society (SCIC) based in La Rochelle raises awareness among local stakeholders and supports them in understanding their carbon footprint and working to reduce it. “We are currently supporting seven municipalities and around twenty companies of all sizes. It’s a lot of work, because the level of information on this subject is generally quite low”, testifies Anne Rostaing, the general manager. The organization, which really launched at the end of 2020, has set itself the objective of contributing to the reduction of 40,000 tonnes of CO2 in three years.
All with emission reduction projects, but also capture. The cooperative strongly believes, for example, in the restoration of wetlands such as marshes. Eric Chaumillon considers the initiative vital. “With the mangroves, these wetlands constitute the second best ecosystem in the world to sequester carbon. They are real Swiss Army knives, because they will also limit the risk of flooding and submergence by acting as an expansion zone flood, even a natural barrier when the marsh will rise thanks to the sediments deposited by the sea. The marshes, one of the emblematic landscapes of Charente-Maritime, and perhaps its best ally facing the ocean.
(1) Eric Chaumillon, author of Hey… the sea is rising! Chronicle of an announced wave published by Plumes de Carotte.