This municipality in Loire-Atlantique is working on a new management plan to deal with flooding

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THE torrential rain of Wednesday October 9, 2024 remain anchored in memory, in Saint-Brevin-les-Pins (Loire-Atlantique) as in a good part of the Pays de Retz. Roads cut, senior residence Les Résidentiels evacuated…

That day, almost 80 millimeters of water fell on the floors when passing the depression Kirk. Luckily, the wind was limited and the tidal coefficients relatively low, limiting the risks of wave-submersion and a new Xynthia… But the depression highlighted the faults in the rainwater network of the town, old and undersized in places.

Deficient networks

If Avenue du Pont-Renaud found itself engulfed by water, it is because the Bodon retention basin, right next to it, overflowed.

If multipurpose room no. 2 finds itself flooded with each heavy rainfall, it is because Avenue de la Guerche is elevated in relation to the building. Because of this altimetry problem, the water rushes down from the ditches of the Route bleue, “crosses” the college, to enter the room…

A “more prospective” management plan

During the municipal council meeting of November 4, 2024, the question of rainwater management came on the carpet. What lessons can be learned from these repetitive floods and, probably, likely to be repeated again? How to limit runoff?

The City of Saint-Brevin did not wait for Kirk to launch a diagnosis of the state of the network, list sensitive points.

We are currently working on a more forward-looking stormwater management plan. This is something that we initiated from the start of the mandate, but it is clear that climate change is forcing us to review our management more carefully.

A design office will be commissioned to work on this issue in 2025. Once this diagnostic phase is completed, an action plan will be defined and large-scale work can be launched with priorities for the most exposed areas. “It’s a long-term job,” summarizes Alain Coutret, assistant for works and roads.

More than €100,000 each year

Each year, a recurring line of approximately €100,000 is included in the road budget for rainwater management. Cleaning of ditches, pruning, de-waterproofing, but also hydrocleaning of nozzles (additional €20,000), removal of sand from outlets (of La Courance and Rue de l'Église) every year…

Practices evolve.

Today, rainwater management is no longer just about sending it back to the sea. There is a whole upstream management process.

“For example, when we redo the sidewalks, we remove the coating, we sand and we put back a draining coating,” specifies the elected official.

With its two flagship projects of the mandate, the Padioleau promenade and the Pointeau car park, the City has also worked on the renaturation of the soil (tree planting, creation of valleys, etc.).

Convince, even constrain

Beyond its desire to act, the municipality also wants to convince through awareness among individuals and businesses on the recovery of rainwater, the maintenance of shoulders, etc.

“There are small everyday actions that can help. For example, think about removing the pine needles that block the drains. Our services are limited, but things can go very quickly,” says Alain Coutret.

Therefore convince, even constrain on the regulatory level. “With the future local intercommunal urban planning plan, we are working on the establishment of a maximum coefficient of waterproofing of the plotcontinues Dorothée Pacaud. Afterwards, the question is how do we control? “.

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