how municipalities adapt town planning to avoid the worst

Devoid of trees and houses, without relief, the former Glacis district of the city of Blois (Loir-et-Cher) resembles a vast wasteland. In the middle of this desolate grass-covered space stands a stone house. The windows have been removed, but you can still see the yellow flower wallpaper covering the walls. The building is the last vestige of an area which once accommodated around a hundred families in the Bouillie plain, very close to the city center.

It was in 2004 that this pioneering town hall – followed by Agglopolys, the Blois urban community – launched an ambitious project to destroy the buildings and redevelop this area. Located between the Loire and the Cosson, it is particularly vulnerable to flooding. In the event of bad weather, its infrastructure can turn into projectiles, endangering the 5,000 residents of the neighboring district. “We want to transform the Bouillie plain into a place where waterways can overflow without causing damage,” explains Vanessa Besseau, development operations manager in Blois. In a few years, there will be agricultural gardens, a walking area… We also decided to design a kindergarten, with removable facilities. »

The majority of Blois elected officials, from both the right and the left, supported the project. Because the issue goes beyond political divisions. According to the Ministry of Ecological Transition, one in two municipalities is located, entirely or partially, in a flood zone. Clearly, one in four French people are affected.

The disaster can be caused by a river overflowing its bed, a rough sea hitting the coast, the rise of water tables, etc. According to IPCC experts, the frequency of heavy rainfall has been increasing in most land areas since the 1950s. “As the climate warms, the mass of water contained in the atmosphere increases in the form of vapor,” explains Magali Reghezza-Zitt, doctor in geography and planning. This change leads to increasingly heavy precipitation and severe weather. »

This is evidenced by the disasters that have saturated our screens and our conversations in recent months. No one has forgotten the images from Valencia, Spain, where 230 people died under downpours of water flowing through a heavily concreted urban area. In France, the winter of 2023 was marked by intense rains which hit Nord-Pas-de-Calais several times, causing devastating floods. More than 200 municipalities have been classified as in a state of natural disaster. Last October, the South-East and Île-de-France were affected in turn, resulting in damage of between 350 and 420 million euros. That’s it for today. But what will happen tomorrow? The latest IPCC report predicts an increase and increased frequency of floods due to climate change, which in particular causes rising water levels.

Increase green spaces

Aware of the issue, more and more municipalities have chosen to adapt to this new climatic situation by rethinking their town planning. It is no longer just a question of protecting ourselves from water, but of giving it back its freedom, by creating green spaces and removable infrastructure allowing it to circulate. “A flood does not create damage if the water does not encounter any obstacle and is able to drain into the ground,” explains Ludovic Faytre, head of major risks and development studies at the Paris Region Institute. In an airy city with green spaces, water can flow into certain areas without damage. But in a town where the soils are artificial, streets covered with concrete and asphalt, it flows and invades the space with tenfold force. »

In Blois, the municipality has slowed down the artificialization of land to better integrate nature into urban spaces. “From the 19th century, communities and engineers had built dikes and dams in all directions to be able to build on flood-prone areas,” recalls Sylvain Rode, lecturer in spatial planning at the University of Perpignan. But now, these solutions are no longer enough. Entire sections of the city must be revegetated to give water the opportunity to spread. »

However, the transition from theory to practice is not painless. The Blois urban community fought for fifteen years to be able to demolish the Glacis district. Some families have lived for several generations on this plain with a pleasant living environment, surrounded by trees and equipped with sports infrastructure.

“It was unthinkable to expropriate the inhabitants,” recognizes Christophe Degruelle, president of Agglopolys. We negotiated the amicable repurchase of each house, with a 5% increase. » Elected officials benefited from the Barnier fund, created by the State in the 1990s to buy buildings vulnerable to natural disasters. Some 24 million euros were granted to the city, as part of a vast redevelopment plan for the Loire.

In the Glacis district, some of the residents quickly agreed to be compensated, before moving to the surrounding area. Others resisted for many years, like Éric Prieur, now deceased. In the 2000s, this retired nurseryman founded a protest collective against the project. “No to the ZAD de la Bouillie”, proclaimed a banner at the entrance to his house. “In 2016, a flood flooded the neighborhood and people were afraid,” says his son, Jean-Jacques. But my father was stubborn, he had lived in the neighborhood for seventy years and he was particularly attached to it. » The last house on the plain, with wallpaper dotted with yellow flowers, should be demolished in the coming months. It will give way to shared gardens and a cycle path.

The construction site, which covers 350 hectares of the Bouillie plain, is due to begin at the end of 2026. Time for the community to carry out environmental and archaeological studies of the land, which could house vestiges of the Merovingian era. . The path to greening is long and expensive, but for environmental specialists, it is moving in the right direction. “In the past, villages were nestled on heights, sheltered from waterways, and agricultural land was in the flood zone,” explains Magali Reghezza-Zitt. The trend reversed from the 1950s. Cities became more dense and spread out towards rural areas, eating away at agricultural land and valleys. With the development of the car, we have built highways, houses, industries all around waterways… We have made our infrastructure vulnerable. »

Driven by the imperatives of economic growth, the municipalities followed the movement. In the 1970s, the artificialization of land intensified, with the ideal of the “suburban house”, individual housing becoming a symbol of comfort in the society of the Trente Glorieuses. Unaware of environmental risks, some mayors are densifying their territory at a breakneck pace, particularly in coastal areas. Seaside tourism is booming, with its luxury and cheap hotels, its beaches covered with parasols and its second homes.

In the Alpes-Maritimes, the town of Mandelieu-la-Napoule has become over time one of the jewels of the Côte d’Azur. Flooded with sunshine, the city charms Nordic tourists and French retirees, thanks to its marina and its castle renovated by American billionaires. Made up of 40% second homes, it welcomes a wealthy population, who sometimes arrive by yacht. Like many seaside resorts, Mandelieu is the result of unreasonable urbanization. To allow boats to access new ports, the arms of the rivers which cross it – the Riou and the Siagne – have been diverted.

A heavy human toll

In this south of France frequently affected by Cévennes episodes, the floods are rapid and spectacular. In October 2015, intense rain fell on Cannes and Mandelieu and the rivers overflowed. Toll: 20 dead. The victims number in the hundreds and the damage amounts to more than 600 million euros. “I had major construction projects for my city until the flood,” sighs Sébastien Leroy, mayor of Mandelieu (LR). But I’ve seen people lose everything, overnight. That’s when I understood that I had to think differently. »

Carole, 74, lives in a residential building on the banks of the Riou river. “I saw like a wave coming and flooding everything that was on the ground floor,” she remembers. When I went down to the underground parking lot a few hours later, there were dead people. Some had wanted to get out to save their car but it was too late. »

A few meters further, Julie, 47, walks her boxer dog, a cigarette in her hand. This former resident of Nord-Pas-de-Calais considered moving several times after the flood. “But I built my life here!” she exclaims. And the neighborhood has become safer since the town hall redeveloped everything. » With a circular gesture, she points to the brand new park, which allows the Riou to spread without damage in the event of flooding.

During the last Cévennes episode, in October 2024, the watercourse left its bed without reaching neighboring residences. A successful bet for the city, which transformed this former tennis court and renatured the banks of the river, from 2020. In total, the municipality invested 35 million euros and acquired three other plots. Very close to the new park, the 14 hectares of Minelle orchards must also serve as a flood expansion zone. On this fenced area, sheep and cows graze, under the watchful eye of two shepherd dogs. The town hall said no to the real estate developer Groupe Casino who wanted to build housing in this flood zone. A battle lasting several years, punctuated by administrative imbroglios.

As necessary as they are, these redevelopment campaigns are not enough, experts nevertheless point out. In a world where temperatures are increasing every year, natural disasters are becoming more intense and difficult to manage. Faced with this, many local elected officials are calling on the State to define an ambitious strategy to limit the risks of flooding.

Currently, only the Barnier fund allows communities to finance work to adapt to disruption and its consequences. At the end of October, former Prime Minister Michel Barnier announced that it would increase to 300 million euros in 2025. “This is quite insufficient for all the municipalities,” storms Sébastien Leroy, the mayor of Mandelieu. Today, it becomes vital to adapt to protect our inhabitants. The State must take its part! » But in a France subject to an unprecedented political crisis and where budgetary priorities are piling up, urban adaptation to climate change is not making headlines. Until the next disaster.