To protect Paris from floods, rural areas sacrifice land

Vanvey, Leuglay (Côte d’Or) and Villars-Santenoge (Haute-Marne), report

Lionel Guenin does not only have tender words when he talks about Parisians, in particular these « executives locked in their offices who decree standards in total disconnection with the realities on the ground ». In his sixties, quick-spoken and incisive, the competition horse breeder and organic farmer from Haute-Marne nevertheless participates in protecting Ile-de-France residents from flooding.

In the event of flooding of the Ource, a tributary of the Seine which winds through its land, its meadows will be completely flooded. So much water that will not flood into Châtillon-sur-Seine, Troyes and Paris, located 250 km downstream. This was not the case a few months ago when Damien Dondaine, technician at the Public Establishment for Water Development and Management (Epage) Sequana — which manages the watershed of the Seine and the ‘Aube in an area between Côte-d’Or, Haute-Marne and Yonne – passed by there.

Flattening the banks, returning to the initial route of the watercourse… he proposed to the farmer to rework the banks of the river over 400 meters in order to create a flood expansion zone on his land (ZEC), a natural space over which the river can overflow freely and thus reduce the quantity of water flowing downstream. If water can now invade this valley floor to a height of several tens of centimeters, the towns and villages downstream should be spared, or at least less affected. This will reduce the grazing area for Lionel’s horses, but his other agricultural activities, established elsewhere, will not be affected.

Thus, the contribution of farmers and landowners who work along the watercourse will be felt as far as the capital, or even as far as the Seine estuary. Proof of the interest of the subject: the Seine Grands Lacs establishment – ​​which monitors flood risk in Île-de-France – has been financing some of the projects carried out by Epage Sequana for several years.

Nearly a million Ile-de-France residents in flood zones

In 2014, a report from theOECD — the most recent on the subject — warned of the alarming state of fragility of the Ile-de-France metropolis in the face of flood risk. Since the historic flood of the Seine in 1910, which flooded the capital for more than a month, the vulnerability of Paris and the inner suburbs has increased considerably. The urbanization of certain departments has increased the number of housing units in flood zones, while climate change could also favor a regime of more abundant rain.

From now on, « more than 900,000 people live in flood zones on the axis of the Seine or the Marne and nearly 1.5 million are in electrical fragility »indicates the head of major risk studies at the Paris Region Institute, Ludovic Faytre.

Critical installations have also proliferated in certain particularly exposed areas, such as the port of Gennevilliers (Hauts-de-Seine), where many polluting and waste management activities are concentrated. « In the context of a major flood of the type of that of 1910, it is estimated that the cost of direct damage to property, buildings, infrastructure, stocks and equipment of companies, “network” disruptions, could amount to at 30 billion euros »confirms Paris City Hall Deputy Pénélope Komitès, notably in charge of resilience.

Insufficient reservoir lakes

To anticipate this risk, the metropolis has long relied on its four large reservoir lakes located in Aube, Marne and Nièvre, built during the last century, which can hold 830 million cubic meters of water. For their construction, the solidarity of rural areas had already been called upon. In 1974, « three villages were submerged during the flooding of Lac du Derbetween the Marne and Haute-Marne, says the president of the association of disappeared villages, Christian Collot, on the telephone. Between 350 and 400 people lived there. Lots of farmers. For this generation it was difficult ».

However, the flood risk has not been completely contained in the Seine valley. In October 2024 alone, flooding in 380 municipalities was recognized as a natural disaster, including 46 in Yvelines and 16 in Essonne. In reality, a flood like that of 1910 could bring five times more water (4 to 6 billion m³ of water, depending on the sources) than the storage capacities of the lakes.

« I’m impatiently waiting for the next flood to see the results »

Today, the entire watershed is affected by the development of flood expansion zones, from the sources of the Seine, in Côte-d’Or, to the estuary, assures the president of Seine Grands Lacs, also president of the Greater Paris metropolis, Patrick Ollier. « We identified 212 ZEC which will be put in place within two to three years »he adds. A huge job, since on each project, it is necessary to convince all the landowners in turn. « Around fifteen per projectbelieves Damien Dondaine. If only one refuses, the project is blocked. »

About twenty kilometers downstream from Lionel Guenin’s farm, in Leuglay, a town of 300 inhabitants located in the Côte d’Or, the meanders of the Ource have also been reworked over 1.4 km. The water can now overflow over 5.5 hectares. Residents, often flooded, will also be able to keep their feet dry, since the water will only overflow on the other side of the river. « I’m impatiently waiting for the next flood to see the results »smiles the technician, on this cool December morning.

Damien Dondaine also went 10 km further down, on the land adjacent to the Schmit factory, in Vanvey, a town of 245 people. Over 150 meters, the merlons of the Ource were demolished, allowing the river to extend over 1.5 hectares. Result: during the next flood, « employees will be able to continue working »rejoices the mayor of Vanvey and president of Epage Sequana, Philippe Vincent. In total, « the projects we are working on should allow us to retain 1.5 million cubic meters of water »he rejoices.

Of the “ ecosystem services » to be remunerated

Under the winter sun, wet feet and ears lulled by the flow of water, crossing the ZEC de Leuglay offers a new relationship with water. The river already seems to be overflowing. Yet, « it’s pretty low these daysnotes Damien Dondaine. The gentle slope allows a more direct connection with the water. This summer, young people came to swim. This never happened before ». In addition, this makes it possible to create diversified habitats, favorable to a whole host of fauna and flora, such as wader birds or certain species living in hydrophilic meadows.

Despite the omnipresence of water in the valley, not all farmers are convinced. « I don’t just make friends here »observes the technician. On the field adjacent to that of Lionel Guenin, the river flows in a straight line, framed by merlons and dikes, which direct the water downstream. « That’s everything you shouldn’t do »he sighs. Various cereals are grown there and sprayed with pesticides when the season comes, also regrets the farmer, who has convinced many surrounding farms to go organic.

« The main obstacle is the difficulty in mobilizing land »

To encourage farmers, Seine Grands Lacs now offers to compensate them when their fields are over-flooded. This is what happens when, in order to limit damage to other plots still spared by a flood, water is redirected towards those which are already flooded.

A measure obtained through hard struggle in 2018, when 24,000 hectares of agricultural land had suffered losses linked to excess flooding in Seine-et-Marne. Eighty farmers then demanded that the role of agricultural land in the flood zone be recognized as being of public utility, estimating that 2,155 hectares of wheat, rapeseed, barley and winter pea crops had been destroyed, they reported to the Parisian. « The farmers were presented with a fait accompli. We took advantage of this moment to argue that the agricultural world should be compensated »specifies Laurence Fournier, of the Departmental Federation of Farmers’ Unions (FDSEA) of Seine-et-Marne. The negotiated rate is 1,000 euros per over-flooded hectare.

But the model still struggles to convince. « The main obstacle to the implementation of ZEC » stay « the difficulty in mobilizing land, […] despite existing compensation schemespoints out the Senate, in a September 2024 report. Constant dialogue with farmers should be ensured […]emphasizing the rarity of the constraints of “overflooding”, with a return of fifty or one hundred years ». In reality, going into ZEC requires rethinking production over the long term, imagining suitable crops or grazing for livestock. A change in practice that requires long-term support.