After two and a half years of work but more than ten years of reflection, “the mission is accomplished” and the “locker” of the Seine Bassée, “which was impossible to achieve, is here today”welcomed Patrick Ollier, president of Seine Grands Lacs, the manager of this hydraulic work, and of the Métropole du Grand Paris during a visit.
The work, which cost 114 million euros, is in fact a gigantic area of 360 hectares surrounded by a 7.6 kilometer dike. In the event of flooding, pumps are turned on to inject 10 million cubic meters of water into this area, the equivalent of 4,000 Olympic swimming pools with a depth of 2 meters. This operation should make it possible to lower the level of the Seine downstream “up to 15 centimeters”according to a press release.
World Heritage France: Paris sur Seine
“It’s solidarity from upstream to downstream”rejoiced Mr. Ollier, while indicating that this would not have been possible without solidarity in the other direction, the Greater Paris metropolis helping to finance certain projects.
And “upheaval” disproportionate
“You accepted the constraints that were imposed on you”declared the elected official addressing the mayors and owners concerned, summarizing the tensions and fears which surrounded this project imposed by the State, and against which all the municipal councilors of the surrounding communes had voted in 2020.
“We are worried”especially regarding “of the flood risks that there may be in the village”more “we have no choice”had testified a few days earlier to AFP Stéphanie Banos, mayor without label of Châtelay-sur-Seine.
She recognizes, however, that the work has “went very well” despite initial fears and that communication with the authorities and Seine Grands Lacs was very good.
“The upheaval (for biodiversity) caused by this gigantic project in relation to the gains from flooding is disproportionate”for his part tackled Jean-François Dupont, co-president of France Nature Environnement Seine-et-Marne (FNE), who filed, with others, an appeal to the administrative court. This was rejected but opponents appealed.
If the few centimeters gained may seem small, this could represent 40 to 70 million euros in avoided damage, defended Emmanuelle Lucas, director of territorial action and hydrology for Seine Grands lacs, citing figures from the public inquiry.
“We will never be able to protect Île-de-France from a completely extreme major flood, but thanks to these works, we are greatly reducing some of the damage”she summarized.
Flood expansion zones
Some opponents make the link with another project, that of the widening of the river connection between Bray-sur-Seine and Nogent-sur-Seine.
This one, managed by Voies navigables de France, “will accelerate the flow of the river upstream” while the locker aims to slow it down, explains Mr. Dupont.
If the defenders of the projects highlight the expert opinions affirming that the two works will have no impact on each other, a source familiar with the matter recognizes that the enlargement is a “purely economic demand” Who “not going in the right direction” from the point of view of flood prevention.
The numerous oppositions did not get the better of the Seine Bassée system, but they probably put an end to the initial project, which included a total of nine traps.
Asked about the future of the other works, Mr. Ollier declared that it was necessary “wait and see how (this one) works”while other interlocutors half-heartedly acknowledged that it was unlikely that they would see the light of day, particularly due to funding issues.
Today, the emphasis is placed on the “flood expansion zones“that is to say private land whose owners, often farmers, accept that they be used to receive surplus water in the event of flooding, in exchange for a certain sum of money. A device that is simpler to set up than a locker, and probably less expensive.
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