As soon as the start button is pressed, the pumps activate with force, creating large splashes with a deafening noise. On this foggy and cool morning of Wednesday January 15, 2025, near Châtenay-sur-Seine (77), Patrick Ollier, the president of the Métropole du Grand Paris and the territorial public establishment of the Seine Grands Lacs basin (SGL), seems in heaven. After more than two and a half years of work and an investment of 114 million euros shared between the State and the said community, the Seine Bassée pilot locker is entering the “test” phase, under the aegis of the former minister.
With a total area of 360 hectares, crossed by a 7.6 km embankment dyke with a height of 2 meters, this new hydraulic structure is almost unique in France. Its purpose is to retain, thanks to a large pumping system, part of the water from the Seine in the event of a major flood, and therefore to limit flooding downstream, from the confluence of the Seine and the Yonne to Montereau. -Fault-Yonne (77) and throughout the Paris metropolitan area.
The creation of this structure was born from a simple observation: “We realized that the moment when the floods of the Seine are the strongest coincides with that when the flood of the Yonne arrives”, indicates Baptiste Blanchard, the director General of Seine Great Lakes.
10 million m³ collected in 66 hours
Also, as soon as such an episode occurs in the future, “we will take water from the Seine in a controlled manner to reduce its flow before that of the Yonne tumbles. Because it is the concomitance of flood peaks which aggravates the water levels and the related damage downstream of the Ile-de-France river. » As it stands, 10 million m³ of water will be pumped into the Seine and stored in a record time of 66 hours. “We are talking about an effect of 10 to 15 cm of water gained, depending on the flood volumes,” he notes.
-Thanks to a sophisticated measurement system, the operator will be able to anticipate floods.
France
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