That’s it, barring a 100-year flood, the Groussayons, residents of the Groussay district in Rambouillet, will no longer be flooded in the event of a big storm. A water storage basin was inaugurated on Thursday.
Invisible, since it is underground, with just a house to locate and enter it, the Groussay basin is a large tank of 6,000 to 7,000 m³. It helps prevent flooding by storing water during heavy rainfall while the downstream station manages the flow.
This basin is the result of several years of work. First initiated in 2016 by Marc Robert, then mayor, the delegation of authority was granted to Rambouillet Territoires. This basin is then part of the sanitation master plan. The work began in August 2022.
The technical data were explained by Sophie Brinstex, water and sanitation director at the urban area, during the official inauguration which allowed a few elected officials, employees and partners, on the site, to descend to the bottom of the tank. “This pool, with a diameter of 22 meters, is buried 22 meters deep. Its foundations are buried up to 50 meters deep in order to ballast it sufficiently given the nature of the soil. »
Two episodes of flooding
It must be understood that before the construction of this large basin 20 m high, when it rained, all the wastewater (sewer and rainwater) on this side of the RN10 went into the sewers in a unitary network and in the Groussay marsh. What was not absorbed by the Guerville station overflowed. It was sewage, often made up of solid and foul-smelling waste. “This retention basin made it possible to create two pipes: one collecting wastewater and one collecting rainwater. In the event of bad weather, this type of network ensures the evacuation of rainwater directly into the natural environment, thus making it possible to avoid saturating the wastewater networks,” explain the representatives of Rambouillet Territoires.
There were two flooding episodes in 2016, with nearly 1.80 meters of water, and 2018, which affected not only the population, but also historic buildings. “In places, there was more than a meter of water, causing certain situations of despair,” recalls Véronique Matillon, mayor of Rambouillet.
This new basin is guaranteed not only against flooding, but also, by its treatment method, the management of bad odors.
To Sophie’s greatest pride, this project obtained the “Victory for local investment and prevention of environmental risks”. She also had the pleasure of seeing that it worked at the beginning of the week, during a storm.
