The Paris town hall inaugurated, on Thursday, the Austerlitz rainwater and wastewater retention basin, supposed to limit pollution of the Seine in the event of storms, three months before the Olympic Games events planned in the river. A tribute was also paid to Amara Dioumassy, the worker who died during the construction site.
Published on: 05/02/2024 – 12:53 Modified on: 05/02/2024 – 18:17
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An underground cathedral in the center of Paris. The Paris town hall inaugurated, Thursday, May 2, a large water storage basin under the Austerlitz station which will help to purify the water of the Seine and open it to swimming, three months before the planned Olympic events in the river.
This basin dug underground between the Austerlitz station, the historic entrance to the La Pitié-Salpêtrière hospital and the aerial metro should be able to accommodate up to 50,000 m3 of waste and rainwater in the event of heavy rains, and thus prevent this polluted water from ending up in the river.
The equivalent of 20 Olympic swimming pools, repeats the Paris town hall, which had a cylinder 50 meters in diameter and 30 meters deep built, for a final budget of around 100 million euros. A dizzying work on the descent.
Its 16 pillars, called “barrettes”, go up to 80 meters underground, or 50 meters further than the bottom of the basin, accentuating the verticality of the site.
“Second Cathedral of Paris”
“It’s the second cathedral in Paris,” comments Antoine Guillou, the deputy in charge of cleanliness and the sanitation network, which must become more “resilient” with this basin.
The construction site of the Austerlitz basin, a storage and treatment basin for the water of the Seine, in Paris on June 15, 2023. © Anne-Christine Poujoulat, AFP
Created by the engineer Eugène Belgrand in the middle of the 19th century, the capital’s old sewer network is unitary, that is to say mixing wastewater and rainwater.
However, its operation “is very dependent on the weather”, summarizes Antoine Guillou: in the event of heavy rainfall, 44 storm overflows spit this mixture into the river to prevent the sewers from overflowing.
By absorbing this overflow, before returning it to the sanitation network via a pumping system, the Austerlitz basin must make it possible to “reduce the volume” of unclean water discharged into the Seine, underlines Antoine Guillou.
“In principle and in volume, there is nothing exceptional about it. What is exceptional about it is its location in the heart of Paris,” explains Samuel Colin-Canivez, the network’s major works manager. Parisian sanitation system.
More than a billion euros invested
It is a major work of the Bathing Plan, in which the authorities have invested around 1.4 billion euros to allow the general public to dive into the Seine from 2025. Spills into the Seine have already been reduced tenfold since the end of the 1990s.
The Paris 2024 Olympic Games (from July 26 to August 11), which are to celebrate the return of this historic practice, with the holding of marathon and triathlon swimming events in the river, have made it possible to accelerate the work.
Paris: wastewater spills into the Seine during intense rains. © Nalini Lepetit-Chella, Sabrina Blanchard, AFP
But in August 2023, the rehearsals turned into a nightmare for the organizers, forced to cancel the marathon swimming competition because the water quality thresholds were clearly exceeded, after heavy rains.
“All the investments do not make it possible to cope with this episode” of last summer, “extremely rare”, but it “reduces its impacts”, measures Antoine Guillou.
“Bathability criteria”
Former president of France Nature Environnement (FNE) Île-de-France, Michel Riottot affirms that a “big, quick rain” will quickly “saturate” the new structure.
“In Paris, sewers, tunnels and basins like Austerlitz store 1.9 million m3 of water. A small rain of 10 mm is 1 million m3. With a big Cévennes rain of 20 mm, you will overflow with everywhere”, calculates this former research engineer at the CNRS.
“When we (have) intense rain, in any case, we will reject it and we will not reach the swimmability criteria,” recognizes Samuel Colin-Canivez. But “we will inevitably improve on the bacteriological load that we give to the (natural) environment. So we will gain in number of swimmable days”, he insists.
The construction site of the Austerlitz basin, a storage and treatment basin for the water of the Seine, in Paris, March 13, 2024. © Anne-Christine Poujoulat, AFP
“We can understand that there are a lot of skeptical people,” adds Antoine Guillou, recalling that it has been “a century since swimming in the Seine was prohibited.”
According to the town hall, thanks to Austerlitz, “the spill gates will now only be open for the heaviest rains, on average twice a year”.
With AFP
