Concrete reservoir under Paris

Under the square named after physicist Marie Curie in the 13th arrondissement, a massive concrete cylinder was built to collect rainwater and wastewater during heavy storms. The structure has a diameter of 50 meters and can hold up to 50,000 cubic meters of water, which is equivalent to 50 million liters.

Construction details and challenges

The reservoir is 30 meters deep and includes 16 pillars extending 80 meters underground. A tunnel boring machine named Sequana worked for six months to complete the excavation by the end of June 2023. The project faced challenges, including a worker's death in 2023, which was acknowledged during the May 2024 inauguration.

Official recognition and event

The reservoir was inaugurated in May 2024 in the presence of mayor Anne Hidalgo, the minister of sports, and representatives of Paris 2024. Deputy mayor Antoine Guillou called the structure "Paris's second cathedral," highlighting its significance for the city.

Sewer system and storm management

Paris's sewer system traditionally mixes wastewater and rainwater in the same pipes, leading to overflow into the Seine during heavy storms. To address this, two water intakes were built on either side of the river to divert excess water into the new reservoir, reducing the need for storm overflows.

Operational goals and performance

The City of Paris aims to open the valves discharging water into the Seine only twice a year, down from 10 to 15 times previously. On June 19, 2024, the reservoir received 40,000 cubic meters of water after a storm, operating for the first time.

Olympic and environmental impact

The reservoir was crucial for making the Seine swimmable for the Olympic and Paralympic open water events. It is part of a broader plan to improve the river's quality, with the city's share of the cost estimated at 90 million euros. The structure was inaugurated in May 2024 after construction began in August 2020.