A centennial flood?
A centennial flood is one whose probability of occurring in any given year is 1 in 100. It does not mean a flood that occurs every 100 years.
The Seine’s last centennial flood occurred in 1910. The waters of the Seine rose over a 10-day period, and the river peaked at 8.62 meters on the hydrometric scale at the Austerlitz Bridge. Half of the transport network was totally unusable for months, and some passengers even took to getting around by boat in the flooded tunnels.
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How do we prevent the metro from filling up with water?
To avoid flooding, we regularly carry out simulation exercises.
- Therefore, in December 2018, during a training session on the forecourt of Balard station, we mobilised 40 staff members to build aluminium and breeze-block protectors to prevent water entry, which could occur through air vents, for example. In addition, a crisis unit, bringing together all the internal players concerned by the flood risk (operations, maintenance, etc.) was also set up to coordinate actions and take part in crisis management with our partner for the exercise, the 15th arrondissement City Hall, and the other operators.
- A similar scenario occurred in 2016: from 7 to 18 March, the Paris police organised a flood simulation exercise codenamed EU Sequana 2016, in which our staff played a major role. Concrete block walls, aluminium siding and water barriers were installed on five of our sites, and we set up an ad hoc crisis management centre that brought together all of our group’s flood risk prevention teams.
- Let’s go back a few years. It is 8 a.m. on Tuesday, 29 January 2013, and it is raining in Paris. In front of our head office at Quai de la Rapée, in the 12th arrondissement, six men are unloading construction materials. They have four hours to set up some 100 metres of stainless steel barriers. Over the course of the day, our parent company is the theatre for an annual simulation exercise, as part of our flood risk prevention plan.
Discover how RATP is preparing for the flood of the century...
In concrete terms, major flooding of the Seine creates enormous material risks: tunnels filling with mud and debris, destruction of tracks and facilities, electrical equipment malfunctions… An unmanaged flood would have an impact on all of our lines and would paralyse our entire transport network!
Retention ponds and protective embankments
Several retention ponds located near Paris can be used to manage the small floods that occur regularly. When the river suddenly rises, their combined action can reduce the water level by 70 cm.
In addition to retention ponds, and in the event of large-scale flooding, our flood risk prevention plan calls for the construction of embankments to protect the numerous sites at risk. To do this, we must transport lots of building materials to the sites needing extra protection.
A few figures?
With a surface area of 2400 m², the Bonneuil-sur-Marne storage site houses 273 cement mixers, 173 power generators, and 171 wheelbarrows. 70,250 concrete blocks, hundreds of sacks of mortar, lumber and plywood are also stored at various storage sites between Chartres and Fontenay-sous-bois. Nearly 100 lorries can be mobilised to transport building materials, and 1000 employees are ready to intervene to build the necessary protective structures in case of a flood.
Our flood risk prevention plan is calibrated according to the 1910 flood. It has already enabled us to handle several small-scale floods. The initial investment is about 6 million euros, which is 4 to 10 times less than the costs linked to the risk of a major flood. It is an indispensable plan of action, in view of the potential damages!