VIDEO – Giant basins and tunnels: to protect against floods, Nîmes invests massively

The Antiquailles basin is a titanic construction site. After 15 years of work, this six-hectare quarry will become the largest water retention basin in the city. With the objective of becoming a barrier against flooding.

“In the city of Nîmes, there are 19 retention basins which have a total capacity of one million cubic meters of water. And this quarry basin, alone, will represent 1,800,000 cubic meters of water,” explains to 1 p.m. on TF1 Claude de Girardi, elected LR at the Métropole de Nîmes, responsible for the management of aquatic environments and floods. That’s the equivalent of 720 Olympic swimming pools.

Nine dead in 1988 floods

The city of Nîmes is using drastic measures to protect itself from flooding because it remains traumatized. On October 3, 1988, torrential rains ravaged the Gard capital. In three hours, the equivalent of a month’s rain fell. Nine people died and the water reached, in places, three meters high.

Danielle Cazès was 35 years old that day. “There were no more doors, no more windows. Because everything had been demolished by the cars”she remembers. In the streets, the walls have retained the scars of water. “I would have died. If I had been there, I would have died. That’s why I went up to the first floor in the house.”

Despite the sums (…) on a thousand-year-old flood, it will not be enough

Franck Proust, president of Nîmes Métropole.

The flooding was aggravated by the cadereaux, designed to channel rainwater but which were undersized at the time. “We have a structure which has a very limited capacity. Of the order of 2 to 3 m3 per second. In 1988, we had more than 200 m3 per second which presented themselves here. And so obviously, once that does not passes further below, it came to submerge the whole city”, explains Jean-Luc Nuel, head of the flood prevention service at the Métropole.

Since then, the city has stepped up work to enlarge and widen them, like the Paris metro or the Channel Tunnel. To do this, under the feet of the people of Nîmes, tunnel boring machines advance 15 meters every day. “We are going to be in a 10-fold increase in these flow capacities. And so in the long term, this is where the flood waters will come to be evacuated into this tunnel of 3 m3 in diameter,” adds Jean-Luc Nuel.

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If Nîmes invests to protect itself as much as possible from flooding, the authorities remain lucid. “We are going to protect the city and the urban area for a hundred-year flood. But despite the sums, 400 million euros, for a thousand-year flood like October 3, 1988, that will not be enough,” advances Franck Proust, president of Nîmes Métropole.

The people of Nîmes have therefore learned to live with the risk of flooding, and more than half of them live in flood zones. To protect himself, Gilles Baures invested in five inflatable cofferdams, which retain water. “There are orange alerts where we see that it is already starting to fall a little. We position them and we are at peace. We sleep a little better,” he confides. This equipment is fully covered by the city. Nearly 500 households have now benefited.