How do wateringues work, this water evacuation system, criticized after the floods in Pas-de-Calais?

After historic rains in November 2023 and an unprecedented rise in water levels, Pas-de-Calais is once again prey to floods

How do wateringues work, this water evacuation system, criticized after the floods in Pas-de-Calais?

After historic rains in November 2023 and an unprecedented rise in water levels, Pas-de-Calais is once again prey to floods. Like a scenario that repeats itself tirelessly, 169 municipalities are affected by these new floods, 500 homes are deprived of electricity and 2,000 residents have no access to drinking water, declared the prefect of Pas-de-Calais. , Jacques Billant. The department remains on red alert for floods.

Wateringues, a water evacuation system, created almost a thousand years ago in France, are nevertheless supposed to prevent flooding and protect agricultural land. But their effectiveness has been called into question since recent episodes of severe weather.

A system specific to Flanders

As ingenious as they are fragile, watering machines are best known in Belgium and the Netherlands. In France, this system covers the Calais-Dunkerque-Saint-Omer triangle, in order to protect the approximately 450,000 inhabitants from flooding on the Aa and Liane rivers. Because this area is a polder: land reclaimed from the sea and therefore located below the level of high tides.

Concretely, it is a network of 1,500 kilometers of ditches and canals which communicate with each other in order to regulate the water level of low-lying lands, and if necessary, evacuate excess water towards the sea, as the recalls the Intermunicipal Wateringues Institution (IIW). At low tide, the locks are opened to discharge these surpluses into the North Sea – gravity thus doing its work – while at high tide they are closed to prevent flooding of the land. In the event of excess water in the watering stations, the pumps come into action to speed up evacuation.

Inadequacy and lack of maintenance

In September 2023, a report from the Regional Chamber of Accounts pointed out “the fragility of the hydraulic system accentuated under the effects of climate change” and expressed concern about the increase in the population (INSEE projects more than 500,000 inhabitants in 2050 ), the increase in urbanized areas, soil waterproofing, runoff and volumes of water to be evacuated.

Also, the obsolescence of the system is pointed out: “The canals to be transferred [which can be watering holes but also navigation routes] are in poor condition (…). A limited number of them are likely to overflow and cause flooding,” observes the court, which then recommended restoration or cleaning work. An argument taken up by Allan Turpin, mayor of Andres, an affected Pas-de-Calais commune, and president of the Stop Floods Pas-de-Calais association, who deplores on LCI “the banks are sagging”.

“We can no longer find the parts” for the pumps

A problem which, if it is resolved, is not sufficient for the councilor due to a “lack of pumping” and pumps, some of which have not been changed for “around forty years”. years” – in November 2023, two Dutch pumps were sent as reinforcements. “Unfortunately, watering holes are difficult to maintain. Some pumps, for example, are so old that we can no longer find the parts,” Bertrand Ringot declared to France 24 in November 2023. The mayor of Gravelines and president of the IIW specifies that he has multiplied the institution’s budget sevenfold. since 2017.

Who is responsible for this lack of maintenance? Three main players share the management of the watering holes. At the most local scale, these are the sections of watering stations, small areas cut up by ditches responsible for maintaining the watering stations. The main arteries of the network are managed by the Voies navigables de France, while the IIW is responsible for carrying out major evacuation works and ensures their operation and maintenance.

Beyond the structural problem posed by watering holes in the event of heavy flooding, the priority, for elected officials and residents, is the immediate evacuation of the water. The Minister for Ecological Transition, Christophe Béchu, promised “exceptional responses” during a visit to Pas-de-Calais on Thursday.