This is one of the areas of major concern in the face of repeated episodes of drought: the supply of drinking water. In Nantes, the situation has become very tense, particularly due to the sludge. Sediments which go up the bed of the Loire to the catchment point, located just upstream of the metropolis.
The muddy plug is as old as the Loire… It floats where salt water and fresh water meet. Recognizable by its brown color, this natural mass of sediments decomposed on contact with salt, threatens the drinking water supply in Loire-Atlantique.
Recognizable by its brown color, the muddy plug floats where salt water and fresh water meet • © France 3 Pays de la Loire
Caught between the pressure exerted by the ocean and that of the river, the cork moves with the tides. But in the event of drought, the low flow of the Loire is no longer able to cope with the power of the sea… Then the cork sinks until it dangerously approaches the catchment point located in Mauves-sur-Loire and disrupt water treatment.
“All these suspended matter must be removed, and as a result, it forms a lot of mud which settles in the structures and at a given moment, we reach the limits of the system,” notes Pascal Roussiès, technical manager for drinking water production in Nantes metropolis.
The muddy plug is made up of sediments which flow up the bed of the Loire to the catchment point, upstream of Nantes • © France 3 Pays de la Loire
In 2019, the water plant had to stop production for several hours. Water towers took over and maintained the supply, but their autonomy does not exceed 24 hours. A warning for the authorities.
Half of the homes in Loire-Atlantique, and 90% of the Nantes metropolitan area, are supplied with drinking water thanks to the Mauves-sur-Loire plant.
Pascal Roussies
Technical manager for drinking water production in Nantes metropolis
“Tomorrow, there could be several scenarios. We can imagine, that’s what we hope, that there will be a flood of the Loire strong enough to evacuate this blockage at sea which would make it possible to do a reset, explains Pascal Roussiès. But if the next summers are similar to the summers we are currently experiencing, the scenario will become worse and worse.”
Half of the homes in Loire-Atlantique are supplied with drinking water thanks to the Mauves-sur-Loire plant • © France 3 Pays de la Loire
Without waiting for the worst, several options are on the table: rolling back the collection plant or adapting water treatments.
Expensive projects, but almost inevitable, since the IPCC of Pays de la Loire predicts a drop in the flow of the river by 50 to 70% by the end of the century.
duration of video: 00h01mn57s
In Nantes, drought threatens the drinking water supply, particularly due to the silty plug • ©France Télévisions / Carla Butting / Valérie Brut
A report by Carla Butting and Valérie Brut
2023-10-26 17:21:57
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