At the wheel of her car, Julie Camus climbs the narrow and winding road which overlooks the suburbs of Chambéry and Lake Bourget (Savoie), clinging to the Épine massif. She parks the vehicle near a discreet hatch, which protects access to a concrete block buried in the ground of a patch of grass. The young person in charge of water resources and environment at the agglomeration's water service turns the key and opens the heavy metal door to reveal the precious treasure hidden on the site: a spring.
Here, the Grand Chambéry water agency captures tens of liters of water every second, injected into the drinking water network. The spring fills the small underground basin in a noisy tumult, and part of the water rushes into pipes. The overflow is discharged back into the watercourse to resume its natural path. It has worked like this on dozens of springs around the lake, for centuries... But the local authorities are planning a revolution.
In a few months, at least 15 liters of water per second will have to flow into the stream, to preserve its biodiversity, especially the species that live there. This is the refund rate. "Today, we take everything we need, even if it means drying it out," explains Cyrille Girel, from the water service. A radical change of paradigm, because "the river will now be a priority, not human consumption".
A big bang that stems from the water resource management plan (PGRE) adopted in 2016 by Cisalb, the body that coordinates water management around Lake Bourget and Chambéry. “In 2022, details Julie Camus, we could only have exploited this source eight to nine months out of the year with this rule. Millions of euros are therefore invested in connecting the networks that were not connected to the pumping of groundwater from Chambéry and the lake, in order to be able to do without sources during periods of tension.
The PGRE also provides, in addition to these restitution flows, a plan to fight against leaks, support for farmers and industrialists to reduce their water consumption with more economical equipment, education for the inhabitants and commitments from the municipalities. “You have to take the whole chain into account, underlines Cyril Girel, because if you prevent yourself from pumping in a source but others come to take everything downstream, it is useless. »
An "ambitious" plan, according to elected officials, "which has given a head start" on the repeated droughts of recent years, greets Marie-Claire Barbier, president of Cisalb and mayor of a municipality in the sector. Drought in the mountains? "It's counterintuitive, because we are next to the largest French lake, but yes, we lack water," agrees Renaud Jalinoux, director of the organization. Impossible to be satisfied with it: it is necessary to diversify the sources of supply so as not to be vulnerable to possible pollution, bacteria and other invasive algae.
And these sources dry up all the more as global warming is stronger in the Alps: when the PGRE was adopted in 2016, it was thirty years in a row that the annual average temperature was above normal. “The sea ice has melted 140 meters in fifty years: it is the equivalent in water of Lake Annecy which has disappeared. »
“Droughts are more and more frequent and later and later,” says Florent Bérard, water resources project manager at Cisalb. We have less and less snow [which feeds the watercourses by melting, Editor's note], the flow of our rivers is decreasing..." And to shower the hopes of those who believe in a "miracle solution": "It doesn't there isn't, we have to readapt our uses to the resource. In other words by Marie-Claire Barbier, "be aware that it's not open bar".
On the development side, the Cisalb and the communities of municipalities do not forbid anything. At La Motte-Servolex, between Chambéry and the lake, a water reserve has been overlooking the valley for three years. This oval basin of 12,000 m3, waterproofed by a green plastic tarpaulin, allows the three neighboring farmers to irrigate 7 hectares of market gardening and arboriculture. An installation called "hill reservoir", which is furiously reminiscent of the mega-basins against which environmental activists are rising, although ten to fifteen times smaller.
"However, it has nothing to do with it," Florent Bérard immediately defuses. Here, we do not pump water from the aquifers to store it in the open air. And to point to the highway which passes a few meters higher, behind a row of trees. A nearby ditch evacuates rainwater, and is therefore now used to supply the basin. The project was able to materialize without dispute, because Cisalb brought everyone together around the same table to find the solution, farmers as well as environmental associations.
"Faced with drought, we must not be dogmatic, do not rule out any solution a priori. But what works here would surely not work opposite, "warns the project manager. At the same time, farmers have been supported to invest and review their irrigation system to consume less, because "the goal is not simply to have water to use it anyhow behind it".
Marie-Claire Barbier agrees: "More than finding alternative means, the urgency is to reduce our water needs. With his "step ahead", does the Savoyard water manager take up the challenge? The results of this PGRE, which came to an end in 2022, are being drawn, but Florent Bérard recognizes that overall water consumption has not really decreased, "because the territory is very dynamic and continues to attract new residents and businesses". The economies are working, but they only allow, for the moment, to absorb the expansion of the agglomeration.
The record drought of summer 2022 has, like everywhere in France, shaken even the best prepared. The concern is growing, especially since the winter has not been better. “In February, alarmed Florent Bérard, we had only 5 millimeters of rain. And there is already no more snow on our massifs, although it is only the beginning of March! Despite the revolution already initiated by Cisalb, its president no longer hesitates to talk about quotas. "If pedagogy is not enough, let nothing change... If we have to do it, we will do it." »
