It represents almost three quarters of the fresh water available in the Paca region. The Durance and its main tributary the Verdon, two rivers having their sources in the Alps are essential to Provence. Its domesticated waters run through nearly 5,000 kilometers of canals which irrigate more than 170,000 hectares of crops (of the 581,000 used, including fodder)Alpes-de-Haute-Provence, Var, Bouches-du-Rhône and Vaucluse and flow from the taps of three of the five million inhabitants of the region, including the cities of Aix and Marseille.
In summer, thousands of tourists take advantage of the activities offered by its medium-altitude artificial lakes, whose facilities by EDF, built from the 1950s, make it possible to mobilize hydroelectric power equivalent to two nuclear power plant units. This shows the often overlooked importance of the “Verdon-Durance system” for human activities in Paca.
A system that “touches climate change”, observes Franck Belloti, deputy director of EDF hydroméditerranée. On these rivers EDF operates 23 hydroelectric plants and 16 dams, including three giants, those of Serre-Ponçon (Hautes-Alpes), Sainte-Croix and Castillon (Alpes-de-Haute-Provence), store nearly 2.3 billion cubic meters of water. Water towers with volumes such as one would think them inexhaustible.
But the historically low levels reached last summer under the effect of an intense drought served as a reminder of the precariousness of this balance. The consequence is a drop in hydroelectric production capacity. “In 2022, we produced only 40% of our usual returns”, illustrates Franck Belloti. Yields which usually contribute up to 35% of the electricity production of the Paca region.
In 2022, the water war narrowly avoided
And the year 2023, hit for the time being by an equally historic winter drought, seems to have started under the same auspices, even if the rains of this autumn have recharged the reservoirs. A welcome resource which made it possible to cope with the peaks in electricity consumption in January. “In January, we produced a lot. About 700 gigawatt hours, or the consumption of 3.2 million inhabitants. Hydroelectric is the only storable energy. Its role is to balance the network and to intervene during the points periods, in the morning and in the evening. In twelve minutes, we open the floodgates and can put the equivalent of two nuclear units on the network,” he explains.
The time is now, already, to fill the reservoirs so as not to relive the same conflict of last year around the uses of water. “We had come very close to the water war”, recalls Christian Doddoli, general manager of SMAVD, (Joint Syndicate for the Development of the Durance Valley) public establishment in charge of coordinating the sharing of water uses. . “The people upstairs said it’s our water! Those at the bottom said they had the right to do so. We played the blue helmets, ”summarizes Christian Doddoli.
The tourism stakeholders around the Sainte-Croix and Serre-Ponçon lakes had indeed suffered greatly from the low levels of these reservoirs and the farmers had been forced to reduce their withdrawal from 25% to 60%, as for those in the valley of the Buëch, a tributary of the Durance. With very important economic consequences for these two sectors of capital activity. To avoid this this year, a drought monitoring committee, bringing together the public authorities as well as the various actors, has planned to meet on March 15. This while half of the municipalities of the Var are already on drought alert and the Bouches-du-Rhône department on “vigilance”.
However, “the situation on the Verdon-Durance system is less complicated today than last year” he assesses. “The snow cover in the Southern Alps, whose melting feeds the Serre-Ponçon lake, is 50% higher than last year, even if it remains 20% lower than average”, illustrates -he. “But without normal rainfall, we recommend no longer producing electricity by the summer,” he explains, relying on modeling tools.
The challenge therefore is to save the resource in order to reconcile all its uses. And with a 2022-like scenario set to become, if not the norm, more and more frequent, the question of modernizing tools that date from the middle of the last century also arises. “It is estimated that there are nearly 200 million cubic meters of water lost in leaks from the various canals”, advances Christian Doddoli. A “waste” equivalent to 8 meters in height of the Serre-Ponçon lake.
The fact remains that these developments have made it possible to contain the lack of water. “The elders saw big. These large reservoirs are also a response to these climate changes and offer great resilience. They protect farmers and municipalities from water shortages,” says Franck Belloti. “Without a dam, the Durance would have been dry in the summer of 2022. That’s why they were also originally designed, not so much to avoid its floods which could have been devastating in the past. And without these facilities, life here would not be the same”, concludes Christian Doddoli. We’ll just have to get used to doing with less, so that everyone can continue to benefit from this emblematic and vital river in Provence.