Before the lake and dam
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Tributary of the Rhone, the Durance is one of the most powerful French torrential rivers. 55% of its water comes from snowmelt . Men undergo at the same time floods and seasonal shortages. In 1843 and 1856 , when floods devastated the region of Avignon , the idea of ??" taming " the Durance became clearer…
Arranging the Durance, a necessity ...
« Parlamen, mistrau e durenco soun li tres flev de la prouvenco »"they said once (the Parliament , the Mistral and the Durance are the three plagues of the Provence) !
Before the dam of Serre- Ponçon the Durance was indeed an unpredictable and indomitable river. It was marked both by devastating floods, as was the case in 1843 and 1856 , as by periods of severe drought , especially in 1895. Jean Giono said about the Durance : "It is not that she is bad, but for her, good and evil, it's the same ."
For a long time this capricious hydrology made the planners think about the construction of a big reservoir upstream to the river. A dam would allow to collect small and medium floods and to store water to restore in difficult times of summer, when it is scarce. The great flood of 1856 and its ravages mark a turning point. It was decided for the first time to take action. It is about examining the feasibility of creating dams on the Durance, the Buëch, but also on the Verdon. The first recognitions since 1857 are made on six locations including Sainte Croix du Verdon and Serre -Ponçon. On the Durance, all trails lead indeed to the site of Serre-Ponçon, an ideal place with a relatively narrow channel, 2 km downstream of the confluence of the Ubaye. At that time, experts estimate that the foundation rock lays under a layer of only 8 meters of sediment. But at each new approach, surveyors realize polls deeper than before without touching the rock. Finally, around 1900, polls show that the rock is actually 110 meters below the sediment. At that time, no technique allows to anchor a dam on such a thick layer of alluvium. Faced to this impassable obstacle, the project of Serre-Ponçon is abandoned.
In 1899, and for several decades, Ivan Wilhelm, a polytechnic born in Moscow, tries to solve the problem. Until the 1940s, with his team of engineers, he imagines what might be the dam of Serre-Ponçon, but without solving the problem of the depth of the foundation rock. It was not until after the war that technical progress gave hope to a realization.
At that time, the Americans develop a new type of dam on the Missouri, capable of anchoring on such significant thicknesses of sediment. They use a technique of deep injections coupled with a dam in soil instead of concrete. In 1948, almost a century after the initial studies, the construction of a dam at Serre-Ponçon is technically possible. Recently established in 1946, Electricité de France is charged with the project which in 1951 obtains the favorable opinion of the Technical Committee on Large Dams. The project not only plans the construction of the dam of Serre-Ponçon, but also the development of the entire Durance with the construction of a channel over 250 km.
The Law of 1955: birth of a project in territory planning
Given the scale of the project which requires a real logic of territory planning, the decision to launch the project is the object of a law. The project is declared as public utility by the law published in the Official Journal of 5 January 1955, signed by the President of the Republic, at that time René Coty, and several ministers including the minister of Internal affairs, François Mitterrand.
This law, entitled "Law of development of Serre-Ponçon and Lower Durance" defines three missions to the development of the Durance:
- the provision of energy,
- irrigation and water supply ,
- Limitation of the effects of floods.
In this way the law reflects the desire of the legislature to associate hydropower to the irrigation of agricultural land of the Provence. For this reason, the Ministry of Agriculture participates in financing the project equal to 12.3% in return of a water reserve for use in agriculture. Electricité de France is given the concession of hydroelectric falls of the Durance for a period of 75 years, by a decree signed on 28 September 1959. This one is annexed by the book of charges fixing precisely the rights and obligations of Electricité de France.
Une prospérité nouvelle en Provence - Provence Magazine - 06/08/1955