Espinasses, Rousset, Savines-le-Lac - Serre-Ponçon works

• departments: Hautes-Alpes - Alpes-de-Haute-Provence
• municipalities: Espinasses, Rousset, Savines-le-Lac (Hautes-Alpes), La Bréole (Alpes-de-Haute-Provence)
• naming: Works of Serre-Ponçon
• authors: Ivan WILHELM, Jean de MAILLY (architects), Jean COURBON, Jean PROUVE (engineers)
• date: 1955-1961
• protection: unprotected building
• label patrimoine XXe: Commission régionale du patrimoine et des sites (CRPS) of 28 November 2000

The devastating floods of 1843 and 1856, and subsequently the summer shortages, led to the construction of a large water storage tank on the Durance in the 20th century. The site of Serre-Ponçon, which has a relatively narrow gully 2 km downstream of the confluence of the Ubaye, seems the most appropriate, despite the difficulty of building on a deep and permeable alluvial bed. For more than a quarter of a century, Ivan Wilhelm, a polytechnic graduate born in Moscow in 1867, tried to solve the problem, and it was only in 1948 that the evolution of techniques made it possible to produce the work.
 
Electricity of France created in 1946, is entrusted with the project which is declared of public utility by the law of 5 January 1955, entitled "law of development of Serre-Ponçon and Basse-Durance", which marks the legislator’s desire to associate irrigation with hydroelectricity.

Electricité de France conducts systematic soundings to define the shape of the bedrock. Development work began in 1955 and the dam was opened at the end of 1959 and completed in May 1961.
Because of the extremely deep rocky foundations, the foundations of the Serre-Ponçon dam could only be built on the alluvial deposits of the Durance. In order to accommodate possible settlements, the dam itself is made of loose materials, and therefore cannot accommodate the power plant. The latter is dug on the left bank of the rock, as are the driveways, the forced pipes, the escape galleries, and various access and passage routes.
The power plant consists of 3 rooms dug into the rock, sufficiently distant from each other so as not to compromise the overall performance. These 3 underground rooms are vaulted and the search for economic significance has led to the realization of imposing volumes, one of which is more than 100 meters long.
The first room, called the Valve Room, houses, as the name suggests, the valves to remove the turbines from the water. The second room contains the 4 "francis" turbines, each topped with an alternator. The third room finally houses the power transformers. An access tunnel also dug into the rock allows access from the outside to these 3 successive rooms.
It is at the foot of the dam and the mountain housing the power plant that are located the administrative premises that host on the site more than 15 EDF agents. The 225,000 and 150,000 volt High-Voltage substations form a separate unit, located a little higher at the foot of the dam.
Moreover, the creation of the development required the relocation of infrastructure (road network, SNCF network), and the construction of bridges, including that of Savines to connect the right and left banks of the Serre-Ponçon dam.

It was to the engineer Jean Prouvé (1901-1984), associated with the architect Jean de Mailly (1911-1975) grand prix of Rome in 1945 who collaborated notably in the realization of the CNIT and towers of the Defense, the design of the underground rooms and the administrative building located outside. The Savines bridge was built by engineer Jean Courbon (1913-1986) technical director of GTM.

Serre-Ponçon is the head reservoir of the Durance hydroelectric development. It is part of a set of 19 remote-controlled factories from the central control station located in Sainte-Tulle. The water stored in the reservoir is turbinated by the power station at the heart of the structure and then discharged into the basin formed by the Espinasses dam. This allows the water to be diverted to the EDF de la Durance canal, which will supply 15 power plants to the Berre pond.
 The works of Serre-Ponçon (dam, power station, bridge of Savines) have been awarded the label Patrimoine du XXe siècle. The Jouques plant (Bouches-du-Rhône) has been listed as a historic monument since 1989.

Beyond the hydroelectric equipment created, the construction of the Serre-Ponçon dam (3,000 ha) has considerably modified the landscapes of the Durance valley and the economy of this valley, which until then remained very deprived, promoting agriculture but also tourism with the lake as a pole of attraction.

• Editor: Martine Audibert, drac paca crmh, 2004
• Sources:
  - Lyon-Caen Jean-François, Menegoz Jean-Claude, Electrical cathedrals, architecture of the Dauphiné hydroelectric power plants, Grenoble, Musée dauphinois, 1991
  - and with the collaboration of Electricité de France