Over time

Explore the fascinating history of the Durance River before the lake and dam. Discover the need to develop this powerful torrential river, the technical challenges of the Serre-Ponçon project, and its impact on Provence. Immerse yourself in the details of the dam's construction, a technical and human feat, and understand the multiple missions of this work at the service of the community.

Serre-Ponçon avant le barrage
Michel Baudry

Before the lake and dam

A tributary of the Rhône, the Durance isone of France's most powerful torrential rivers. 55% of its water comes from melting snow. People suffer from both flooding and seasonal shortages. In 1843 and 1856, when catastrophic floods ravaged the region, the idea of "taming" the Durance took shape...

Managing the Durance, a necessity...

"Parlamen, mistrau e durenco soun li tres flev de la prouvenco" (Parliament, Mistral and the Durance are the three scourges of Provence)!

Before the Serre-Ponçon dam was built, the Durance was an unpredictable, untamable river. It was marked as much by devastating floods, as in 1843 and 1856, as by periods of profound drought, most notably that of 1895. Jean Giono once said of the Durance: "It's not that she's mean, but for her, good and evil are one and the same"

This capricious hydrology has long prompted developers to consider building a large reservoir upstream from the river. A dam would enable the river to withstand floods and store water for release at difficult times in summer, when water is scarce. The devastating flood of 1856 marked a turning point. For the first time, it was decided to take action. The feasibility of damming the Durance, Buëch and Verdon rivers was examined. The first surveys were carried out in 1857 at six sites, including Sainte Croix du Verdon and Serre-Ponçon. On the Durance, all the surveys led to the Serre-Ponçon site, an ideal location with a relatively narrow narrows, 2 km downstream of the Ubaye confluence. At the time, experts estimated that the foundation rock lay under only 8 metres of sediment. But with each new campaign, the surveyors drilled deeper and deeper, without touching the bedrock. Finally, around 1900, the drilling campaigns showed that the rock was in fact 110 metres below the sediment. At the time, there was no technique for anchoring a dam on such a thick layer of alluvium. Faced with this insurmountable obstacle, the Serre-Ponçon project was abandoned.

In 1899, and for several decades afterwards, Ivan Wilhem, a Moscow-born polytechnician and Gapençais Ponts et Chaussées engineer, attempted to solve the problem. Until the 1940s, he and his team of engineers imagined what the Serre-Ponçon dam might look like, but failed to overcome the problem of the depth of the foundation rock. It wasn't until the post-war years that technical progress gave us hope that the dam could be built. During this period, the Americans developed a new type of dam on the Missouri River, capable of anchoring itself in thick layers of sediment. They used a technique of deep injections coupled with an earthen rather than concrete dam.

In 1948, almost a century after the first studies, the construction of a dam at Serre-Ponçon was technically feasible. Newly created in 1946, EDF was entrusted with the project, which was approved by the Comité Technique des Grands Barrages in 1951. The project included not only the construction of the Serre-Ponçon dam, but also the development of the entire Durance river, with the creation of a 250 km-long canal.

The 1955 law: the birth of a regional planning project

In view of the sheer scale of the project, which had a real regional development dimension, the decision to launch the project was enshrined in law. The project was declared to be in the public interest by a law published in the Journal Officiel on January 5, 1955, signed by the then President of the Republic, René Coty, and several ministers, including the Minister of the Interior, François Mitterrand.

<> This law, entitled "Loi d'aménagement de Serre-Ponçon et de la Basse Durance" (Serre-Ponçon and Lower Durance Development Law) defines three missions for the development of the Durance:

  • energy supply,
  • irrigation and water supply,
  • flood control.

The law thus marks the legislator's desire to combine hydroelectricity with the irrigation of Provence's farmland. The French Ministry of Agriculture contributes 12.3% of the project's funding, in return for a water reserve for agricultural use. Électricité de France, now EDF, was granted a 75-year concession for the Durance hydroelectric falls by a decree signed on September 28, 1959. Attached to the decree were specifications setting out in detail the rights and obligations of Électricité de France, now EDF.

To mark the occasion, an educational report entitled "Prospérité nouvelle en Durance" (New prosperity in the Durance) was produced to demonstrate the benefits of the economic development and social well-being that would result from the dam's construction (INA archives).

See the video

Building the dam

A technical and human feat...

Following tests and preparatory work in the late 1940s, construction began in 1955, 54 months later. In June 1960, construction of the dam was completed, while filling of the reservoir began on November 16, 1959: ten months later, the Ubaye and Durance valleys, completely flooded between the Serre-Ponçon clue and the Roc d'Embrun plain, offered a new world... Up to 3,000 workers were on site at the same time, at the peak of activity in July 1959.

Preliminary work began in 1955, with the installation of site facilities commensurate with the size of the project: compressed air plant, washing and screening station to prepare the aggregates used in concrete manufacture, concrete plant, 2,300 m² of workshops to maintain and repair an extremely large fleet of public works machinery. An 800-bed housing estate is built in Espinasses to accommodate bachelors. a further 300 housing units were built near the site.

The first real project was the detour of the Durance River, prior to the construction of the dike. To this end, a temporary diversion consisting of 2 tunnels 900 m long and 10.50 m in diameter was dug into the rock on the left bank of the future structure. The diversion was completed on March 29, 1957. Colossal resources were deployed for the time: a drilling unit with 3 "jumbos" (huge pick hammers mounted on crawlers), telescopic metal formworks mounted on rolling gantries and a concrete-mixing train.

At the same time, we had to think about re-establishing the communication routes that would be cut off by the impoundment of the lake. We took the opportunity to modernize them. Over 14 km of rail track and 3 S.N.C.F viaducts were built. As well as 50 km of roads and over 2.5 km of bridges, including the 924 m long Savines viaduct. These projects cost more than the construction of the dam itself...

Discover the April 4, 1957 report for the national news: "Travaux sur la Durance" (INA Archives)

Construction of the dam and plant

Over a 39-month period, from March 1957 to completion in June 1960, 30 million tonnes of materials were moved and transported along the site roads. Building the dam alone required 14 million m³ of earthworks (6 times the volume of the Great Pyramid of Cheops). The dam is 600 metres wide and 650 metres thick at the base. To transport these enormous quantities of rock, 35 "Euclid" semi-trailers, imported from the USA, are capable of loading 60 tonnes into their tippers. In a single day, up to 1,500 300-horsepower vehicles pass through the site to place 20,000 m³ of material compacted by 3 tire rollers weighing 35 to 45 tonnes and 2 "sheepsfoot" rollers weighing 18 tonnes. The machines sweep over the dike non-stop from 2 am to 10 pm. A Euclid driver earns around three times what an office worker does. But it's a hard and dangerous job... While on the surface, shovels, dumpers, tractors and rollers go round and round, in the heart of the rock, a gigantic underground cathedral gradually takes shape to form the factory.

The granite was of excellent quality, enabling all excavations to be carried out without the need for support. By the end of 1958, the three caverns built in parallel to house the transformers, machines and foot valves, were available to manufacturers of electromechanical equipment.

The construction site had some memorable moments. On June 14, 1957, a flood of 1,700 m³/s (the highest known after that of May 1856, which had reached 1,800 m³/s) disrupted the work. At that time, only one temporary diversion gallery was in operation. The cofferdam built upstream of the dike to protect it was submerged, fortunately without too much damage. Another delicate operation was the transport of the 4 alternator rotors from the manufacturer's workshops. The 260 tonnes of each rotor were transported by road on a low-loader.

Launching the water and the disappearance of Savines and Ubaye

On November 16, 1959, the dam gates closed to begin filling the reservoir. 18 months later, on May 18, 1961, the lake was full for the first time. When the reservoir was filled, the villages of Savines and Ubaye, located below the 780-meter mark, were submerged.

It was decided to rebuild the village of Savines. There were lively discussions as to whether the new village should be built on the left bank or on the sunnier right bank. The left bank, that of the original village, was chosen, necessitating the construction of the 920-meter-long bridge crossing both banks of the lake. EDF financed the reconstruction of communal buildings and a new church, with its resolutely modern originality, symbolized the village's renewal.

In Ubaye, the village was not rebuilt, but the cemetery was moved to the lakeside. The dam's impoundment required the relocation of almost 1,500 people...

Discover: "La mise en eau du barrage de Serre-Ponçon" - Regional report for the national newspaper - 02/04/1960 (INA archives)

Algerian war prevents inauguration

The Serre-Ponçon dam was never officially inaugurated. General de Gaulle was to have presided over the ceremony, but the Algerian war disrupted plans. The postponement never materialized.

Construction costs

The breakdown of total expenditure, estimated at 50 billion old francs, is as follows:

  • Dike and waterproofing: 23
  • Ancillary structures and plants: 21
  • Hydro and electromechanical equipment: 13
  • Restoration of communications: 27
  • Land purchase: 13
  • Studies and tests: 3

A multi-purpose work serving the community

The 1955 law that led to the construction of the Serre-Ponçon dam gave the Durance development three missions: to generate electricity, to ensure water requirements for irrigation of the Lower Durance and to control flooding. While EDF takes great care to fulfill its primary public service mission of producing electricity from clean, renewable energy, it is also positioning itself at Serre-Ponçon as a water manager for a wide range of uses: power generation, irrigation, drinking and industrial water supply, fishing, tourism, water sports and whitewater activities.

With this in mind, EDF agreed on June 16, 2008 to make the Serre-Ponçon public hydroelectric domain available to SMADESEP for the purposes of tourism management and development. To support this territorial development, the concession-holder also agreed to maintain a minimum level for tourist operations during the high summer season. This level, set at 5 meters below the normal hydroelectric operating level, corresponds to the lake level below which most water sports activities begin to suffer severely. Included in the concessionaire's hydroelectric operating conditions, it must be respected at least every year from July 1 to August 31.

Serre-Ponçon: first link in a 250km hydroelectric chain

The Serre-Ponçon power plant produces around 700 million kWh per year, equivalent to the consumption of the Hautes Alpes department. With a capacity of 380 MW (1/3 of a nuclear reactor), it is the most powerful hydropower plant in the Provence-Alpes-Côte d'Azur region, and one of the most powerful in France.

But Serre-Ponçon is also the reservoir from which the EDF Durance canal begins. A veritable energy backbone, this canal carries the water stored in the Serre-Ponçon reservoir over 250 km to the Saint Chamas plant on the shores of the Etang de Berre. Along the entire length of the canal, 15 hydroelectric power stations successively turbinate the water. Upstream of Lac de Serre-Ponçon, 8 hydropower plants have been built on the Durance and its tributaries. Together with the power stations on the Verdon, a tributary of the Durance, the Durance-Verdon hydroelectric chain comprises 32 power stations. Together, they form one of the five largest hydroelectric resources in France (1/6th of the country's peak hydroelectric capacity). The Durance - Verdon complex has a production potential of 7 billion kWh. This corresponds to :

  • 10% of French hydropower production,
  • 40 to 60% of the Provence-Alpes-Côte d'Azur region's electricity production, essential for a region that today consumes twice as much electricity as it produces.
  • 15 to 20% of the Provence-Alpes-Côte d'Azur region's electricity consumption.

19 of the power stations in the Durance - Verdon chain are controlled remotely and simultaneously by computer, from the Sainte-Tulle Joint Control Centre, near Manosque. This centralized operation guarantees synchronized operation of 2,000 MW of power - the equivalent of two nuclear reactors. In less than 10 minutes, this production potential can be mobilized, an invaluable asset for responding in real time to variations in electricity consumption or for dealing with power system failures.