Serre-Ponçon Dam

In brief

Where the Durance and the Ubaye meet, Serre-Ponçon is a major structure of the Durance system. Before it, the Durance was nicknamed the "third scourge of Provence", because of its floods. Today, this earth dam is used to produce electricity, irrigate, supply water and for tourism.

How does it work?

Serre-Ponçon is an embankment dam, with a story of ingenuity:

• Under the river, there was a buried canyon, filled with more than 100 meters of sand and gravel that let water through.
• Engineers first built, underground, a very deep watertight cut-off wall in these alluvial deposits, then raised the dam: a mountain of 14 million cubic meters of earth and rock.
• Its power plant, dug underground, produces electricity, then the water leaves in a canal that feeds 15 other power plants all the way to the Étang de Berre.

Key facts

• The lake: about 1.2 billion cubic meters, enough to fill nearly 500,000 Olympic swimming pools.
• Height: 123 m. Commissioned in 1960.

Words to know

• Confluence: a place where two rivers join.
• Scourge: a great misfortune that keeps coming back.

Did you know? In the middle of the lake, you can see the tiny Saint-Michel chapel, on a small island. It recalls the landscape from before, when the villages of Savines and Ubaye were swallowed up when the lake was filled.

Going further

Serre-Ponçon is the largest artificial lake of mainland France by volume. But in French Guiana, the Petit-Saut lake is even larger, with about 3.5 billion cubic meters.