The Selune river and its dams

The Selune is one of four coastal rivers that flow in the Bay of Mont Saint Michel (Normandy), along with the Sée, Couesnon and Sienne. The Selune rises at Saint-Cyr-du-Bailleul and flows for 85 km (Source: BD Carthage 2017) to the Bay of Mont Saint Michel, where it shares an estuary with the Sée. Its catchment area covers 1083 km² (Source: SAGE Sélune) and extends over 3 departements: La Manche, Ille-et-Vilaine and Mayenne. Its main tributaries are the Airon, the Lair, the Beuvron, the Cance, the Gueuche, the Argonce and the Oir.

Two hydroelectric dams were built in the early 20th century on the main course of the Sélune: the La-Roche-Qui-Boit dam (16m high) and the Vezins dam (36m high).

History of the Selune dams

Construction of the La-Roche-Qui-Boit dam began in 1915, after the Société des Forces Motrices de la Sélune was awarded the concession in 1914. The dam was commissioned in 1921 to meet local electricity needs. Electricity was supplied to distribution companies, industrialists such as the Brecey distillery, and towns: Avranches, connected in 1920, then Ducey, Granville, Mortain and Fougères. Faced with a growing demand for electricity, in 1921 the Société des Forces Motrices de la Sélune applied for a concession to build a second hydroelectric dam upstream. Construction work began in 1929, and the Vezins dam was commissioned in 1932. In 1946, operation of the two dams was transferred to Electricité de France (EDF). The Vezins dam remained State property, while the La Roche-Qui-Boit dam belonged to EDF.

Both structures were designed by Albert Caquot. Their architecture was highly innovative for the time: they were multiple-arch reinforced concrete dams supported by buttresses. The La-Roche-Qui-Boit dam was the first dam of this type to be built in France.

The two dams form an inseparable complex, supplying electricity to several towns and industrial plants such as the shoe factories in Fougères. La-Roche-Qui-Boit serves as a demodulation basin for hydropeaking (downstream discharge flow management) generated by the Vezins dam, which is eight times more powerful. Between them, the two dams produce 27 GWh a year, which is equivalent to the consumption of a town of 15,000 people (Source: ARTELIA 2014). This production corresponds to :

• Around 6 wind turbines of 2 MW (Source: ARTELIA 2014)
• 1/1,000th of that provided by the Flamanville nuclear power station, commissioned in 1985-1986 in the same departement
• 5% from the Rance tidal power plant in Ille-Et-Vilaine (Source: ARTELIA 2014)

The Selune lakes, places of life

From the 1930s onwards, with the advent of lakes, new recreational activities began to appear: fishing, walking, canoeing, etc. Fishing became a major activity around the lakes, with the installation of numerous pontoons and sheds and the creation of several fishing associations that stocked the lakes. Tourism around the lakes took off in the 1980s and 1990s with the development of a number of accommodation and leisure facilities. These include, among others, the La Mazure leisure centre, the Bel Orient self-catering village and the Ange Michel theme park.

To find out more about the history of the Sélune, the lakes, their uses and the fishing huts, visit the website of our socio-geography research team.