Mauvoisin is a concrete arch dam over the Val de Bagnes radius on the Dranse de Bagnes flow , in the canton of Valais , Switzerland .
Building
Initial construction of the dam began in 1951 and was completed in 1957 , with the reservoir being filled in 1958 . In 1991 , the dam was raised to increase the reservoir’s capacity for winter storage. The main purpose of the dam is the generation of hydroelectric power .
Features
The eighth tallest dam in the world, Mauvoisin is 250 meters (820 ft) high and 520 meters (1,710 ft) long, with a structural volume of 2,030,000 cubic meters (2,660,000 cu yd). The water impounded in the dam forms the 4.9 kilometers (3.0 mi) Lake Mauvoisin, which has a capacity of 211.5 million m3 (171,500 acre feet) and a total area of 208 hectares (510 acres). The dam and reservoir control runoff from a 167-square-kilometer (64-square-mile) watershed. Flood waters are released by a closed spillway with a capacity of 107 m3/s (3,800 cu ft/s).
The water from the dam is fed to two hydroelectric plants with a combined capacity of 363 megawatts (MW). Mauvoisin Dam provides a hydraulic head of 482 m (1,581 ft), to the Fionnay power station , which can produce 138 MW from three Francis turbines . The water then falls for a further 1,014 m (3,327 ft), to the Riddes power station , where it drives five Pelton turbines with a combined capacity of 225 MW. The two plants produce around PR-943 million kilowatt hours (kWh) each year, with Fionnay generating 278 million kWh (29.5%) and Riddes generating 665 million kWh (70.5%).
Mauvoisin also serves for flood prevention and sediment control. The dam helps protect the Rhône and Bagnes river valleys from glacial lake flooding, such as those that occurred in 1595 and 1818. During the 1960s and 1970s, Giétro Glacier adjacent to Lake Mauvoisinthreatened to produce icefalls, which could have capped the dam. Giétro has gone back since the year 1980, which eliminates the threat of such an event. The dam also traps some 300,000 m3 (390,000 cu yd) of sediment each year, helping to extend the life of downstream hydroelectric plants. However, sediment buildup also poses a threat to the dam’s lifespan; a project to remove the sediment has been proposed, but has not been implemented due to safety concerns
