Grande Dixence Dam

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The Grande Dixence dam, at the head of the Val d'Hérens in the canton of Valais in Switzerland, is at 285 metres high one of the worlds tallest dams. It holds back a lake, the Lac des Dix, around 4 km long. When full, the lake is up to 284 metres deep and contains 400 million m³ of water.

Lac des Dix

Location	Valais
Coordinates	46.08° N 7.4° ECoordinates: 46.08° N 7.4° E
Lake type	reservoir
Primary outflows	Dixence
Catchment area	420 km²
Basin countries	Switzerland
Max length	5.3 km
Surface area	3.65 km²
Max depth	227 m
Water volume	400 mio m³
Surface elevation	2365 m

The dam

Map

The top of the dam is at an altitude of 2,365 metres in a steep mountain valley. Tunnels bring the water to three power stations in the Rhône valley over 1,800 metres below.

The dam is situated on the relatively small Dixence river, but collects a large amount of water thanks to a system of water supply tunnels over 100 km long bringing water from other rivers and valleys. Most of the water comes from glaciers which melt during the summer. The lake is usually full of water by late September, and is allowed to empty during the winter, reaching its lowest point around April.

The first Grande Dixence Dam was constructed between 1929 and 1935. A second dam that would flood the first was built between 1951 and 1965, and was filled on July 17, 1957. The first dam can still be seen when the water level is particularly low.

From 1993 to 1998 a high-pressure pipeline was built to considerably increase its peak capacity. It transported water 1,800 metres down to an additional power facility. The pipeline was welded using a new type of steel; it is out of service since it burst in December 2000, with the flood wave killing three people. Work on a replacement pipeline has recently started, with use of a more common steel and additional safety measures.