Grande Dixence dam, at the head
of the Val
d'Hérens in the
canton of Valais in Switzerland, is at 285 metres (935 ft) high one of
the world's tallest
dams and the highest in Europe.
holds back a lake
, the Lac des
, around 4 km (2.5 mi) long. When full, the lake
is up to 284 metres (932 ft) deep and contains 400 million m³
(100 billion gal) of water.
Lac des Dix
Construction steps, 1953 - 1961
The top of the dam is at an altitude of 2,365 metres
(7,759 ft) in a steep mountain valley. Tunnels bring the water
to three power stations in the Rhône
valley over 1,800 metres
(5,900 ft) 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 (60 mi) 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 (5,900 ft) 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.