A concrete giant in the Alps
Mass with class: the Grande Dixence Dam in Switzerland
Gravity dam Grande Dixence
The canton of Valais lies in the south of Switzerland. Imposing mountains such as the Matterhorn, idyllic valleys and crystal-clear mountain lakes characterise the region. 17 kilometres south of Sion, the capital of the canton, and nestled between numerous snow-capped peaks, the Grande Dixence Dam – a technical marvel of human engineering – rests in silence.
The Grand Dixence Dam is a gravity dam. This means that in contrast to an arch dam, which diverts the pressure through the dammed water horizontally, it holds back the dammed water using solely its own weight. This requires an incredible mass to resist the prevailing forces. The concrete colossus rises to a height of 285 metres, while the width in the lower part is 200 metres. With these dimensions, the Grande Dixence Dam has a total weight of 15 million tons. This makes it heavier than the Great Pyramid of Giza. With its concrete volume, a wall that is 1.5 metres high and 10 centimetres wide could be built around the earth.
Small-scale origins
At the ends of the Val d’Hérens valley, at an altitude of 2,400 metres, the former Cheilon Glacier formed the Val des Dix valley. The first Dixence Dam was built there in 1926 – with a crest height of 85 metres. In order to meet the increasing demand for electricity, the Chandoline power plant produced energy for the first time in 1934. In the next expansion phase between 1947 and 1951, another dam was built on Lac de Cleuson lake, which increased its capacity.
An eleven-kilometre long transport cable car, installed specifically for the construction of this dam, transported the cement directly from the station to the construction site. Special cylindrical buckets could be transferred directly from the track to the cable car. Each of these buckets could transport 400 kilograms of cement! This system was so successful that it was used at many other dam construction sites.
Even higher aspirations
1951 marked the birth of a mega-project of unimaginable scale: The world's highest concrete dam was to be built. The mineworkers had to fight their way through the bare rock – always surrounded by darkness, dust and the risk of being buried alive. With untiring effort, they drilled 100 kilometres of tunnels into the mountain, which reach the foot of the Matterhorn. They form the arterial network that supplies the reservoir with water. The construction material for the dam came from the moraine of Prafleuri. More than 1.3 million tons of cement were required for the dam alone. The concrete blocks are 16 metres thick and were joined together in such a way that they provide an extraordinary level of resistance and tightness.
The working conditions at an altitude of over 2,000 metres put all those involved to the test during the construction: The rain, snow and cold took a lot out of the people. The risk of avalanches and rockfalls as well as the conditions in the tunnels were challenging. On 22 September 1961, after ten years of construction, the last concrete bucket was finally set down at the Grande Dixence Dam.
From the kinetic energy of the water into electric power
With the greatest of efforts, the people tamed the water and rock. But the dam is only the exterior of the huge hydropower complex. The great fascination lies hidden inside: The main collecting tunnel brings together the water from the catchment area, which extends over a total of 420 square kilometres. All the water that flows between the Mischabelhörner, Matterhorn and Mont Gelé mountains is collected here. The hydropower plants are supplied with water from 35 glaciers through 75 water catchments and five pumping stations. On average, 500 million cubic metres of water are collected each year. Three power plants in the valley generate a total output of 2,000 megawatts. This corresponds to one fifth of the electricity that can be stored in Switzerland. This means that around 500,000 households can be supplied with sustainable electricity.
The power of water
Our society is becoming more and more technology-driven. This also increases the thirst for energy. Hydropower is one of the resources that can be used to generate renewable electricity. Unlike wind or sun, it is not so heavily dependent on the whims of the weather. Dams like the Grande Dixence Dam allow water to be stored and released in a controlled manner when rainfall is low or energy demand is high. In this case, in an environment that could hardly be more inhospitable, mastering water means ensuring the energy supply of tomorrow – breathtaking, fascinating and powerful at the same time.