Dams and Reservoirs

Dams and Reservoirs

An overall view of the Katse hydroelectric power plant dam in Lesotho, South Africa. (Source: © Adele De Witte / stock.adobe.com)

An overall view of the Katse hydroelectric power plant dam in Lesotho, South Africa.

A characteristic feature of hydroelectric power plants is the dam wall, which forms a kind of plug in the lowest part of the basin, retaining the water. The most popular material for building dams is concrete since it allows for dams to be as high as several hundred meters. Older and smaller dams can be earth-filled, masonry, steel or wooden. The dam structure must be frequently checked for wear and damage. It is very important that a watertight connection between the dam and the bedrock and the sloped banks is maintained. Every dam should be fitted with safety gates at the bottom and spillways at the top which allow for regulating the water level and protecting the dam from overflow in the case of flooding. The biggest dams, holding the most water, are built for accumulation hydroelectric power plants.

Aside from drawing energy from watercourses dammed reservoirs can also serve as sources of drinking and irrigation water. Dams protect from floods and make water transport possible.

A modern concrete dam. (Source: © inacio pires / stock.adobe.com)
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Glen Canyon — this concrete arched dam stems the Colorado river, forming the second largest reservoir in the US, Lake Powell. (Source: © PictureArt / stock.adobe.com)
An earth-filled dam is built only from dirt and rock. (Source: © rlesyk / stock.adobe.com)
The spillways on the left part of the dam are used to release water from the reservoir in a controlled fashion, while in the right part water is fed to the turbines. (Source: © FLIsom / stock.adobe.com)
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Dam Types

Dams can be categorized as gravitational if the water is retained by the sheer weight of the dam. Other types are the concrete arch dams or pillar supported dams.

Earth-filled gravity dams

Earth-filled gravity dams

Earth-filled dams oppose the water pressure by their weight. The dam can be filled with earth or stones. The water side of a stone-filled gravity dam is usually protected by a watertight layer made of concrete, stone or steel plates or other waterproof materials. The core of an earth-filled dam consists of clay that will not let any water seep through. The water side of the dam is built from solid materials in order to prevent an erosion of the core. Earth-fill dams require special spillways that can withstand erosive water currents.

Concrete arch dams

Concrete arch dams

Concrete arch-shaped dams are thin shells firmly anchored in the steep slopes of surrounding deep canyons. The concave shape of that shell allows for the immense water pressure to be directed to the stone walls of the canyon.

Earth-filled gravity dams / The edge of a earth-fill gravity dam and its reservoir-facing side. (Source: © beibaoke / stock.adobe.com)
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Earth-filled gravity dams / The earth-filled gravity dam of the Jordanelle Reservoir on the Provo River, Utah, USA. (Source: © Ritu Jethani / stock.adobe.com)
Earth-filled gravity dams / The 123 m high earth-fill dam of Serre-Poncon in the Alps is one of the largest dams in western Europe (France). (Source: © Pictures news / stock.adobe.com)
Earth-filled gravity dams / A hydroelectric power plant with a rock-fill dam, built on the Gunnison River, Colorado, USA. (Source: © Jim / stock.adobe.com)
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Earth-filled gravity dams

Concrete gravity dams

Gravity dams are usually built from heavy mixtures of concrete and rock and they retain water only by their weight. Their cross section is of a triangular shape, with the base wide and the upper rim narrow. The water sides of these dams are perpendicular to the water surface.

Concrete arch dams

Buttress dams

Made of reinforced concrete, these dams are supported by several pillars on the air side. Depending on the size and technology, the pillars are 5 to 30 meters apart. Thus less building material is needed on the wall of the dam.

Concrete gravity dams / A giant concrete gravity dam. (Source: © tonisalado / stock.adobe.com)
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Concrete gravity dams / The curved concrete gravity dam of Shasta on the Sacramento river in California, USA. It is 1,000 m long and at its base 165 m thick. (Source: © Cayetano / stock.adobe.com)
Concrete gravity dams / The concrete three-stage arched dam of the largest artificial lake in Western Europe, Alqueva, Portugal. (Source: © inacio pires / stock.adobe.com)
Concrete gravity dams / The concrete dam of the Grimsel Pass hydroelectric power plant, built at more than 3,000 m above sea level. Along with other power plants in the area it supplies electricity to over a million people (Switzerland). (Source: © ivan kmit / stock.adobe.com)
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