Dam Constructions
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Dam Constructions

Dams are the commonest man made water barriers.

Dams are build across rivers for one or all the following reasons:

• To create reservoirs

• To generate electricity

• To feed irrigation systems

• To control floods

The colossal Nurek Dam on the Vakhsh River in Tadjikistan in the Soviet Union stands 317 metres high and is 730 metres long. It provides hydro-electric power for the local people, plus irrigation and drinking water for an area of more than 10,000 sq km.

Dams are build in one of two ways. They are either made of rock and earth fill or of concrete. Rock-and-earth fill dams have to be much thicker than concrete structures because they depend on sheer weight for their strength, rather than the structured properties of reinforced concrete. They are mainly used to create irrigation reservoirs in relatively flat and wide river valleys.

Earth dams can also be far bigger than concrete ones. The largest one in the world is the Pati dam on the Pavana River in Argentina, which is 174.9 km long, 36 metres high and is made of 238 million cubic metres of compacted earth-and-rockfill. For comparison, the largest concrete dam in the world is the Grand Coulee Dam on the Columbia River in Washington State, USA. This is 1,272 metres long, 167 metres high and 8 million cubic metres of concrete were poured into the structure during construction. Typically, concrete dams are build across narrow valleys, where the ends of the dam can be securely anchored on the rocky sides of the valley.

Whatever the design of the dam, it must be broader at its base than at its top. This is because the pressure of water against the face of the dam increases with depth. A sluice or spillway is always build into the design so that, when the water level is close to the top of the dam, water can be let out of the reservoir. If the water was allowed to simply overflow, it might easily undermine the dam and cause it to collapse.

The designers and builders of large dams carry a heavy responsibility: if a big dam breaks, thousands of people and animals could be drowned and the devastation to communities could equal that of a natural disaster. The sea is the other great mass of water that man sets out to control. Natural areas of sheltered water, where ships can seek refuge from storms and unload their cargo, are usually extended and improved with harbour walls. Where possible, harbour walls are build out into the sea from opposite sides of the harbour, leaving only a narrow entrance giving access to the open sea.

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