What Is a Dam and How Does It Function?
Dam is a barrier built across a river or sea which is high enough to stop the water flowing over it. In a river dam, the water which is held back forms a reservoir. Reservoirs created by dams not only suppress floods but also provide fresh water which is sent through pipes to homes for drinking and washing, or used to water crops. The water can also be used for hydroelectric power schemes.
Dams have two main functions. The first is to store water to compensate for fluctuations in river flow or in demand for water and energy. The second to raise the level of the water upstream to enable water to be diverted into a canal or to increase ’hydraulic head’ –– the difference in height between the surface of a reservoir and the river downstream.
The creation of storage and head allow dams to generate electricity (hydropower provides nearly a fifth of the world’s electricity); to supply water for agriculture, industries and households; to control flooding; and to assist river navigation by providing regular flows and drowning rapids. Other reasons for building large dams include reservoir fisheries and leisure activities such as boating.
Today, artificial dams are made of rock and clay or concrete. Dams have been built for more than 5000 years. The highest dam in the world is the Jinping-I Dam in Sichuan, China. Sitting across the Yalong River, the dam uses a double curvature thin arch, and reaches 305 m (1,000 ft) high – 5 m (16 ft 4.8 in) taller than the Eiffel Tower in Paris. The dam wall has a crest length of 568.5 m (1,865 ft). The largest concrete dam is the Grand Coulee Dam across the Columbia River in the U.S.A. It is 167 m (550ft) high and 1272 m (4140 ft) long.