Uses of Dams
Dams are usually built for one or more of the following reasons:
To provide a supply of water for towns, cities and mining sites; eg Warragamba Dam, Australia is the main water supply dam for the city of Sydney.
To contain and store waste (tailings) from mines; eg Omai Tailings Dam, Guyana, South America which stored waste from a gold mining operation.
To provide a supply of water for the irrigation of crops; eg Burrinjuck Dam, Australia which was built as the main head water storage for the Murrumbidgee Irrigation Area in New South Wales.
To generate electricity in hydro-electric power stations; eg Itaipu Dam, Brazil is the largest hydro-electric power station in the world.
To help control or mitigate floods; eg the Tennessee Valley Authority dams in the U.S.A. which help control floods on the Tennessee, the lower Ohio, and the lower Mississippi Rivers.
Many dams are multipurpose and most dams have at least some flood mitigation effect in addition to their primary purpose. Dams built specifically for flood control may have some of their storage capacity kept empty during normal river flow conditions so that space is available to store excess water inflow under flood conditions. The flood mitigation effect of a dam is such that the downstream river height at the peak of the flood is reduced but, after the peak has passed, the river levels usually remain high for a longer period than would have been the case if the dam had not been built. This is because excess flood water is only stored behind the dam temporarily and is slowly released from the dam in the days and weeks after the flood peak has passed.
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