Dams can be formed by human agency, natural causes, or by the intervention of wildlife such as beavers. Man-made dams are typically classified according to their structure, intended purpose or height.
Based on structure and material used, dams are classified as timber dams, embankment dams or masonry dams, with several subtypes.
Intended purposes include providing water for irrigation or town or city water supply, improving navigation, creating a reservoir of water to supply industrial uses, generating hydroelectric power, creating recreation areas or habitat for fish and wildlife, flood control and containing effluent from industrial sites such as mines or factories. Few dams serve all of these purposes but some multi-purpose dams serve more than one.
According to height, a large dam is higher than 15 metres and a major dam is over 150 metres in height. Alternatively, a low dam is less than 30 m high; a medium-height dam is between 30 and 100 m high, and a high dam is over 100 m high.
A saddle dam is an auxiliary dam constructed to confine the reservoir created by a primary dam either to permit a higher water elevation and storage or to limit the extent of a reservoir for increased efficiency. An auxiliary dam is constructed in a low spot or saddle through which the reservoir would otherwise escape. On occasion, a reservoir is contained by a similar structure called a dike to prevent inundation of nearby land. Dikes are commonly used for reclamation of arable land from a shallow lake. This is similar to a levee, which is a wall or embankment built along a river or stream to protect adjacent land from flooding.
An overflow dam is designed to be overtopped. A weir is a type of small overflow dam that can be used for flow measurement.
A check dam is a small dam designed to reduce flow velocity and control soil erosion. Conversely, a wing dam is a structure that only partly restricts a waterway, creating a faster channel that resists the accumulation of sediment.
A dry dam is a dam designed to control flooding. It normally holds back no water and allows the channel to flow freely, except during periods of intense flow that would otherwise cause flooding downstream.
Diversionary dams
Timber dams
Embankment dams
Masonry dams
Gravity dams
Arch dams
Steel dams
Cofferdams
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