A dam is a barrier that impounds water or underground streams. Dams generally serve the primary purpose of retaining water, while other structures such as floodgates or levees (also known as dikes) are used to manage or prevent water flow into specific land regions. Hydropower and pumped-storage hydroelectricity are often used in conjunction with dams to generate electricity. A dam can also be used to collect water or for storage of water which can be evenly distributed between locations.

Dams can be formed by human agency, natural causes, or even by the intervention of wildlife such as beavers. Man-made dams are typically classified according to their size (height), intended purpose or structure.

Based on structure and material used, dams are classified as easily created without materials , arch-gravity dams, embankment dams or masonry dams, with several subtypes.

Classification and Types of dams

Classification of dams on the basis of materials used in dam construction

Based on purpose

• Storage dam or impounding dam - it is constructed to create a reservoir to store water during periods when there is huge flow in the river (in excess of demand) for utilisation later during periods of low flow (demand exceeds flow in the river). Water stored in the reservoir is used for irrigation, power generation, water supply etc. By suitable operation, it can also serve as a detention dam.
• Detention dam - it is primarily constructed to temporarily detain all or part of the flood water in a river and to gradually release the stored water later at controlled rates so that the entire region on the downstream side of the dam is protected from possible damage due to floods. It may also be used as a storage dam.
• Diversion dam - it is constructed to divert part of or all the water from a river into a conduit or a channel. For diverting water from a river into an irrigation canal, mostly a diversion weir is constructed across the river.
• Coffer dam - it is a temporary dam constructed to exclude water from a specific area. It is constructed on the u/s side of the site where a dam is to be constructed so that the site is dry. In this case, it behaves like a diversion dam.
• Debris dam - it is constructed to catch and retain debris flowing in a river.

Based on hydraulic design

• Overflow dam or overfall dam - it is constructed with a crest to permit overflow of surplus water that cannot be retained in the reservoir. Generally dams are not designed as overflow dams for its entire length. Diversion weirs of small height may be designed to permit overflow over its entire length.
• Non-overflow dam - it is constructed such that water is not allowed to overflow over its crest.

Based on material of construction

• Rigid dam - it is constructed with rigid material such as stone, masonry, concrete, steel, or timber. Steel dams (steel plates supported on inclined struts) and timber dams (wooden planks supported on a wooden framework) are constructed only for small heights (rarely).
• Non-rigid dam (embankment dams) - it is constructed with non-rigid material such as earth, tailings, rockfill etc.
  • Earthen dam – gravel, sand, silt, clay etc
  • Tailings dam – waste or refuse obtained from mines
  • Rockfill dam – rock material supporting a water tight material on the u/s face
  • Rockfill composite dam – Rockfill on the d/s side and earth fill on the u/s side
  • Earthen dams are provided with a stone masonry or concrete overflow (spillway) section. Such dams are called composite dams.
  • In some cases, part of the length of the dam is constructed as earth dam and the rest (excluding the spillway) as a masonry dam. Such dams are called masonry cum earthen dams.

Based on structural behaviour

• Gravity dam
• Arch dam
• Buttress dam
• Embankment dam

Classification of dam types with respect to size / height of the dam

• Low dam / Small dam (How to build small dams)
• Medium dams
• High dam / Large dams

Classification of dam according to its purpose/use

• Water supply dam / Irrigation dams
• Power dams
• Multipurpose dams
• Flood control dams

Monographs and brochures

ICID: Role of Dams for Irrigation, Drainage and Flood Control (2000)