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A dam is a barrier that impounds water or underground streams. Reservoirs created by dams not only suppress floods but also provide water for activities such as irrigation, human consumption, industrial use, aquaculture, and navigability. Hydropower is 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 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.

The word dam can be traced back to Middle English, and before that, from Middle Dutch, as seen in the names of many old cities. The first known appearance of dam stems from 1165. However, there is one village, Obdam, that is already mentioned in 1120. The word seems to be related to the Greek word taphos, meaning "grave" or "grave hill". So the word should be understood as "dike from dug out earth". The names of more than 40 places (with minor changes) from the Middle Dutch era (1150–1500 CE) such as Amsterdam (founded as 'Amstelredam' in the late 12th century) and Rotterdam, also bear testimony to the use of the word in Middle Dutch at that time.

Early dam building took place in Mesopotamia and the Middle East. Dams were used to control the water level, for Mesopotamia's weather affected the Tigris and Euphrates rivers.

The earliest known dam is the Jawa Dam in Jordan, 100 kilometres (62 mi) northeast of the capital Amman. This gravity dam featured an originally 9-metre-high (30 ft) and 1 m-wide (3.3 ft) stone wall, supported by a 50 m-wide (160 ft) earth rampart. The structure is dated to 3000 BC.

Function Example
Power generation Hydroelectric power is a major source of electricity in the world. Many countries have rivers with adequate water flow, that can be dammed for power generation purposes. For example, the Itaipu Dam on the Paraná River in South America generates 14 GW and supplied 93% of the energy consumed by Paraguay and 20% of that consumed by Brazil as of 2005.
Water supply Many urban areas of the world are supplied with water abstracted from rivers pent up behind low dams or weirs. Examples include London, with water from the River Thames, and Chester, with water taken from the River Dee. Other major sources include deep upland reservoirs contained by high dams across deep valleys, such as the Claerwen series of dams and reservoirs.
Stabilize water flow / irrigation Dams are often used to control and stabilize water flow, often for agricultural purposes and irrigation. Others such as the Berg Strait dam can help to stabilize or restore the water levels of inland lakes and seas, in this case the Aral Sea.
Flood prevention The Keenleyside Dam on the Columbia River, Canada can store 8.76 km3 (2.10 cu mi) of floodwaters, and the huge Delta Works protects the Netherlands from coastal flooding.
Land reclamation Dams (often called dykes or levees in this context) are used to prevent ingress of water to an area that would otherwise be submerged, allowing its reclamation for human use.
Water diversion A typically small dam used to divert water for irrigation, power generation, or other uses, with usually no other function. Occasionally, they are used to divert water to another drainage or reservoir to increase flow there and improve water use in that particular area. See: diversion dam.
Navigation Dams create deep reservoirs and can also vary the flow of water downstream. This can in return affect upstream and downstream navigation by altering the river's depth. Deeper water increases or creates freedom of movement for water vessels. Large dams can serve this purpose, but most often weirs and locks are used.

  • Permeability of the surrounding rock or soil
  • Earthquake faults
  • Landslides and slope stability
  • Water table
  • Peak flood flows
  • Reservoir silting
  • Environmental impacts on river fisheries, forests and wildlife (see also fish ladder)
  • Impacts on human habitations
  • Compensation for land being flooded as well as population resettlement
  • Removal of toxic materials and buildings from the proposed reservoir area
  • Arenillas, Miguel; Castillo, Juan C. (2003). "Dams from the Roman Era in Spain. Analysis of Design Forms (with Appendix)". 1st International Congress on Construction History [20th–24th January]. Madrid. 
  • Hartung, Fritz; Kuros, Gh. R. (1987). "Historische Talsperren im Iran". In Garbrecht, Günther. Historische Talsperren. 1. Stuttgart: Verlag Konrad Wittwer. pp. 221–274. ISBN . 
  • Hodge, A. Trevor (1992). Roman Aqueducts & Water Supply. London: Duckworth. ISBN . 
  • Hodge, A. Trevor (2000). "Reservoirs and Dams". In Wikander, Örjan. Handbook of Ancient Water Technology. Technology and Change in History. 2. Leiden: Brill. pp. 331–339. ISBN . 
  • James, Patrick; Chanson, Hubert (2002). "Historical Development of Arch Dams. From Roman Arch Dams to Modern Concrete Designs". Australian Civil Engineering Transactions. CE43: 39–56. 
  • Schnitter, Niklaus (1978). "Römische Talsperren". Antike Welt. 8 (2): 25–32. 
  • Schnitter, Niklaus (1987a). "Verzeichnis geschichtlicher Talsperren bis Ende des 17. Jahrhunderts". In Garbrecht, Günther. Historische Talsperren. 1. Stuttgart: Verlag Konrad Wittwer. pp. 9–20. ISBN . 
  • Schnitter, Niklaus (1987b). "Die Entwicklungsgeschichte der Pfeilerstaumauer". In Garbrecht, Günther. Historische Talsperren. 1. Stuttgart: Verlag Konrad Wittwer. pp. 57–74. ISBN . 
  • Schnitter, Niklaus (1987c). "Die Entwicklungsgeschichte der Bogenstaumauer". In Garbrecht, Günther. Historische Talsperren. 1. Stuttgart: Verlag Konrad Wittwer. pp. 75–96. ISBN . 
  • Smith, Norman (1970). "The Roman Dams of Subiaco". Technology and Culture. 11 (1): 58–68. doi:10.2307/3102810. JSTOR 3102810. 
  • Smith, Norman (1971). A History of Dams. London: Peter Davies. pp. 25–49. ISBN . 
  • Vogel, Alexius (1987). "Die historische Entwicklung der Gewichtsmauer". In Garbrecht, Günther. Historische Talsperren. 1. Stuttgart: Verlag Konrad Wittwer. pp. 47–56 (50). ISBN . 


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