What is Dam?
A '''dam''' is a large [[wall]] or barrier that blocks or stops the flow of [[water]], forming a [[reservoir]] or a [[lake]].<ref>[http://www.bartleby.com/61/45/D0014500.html The American Heritage Dictionary of the English Language, Fourth Edition]</ref> Most dams have a section called a spillway or [[weir]] over which, or through which, water flows, either sometimes or always. Dams generally serve the primary purpose of retaining water. The tallest dam in the world is the 300 meter high Nurek Dam in [[Tajikistan]]. == History == Some of the first dams were built in [[Mesopotamia]] up to 7,000 years ago. Modern dams are built with [[arch]]ed walls of [[Reinforced concrete|steel rod-reinforced concrete]]. The arched wall is a very strong shape which helps the wall to withstand the huge weight of the water. == Reasons for building dams == There are a number of reasons that people build dams. Some countries build dams to control the flow of water in the downstream river systems, and prevent [[flood]]ing. Other countries build dams to generate electricity using [[Hydroelectricity|hydroelectric]] [[turbine]] [[generator]]s. Other countries use dams to store water for use in [[irrigation]] (for [[farming]]) or [[drinking water|drinking]] by people. <gallery> Image:Arch dam Oymapinar (Manavgat River, Turkey).JPG|Arch dam in [[Turkey]]. Image:Drei-Schluchten-Damm (Jangtse).jpg|[[Three Gorges Dam]], [[China]] Image:AswanHighDam Egypt.jpg|Aswan High Dam in [[Egypt]]. Image:Srisailam-dam-with-gates-open-2.jpg|Srisailam Dam in [[India]]. </gallery> ==Notes== {{commons|Dam}} {{reflist}} {{Civil engineering}} [[Category:Civil engineering]] [[Category:Dams| ]] [[Category:Flood control]]