Mega Dam

Megadams: Pros, Cons, and Consequences
 
Humans have diverted water from its natural channels throughout history.  Remains of water storage dams are found in Jordan, Egypt and other parts of the Middle East dating back to at least 3000 BC., 5000 years ago.  
 
However, the era of large dams or "megadams" was ushered in by the Bureau of Reclamation Act of 1902.  “Large dams” are officially defined by the World Commission on Dams as having heights greater than 15 m, or reservoir capacities greater than 3,000,000 cu meters.”  By these criteria, there are 45,000 large dams world wide spead over 150 countries, and their combined reservoirs cover an area larger than the country of France.  Of these dams, about half are used exclusively or primarily for irrigation, accounting for 271 million irrigated hectares (271 sq km? If 1 ha=10E4 m).
 
Even the biggest and most prominent of the U.S. dams and their associated lakes (Grand Coulee, Hoover (221 m high), Glen Canyon, 215 m high) are dwarfed by a number of other dams around the world (e.g., Owen Falls, Uganda; Kariba, Zimbabwe/Zambia; Bratsk, USSR; High Aswan, Egypt, Akosombo, Ghana;and, potentially, Rogun in the USSR, or Three Gorges, China, and others.) 
|Rank No.          |Name of Dams                |Country             |Height (m)          |Year Completed                |





|Benefits of dams                                                       |                                                                      |
|Water storage                                                         |                                                                      |
|Flood control                                                         |Floods affected the lives of 65 million people between 1972 and 1996. |
|Irrigation                                                             |Dams contribute to 12-16% of world food production.                   |
|Electrical Power Generation...