Dams

Overview
Dams have been built with the intention to improve human quality of life by diverting water for power, navigation, and flood control, but have also resulted in human health concerns and environmental problems. Dams benefit people by providing usable, reliable water sources. In the once swampy San Joaquin Valley, Calif., they have created an area that now provides a quarter of America's food supply. Hydroelectric dams provide 13% of the total power generation in the United States which prevents over 200 million tons of carbon dioxide emissions. They make 70% of the power generated in Latin America. However, dam projects can produce greenhouse gases by flooding areas and increasing the rate of decomposition, emitting carbon dioxide and methane. A UN commission was set up in 1997 to monitor and evaluate impacts of current, existing and future dams (both positive and negative). The one thing that remains clear is that the need for energy and water will not go away.

 
Is it Worth a Dam?
In 1936, the first mega-dam, the Hoover Dam, was built on the Colorado River in Black Canyon, near what was then the little town of Las Vegas, Nevada. Standing 221 m high, three times the size of the Statue of Liberty, it was the largest dam in the world. Its massive concrete walls held back the waters of Lake Mead, a 160-km-long body of water heavy enough to bend the earth's crust. Nine more large dams diverted the Colorado River's water into Arizona, Nevada, and southern California, fueling the growth of major cities and helping to turn the arid West into a lush and lucrative garden.

Shifting points of reference . Once the biggest dam on earth, the Hoover Dam, built in 1936, now appears unremarkable compared to some of the world's more recently built mega-dams.
Photo credit: United States Bureau of Reclamation
The Colorado dams were part of a dam-building fever that encompassed the globe. Dams harnessed the world's major rivers, including the Danube, the Nile, the...