Wednesday, September 29, 2010

Low water in Lake Mead

Environmental Expert via WaterLink International: In August 2010, Lake Mead reached its lowest level since 1956. Two images from the Thematic Mapper on the Landsat 5 satellite show some of the stark changes on the eastern end of the lake since 1985. The largest reservoir in the United States was straining from persistent drought and increasing human demand.

…Located on the Colorado River, east of Las Vegas and west of the Grand Canyon, Lake Mead provides power and water for human activities in Nevada, Arizona, southern California, and northern Mexico. The reservoir grew up behind the Hoover Dam when it was built in the 1930s, and it can hold the equivalent of the entire flow of the Colorado River for two years.

The maximum capacity of Lake Mead is 28.5 million acre-feet (35 cubic kilometres) of water, with an acre-foot equalling the amount required to cover one acre to a depth of one foot. According to records from the U.S. Bureau of Reclamation, the lake held roughly 27.8 million acre-feet of water at its high point in 1941, and levels have fluctuated through drought in the 1950s and the filling of another upstream reservoir, Lake Powell, in the 1960s.

Lake levels rose steadily through the 1980s, reaching 24.8 million acre-feet in August 1985, when the left image was taken. But as of August 2010 (right image), Lake Mead held 10.35 million acre-feet, just 37 percent of the lake's capacity.

Lake Mead reached its August 2010 low after decades of population growth in the American Southwest and twelve years of persistent drought. According to the U.S. National Park Service, the amount of water flowing out of and evaporating from Lake Mead has consistently exceeded the amount of incoming water in recent years….

Lake Mead and Hoover Dam water intake towers, as seen from the Arizona side of Hoover Dam in July 2009. Note the "bathtub ring," showing where the water level used to reach. Shot by Cmpxchg8b, who has released the image into the public domain


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