Graph of the Day: August Water Volume in Lake Mead, 1941-2010
By Michael Carlowicz
23 September 2010 In August 2010, Lake Mead reached its lowest level since 1956. The largest reservoir in the United States was straining from persistent drought and increasing human demand. 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. Badger Cove, Driftwood Cove, and Grand Wash Bay have receded to become valleys and channels of the Colorado River, which flows in from the east (image right). The shores around the lake display the “bathtub ring” effect, with a chalky white outline marking new shoreline where sediments had previously accumulated below the water. 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. … Lake levels rose steadily through the 1980s, reaching 24.8 million acre-feet in August 1985, when the bottom image was taken. But as of August 2010 (top 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 12 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. Approximately 800,000 acre-feet evaporate yearly, and the water flow from the upstream reaches of the Colorado River has been far below normal since the start of the drought in 1998. Refilling the lake depends almost entirely (96 percent) on snowmelt from the Rocky Mountains and how much of that water is released from dams and reservoirs in the upper basin of the Colorado (Wyoming, Colorado, Utah, and New Mexico). …
