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A River Divided: Earth Image of the Week May 20, 2011
Satellite Image of Newfoundland.
The modern Salton Sea, between Mexicali and Palm Springs, was formed in 1905 when a manmade irrigation system was overwhelmed by a Colorado River flood. The environmental mishap inspired the construction of the Hoover Dam near Las Vegas.
One of the natural wonders that have allowed humans to turn the southwestern deserts green is water gathered in an expansive watershed that covers parts of five states and delivered by the Colorado River.

The image to the right of the river’s lower reaches was captured by NASA’s Terra satellite on May 12, 2011.

Large-scale diversions of water for agriculture, and to a much lesser extent for municipal water supplies, have so diminished the flow of the river that it no longer consistently reaches the Gulf of California, its natural terminus.

Evaporation over the Southwest’s arid landscape also contributes to the loss of the river’s volume, and that of canals that deliver water to fields across parts of Arizona and Southern California.

Despite the added water from the Gila River at Yuma, the Colorado is often barely a trickle when it reaches the Mexican border.

While the Mexicali Valley in northern Baja California has Mexico’s most expansive irrigation system and a vibrant agricultural sector, it appears far less verdant in satellite images due to thirsty fields to the north.

Crops south of the border are mainly irrigated by a series of aquifers in the valley. But seepage from the All-American Canal just north of the border is believed to be a key additional source of water for farmers to the south.

A proposed concrete lining for the canal would cut off billions of gallons of leaked water, which is used to irrigate onions, alfalfa, asparagus and other crops around Mexicali.

Image: NASA MODIS Rapid Response System