Deadly efficiency

Since the 1940's, farmers in the Mexicali Valley in Baja California have relied on leakage from the All-American Canal to irrigate their fields. The 80 mile-long channel runs from the Imperial Dam, north of Yuma, Ariz., along the U.S./Mexico border, ending near Calexico. It diverts about 3.1 million acre-feet of Colorado River water to nine Southern Calif. cities and waters 500,000 acres of Imperial Valley farmland every year.  

Because the Bureau of Reclamation originally dug the channel through sandy dirt, leaving it unlined,  about 67,700 acre-feet, or 2 percent, of that water escapes on a yearly basis through the absorbent walls of the canal, filling wells in the Mexicali valley across the border and watering thousands of acres of wetlands. However, this unintended generosity finally dried up last Saturday as California officials gathered to celebrate the completion of a new, $300-million  project which replaced a 23-mile section of the dirt canal with a concrete-lined channel. 

Conserving  67,700 acre-feet per year may alleviate some of the pressure on Southern Calif. to get more water from the Sacramento or Colorado Rivers. It will provide 16,000 acre-feet per year in water rights for the Mission Indians and other local groups. However, it will also dry up 3,000 acres of prime agricultural land in Mexico, and over 15,500 acres of  wetlands.  

Funded by the San Diego County Water Authority and the state government, the plan to line the canal was approved by Congress in 1988, but lawsuits from the Mexican government and protests from environmentalists have slowed its progress. See Matt Jenkins' 2007 story, "The Efficiency Paradox," for an exploration of how the canal's sloppy engineering has sustained ecosystems as well as thousands of Mexican farmers.

The Andrade Mesa Wetlands are little known because they are isolated -- which also means that they are blessedly free from human disturbance and cattle grazing. According to Edward P. Glenn, professor of environmental science at the University of Arizona, the 2 percent loss from the canal has created a unique network of small oases where water seeps up in low places between the sand dunes. The differences in salinity between the brackish pools provide a range of habitat for 43 species of birds, including endangered species like the Yuma Clapper Rail.