National Geographic : 1991 Jun
Plumbing the West "( TE HAVE in the Colorado San American Nile await Sing regulation," said Los Angeles water investigator Joseph B. Lippincott in 1912. Since that time the river has been "regulated" almost out of existence and now rarely emp ties into the Gulf of California. With scores of reservoirs and diversion dams, hundreds of miles of aqueducts and tunnels, dozens of pumping stations, thousands of miles of canals, and more than 30 hydroelectric plants, the river basin contains one of the world's most con trolled river systems. Riverwide regulation began with the 1922 Colorado River Compact, which divided seven western states into upper and lower basins (map) and allo cated 7.5 million acre-feet of water a year to each. A 1944 treaty with Mexico guaranteed that country 1.5 million acre feet annually. Although the Col orado was committed to deliver 16.5 million acre-feet, its annual flow has averaged only 14 mil lion since 1930, and evaporation from reservoirs removes another 2 million. As long as some states con tinue to use less than their share (inset), others can siphon off more. But as populations rise and states in both basins com plete water projects, the Colora do will be virtually tapped out. CANADA U ST ES MEXICO WATER IN, \ WATER OUT \.° q,, 1990 *o I'^,^ ^ : .I %1 C Hoover am impo Mead (which cani Years' rivr flow) / atesfour billion k Hours of hydroele a year. 9 e/~w Beneath Imperial Valley's pro ductive farmland lie 1,400 miles / of pipeline carrying salty drain age to rivers that empty into >' the Salton Sea. Salinity level increases from 50 parts per million (ppm) at the Col orado's source to more than 700 ppm at Imperial Dam-far above the U. S. potable water standard of 500 ppm. The quality of the water reaching Mexico must be within 115ppm of that found at ImperialDam.