The Colorado River Salinity Problem: Direct Economic Damages in Mexico

hundred miles from its headwaters in the Rocky Mountains before it discharges into the Gulf of California in Mexico. In common with most rivers in arid lands, the Colorado accumulates dis-solved salts (salinity) in its course to the sea. These salts are picked up from both natural sources (dis-solved in surface runoff or discharged from salt springs) and man-made sources (irrigation return flows, municipal and industrial discharge). From a near pristine quality in the high mountains, the mineral concentrations in the waters of the Colo-rado reach 800-900 parts per million (ppm) in the lower basin, and still higher levels in Mexico. The "United States-Mexico Treaty for Utiliza-tion of Waters of the Colorado and Tijuana Rivers and of the Rio Grande, " signed in 1944, provides that Mexico is guaranteed an annual quantity of 1.5 million acre-feet (m.a.f.) of the waters of the Colorado River. Neither the quantity nor the quality of the water was an issue until about 1961. Prior to that time, Mexico had received flows well in excess of treaty requirements, which served to dilute saline irrigation return flows from the U.S. to a quality very nearly of that utilized in California and Arizona. (Physical, legal and economic aspects of the problem are detailed in the "international Symposium on the Salinity of the Colorado River.&quot