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N o o U':' chapter 2 SALINITY IN THE COLORADO RIVER BASIN The Colorado River Basin The Colorado River stretches 1,400 miles through the southwestern United States and northern Mexico before emptying into the Gulf of California, Its drainage basin covers a 244,000 square mile area and includes portions of the five driest stales in the nation (Nevada, Arizona, Utah, Wyoming, and New Mexico), the sevenlh driest (Colorado), and the desert por- tions of California, The climate of the Basin ex- tends from the snowpacked Rockies and high plains of Wyoming and Colorado to the arid dese.rt of Arizona. The water rc~ources of the Colorado River Basin are inadequate in quantity to meet all legitimate demands for their use, even though wate.r is customarily utilized by a succession of users as it nows downstream, The Colorado R ivcr waters currently irrigate 2.5 million acres in t he Basin and thousands of acres outside the Basin through export. The river provides water for about 2.5 million people in the Basin, and through export provides full or supplemental sup- plies to another population of 14.5 million and irrigates hundreds of thousands of acres of farmland outside of the Basin, .primarily in southern California but also in eastern Colorado and central Utah, In addition, the river supplies 1.8 million people and irrigates about a half a million acres in Mexico. Estimates from the seven Basin states indicate that California, Arizona, New Mexico, and Nevada have already or within the next several years will be fully using their Compact apportionments, The growing demands for water by metropolitan populations and pOlentiallarge demand by manufacturing in- dustries and by mineral and energy developers, in addition to the heavy dependence on water by agriculture, will cause an ever-growing gap be- tween water supply and need, This may force both a curtailment of some demands and a reallocation of water supplies among potential users, resulting in some negative economic, so- cial, and environmental consequences. Colorado River Salinity and Its Causes A companion problem to limited supply is that of water quality. The Colorado River grows naturally salty from its headwaters through the seven basin states to the Gulf of California. In the Lower Basin states (Arizona, Nevada, and California) and in the Republic of Mexico, salinity can reach levels that reduce the river's usefulness and cause economic penalties to many water users. As expected economic development continues, salinity will increase unless offset by salinity control measures to remove over one million tons of salt per year from the river. Nearly half (47 percentS) of the river's salinity occurs naturally as the river and its tributaries dissolve minerals and salts from river beds, receive runoff that has transversed saline land, and are fed by saline springs and groundwater returns, The hot dry climate in- creases river and reservoir evaporation, funher concentrating the-se salls. Even without the development created by man, the Colorado would remain saltier than most other rivers in (his country. Irrigated agriculture is the major man- created contributor to Colorado River salinity 5U.S. Department of the Interior, Bureau of Reclamation. Colorado River Water Quality Ofrice, St:lluS Report: rolnrndo River Waler Ou.ality Impr'rlVr.menl ProVNlm Denver, Colorado: author, January 1983, p. 4.