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Show CHAPTER XIII THE MEXICAN SALINITY PROBLEM A. Background The background of the Mexican Water Treaty, the negotiations in 1930 and in 1941-43, the discussions between the State Department and the Colorado River Basin States, and the events leading up to its ratification, are discussed in Chapter XIV, "The Hoover Dam Documents," 1948, Wilbur and Ely, pages 152 through 167. They are also summarized in Chapter I.F. hereof. (The text of the Mexican Water Treaty appears in Appendix I F.I.) The Colorado River waters and ground-water pumping has irrigated approximately 475,000 acres of land in Mexicali and San Luis Valleys in northwestern Mexico. Mexicali, a city of about 400,000 people, obtains water from the Colorado River. Since 1972, Tijuana, with a population of about 500,000, has been receiving a supplemental supply of about 8,000 acre-feet of Mexican Treaty Colorado River water under a temporary agreement with several California agencies, including The Metropolitan Water District of Southern California and San Diego County Water Authority. Upon completion of an aqueduct now under construction in Mexico, Mexico will deliver 100,000 acre-feet per year to that city. No problems arose with regard to water deliveries to Mexico between 1945 and 1961 since the salinity of the waters delivered at the Northerly Boundary was generally within 100 parts per million (100 p/m) of the water at Imperial Dam, the last major structure diverting water for users in the United States. In 1961, two unrelated events occurred which affected the salinity of the Mexican water deliveries. First, was the action of the Wellton-Mohawk Irrigation and Drainage District, which represents the Wellton-Mohawk Division of the Gila Project in southwestern Arizona, authorized by the Gila Reauthorization Act of July 30, 1947, 61 Stat. 628, and whose construction by the United States Bureau of Reclamation was completed in 1952. In 1961, the District commenced operation of a system of drainage wells in the District which discharged saline water with approximately 6,000 p/m into the Colorado River below the Imperial Dam but above the Mexican point of diversion. This increased the salinity of the water deliveries to Mexico from an average of around 800 p/m in 1960 to nearly 1,400 p/m in 1961 and to 1,500 p/m in 1962. The daily salinity readings at times exceeded 2,000 p/m. Secondly, there was a sharp reduction in riverflows to Mexico because of increased storage in Lake Mead. This was in anticipation of the closure of the gates at the recently constructed Glen Canyon Dam in the Upper Basin in order to begin storage of water in Lake Powell, the reservoir behind Glen Canyon Dam. For example, in the 10-year period from 1951 to 1960, Mexico received an average of 4.24 maf/yr at the Northerly International Boundary, whereas for the succeeding 10-year period from 1961 to 1970, the flow averaged 1.52 maf/yr, a quantity sufficient to fulfill the Treaty obligation of 1.5 maf/yr. This average annual reduction of 2.72 maf/yr of dilution water contributed to the increased salinity. Hence, the reduction in riverflows were incident to increased storage and use in the United States, closer controls by the Bureau of Reclamation, and lower years of runoff (J. R. Friedkin, "a Review of the 1944 Treaty Operations - 1969"). Parenthetically, it should be noted that in the past several years approximately 525,000 acre-feet per year of the 1.5 maf/yr guaranteed to Mexico under the Treaty have come from drainage water below Imperial Dam. Of the 525,000 acre-feet per year, the Wellton-Mohawk Division contributed about 220,000 acre-feet, other projects in the Yuma, Arizona, area contributed about 165,000 acre-feet, and 140,000 acre-feet per year of drainage water from Yuma Valley was delivered to Mexico at the land boundary near San Luis, Mexico (M. B. Holburt, "International Problems of the Colorado River," 1974). B. Mexico's Objections to Salinity In November 1961, Mexico strongly objected to the salinity of the Colorado River waters received by it and negotiations between the United States and Mexican Governments took place to resolve the matter. 217 |
