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. '-" o t::I>. C . . HISTORY OF WATER KESuURCE DEVELOPMENT (continued) The plan also contemplates the use of saline water for industrial purposes whenever practicable, programs by water users to cope with higher salinity water, improvements in irrigation systems, and ~anagement to reduce salt pickup, studies of lneans to minimize salinity in municipal discharges, and studies of future possible salinity control programs not now included in the plan. 4. Relations with Mexico The average annual salinity of the \rJater delivered to Hexico at the Northerly International Boundary (NIB) increased in 1961 from aLout 800 mg/L to nearly 1400 mg/L and to over 1500 mg/L in 1962. Tile completion of the drainage wells and subsequent pumping of 151,500 acre-feet (lb6 x 106m3) of drainage water in 1961 from the ;Iellton-Hoi,awk District auded over 1 million tons (900 000 tl of salt to the Colorado River. The uistrict further increased their pumping to 213,000 acre-feet \2G3 x 106m3) in 1962 and added over 1.7 million tons ([.5 x 106 tl of salt. If the flow in 1961 leaving Imperial Dam and arriving at the NIB had remained at the same volume as in 1960, the salinity at the NIB would have been less in 1961. Since the flow in 1961 was limited to apr-roximately the treaty obligation, about 800,000 acre-feet (1000 x 106m3) less than in 1960, a larger salinity was observed resulting in a water quality of nearly 140U mg/L at the NIl!. The reduced flow '.'as the result of low run oft and the installation of structures in the Colorado River Basin in the United States that allowed retention of large volumes of water for future use. Approx- imately 75 percent of the rise in the salinity at the NIl! was caused by Wellton-Hohawk drainage returns. The remaining 25 percent was caused by the reduction in tile exce6S deliveries to Mexico. The increase in salinity resulted in negotiations between tIle United States and Mexico. In March 1965, Minute No. 218 WaS signed and appruved by the two Governments. Beginning on November 10, 19u5, Wellton-Hohawk draina~e flows were bypassed around Morelos Da~ and replaced by water from other United States sources during teriods of miniillum flow which aQounted to about 55 000 acre-feet (68 x 10 m3)per year. The minimur.l flow of 900 ft3/s (25 m~/s) at the NIB occurs during the winter months for a period not to exceed 180 days. This agreement was in effect until June 30, lY72, and reduced the average annual salinity of waters delivered to ~lcxico at NIB under the treaty to about 1245 mg/L. On July 14, 1972, another agreement, Minute No. 241 WaS entered into. This Minute provided that tile United States would increase tile iJypass of Wellton-Mohawk drainage, without charge against scheduled treaty deliveries to Mexico to the annual rate of 118,000 acre-feet (146 x 106m3) and sub- stitute equal volumes of other waters of better quality to be discharged to the Colorado River above Marelos Dam. This reduced the salinity of waters delivered to Mexico at NIB under the treaty by an estimated 100 mg/L. Minute 241. with three extensions, was in effect from July I, 1~7L, through December 31, 1972. 24