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. . natural river channel, it becomes clearly understandable why the exact amount required by irrigators at Imperial Dam some- times differs from the quantity available at that point. N c..,) 0, o During this past calendar year Mexico has been permitted to schedule delivery of a guaranteed quantity of l.5 maf under the Treaty. The Treaty sets out minimum and maximum rates of de- livery during certain seasons of the year. During the October- February period, the minimum order is 900 cfs; during the re- maining period of the year from March through september, the minimum order is 1500 cfs. During the March-September period, Mexico usually diverts at rates in excess of the minimum,but during the October through February period, the periods of low irrigation requirements, Mexico ordinarily orders only the minimum under the ~reaty, or 900 cfs. Last October l, Mexico reduced her order to 900 cfs and has continued to order at this rate through the end of December 1961. Operating irrigation projects in the United states below Imperial Dam have developed their canal and drainage systems to the ex- tent that drainage and waste returns to the river below Imperial Dam, along with returns to the river from the desilting basins at Imperial Dam and seepage return flows to the river above the boundary, amount to quantities a little in excess of Mexico's minimum order under the Treaty during the October-February period. During this period we do not schedule release of water at Imperial Dam to meet Mexico's order. This condition was forecast many years ago and i6 the reason that provision was made in the Treaty for a minimum order of 900 cfs. During this past year a drainage system constructed on the well ton-Mohawk Division of the Gila Project was completed and drainage waters therefrom have been conveyed to the Colorado River channel above Yuma. This drainage return flow to the river amount to about 300 cfs or about one-third of Mexico's minimum order during this period of the year. This Wellton- Mohawk drainage water carries concentrations of dissolved solids totaling approximately 6,000 ppm which, when mixed with other drainage and return flows arriving at Morelos Dam, carry approximately 2,500 parts per million of dissolved solids. Early in December Mexican water users protested through official channels to our State Department the delivery of the highly saline water. At 10 a. m. on December l5, 1961, the Mexicans closed the diversion gates at Morelos Dam, and the gates re- mained closed during the remainder of December. Information Bulletin #l8 -3- January l2, 1962 '~j h'