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<br />000294 <br /> <br />Mexico at the Northerly International Boundary (NIB). The remaining Yuma area <br />agricultural drainage water continues to be included in the NIB deliveries. The Minute <br />recognizes that such inclusion increases the salillity Of the Colorado River as it flows from <br />Imperial Dam to the NIB and that the volume and salinity ofthe remaining Yuma area <br />saline agricultural drainage varies from year to year. The agreed upon method of salinity <br />management was to limit the increase in the flow weighted average annual salinity between <br />Imperial Dam and the NIB to no more than 115 ppm5, plus or minus 30 ppm. <br /> <br />The adoption of the above-described salinity differential as the method for measuring <br />compliance with the salinity management objectives allows the United States to comply <br />with Minute No. 242 by either bypassing all ofthe Wellton-Mohawk Division saline <br />agricultural drainage to the Cienega or by desalting and returning that water to the <br />Colorado River for delivery to Mexico at the NIB. As mentioned in the Introduction to this J <br />report, the United States has met the salinity management objective in recent years through /11 <br />bypassing the flows rather than operating the YD~.J This action is--sohdy'within the , ,1 ( \. <br />\~'Gtion eftll..Bnil.d ~t'<lell....a does not create any entitlement or obligation to continue~ L.{i\v;! <br />~assmg these flows. ' / V <br /> <br />Shown in Figure 1, the YDP is currently in ready reserve mode. When operating, the YDP l <br />would be able to recover from about 70,700 acre-feet per year to about 85,400 acre-feet per <br />year of the total 108,000 acre-feet per year that on average arrives at the YDP. The Bypass <br />Drain would transport the remaining 37,300 acre-feet per year to 22,600 acre-feet per year <br />of~P reject brine to the Cienega. <br /> <br />Wellton-Mohawk Division Drainal!e Reduction Measures <br /> <br />When Minute No. 242 was approved in 1973, agricultural drainage water from the <br />Wellton-Mohawk Division averaged about 210,000 acre-feet per year with salinity levels <br />of about 4,000 mg/I. Today, the volume amounts to about 108,000 acre-feet per year with <br />a salinity of about 2,800 mg/I. This change is the result of a series of actions undertaken by <br />the Wellton-Mohawk Irrigation and Drainage District in association with the Bureau of <br />Reclamation, the U.S Department of Agriculture and other cooperators. <br /> <br />Under Title I ofthe Act, the authorized irrigable acreage ofthe Division was reduced from <br />, .l2.t000 to 65,000 a.E.res, with about 6,000 acres of high water use land being retired through <br />purClfase or exchange. This program has reduced the agricultural drainage from the <br />Division by about ~O acre-feet per yejIJ. <br /> <br />Through a cost-shared program between District landowners and the Natural Resource <br />Conservation Service, USDA, on-farm water management practices have been improved. <br />The programs have included laser leveling of farm fields, concrete lining of on-farm <br />delivery ditches, climate sensitive irrigation scheduling and other related activities. This <br />program has reduced the agricultural drainage from the Division by about 30,000 acre-feet <br />per year. - <br /> <br />~, <br /> <br />5 Parts per million. At the salinity levels associated with Colorado River water delivered to Mexico, salinity <br />concentration measured in ppm is approximately equivalent to concentration measured in mg/l. <br /> <br />12 <br />