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.' Gravity Main Canal siphon under the Gila River, at the western end of the District. At this point, the return flow was measured and allowed to flow into the normally dry Gila River and thence into the Colorado. The first effluent came out of this channel on 10 February 1961. The return flow channel has since been e,:tended, in stages, beyond the western 1 imit of the Wellton-Mohaw~ District, all the way to the Colo,'ado River main channel, near Yuma. Coincidentally, the closing of Glen Canyon Dam on the upper Colorado River, and the sudden decreased flow of that river occurred at about the same time that Wellton-Mohaw~'s return flow ,;:,howed up as a "point source" discharge directl y into the Colorado. GENERAL COMMENTS ON DF:A I NAGE Qual ity lmp~ovement, W-H Retu~n Flows Wellton-Mohaw~ return flows improved in qual ity from 6500 ppm salts in 1961 to 3800 ppm in 1973 and to about 3000 ppm in 1990. It is almost certain that the predicted "flattenin'~ out", or slowing in imorovement, has occurred. Additional improvement in the qual ity of return flows is unl ikely. Indeed, qual ity of return flows might well have been adversely affected bv the program of acreage reduction, since less deep percolation would naturally result in less dilution of the ground water. Qual ity Dete~ioration, Colorado Rive~ Qual ity generally decreases, with or without use, as ,'iver water flows downstream. The sal inity of Colorado River water at Imperial Dam increased from 693 ppm in 1945 to 894 in 1970, decreased to 820 in 1977, and was near 900 ppm in 1990, with wide downward fluctuations during years of flooding. Return Flow Reduction Efforts underta~en within the boundaries of Wel. ton-Mohawf, to reduce ,..'eturn flows and to he1 p achieve the qual ity guaranteed to Mexico by Minute 242, authorized by Publ ic Law 93-320, include the following, A. Acreage Reduction The initial step in reducing the return flows from Wellton-Mohawk was the el imination of 10,000 acres of either undeveloped land, or land with low water-use efficiency. In the case of developed, but low efficiency land, the bulk was citrus, on sandy soils. In all such cases, the purchase of the lands by the federal government waS negotiated with willing sellers.