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<br /> <br />W <br />N <br />N <br />~ <br /> <br />A severe municipal water salinity problem caused by <br /> <br /> <br />irrigation return flows recently occurred in the Lower <br />Colorado River. Saline water in an aquifer underlying the <br />Well ton-Mohawk Irrigation District near Yuma, Arizona is <br />drained by a series of large-capacity wells drilled to <br />control the water table (8). The discharged effluent <br />greatly increased the salinity of the Colorado River at <br />Yuma. The company that supplied domestic water to the city <br />had to abandon its intake structures in the river and obtain <br />potable water by diversion at Imperial Dam, approximately 15 <br />miles upstream. Downstream users in Mexico, however, had no <br />alternative source of supply and the salinity of the <br />Colorado River flowing into Mexico is the subject of <br />international negotiations (9). <br /> <br />~~!g~_Q~~g~!2Bl!y~g <br /> <br />salinity created by irrigation generates additio~al <br /> <br /> <br />problems for the downstream user. Saline water may increase <br /> <br /> <br />the salinity of the root zone environment of the soil. <br /> <br /> <br />Elevation 9f soil salinity may inhibit seed germination, <br /> <br /> <br />reduce crop yields and prevent the growing of crops having <br /> <br /> <br />low salt tolerances. In extreme instances, salt buildup may <br /> <br />even cause the removal of land from agricultural production <br /> <br />(Figure 8). production of vegetable crops having low salt <br /> <br />26 <br />