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<br />I . <br /> <br />, <br /> <br />ASSESSING STRATEGIES FOR coNmol ~ FAA4-0ERIVED <br />SAUNIlY IN 11iE lJIPER COlORADO RIVER BASIN <br /> <br />~ <br />~ <br />o <br />N <br /> <br />Over twelve mlllion residential water users and the crops on over one <br />million irrigated acres in the southwestern U.S. and Mexico are, to varying <br />degrees, adversely affected by salinity (dissolved mineral salts) in Colorado <br />River water. Salinity levels which exceed roughly 500 m111igrams per liter <br />(mg/l) can reduce agricultural productivity and shorten the useful life and <br /> <br />increase operating costs of pipes and water-using equipment in households and <br />industries. The U.S. Environmental Agency (1971) attributes about 55~ of the <br />concentration of dissolved salts measured in the lower reaches of the river to <br /> <br />natural sources, which include salt springs and surface runoff from the <br />sedimentary geologic formations and so11s common throughout the basin. An <br />estimated 37~ of the measured salt concentration is assigned to diffuse <br />irrigation return flows, primar11y from Upper Basin sources in Colorado, Utah <br />and Wyoming. Industrial and municipal contributions are negligible, so most of <br />the balance arises from the concentrating effects of reservoir evaporation. <br />Irrigation of crops implies eventual concentration of salinity in 5011 <br />moisture, because the small amount of salts invariably dissolved in the water <br /> <br />remain after a portion of the water is evaporated from growing plants. In <br />order to preserve productivity, irrigators must leach salts from their soils by <br />excess irrigation (Young and Horner). The resulting saline waters often <br />accumul ate in groundwater deposits and drain into neighboring streams. Saline <br />return flows from irrigated lands in the Upper Colorado Basin are unusual in <br />that most of the salt loading derives from the dissolving of soluble salts with <br /> <br />1 <br />