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<br />The Salinity Problem <br /> <br />Closely allied with the antici- <br />pated problems of water <br />supply is the present prob- <br />lem of salinity. Salinity or <br />mineral pollution in western <br />rivers of the United States <br />is not a new or unique situa- <br />tion. I n other parts of the <br />world, entire civilizations <br />have been abandoned due <br />to salinity effects on agri- <br />culture. High salinity levels <br />in the Colorado River were <br />recognized as early as 1903. <br /> <br /> <br />Salt accumulated in tile drains, <br />Imperial Valley, California <br /> <br />Salinity Sources <br /> <br /> <br />002966 <br /> <br />Generally, dissolved mineral <br />concentrations normally <br />increase from headwaters to <br />mouth. I n western arid re- <br />gions, such as the Colorado <br />River Basin. this increase <br />is intensified because, unlike <br />in humid zones, salts have <br />not been weathered out of <br />the soil and rocks. Man's <br />consumptive use of river <br />water also causes increases <br />in salt concentration. Direct <br />salt loading of the river from <br />natural springs. weathering <br />of mineral-bearing rocks. <br />and pickup of salts from <br />irrigated soils add to the salt <br />concentration of river water. <br />Estimates indicate that about <br />half of the present salt con- <br />centration in the Colorado <br />River at Hoover Dam can be <br />attributed to natural sources. <br />The remaining half is man- <br />induced. <br /> <br />47% Natural Sources <br />37% Irrigation <br />12 % Reservoir <br />Evaporation <br />3% Exports <br />1% M&I <br /> <br />