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<br />. <br /> <br />. <br /> <br />Co&) <br />00 <br />Q <br />l\) <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />Problems of Using the Waters of the <br />Arid Colorado River Basin <br /> <br />The waters of the Colorado River Basin are used by man for a <br /> <br />variety of purposes, including domestic, industrial, municipal, irri- <br /> <br />gation, production of hydroelectric power, preservation of fish and wild- <br /> <br />life, and recreation. Water also is exported for use in other basins. <br /> <br />The most significant of these uses from the standpoint of water con- <br /> <br />sumption, and that which has pe:thaps the greatest influence on salinity <br /> <br />levels, is irrigation. Summertime flows in the lower reaches of many <br /> <br />tributaries are composed largely of return water from irrigated areas. <br /> <br />These return flows generally affect the concentration of salts dissolved <br /> <br />in the streams. <br /> <br />Composition of Salinity and Water Uses. In terms of man's use of <br /> <br />water, however, the kinds of dissolved salts, in addition to the salinity <br /> <br />level, are important. For example, the calcium ion is generally not <br /> <br />toxic to plants and often is beneficial to the soil structure. Thus, high <br /> <br />concentrations of calcium in irrigation waters usually are not detrimental. <br /> <br />On the other hand, calcium causes a water condition known as "hardness" <br /> <br />which often is regarded as a disadvantage for domestic and some indus- <br /> <br />trial water uses. High levels of the sodium ion produce a "soft" water <br /> <br />for domestic supplies, but create a very undesirable water for irrigation <br /> <br />purposes. Thus, processes, whether natural or man-induced, which <br /> <br />tend to alter the proportions of dissolved ions in the water can profoundly <br /> <br />11 <br />