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<br />. <br /> <br />. <br /> <br />CHAPTER IV <br /> <br />PROBLEMS AND NEEDS <br /> <br />increased management costs. Agricultural losses begin when salinity <br /> <br />levels reach 700-850 mg/L, depending upon the soil condition and type of <br /> <br />crops grown. <br /> <br />Salt loading occurs as a result of weathering and dissolution of the <br /> <br />soluble salts in soil and substrata. In addition, salt concentration <br /> <br />Occurs because of consumptive use, such as agricultural or industrial <br /> <br />applications of the water in the basin. Generally, the application of <br /> <br />irrigation water results in increased salt concentrations because of both <br /> <br />loading and consumptive use. The salt load fluctuates annually with the <br /> <br />overall basin water supply. Without management, as the states continue <br /> <br />to develop their compact-apportioned waters, the river's salinity at <br /> <br />Imperial Dam is projected to increase. <br /> <br />As the following graph indicates, since 1949 the general trend of <br /> <br />salinity at Imperial Dam has been upward, although Slnce 1970 the <br /> <br />salinity has decreased. This downward trend recently is believed to be a <br /> <br />result of the construction of Colorado River Storage Project reservoirs <br /> <br />such as Glen Canyon. It is theorized that these reservoirs while <br /> <br />filling are retaining a portion of the salts that would otherwise be <br /> <br />flowing down to Imperial Dam and reflecting lower salinity levels at <br /> <br />the measuring stations. This is believed to be a temporary phenomenon <br /> <br />and the projected levels through the year 2010 (without water quality <br /> <br />improvement projects) are expected to follow the overall rising trend <br /> <br />as shown in the graph on the following page. <br /> <br />001488 <br /> <br />14 <br />