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<br />w <br />w <br />''':> 1200 <br />e <br /> 1100 ~ - <br /> .. <br /> .. <br /> ~ .. <br /> - .. <br /> " <br /> " 1000 '" <br /> ~ '" <br /> 0 , <br /> ~ <br /> 0 900 879 mglL ; <br /> ~ <br /> 0 <br /> w <br /> > <br /> ~ <br /> 0 800 <br /> ~ <br /> !<! <br /> 0 <br /> ~ <br /> " <br /> ~ 700 <br /> 0 <br /> ~ Historical <br /> - - - - - Protected 1 <br /> 600 <br /> <br /> <br /> <br />500 <br />1940 <br /> <br />1950 <br /> <br />1960 <br /> <br />1970 <br /> <br />1980 <br /> <br />1990 <br /> <br />2000 <br /> <br />2010 <br /> <br />.l1 Without Waler Quality Improvement PtOljram <br /> <br />Figure 2. - Recorded salinity levels at Imperial Dam with projections <br />through the yedr 2010. <br /> <br />In any river system, salinity concentrations arise from a salt loading <br />effect and a salt concentratl"9 effect. Salt loading may be regarded as <br />the pickup of salt due to mineral weathering and dissolution of the soluble <br />salts residing in so; I and substrata. Salt concentrating effect is due to <br />the evapotranspiration of the water carrying a finite salt load or the <br />export of high Quality water out of the Basin. Generally, the application <br />of irrigation water results in increased salt concentrations because of <br />salt loading and concentrating effects of consumptive use. The evaporated <br />or transpired water is essentially free of salt; hence. the remaining <br />return flows carry the total salt burden. As water is evaporated from the <br />ocean or other free water surfaces. alterations in the composition and <br />concentration of the dissolved constituents begin to occur and continue as <br />the concentration progressively increases. <br /> <br />3 <br />