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<br />~;' <,-- <br /> <br />w <br />CD <br />o <br />o <br /> <br />Weather Modification <br /> <br />The CREST demonstration program would be pursued separately from the salinity <br />program from 1986 through 1993 and cost $88 mi 11 i on in 1983 doll aI's. By CRSS <br />projectiqns, this could reduce the salinity at Imperial Dam through dilution <br />by about 13 mg/L from 1989-1993. <br /> <br />A subsequent, full basin operational program could begin in 1993, or when <br />authorized, and, depending on when and how the additional water is put to <br />use, redu,ce salinity by up to 100 mg/L at Imperial Dam by diluting flows. <br />This program would cost approximatly $12-16 million per year in 1983 dollars. <br />An overvi~w of the potential for water supply enhancement in the basin is <br />discussed; in more detail in appendix A. <br /> <br />Based on present CRSS assumptions, little new ,wa,J;.eof, from weather modification <br />will be used in the next 20 years in the Upper Basin. 'Therefore, the extra <br />water will be available for dilution until it is put to use. f-Iowever, if <br />river flows are increased in the Upper Basin, the present projected water <br />uses may ~e low for augmented flows, and the time this extra water might <br />be available for dilution would be less than now anticipated. Regardless <br />of the impact of weather modification flows and its associated diluting <br />effect, additional salinity control projects need to be in place by 1994 <br />to meet the standards. <br /> <br />Uncertainty Analysis in Salinity PrOjections <br /> <br />Although the numeric criteria have remained fixed since 1975, the target <br />loads to meet the cri teri a cont i nua 11y change to meet future project ions. <br />The "target" ,in this case is the reduction in salt load necessary to main- <br />tain compliance with the TDS numeric criteria at the three stations in the <br />Lower Basin under projected conditions of basin hydrology and water resources <br />development. Thus, .management must deal with the inherent uncertainty of the <br />program due to (,l}'the target load reduct"ions that cannot be precisely <br />defined, (2) the broad range of alternative solutions, (3) the incomplete <br />data on control options and effects, and (4) the lack of complete under- <br />standing of the interactive salt load/hydrologic system and of the reservoir <br />impacts. <br /> <br /> <br />Dealing with this program uncertainty has encouraged a conservative bias <br />in past projections of uncontrolled salinity levels. For example, in 1972, <br />Reclamation's projected TDS at Imperial Dam for the year 2000 was 1250 mg/L; <br />in 1974, p~ojections were scaled down to 1116 mg/L; and in 1983, the corre- <br />spondi ng TOS was further revi sed downward to 1010 mg/L. The most reCent CRSS <br />nJI'!~"~,,,",..ts"'930 mg/Lby,.the,;ye,-a",'.2000. These shifts have occurred becauSe <br />dria reduction of expected Upper Basin depletions, extension of the projec- <br />tion base from 1941-72 to 1906-83, and the elimination of a 400,000 ton per <br />year error found in early analytial procedures. <br /> <br />-~ <br />, <br /> <br />.~ <br /> <br />Since the program began in 1972, Reclamation has been developing a flexible <br />model to improve estimates of future requirements for salt load reduction. <br /> <br />~ <br /> <br />37 <br /> <br />