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<br />Study Approach <br /> <br />A wide variety of interests and priorities must be considered in <br />operating the Colorado River system, and no attempt has been made to <br />perform economic evaluations of the various strategies. As agreed <br />when the study began, only those strategies that are permitted by the <br />present Operating Criteria are evaluated and no recommendation for an <br />overall "best" operating strategy is made. The study is limited to <br />short-term uses of water that are surplus to the system. The results <br />of the study should be used as a management tool for assessing the <br />general impacts of different alternative operating strategies and as a <br />guide for futher study if required. <br /> <br />The CRSS (Colorado River Simulation System) computer model was used to <br />examine five possible strategies for operating the Colorado River <br />reservoirs (particularly lakes Mead and Powell). These strategies <br />included (1) a base case that schedules no surplus releases (releases <br />in excess of minimum downstream demands) but encounters unscheduled <br />flood control releases, and (2) a set of four alternative strategies <br />that schedule varying levels of surplus releases, resulting in fewer <br />unscheduled flood control releases. <br /> <br />The alternative operating strateQies are identified by the level of <br />probability assumed with each strategy and called an assurance level. <br />A very low assurance level (close to 0.00) operates similar to the <br />base case and produces similar results. The strategies studied were <br />the 0.70, 0.80, 0.90, and 0.99 assurance levels. <br /> <br />More detailed discussions of the base case and the alternative strate- <br />gies are presented later in this summary and in Sections 2 and 3 of <br />the ma in report. <br /> <br />Figure 1 provides a summary of some of the general trends associated <br />with the base case and low-assurance strategies compared to those <br />associated with the high-assurance strategies. An assurance level is <br />represented by the probability of avoiding unscheduled releases that <br />would likely result in spills or flooding downstream. Thus, a high <br />assurance level operation strategy will increase available space and <br />reduce the chances of unscheduled flood control releases. Conversely, <br />a low assurance level strategy will reduce available space and <br />increase the probability of unscheduled flood control releaseS. <br /> <br />Generally, the higher-assurance strategies produced (1) more power <br />generation in both Basins, (2) additional scheduled surplus releases <br />for Arizona and California water users, and (3) slightly lower water <br />levels in the reservoirs for conservation purposes. <br /> <br />2 <br />