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EXECUTIVE SUMMARY The primary purpose of this report is to summarize the preliminary evaluation of alternatives for supplying an annual average of 20,000 acre-feet of water to the mainstem Colorado River. This water will be made available to supplement spring peak flows in the reach of the Colorado River 15 miles upstream from its confluence with the Gunnison River to the Grand Valley Irrigation Company (GVIC) Diversion Dam near Palisade, Colorado (the "15-Mile Reach"). Water will be made available to enhance the spring peak flows in those years when the peak is forecast to be between 12,900 cfs and 26,600 cfs at the head of the 15-Mile Reach. Consequently, the 20,000 acre-feet average will be computed on the basis of the years in which the water is supplied. A secondary purpose is to summarize the preliminary evaluation of alternatives for providing flow enhancements to the 15-Mile Reach during the late summer/early fall (July 15 through October 31) period. Providing this water is an identified element of the Final Programmatic Biological Opinion (PBO), (U.S. Fish and Wildlife Service, December 20, 1999). A wide range of alternatives was subjected to a preliminary screening process in this Phase 1 investigation in order to select a relatively short list of alternatives to intensively study in Phase 2. The list of alternatives considered in the Phase 1 preliminary screening process included: • Expanded Coordinated Reservoir Operations, • Grand Valley-Centric Alternatives, • Efficiencies of Conveyance and Distribution Facilities, • New Storage Facilities, • Power Plant Operations and Scheduling, and • Other Alternatives. A total of approximately 35 separate alternatives were considered in these categories in the Phase 1 investigation. (See Table 1 at the end of this report.) As a result of the Phase 1 investigation, the following alternatives were selected by the Executive Committee for further investigation in Phase 2. The disposition of all alternatives is summarized in Table 2 at the end of this report. • Alternatives la, b, c, d, e, f, and g: Expanded Coordinated Reservoir Operations. Alternatives 1 a - Green Mountain Reservoir Operations, 1 b - Ruedi Reservoir Operations, le - Denver Water System Operations, and I g - Reduce Coordinated Reservoir Operations Program (CROP) Constraints will be included in Phase 2 for further investigation. Alternative I c, Ruedi Reservoir Pumpback, will not be further studied in Phase 2 because it depends on physical supplies that would be used by other alternatives which appear to have greater potential for feasibility. Alternative Id, Colorado-Big p:\data\gen\Ocwcb\18133\report\phase-1\exec sum.doc ES-1