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1 Executive Summary 1 Future Conditions Without Project The demands used in this scenario reflect projected development conditions in the year 2040 and the scenario differs from the current conditions analysis only in this respect. The 2040 demands are believed to reflect an average annual basin water consumption of approximately 159,000 of/yr. ' The results of this model scenario show largely the same agricultural shortages as did the current conditions analysis. However, municipal water supply shortages appear in one dry ' year and industrial shortages (mainly to an assumed coal-gasification plant near Craig) are frequent. Reservoir contents show greater drafting for water supply purposes, primarily from Stagecoach and Elkhead Reservoirs. ' Simulated flows at Maybell are substantially lower than those under current conditions, especially in the late summer and fall. Occurrences of zero monthly flow below Maybell (an imprecise but useful indicator of flow conditions) rise from 5 to 22. The median and dry-year flows under this model scenario are also shown on Figure S-1. Future Conditions With Project The demands used in this scenario also reflect projected 2040 development conditions but also include the simulated operation of an enlarged Elkhead Reservoir. The enlarged reservoir was assumed to have a storage capacity of 44,900 of and to fill under a transferred conditional storage right presently held by the River District for the California Park project. ' Two important reservoir operations assumptions reflected in this model scenario are: 1) the transfer of the existing 9,000 of industrial pool in Stagecoach into the enlarged Elkhead Reservoir and the reassignment of the Stagecoach pool to municipal uses, and 2) the release of ' up to 22,200 of/yr from the enlarged Elkhead to supplement low flows at Maybell. These flow support releases were made using assumed minimum monthly flow targets as a release criterion; in most cases these releases were made in the late summer and fall. 1 1 1 The results of this model scenario show largely the same agricultural shortages as did the current conditions analysis; agricultural demands were not assumed to have any new contracts for water from the enlarged Elkhead (only some of those on the mainstem Yampa could benefit anyway). The infrequent future municipal shortages are eliminated by deliveries made from the reassigned pool in Stagecoach. Industrial shortages of up 2,240 of/yr at the assumed coal- gasification plant near Craig will remain unless modifications are made to existing water storage agreements to make those supplies available; if this were done, these industrial shortages would also be eliminated. Stagecoach Reservoir is drafted less in this scenario as industrial supplies are drawn mainly from Elkhead. The enlarged Elkhead is drawn upon regularly for industrial use and instream flow support, though drawdown by Labor Day weekend would be less than 10 feet on the average. Simulated flows at Maybell are generally higher than those under "future without project" conditions though still somewhat lower than under current conditions. The median flows equal or exceed the values in the preliminary flow recommendations. Late season flows S-5