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I I I I I I I I I I I I I I I I I I I DRAFT 8/24/92, Page 12 2. Dowe Flats Reservoir -- Due to a combination of factors including a declining agricultural economy, the slowing of municipal and industrial growth, construction of the Windy Gap Project, and return flows from transmountain diversions, there is currently a large surplus supply of water in the area served by the Northern Colorado Water Conservancy District. However, there are many institutional and legal barriers to the movement of surplus water from the north into the metro area. One possibility for removing some of those barriers could be the development of water storage and distribution facilities that would be useful for serving the needs of both metro Denver and the northern front range. The Southwestern Portland Cement Company has proposed the development of a reservoir in conjunction with the mining of limestone deposits in Dowe Flats to the east of Lyons. This facility could provide storage of up to 90,000 acre-feet of water. By virtue of its location, Dowe Flats could regulate water sources from both the Colorado and South Platte basins. Potential west slope sources include Colorado-Big Thompson/Windy Gap diversions, Thornton's Grand River Ditch shares, Denver's Moffat Diversions (including the contemplated Moffat draft of Two Forks), and the AMAX Molybdenum Company's marketable yield from the Williams Fork. Potential east slope sources include storage of flows from the St. Vrain and Little Thompson Rivers and exchanges via the Colorado-Big Thompson system. 3. Clear Creek Reservoir -- The Colorado Water Resources and Power Development Authority has studied the feasibility of reservoir development on Clear Creek. Options identified in this study would produce a firm annual yield of up to 61,000 acre-feet, with a construction cost of $330 million and an annualized cost of $631 per acre-foot. This cost estimate includes $84 million for relocation of Highway 6. Implementation of this project would require the resolution of significant technical, environmental, and legal issues including potential water quality problems, major Clear Creek Water users, and the users of Highway 6 in Clear Creek Canyon. 4. Other Small Reservoirs - There are a number of other reservoir development proposals that are pending or under development including the Castlewood Canyon project proposed by the town of Parker, the Poudre Reservoir proposed by the Northern Colorado Water Conservancy District and the possible enlargement of Eleven Mile Canyon and Antero Reservoirs on the Upper South Platte being considered by the Denver Water Department. We have not investigated the details or status of these options. Issues to be Addressed While these options are generally of a smaller scale in terms of size, yield and cost, they all have significant issues which are potential barriers to their implementation. Gross Reservoir enlargement is an attractive alternative in terms of site-specific permitting. The development area is already impacted by the existing facility and there is considerable information available from the Metropolitan Denver Water Supply EIS regarding environmental impacts. The primary issues are those associated with additional depletions of stream flows on the west slope in the Fraser and Williams Fork River Basins. It may be possible to mitigation these impacts through operational changes and/or cooperation with the Northern District. Another issues is the engineering problem of determining the best method of adding additional height to the existing Gross Dam. Use of roller compacted concrete appears to be the least costly method, but its technical feasibility has been determined. Other methods of increasing the size of the dam could significantly increase the cost. .