Gunnison - Lake San Cristobal Outlet Mod Project Phase III_Water Activity Summary

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Water Activity Summary: The Lake San Cristobal Outlet Modification Project is intended to replace an annually-placed rock wall with a permanent outlet structure. This structure would maintain the same storage regime that has taken place at the lake for over 50 years. The proposed outlet would allow for more controlled releases from the lake while eliminating the need to place and remove rocks on an annual basis at the lake's outlet. In addition, the new outlet structure would allow development of a local plan of augmentation that would benefit the environment along the Lake Fork of the Gunnison and reduce the reliance on Blue Mesa Reservoir as a downstream source of augmentation water. This project is necessaiv to provide a high-altitude local source of augmentation water that will improve water availability for the Instream Flow Right on the Lake Fork. The stream below Lake San Cristobal would receive flows from storage at times when the stream levels are below the ISF right, thus improving the habitat for fish and other species along the Lake Fork from Lake San Cristobal to Blue Mesa Reservoir. The three entities involved in this project, Hinsdale County, Town of Lake City, and the Upper Gunnison River Water Conservancy District, are Nvork ng cooperatively to meet the needs of their constituents in the Lake Fork drainage. The three applicants have each contributed $10,000 to begin work on Phase I of the design. Phase I includes preliminary surveying and a 65% design incorporating a hazard classification report and initial hydrology and hydraulic analyses. Previous Studies "Feasibility Study, Controlled Outlet Structure, Lake San Cristobal, Hinsdale County, Colorado", by URS Corporation, 2004. A copy of this report was previously provided to CWCB. This study evaluated the concept of constructing a new permanent outlet control structure on Lake San Cristobal. It proposed that a new structure would consist of a steel sheetpile cutoff structure and buried concrete blocks that would allow safe passage of the 100-year flood while maintaining the capability to store 1020 acre feet in priority. Hinsdale County and the UGRWCD have previously received $35,000 of SB179 fiends to conduct a marketing and firm yield study for this project. The results of this study are currently being drafted. Results indicate the firm yield ratio for the water supply is a very favorable 1:1. The marketing study showed that all three applicants' customers would benefit from having additional high-altitude augmentation water available. The need for this augmentation water would become acute should USBR ever terminate its Blue Mesa augmentation water contracts. The three phases of this project include: Phase I (Previous WSRA Funding--$35,000): Evaluate options for providing for storage and release of 960 acre-feet of water in LSC utilizing an outlet structure that has a natural appearance of boulders placed in the water. This task may include surveying and geotechnical evaluation, conceptual alternative design development, hydraulic design, river and lake hydrographs, preliminary budget analysis, and evaluation of pros/cons of each option. The survey work would evaluate ownership boundaries associated with the proposed outlet structure. The final product will be a summary detailing the preferred alternative including cost estimates. Phase 2 (Previous WSRA Funding--$75,265): Complete the geotechnical work and develop a detailed perspective of the underlying geologic condition of the site of the proposed outlet structure. Produce preliminary design documents and construction cost estimates for the selected alternative for District review and consideration. This task includes the hazard classification report preparation and preliminary review/approval by the Colorado State Engineer (SEO), all other permit requirements, and the geotechnical, design, and hydrology reports. Phase 3 (Current WSRA Grant Request--$120,960): Produce final design documents and construction cost estimates. This work includes preparation of the technical specifications, design drawings and details, and applying for 2