Yampa River Basin Research Final Synthesis Report

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• The Flow Rec. - Junior - No Runoff Aug. scenario, which simulates the same operation as the Flow Rec. - Junior scenario except that no storage releases are made for flow augmentation during the months of April, May and June. The CWCB - Junior - No Runoff Aug. scenario, which simulates the same operation as the CWCB - Junior scenario except that no storage releases are made for flow augmentation during the months of April, May and June. Key Model Assumptions The Phase I and Phase II study scenarios were run using a monthly time step over the period 1930 —1982. Model scenarios run during the subsequent O &M studies used an extended 1930 -1994 study period. Modeled water demands in the Phase I and Phase II study scenarios were set at a projected year 2040 demand level, which represents approximately 49,000 of of additional depletion over 1989 levels (considered "current actual conditions" at the time of the Phase I study). Modeled water demands in O &M Study scenarios were set at the level of the CWCB's 52,000 of development carve -out. All modeled demands were configured and/or relocated so as to have access to contract storage in either Elkhead, Stagecoach, or Steamboat Lake (Hayden Station only); this was done to insure that the full demand level or development carve -out would be used to deplete the river. In reality, accomplishing this level of depletion would require some small local storage development, use of pumps and pipelines, etc., to meet tributary demands. In all six scenarios, in -basin water demands were represented as diverting under their existing or assumed future water right priorities. In all six scenarios we assumed the enlargement of Elkhead Reservoir. In the Phase I Study, the enlargement was assumed to provide a total capacity of 46,500 af. Based on better site information obtained during later analyses, the Phase II and O &M studies assumed the enlarged Elkhead capacity to be 44,900 af. In the Phase I Study, Stagecoach Reservoir was also assumed to be enlarged, to a capacity of 52,000 af. This Stagecoach enlargement was not represented in the other scenarios. In all studies the dead storage of the enlarged Elkhead was assumed to be 3,722 af. The active capacity of the reservoir was divided into various pools operated for different purposes. In general, these included municipal and industrial contract pools and an "enlargement" or "augmentation" pool. In the Phase I Study, releases were made from the enlargement pool to meet current and future in -basin demands not adequately covered by existing storage contracts. In the Phase II and O &M studies, releases for in -basin demands were made only from the contract pools while instream flow support releases were made from the augmentation pool. Appendix A Hydrosphere Resource Consultants, 1002 Walnut Suite 200, Boulder, CO 80302 2