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I 1 I I I I I I I I I I I I 1 I heavily upon their direct flow rights from the Cache la Poudre River during the winter. Reservoir releases are needed to augment the natural river flows in the winter, when Greeley's demands exceed the flows or the water available under these decrees; A si de benefit from fi rm yi el d operati ons is that carry-over storage woul d enhance the reservoi r fi shery. A mi nimum pool woul d be available at all times, except during times of extreme drought. Year-to-year operations, which maximize project yield, rely on capturing storabl e water in the reservoi rs in the spri ng, and rel easi n9 water for the North Poudre Irrigation Company in the summer, in exchange for CBT water; This allows the flexibility of delivering raw water to either the Bellvue or Boyd Lake treatment pl ants. Peak sununer muni ci pa 1 demands are sati sfi ed economically and efficiently, and the water supply available for agriculture is increased during the period of highest consumptive use. This operating pattern could also increase winter supplies for the City, if the exchange plan is not impl emented. The major di sadvantage of operating without carry-over storage is that water shortages may occur during a prolonged drought. However, the large amount of Colorado-Big Thompson water owned by the City should amply insure against such a possibility on a system-wide basis. In drought years, CBT water sufficient to meet projected winter water requi rements for the City of Greel ey coul d be transferred to storage in Greeley's high mountain reservoirs during the spring. utilizing river exchanges. Water stored by such transfers would be released during the winter to augment winter streamflows and assure sufficient water is available to the Bellvue Filtration Plant to meet the City's water demands. Reservoir operation studies were conducted for two conditions--restricted and unrestricted operations. Current operating restrictions imposed by the Colorado Office of the State Engineer 1 imit the storage capacity of Comanche; Peterson Lake, and Twin lakes Reservoi rs. Simul ations were developed to compare the restri cted and unrestri cted operati ng condi ti ons associ ated with rehabilitating the dam, spillway, and outlet works for Twin Lakes; The difference in project yield is useful in determining the unit cost of water for repairing the structure. -32-