CRDSS_Task1_15-25_UncompahgreProject

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the irrigation demands increase and the UVWUA begins to divert additional water through the Gunnison Tunnel, generally ramping up the diversions in increments of approximately 200 cfs. Once at capacity, the Tunnel will normally flow full for the remainder of the irrigation season, except during periods of peak runoff on the Uncompahgre River when there is sufficient in-basin water available to satisfy the demands. The UVWUA also owns storage in Taylor Park Reservoir (active capacity of approximately 106,230 acre-feet) and a storage allocation of 10,300 acre-feet of supplemental irrigation water from the Dallas Creek Project (Ridgway Reservoir). These reservoir sources are used when the direct flow rights are incapable of meeting the system irrigation demands. Administration of a Call by the Gunnison Tunnel Prior to the construction of the Aspinall Unit, the UVWUA routinely placed a call against junior water rights on the Gunnison River to satisfy the Gunnison Tunnel demand. After Blue Mesa Reservoir came on line, the large reservoir releases that have been made for hydro power production resulted in the equivalent of a "free river" below the Aspinall Unit reservoirs; for the most part, these releases have provided sufficient water to satisfy the tunnel direct flow right (1,135 cfs) for much of the irrigation season. Furthermore, when the United States acquired the water rights for the Aspinall Unit in 1962, it was generally recognized that storage in the Aspinall Unit reservoirs would be subordinated to upstream junior appropriators to the extent of 60,000 acre-feet (consumptive use). The implication of this subordination is that an administrative call by the Gunnison Tunnel would be absorbed, for the most part, by the storage in Blue Mesa Reservoir. When the inflows to Blue Mesa Reservoir fall off and the United States? storage decree is not in priority, the UVWUA must begin to release water from storage in either Taylor Park or Blue Mesa reservoirs to satisfy the Gunnison Tunnel demand. In the future, if the United States attempts to administer the hydroelectric power release from the Aspinall Unit reservoirs such that they are required to flow past the Gunnison Tunnel (such as for a delivery to endangered fish on the lower Gunnison and Colorado rivers), this would represent a fundamental change of the current United States policies, an d it may be necessary for the UVWUA to strictly enforce its senior direct flow decree at the tunnel against junior water rights on the Gunnison River, including the storage in Blue Mesa. This is noted for consideration in the CRDSS model to ensure that strict administration is an operational option. Administration of a Call on the Uncompahgre River Delivery to the project canals is governed by two key control gages on the Uncompahgre River; one at Delta (the downstream end of the system) and one near Olathe, just downstream of the head gate for the East Canal. During the critical months of the irrigation season, the system deliveries are managed in an attempt to keep the flow at the Delta gage as low as possible (in the range of 200 to 300 cfs). The UVWUA also attempts to keep the flow at the Olathe gage at or near zero. (Note that the Garnet Ditch is downstream of the Olathe gage and is supplied primarily from upstream return flows). In recent years, the UVWUA has attempted to operate its system to avoid, to the extent possible, the necessity of placing an administrative call against junior rights in the Uncompahgre and Gunnison river basins (the "good neighbor policy"). However, certain climatic and hydrologic conditions could occur that would necessitate a call, even if only for a short time. Based on interviews with the UVWUA Manager, the following scenarios describe conditions that could result in a call by the project canals during the critical summer months (July through September). 4 A275 01.09.95 1.15-25 Fosha, Hyre