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Section 7 Availability of Existing Water Supplies ended, the DSS dataset for the Colorado should be extended, including updated irrigated acres and M&I demands. A new StateMod model run should be conducted with the updated dataset to determine if the recent drought is a new critical period. Maintaining or enhancing recreational and environmental flows could also affect future supply availability. Environmental and recreational considerations are further developed in Sections 6 and 10 of this report. For example, a number of endangered fish species, such as the Razorback Sucker and the Humpback Chub, are present in the Colorado River and tributaries, and require special attention. The Colorado River immediately upstream from the confluence with the Gunnison River (15-mile reach) is currently operating under a PBO that may affect the amount of allowable depletions in this upper subbasin to help promote the recovery of four endangered fish species. Coordinated reservoir operations, habitat improvement, stocking, and control of non-native species are other options that can help meet the needs of endangered species. Water is available for future demands out of contract pools in Green Mountain, Ruedi, and Wolford Mountain Reservoirs. There is approximately 10,000 AFY available from Green Mountain, 21,000 AF from Ruedi, and 7,500 AF from Wolford Mountain Reservoirs. Existing and future supply availability out of Green Mountain Reservoir may be affected by minimum storage restrictions recently placed on the reservoir. Historic movement of landslides in the adjacent Town of Heeney are a concern during low water storage levels such as occurred during the recent drought period and caused storage restrictions. If it is determined that the reservoir must maintain these minimum storage levels long term, and storage is not replaced elsewhere, there may be a permanent loss of firm yield for the users of Green Mountain Reservoir. Finally, in addition to future in-basin demands, there will likely be additional diversions through existing transbasin facilities (such as Denver Water's Roberts and Moffat Tunnels and NCWCD's CBT and Windy Gap firming projects) as these transbasin diverters grow into their Colorado Basin water rights and firm existing water rights with east slope storage. These increased transbasin diversions are not included in the present DSS analysis, but will affect future supply availability in the Colorado Basin. SWSI recognizes the need to evaluate future ~~ ~ available supply in the headwaters of the Colorado Basin. This will be evaluated in more detail as part of SWSI's ongoing work in 2005 to 2006. The Denver Water Northern Firming and the NCWCD's Windy Gap Firming Projects, if implemented, could increase average annual diversions from the Colorado to the South Platte by up to 48,000 AFY. The proposed Homestake II or Wolcott Reservoir Projects could also potentially increase transbasin diversions. Historical transbasin diversions from the Colorado Basin are shown in Figure 7-32. Transbasin diversions averaged 482,728 AFY from 1971 to 2003. The locations of transbasin diversions from the Colorado, Gunnison, and Dolores/San Juan/San Miguel Basins are shown in Figure 7-33. 7.3.2.2 Colorado Basin Alluvial Aquifer The distribution of alluvial deposits in the Colorado Basin varies greatly from one reach to the next. The alluvial deposits, as mapped by USGS geologic quadrangle maps, are primarily located near the Towns of Eagle and Gypsum, along the Roaring Fork River, Roan Creek, and from the Town of Palisade to the Colorado-Utah state line. Alluvium is very limited or non-existent in the canyon sections of the Colorado River where the bedrock is exposed (CGS 2003). The saturated thickness of the alluvium in the basin is represented by the interval from the water table to the underlying bedrock. Welder (1987) reported that test holes in the alluvium of Roan and Parachute Creeks penetrated 80 feet and 70 feet, respectively, of saturated permeable sand and gravel. For the Fraser River, Apodaca and Bails (1999) report alluvial saturated thickness ranging from 14 to 45 feet, averaging 21 feet in the spring, and ranging from 7 to 20 feet in the fall with an average of 15 feet. The alluvial groundwater in the Colorado Basin is considered tributary to the Colorado River and users of this resource are administered under the Prior Appropriation System. Except for domestic or other low- volume exempt uses, the use of groundwater in this aquifer requires a water court-approved augmentation plan that describes how depletions to the river will be offset to avoid injury to senior appropriators and to comply with the interstate compact. The location and extent of alluvial aquifer in the Colorado River Basin is shown in Figure 3-13. ~~ Statew~itle Water Supply Inii'iative 7-22 S:\REPORT\WORD PROCESSING\REPORT\S7 11-10.04.DOC