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. . . n"'j- ;.,;;;!., i fJ. L. . ~ _. .- .-J":-"-:~~~-;- IV'- Draft: 04/30/91 wi t:It/r~.... .4~r""'" 7 ./,.: . Cj I Global Climate Change Response Program: Gunnison River Basin -- water use/water rights impact evaluation Identification of proposed ACRM Activities: 1. Develope natural flow estimates for identified stream locations within the North Fork, Smith Fork, Uncompahgre, and Lower Mainstem of the Gunnison Basin. Activity will serve to expand natural flow coverage of Gunnison Basin initiated during the Phase 1 Upper Gunnison-Uncompahgre Basin Feasibility Study. The Phase 1 basin model contained 79 inflow points. Twenty of these inflows were return flows calculated internally by the model and the remaining 59 inflows were input to the model. Descriptions of each inflow arc, as well as all other arcs making up the model network are contained in Appendix A of the " Phase 1 Feasibility Study for the Upper Gunnison-Uncompahgre Basin", Task Memo No.5, Development and Calbration of Basin Model, Comparison of Existing Supplies with Future In Basin Demands", (referred to as Phase 1 report.) The calculated inflows representing return flows from municipal and agricultural water use were located in the Uncompahgre Valley. The inflows which were input to the model were developed by Reclamation. Reclamation prepared a detailed report discussing the inflow development process along with inflow file listings. (Uper Gunnison. Uncompahgre Basin Model Inflow Development, February 1988.) Reclamation developed inflows are of three general types: historical gaged flows, virgin inflows, and virgin flow gains. Historical gaged flows or gains were used to represent the inflows from some basin tributaries. These include the area of the Uncompahgre basin from above Ridgway Dam to the South Canal (except for upper Cow Creek), the North and Smith Forks of the Gunnison River, and the gains to the Gunnison River between Delta and Grand Junction. Virgin inflows and virgin flow gains derived for the remainder of the upper Gunnison and Uncompahgre basins were developed by adjusting gaged flows at 14 reference gaging stations to reflect historical irrigation depletions and other water management influences. The resulting virgin flows at the reference stations were subsequently distributed among smaller sub-basins and tributaries to obtain the virgin inflows used as model input. A significant limitation in the scope of the modeling effort is reflecte': in the decision not to model the North and Smith Forks of the Gunnison River. The decision was made at the outset of the study to focus on water development needs and opportunities in the upper Gunnison and Uncompahgre portions of the basin. Gaged inflows from the North and Smith Forks, and from Grand Mesa tributaries, were assumed to adequately reflect water rights administration in those sub-basins.