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. -, 13 EFFECTS OF THE PROPOSED ACTION Flow Analvsis To determine the effects of the proposed action, an analysis of flow changes was conducted in accordance with the final rule implementing Section 7 of the Endangered Species Act (50 CFR 402). Four levels of water development for the Colorado River were simulated using a computer-based hydrologic model. The ~del used MaS HYDROSS, an accounting type model developed by Reclamation. The levels of water development used in the analysis are as enumerated below: 1. Existillg conditions; 2. Present RIldifi ed; 3. Environmental baseline (post Williams Fork); and 4. EnvinHEental baseline with Muddy Creek depletions. The existing amditions of development were simulated by operating HYOROSS with U.S. Geological Survey gauge data substituted for the HYDROSS natural flow data base at Cameo on the Colorado River and near Grand Junction on the Gunnison River. HYD~ was then operated to reflect historic diversions during the peri od 1952 to 1982. The present lOdified condition reflects the operation of all existing Federal and private pnijects in the study area. Specifically, the analysis consisted of operating the entire HYDROSS network. for the 1952 to 1982 period with depletion levels on all diversions set to the level they were in the 1982 to 1984 period, or at projected levels for those projects not operating in 1982 to 1984. One difference between these flow conditions and actual U.S. Geological Survey gauge data for the period is that each project was operated assuming full development of existing water rights. All projects were operated according to their water right priority and, when there was insufficient water in the stream, they were shorted accordingly. Simulation of maximum project operation represents the cumulative effects of future State or private actions that are reasonably certain to occur. Flow additiOllS to RIldeled reaches between existing and present modified conditions can be attributed to the construction and operation of large reservoirs, ~ as Ruedi and Aspinall Units, in upstream reaches. These reservoirs ~ress peak runoff flows in April, May, and June by storing water during those IIlIltllS. The water is then redistributed and released during other ~nths, dependlllg on demand and/or operating criteria for the reservoir. Flow additions In ~er, December, January, and February can be attributed to releases made ftrpower production, flood control, and maintenance of instream flows. AgriQlltural diversions typically operate from April through October while indusUial and municipal demands contribute to reductions seen in July, August, Sep~. and October.