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change. However, due to miscommunication at the power scheduling office, the upramp portion of the first peaking cycle at Flaming Gorge Dam went from approximately 1,500 cfs to 3,000 cfs, a 1,500 cfs change. After the error was identified, the field sampling was modified to measure the fluctuations associated with the first decrease in dam releases from 3,000 cfs to 800 cfs at the five remaining stage measurement locations, although it was too late to measure the same wave at the two upper-most stations. The stage change for Chew Bridge and Dinosaur Bend would undoubtedly have been larger if the stage changes associated with the descending limb of the first peaking cycle had been measured. 3.3 MODELING RESULTS The extent of ice cover predicted by the ice process model for the winter of 1989-1990 through the winter of 1995-1996 is shown in Figures 39-45, along with the measured daily average air temperature for Vernal, Utah. Modeled results were in general agreement with the historical ice observations. The model predicted formation of a stationary ice cover in the Green River every winter and indicated that the ice cover progressed upstream relatively quickly during cold periods. The modeled ice cover progressed upstream as far as RM 300 almost every winter. However, there was a large variation in the length of time each winter that the ice cover was predicted to remain at this location. During colder winters it was predicted that the ice cover would extend past RM 300 for several months. During milder winters, the ice cover would extend past RM 300 for two weeks or less. 3.4 RIVER HYDRAULIC CONDITIONS: COMPARISON OF STEADY AND UNSTEADY FLOWS Using the unsteady flow model described in Section 2.4.1, the hydraulic parameters of flow depth, flow velocity, and Froude number throughout the Green River study reach were compared under the steady and fluctuating flows that occurred during the 1997 field study. The results for steady flow are listed in Table 6. At the end of the steady flow period, the releases from Flaming Gorge Dam were fluctuated in a typical peaking hydropower pattern and the resulting flows passed through the study reach in a series of peaks and troughs (Figure 18). Hydraulic parameters were estimated for the first peak (Table 7), the first trough (Table 8), the lowest recorded trough (Table 9), and the highest recorded peak (Table 10). The variation in depth between the steady and the fluctuating flows was smallest downstream of RM 280 (+/- 3 cm), moderate between RM 280 and 300 (+/- 8 cm), and largest between RM 300 and 316 (+/- 30 cm). There was a difference in flow velocity of about ± 5 percent between the steady and fluctuating flows downstream of RM 302 and f 15 percent between RM 300 and 316. The change in Froude number (a measure of the hydraulic forces affecting ice formation and breakup) between the steady and the fluctuating flows was f 0.05 downstream of RM 300 and -20-