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Filial Report 3-36 September 2000 of ice cover in the study reach appears to follow a consistent pattern each winter. The daily release schedule of Flaming Gorge Dam, whether steady or fluctuating as a result of hydropower demand, did not appear to affect the basic outline of that pattern. During a field study in 1997, Hayse et al. (2000) compared conditions of ice cover between the downstream end of Split Mountain Canyon and the Ouray Bridge under steady flows of 69 m3/s at the Jensen gage and under fluctuating flows ranging from 48 m3/s to 99 m3/s within a single day. Stage changes measured in Reach 2 during these fluctuations in flow ranged from 24 cm at the Jensen Bridge to 6 cm at the Ouray Bridge, while a stage change of approximately 37 cm was reported at the Jensen gage for this period. At the initiation of fluctuating flows, the upstream extent of ice cover in the Green River was at RK 508.9 and had an average thickness of 21.5 cm. After several days of fluctuating flows, the upper 8 km of the ice cover broke up, but the thickness of ice in the remaining portion of the study reach did not change significantly. On the basis of field studies and an ice-process model developed for the study reach, Hayse et al. (2000) concluded that daily fluctuations within the range of hydropower operations that occurred during the winter of 1997 (22.7 to 85.0 m3/s from Flaming Gorge Dam and 48 to 99 m3/s at the Jensen gage) are unlikely to significantly affect the formation or breakup of ice covers of a comparable thickness downstream of RK 483. The results indicated that the fluctuations would have a more pronounced effect and could affect the formation and breakup of ice cover upstream of that point. Frazil ice deposits several feet thick were observed throughout an 18-km segment (RK 485 to RK 503) during the winter of 1987-1988 when releases from Flaming Gorge Dam ranged from 37 to 67 m3/s (Valdez and Masslich 1989). The principal difference in conditions between the two winters was that air temperatures during the winter of 1987-1988 were considerably colder, contributing to the heavy production of frazil ice in areas upstream of the stationary ice cover. It is likely that large fluctuations in flow during periods with heavy frazil ice production contributed to the transport and deposition of frazil ice under the upstream portion of the stationary ice cover. On the basis of ice-process modeling and field observations, Hayse et al. (2000) concluded that the deposition of frazil ice downstream of the Jensen gage would be unlikely to extend farther than approximately 16 km from the upstream edge of the ice cover during most winters. 3.6 GEOMORPHIC PROCESSES IN THE GREEN RIVER Physical attributes of the Green River and its valley affect the geomorphic consequences of Flaming Gorge Dam release patterns and other characteristics of flow. Recent research on the Green River has focused on relationships between sediment transport and channel morphology over a range of flows in different geomorphic settings. Research summarized in this section and described in abstracts in Appendix B was conducted to provide a basis for refinement of operations at Flaming Gorge Dam by describing details of channel morphology, hydraulics, and sediment transport that are important considerations in describing habitats of the endangered fishes. This section is organized according to geomorphic characteristics (channel planforms) and in-channel and floodplain processes.