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SUMMARY OF RESULTS This study was a detailed investigation of the ice processes on the Green River downstream of Flaming Gorge Dam. The overall goal of the study was to assess the influence of the daily release schedule of Flaming Gorge Dam on the river ice processes. The first step was to analyze historical measurements of water temperature and air temperature, and ice observations. The water temperature entering the study reach (Ouray Bridge, RM 250 to the Chew Bridge, RM 315) was often at 32°F during the winter, and the daily average air temperatures were consistently below 32°F throughout December, January, and most of February. These are appropriate conditions to expect ice to form and, in fact, ice was observed in the Green River study reach during every winter for which records were available. The USGS observations of ice, made in conjunction with their discharge measurements at Jensen, are confounded by the discharge measurement schedule and were not reliable indicators of historical ice presence. Formation of ice cover in the Green River study reach followed a consistent pattern each winter and 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 this pattern. The initial ice observed each winter was frazil ice, transported at the water surface in the form of slush, floes, and pancake ice. A stationary ice cover formed initially near the Ouray Bridge and then progressed upstream. The ice cover was formed primarily by the juxtaposition of floes up to RM 290. Underturning of ice floes and a rougher ice surface seem to be more typical upstream of this point. The upstream extent of the ice cover was typically reported as at least RM 302 and often extended upstream of this point. No ice cover progression has been reported between Chew Bridge (RM 316) and Split Mountain, except for short, isolated stretches during a particularly severe winter. Apparently the river gradient is too steep to allow progression past this point. Analysis of the data collected during the 1997 field survey indicated that daily fluctuations in releases from Flaming Gorge Dam have minimal effect on the hydraulic conditions in the Green River downstream of RM 300 (Jensen Bridge). As a result, daily fluctuations are unlikely to affect the formation of ice cover downstream of this point to any significant degree. Upstream of this point the fluctuations could have a more pronounced effect and can affect the formation of ice cover. -The primary result of daily fluctuations would be to transport frazil ice beneath the ice cover in the reach above the Jensen Bridge. As the cover progresses upstream above Jensen Bridge, the deposition of frazil ice caused by the daily fluctuations would result in an ice cover thicker than would develop in this reach under steady flow. Frazil depositions several feet thick were observed throughout an I 1-mile reach (RM 305 to RM 316) during the winter of 1987-88 when Flaming Gorge Dam was operating under a regime of fluctuating releases. An ice cover that progressed through this reach under conditions of steady flow was observed to have a thickness of about 0.8 feet during the 1997 field survey. The upstream five miles of this ice cover was observed to collapse during the 1997 field measurements shortly after releases from Flaming Gorge Dam began fluctuating on a daily basis. The ice cover was apparently not strong enough to resist the increase in stress caused by the fluctuations in this reach. If the ice cover had propagated upstream during a fluctuating regime, however, the increased thickness caused by 20 n 1 1 1