8028

• UCREFRP Catalog Number: 8028
• Author: Daly, S. F., et al.
• Title: Effect Of Daily Fluctuations From Flaming Gorge Dam On Formation Of Ice Covers On The Green River -Draft.
• USFW Year: 1997.
• USFW - Doc Type: \
• Copyright Material: NO

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EXECUTIVE SUNIIVIARY
' 1. This report provides results and conclusions of a detailed investigation of the ice processes on
the Green River downstream of Flaming Gorge Dam with the overall goal of determining the
~ influence of daily water releases from Flaming Gorge Dam on river ice processes.
2. Historical measurements of water and air temperatures, and historical and current (winter of
1996-1997) ice observations were analyzed. Ice occurred in the Green River study reach (Ouray
Bridge, RM 250 to the Chew Bridge, RM 315) during every winter for which direct observations
were available. Historical observations of ice recorded by the USGS during discharge
measurements were found to be unreliable indicators of historical ice presence because of the
intermittent nature of the observations.
3. Formation of ice cover followed a consistent pattern during winters for which historical
observations were available. The daily release schedule of Flaming Gorge Dam, whether steady
or fluctuating as a result of hydropower demand, was found to have no apparent effect on 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 progressed upstream. Ice cover was formed primarily by juxtaposition
of floes up to RM 290. Upstream of RM 290, underturning of ice floes and a rougher ice surface
were more typical. The upstream extent of the ice cover was typically at least up to RM 302 and
often extended upstream of this point. No complete ice cover was reported upstream of Chew
Bridge (RM 316), except for short, isolated stretches during a particularly severe winter.
Apparently the river gradient is too steep to allow progression past this point during most
' winters.
4. Analysis of hydraulic conditions during the 1997 field survey indicated that daily fluctuations
of releases from Flaming Gorge Dam have little effect on hydraulic conditions in the Green River
downstream of RM 300 (Jensen Bridge). Thus, daily fluctuations are unlikely to affect ice cover
formation downstream of this point to any significant degree. Upstream of the Jensen Bridge
daily fluctuations have a more pronounced effect and can affect ice cover formation.
5. The primary result of daily fluctuations in flow is probably to transport frazil ice beneath the
ice cover in the reach above the Jensen Bridge. As formation of the ice cover progresses
upstream from the Jensen Bridge, deposition of frazil ice caused by the daily fluctuations results
in an ice cover thicker than ice covers that occur through this reach under steady flow. Frazil
depositions several feet thick were observed in this reach during the winter of 1987-88 when
water releases from Flaming Gorge Dam fluctuated daily. The ice cover that developed in this
reach under conditions of steady flow during the 1997 field survey was about 0.8 feet thick.
6. A nume 'cal v
n model of dynamic ice formation m the Green River was de eloped and used to
simulate ice cover formation on the Green River for the winters of 1989-90 through 1995-96.
The ice model results were in general agreement with historical ice observations.
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