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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frazil transport beneath the cover would have provided the cover with increased strength, and
produced a cover strong enough to resist the stresses induced by the fluctuations.
A numerical model of dynamic ice formation in the Green River was developed and used
to simulate the ice cover formation on the Green River for the winters 1989-90 through 1995-96.
The ice model results are in general agreement with the historical ice observations and indicate
the model could be used to evaluate the condition of the ice cover in the study area of the Green
River under a given set of meteorological and hydrological conditions. However, collection of
additional data pertaining to ice formation and breakup in the Green River would be useful for
improving calibration of the flow and ice formation models and would also allow the results of
the models to be validated. In addition, we recommend that steps be taken to provide for
collection of accurate water temperature data within the study reach. Currently the USGS has
stopped collecting water temperatures at the Jensen gaging station. Such information would be
extremely important for future improvements to the ice process models and would also provide
information about the environmental conditions that endangered fishes encounter within the
study reach.
This study provided insights into the relationship between river hydrology, ice processes,
and dam operations. Our results indicate that daily hydropower operations at Flaming Gorge
Dam have little appreciable effect on hydrology and ice processes downstream of the Jensen
Bridge (RM 300). This suggests that, except for the volume of releases, daily fluctuations from
hydropower generation at Flaming Gorge Dam do not appreciably affect river stage or ice
formation and breakup in portions of the Green River containing the primary nursery areas for
Colorado squawfish and used by overwintering adult Colorado squawfish and razorback suckers
(Chew Bridge to Sand Wash). While this suggests that Flaming Gorge Dam is unlikely to be
responsible for changes in ice conditions encountered by adult Colorado squawfish and razorback
suckers that are likely to be found in main channel habitats, we advise caution in reaching the
conclusion that unrestricted dam operations will not detrimentally affect age-0 Colorado
squawfish. Backwater habitats used as nursery habitats by age-0 fish are very susceptible to
inundation and desiccation because of their shallow nature and low-lying sand berms. Additional
investigations aze recommended to characterize conditions in these habitats during winters in
order to better understand the full array of conditions faced by fish during their first winter of
life.
Valdez et al. (1995) reported an average decrease of about 39°Io in the catch rate of age-0
Colorado squawfish from fall (October) to spring (March-April), and hypothesized that winter
ice conditions were negatively affecting backwater nursery habitats. The current study suggests
that dam operations have little effect on ice conditions downstream of the Jensen Bridge, which
is the primary nursery area. If this is true, then perhaps other environmental parameters aze
responsible for the observed decreases in catch rates between fall and spring sampling periods.
One hypothesis is that the age-0 squawfish are passively or actively transported downstream
during the short, but intense, flow spates that occur in March (Figure 4), when nursery
backwaters become inundated. By this time, the young fish are 30-50 mm long and, perhaps,
warming temperatures and rising flows of spring prompt a behavioral response by the young of
this potomadromous species to migrate downstream to warmer, more productive waters. If this
is the case, then overwinter survival estimates from previous studies may have been
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