8270

• UCREFRP Catalog Number: 8270
• Author: Hayse, J. W., S. F. Daly, A. Tuthill, R. A. Valdez, B. Cowdell and G. Burton.
• Title: Effect of Daily Fluctuations from Flaming Gorge Dam on Ice Processes in the Green River.
• USFW Year: 2000.
• USFW - Doc Type: ANL/EA/RP-102041,
• Copyright Material: NO

observed that most of the ice cover present in late January had released or melted. The ice
motion detector located above the Bonanza Bridge (RM 290.4) recorded the timing of the ice
release to be 0335 hours on 5 February 1997. The detector located within the Ouray National
Wildlife Refuge failed to properly record the time of ice breakup.
3.2 1996-1997 FIELD MEASUREMENTS
Ice thickness and river depth data for the individual points on cross sections are shown in
the Appendix. In the downstream portion of the study reach, from the Jensen Bridge to the
Ouray Bridge, roughly half of the channel area was composed of juxtaposed frazil pans and floes
while the remaining area was thermally grown sheet ice. From the Jensen Bridge to Razorback
Island the channel gradient was steeper and the ice cover was rougher, consisting primarily of
juxtaposed frazil pans and floes, as well as unconsolidated (loose) frazil (especially in the three
upstream-most locations).
The thickness of the ice during the field study ranged from approximately 9 to 109 cm
(Table 4, Figure 37). The three greatest values for ice thickness occurred in the three upstream-
most sites prior to initiation of fluctuating flows, but the ice cover represented by these three
measurements consisted of thin layers (approximately 5-10 cm) of solid ice cover underlaid by a
thick layer of unconsolidated frazil. The three upstream-most locations no longer had intact ice
covers during the post-fluctuation measurement period and a statistical comparison of pre- and
post- peaking ice thickness measurements was not possible for these sites. For the remaining
cross sections, there was no significant difference in mean ice thickness among sections and there
was no significant difference in the mean thickness of the ice cover before and after initiation of
peaking flows (Table 5).
Figure 38 presents measurements of stage changes of water and ice surfaces under the
fluctuating flow regime for seven locations within the study area. The stage changes at the
Chew, Jensen, Bonanza, and Ouray bridges were for the surface of the open water that was
present under each of the bridges, whereas the stage changes at Dinosaur Bend, Horseshoe Bend,
and the Ouray Hatchery were for changes in the elevation of the ice surface as the propagation
wave passed underneath. The magnitude of the stage changes ranged from approximately 24 cm
at the Jensen Bridge to 6 cm at the Ouray Bridge.
Note that for the two upstream-most stations (Chew Bridge and Dinosaur Bend) the
complete ascending limb of the stage hydrograph was obtained, but not a complete descending
limb (Figure 38). The original study design for the change from steady to fluctuating releases at
Flaming Gorge Dam called for a downramp to 800 cfs followed by an upramp to 3,000 cfs (a
2,200 cfs change). Under this scenario, the field team planned to obtain data on the first
ascending limb for each of the stage measurement stations, thereby observing a maximum stage
-19-