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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316.6 was estimated to reproduce the stage discharge curve for the Jensen gage (Figure,l9). The
model used a Manning equation downstream boundary to calculate the normal depth at the
downstream-most cross section (located 2 miles below the Ouray Bridge at RM 246.0). Abed
slope of 0.0002 and a Manning's n of 0.035 produced the stage-discharge relationship for the
Ouray Bridge (RM 248.0) shown in Figure 20. The observed stage of 4654.4 ft MSL at a
dischazge of 15,500 cfs is from the Green River Flooded Bottomlands Investigation (FLO
Engineering, Inc., 1996).
Channel Geometry Data
FLO Engineering, Inc. provided 37 surveyed cross sections for the Green River in the
vicinity of the Ouray Wildlife Refuge Area, between RM 248 and 265. These data were in the
format of the HEC-2 water-surface profile model (U. S. Army, 1990) and were calibrated to
observed water levels at a measured flow of 15,500 cfs (FLO Engineering, Inc., 1996).
Additional surveyed cross-section data were obtained from the Bureau of Land Management
(BLM). These cross sections were also surveyed by FLO Engineering, Lic. in conjunction with
the Recovery Program's Channel monitoring Program, and were located in isolated areas
between RM 269 and 290 and in the vicinity of the Escalante Wetlands and Razorback Island
(RM 305-312). The cross-sectional geometry for the remainder of the study reach was estimated
from USGS 1:24,000 scale, 10-ft contour interval topographic maps and from depth
measurements made during the January 25-30, 1997 field study.
Calibration of UNET Unsteady Flow Model
Calibration options for the UNET model include adjustments of the channel bed
roughness, the roughness of the ice cover and the ice cover thickness. In addition, the
hydrographs of water stage simulated by the UNET model may be calibrated by making minor
' changes in the conveyance and storage capacity of selected reaches of river. Conveyance (I~ is
defined as:
1.49 ?
K= AR3
n '
where n = Mannin 's rou hness coefficient• A =flow ea• d =
g g az, an R hydraulic radius. Increasing
conveyance in a reach decreases stage while decreasing conveyance has the opposite effect.
Increasing the storage capacity of a reach delays the arrival of a flood wave at a downstream
location, while decreasing storage reduces the wave's travel time through a reach.
For the 37 surveyed cross sections in the Ouray National Wildlife Refuge Area, bed
roughnesses from the Green River Flooded Bottomlands Investigation (FLO Engineering, Inc.,
1996) were used. For the remaining upstream reaches, an estimated roughness of 0.035 was used
to represent agravel-bedded river with minor surface irregularity and gradual variation in cross
sectional geometry (Chow, 1964).
Ice cover thickness, roughness, and spatial extent for the steady flow period were selected
to represent the January 23-24, 1997 observed pre-peaking period conditions. An ice cover with
' a thickness of 0.7 ft and a roughness of 0.025 was applied to the reach from the Ouray Bridge to
IS