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

HYDRAULIC CONDITIONS IN THE GREEN RIVER DURING THE 1997
FIELD SURVEY
Introduction
In order to understand the influence of the Flaming Gorge Dam release pattern on the
river ice processes, the hydraulic conditions were examined throughout the study reach for two
alternate release schedules. In the first schedule, the releases were held constant for a number of
days. In the second schedule, the releases were varied each day in response to the demand for
hydropower. Given the restrictions on time for this study, the extent of the study reach of the
Green River, and the remoteness of the location, it was not possible to directly measure the
hydraulic conditions throughout the study reach. Rather aone-dimensional, unsteady flow,
numerical model of the Green River was developed to estimate hydraulic conditions. The model
used continuity and momentum equations to describe river flow in finite difference form. The
model solved these equations for each river cross section through multiple time steps. The model
used surveyed or estimated Green River geometry to calculate discharge and stage at every cross
section of the river as a function of time, using the observed upstream discharge as input. The
model was calibrated to match the water surface response to each alternate release schedule
observed during the field survey.
Calibration of the Unsteady Flow Model
The UNET one-dimensional unsteady flow model (U. S. Army, 1995) was calibrated to
steady flow data from the Green River Flooded Bottomlands Investigation (FLO Engineering,
Inc., 1996) and the observed stage hydrographs collected during the January 25-29, 1997 peaking
period. The UNET model simulates unsteady flow in a river channel through solution of the
complete one-dimensional continuity and momentum equations. The equations are solved using
the four-point, implicit, finite difference scheme. The model uses the actual surveyed and
estimated river cross sections, as described below, to represent the river channel. The model
time step can be adjusted by the user. In the results presented here, a 30-nninute time step was
used. The UNET model can also simulate a floating, stationary ice cover with known thickness
and roughness. The composite roughness of the river channel is found by combining the
roughness of the channel bed and the ice cover using the method of Sabaneev (Ashton, 1986).
The model also accounts for the cross-sectional area of the flow blocked by the ice and the
reduction in the hydraulic radius caused by the increase in wetted perimeter due to the ice cover.
A number of different boundary conditions can be set by the user for the upstream and
downstream limits of the channel. In the present case, a known time-varying discharge was
proscribed at the upstream end of the channel and normal depth was set at the downstream end.
Boundary Conditions
The upstream boundary of the model was the observed discharge hydrograph at the USGS
Jensen gage (RM 316.6) for the January 25-30, 1997 period. Because no surveyed channel cross-
section data were available for the upstream end of the study reach, the channel geometry at RM
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