7371

• UCREFRP Catalog Number: 7371
• Author: Stalnaker, C. B., R. T. Milhous and K. D. Bovee.
• Title: Hydrology and Hydraulics Applied to Fishery Management in Large Rivers.
• USFW Year: 1989.
• USFW - Doc Type: D. P. Dodge, ed. September 14-21, 1986.
• Copyright Material: YES

travel time throu~h the side channel. the water at its lower
end might be considerahlv warmer. One solution is to treat
the sid~ channel as an independent stream. By determining
the inlet temperature and side channel flow from indepen-
dent one-dimensional models of the main body of the river.
a simple temperature model can be used to calculate temper-
atures in the side channel.
Some backwaters meet none of the descriptions given
above, but are formed as depressions along the bank or on
the lee sides of point bars in the river. In such areas, the
concentrations of dissolved chemicals may be very close to
those in the main channel, and a one dimensional water qual-
ity model may be totally adequate. However, if there is con-
siderable disparity. between the temperature measured in
these backwaters and in the main channel, a combination of
theory and empiricism may be required. The simplest con-
ceptual approach is to develop a series of monthly or sea-
sonal regressions between the temperature in the backwater
and the average temperature ofthe main channel. Then, by
using a physical process model on the main stream, one can
predict the average temperature at the longitudinal location
of the backwater. The backwater temperature. can then be
estimated by using the appropriate regression. Use of this
approach dictates accounting for local channel features such
as orientation, topographic shading (e.g., canyon walls),
and vegetation that affect the amount of sunlight reaching
a specific area of stream. If these variables are not accounted
for, it is unlikely that a consistent relation will be found
between main channel and backwater temperature. Either
the data must be stratified according to similar topographic
features, or they must be entered as variables in a multiple
regression equation.

Simulations in Specialized Habitats

Side Channels - We illustrate the procedures used in the
analysis of side channel habitats by referring to the Palisade
site on the Colorado River near Grand Junction, Colorado.
The river in this vicinity is typified by repetitive cycles con-
sisting of a small rapids, a long deep pool, and an island with
a divided flow section (Fig. 4). The species of interest in
this section is the Colorado squaw fish (Prychocheilus
lucius), which uses a variety of microhabitat types at various
phases of its life history. Although the adults are believed
to spawn over coarse substrates in fast water, they otherwise
live in deep pools and eddies. Shallow backwaters are
apparently necessary for rearing young squawfish (Tyus et
al. 1984; USFWS 1985)4. Ail of these habitat types are
present at the Palisade site, but most of the shallow back-
water habitat is associated with the small side channel on
the southeast side of the island (Fig. 4). The morphology
of the side channel is similar to that of a small stream, with
a riffle-pool sequence repeating about every 100 m. (The
distance between riffles and pools in the main channel is
more nearly 2000 m.)
Most hydraulic simulations must be started at a hydraulic
control, a physical feature in the channel that establishes the
stage-discharge relation for an upsteam section of river.
However, the first side channel transect (i.e., the south end

4 U.S. fish and Wildlife Service. 1985. Unpublished data.
Regional Office, U.S, Fish and Wildlife Service, Denver, CO.

20

Gravel Road

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LEGEND

o Benchmark
. Headpin
- Transect

FrG, 4. A microhabitat study site on the Colorado River showing
transects, benchmarks, and headpin locations.

of transect 5 in Fig. 4) is a variable backwater; the stage
at this location is determined by the stage at transect 4,
which is ultimately controlled at transect 1. There is a clear
division of flow between the north and south ends of transect
5. The water surface elevation is about 0.5 m higher on the
north side than on the south side. To enable treatment of the
side channel as a separate stream, the stage-discharge rela-
tionship at transect 5 was determined empirically. Once this
determination was made, a starting water surface elevation
was known, and the hydraulic simulation could proceed.
The second relation that was needed was the amount of dis-
charge in the side channel, during different discharges in the
main channel. Transect 7 on the main channel and transect
H on the side channel were placed to determine the total dis-
charge at which flow into the side channel ceased. The rela-
tion between discharge of the side channel and of the main
channel is shown in Fig. 5.

6

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TOTAL DISCHARGE Cm3.s-1)

FIG. 5. Relation between total discharge and side channel dis-
charge at Palisade site, Colorado River.

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