7758

• UCREFRP Catalog Number: 7758
• Author: Stanford, J. A. and P. C. Nelson.
• Title: Instream Flows to Assist the Recovery of Endangered Fishes of the Upper Colorado River Basin.
• USFW Year: 1994.
• USFW - Doc Type: Denver, Colorado.
• Copyright Material: NO

12 BIOLOGICAL REPORT 24
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cEi 250
v
d
t 200
U
N_
0 150
100
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HB-Spawn 18'. q,
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CS-Spawn
Mar May Jul Sep Nov Jan Mar
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10
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4 C
Fig. 6. Generalized relationship between average daily flows in the Green River (Jensen gauge: 1980-91), river
temperatures (° C), and the timing of life history events of squawfish (CS), humpback chub (HC), and razorback
sucker (RZ) (modified from fyus 1990, Tyus and Karp 1991, flow data from U.S. Geological Survey).
involve the frequency and duration of high velocity,
peak flows and associated flux of sediment through
the stream segment (cf., Andrews and Nelson
1989). Hence, occurrence of low velocity habitats is
dynamic in space and time and strongly linked
to the flow regime, sediment supply, and chan-
nel morphology. Numbers and area of low velocity
environments used by squawfish larvae, juveniles,
and sometimes adults in the alluvial Jensen and
Ouray areas of the Green River (Tyus and Haines
1991) apparently are maximized at a given time at
river discharge of 1,381 cfs (numbers) or 1,687 cfs
(area; Pucherelli et al. 1990). However, a river
stage-backwater relationship observed in a par-
ticular year is determined by the volume and dura-
tion of the peak flow events that occurred during
spring runoff or other intense spates in that year or
in the year or two immediately preceding the meas-
urements. Instream flows designed to provide
maximum access for endangered fishes to low ve-
locity habitats must be based on long-term meas-
ures of the relation between peak flows and channel
and backwater configuration, even in river seg-
ments where delivery of sediments is equal to ex-
port (quasi-equilibrium systems). This is especially
true in alluvial segments that may be aggrading,
as in the Escalante Bottom and Ouray areas of the
Green River (Andrews 1986), because channel con-
figurations may change significantly in response to
variable peak flows. As the channel morphology
changes from year to year, a given discharge will
vary in its inundation of backwaters and bottom-
lands, which can profoundly influence fishes and
other biota that must move into backwaters,
flooded bottomlands, and other low velocity habi-
tats from the channel and back again in short (diel)
and long (seasonal) time frames. Therefore, efforts
to build process-response models of flow and physi-
cal habitat relationships (e.g., Harvey et al. in
press) must take into account that flow and sub-
stratum relations in most riverine environments
are stochastic and cannot accurately be described
by linear or logistic functions. Indeed, complex
channels that promote occurrence of low velocity
habitats are virtually always characterized by
nonuniform flows in time and space, whereas many
models often assume uniform flow.
Given that a relationship exists between flow
dynamics and availability of various physical habi-
tats preferred by the fish, what role do these habi-
tats play in the trophic ecology of the river? Except
during periods of high turbidity, the rivers in the