9708

• UCREFRP Catalog Number: 9708
• Author: Grand, T.C., S.F. Railsback, J.W. Hayse and K.E. LaGory.
• Title: A physical habitat model for predicting the effects of flow fluctuations in nursery habitats of the endangered Colorado pikeminnow ‎(Ptychocheilus lucius)‎.
• USFW Year: 2006.
• USFW - Doc Type: River Research and Applications
• Copyright Material: YES

1136 T, c. GRAND ET AL
40 (a) Backwater S
- Predicted
-- Observed
- 30
0
0
-
Cl) 20
...
:::J
...
l!!
Cl) 10
Q.
E
~
0
17-Aug 6-Sep 26-Sep 16-0ct S-Nov
Date
40 (b) Backwater 6
- 30
0
0
-
Cl)
... 20
:::J
...
III
...
Cl) 10
Q.
E
Cl)
.... 0
17-Aug 6-Sep 26-Sep 16-Oct S-Nov
Date

Figure 6, Observed and predicted water temperatures CC) in backwaters 5 (a) and 6 (b) from 22 August 22 to 26 October 2003

As expected from Equation (3), increasing temperature resulted in an initial increase in invertebrate availability
between 0 and 22"C, followed by a decrease as backwater temperature rose further (Figure 5). As indicated by the
significant interaction between fluctuation magnitude and backwater temperature (see statistics above) the
magnitude of the decline in invertebrate availability at temperatures greater than 22"C tended to decrease with
increasing within-day flow fluctuations (Figure 5),
In general, d; (the density of invertebrates available for consumption) tends to decrease with increases in Ie (the
flushing calibration parameter), However, the effect of Ie depends upon themagnirude of the flow fluctuation, As within-
day flow fluctuations increase in magnitude, the suppressive effect of.f~ on invertebrate availability also increases,
resulting in the lowest invertebrate availability when flow fluctuations are great and Ie is equal to one (Figure 5e),
We used a value of Ie equal to 0,25 for the remainder of our analyses, because it should provide a conservative
assessment of flow fluctuation effects (i,e, it overestimates the effects of flow fluctuations), Most of the invertebrate
biomass is assumed to be benthic, having physical structures that enable them to cling to substrates and resist
downstream flushing (Swtzner and Holm, 1982); but some of the food biomass could be free-swimming or planktonic,

Flow.fluctuation simulations

Backwater temperature. Despite differences among backwat.ers in shape and topography (Table I), temperatures
in the six backwaters differed very little in their responses to within-day flow fluctuations (Figure 7), As the
magnitude of flow variation increased from 0 to ::l40% of the mean daily flow, mean daily backwat.er temperatures
declined only slightly (i.e, by only 2 or 30C), despite exchanging up to 60% of the mean daily volume with the
mainstem (Figure 8), The temperature in larger backwaters appears to be more affected by flow variation than
smaller backwaters, Typically, temperature effects were most pronounced during the warmer months (July and
August), when temperature differences between the air and the main stem were greatest. Within the range of
fluctuat.ions actually observed in the Green River, the model predicts effects on temperature to be negligible.
Backwater area, Minimum daily wetted area was greatly affected by the magnitude of within-day flow
fluctuations; however, the magnitude depended on which backwater was considered (Figure 9), As flow fluctuations
.

Copyright ((.' 2006 John Wiley & Sons, Ltd,

River Res, Applic, 22: 1125-1142 (2006)
DOI: J(),lO02/rra