8182

• UCREFRP Catalog Number: 8182
• Author: Bestgen, K. R. and L. W. Crist.
• Title: Response of the Green River Fish Community to Construction and Re-regulation of Flaming Gorge Dam. 1962-1996\
• USFW Year: 2000.
• Copyright Material: NO

evenly-spaced sites. Global models were built; best-fit models had the highest RZ and the fewest
number of parameters.
The model developed for the Green River in lower Browns Park was used for two
additional purposes. First, daily summer water temperature predictions for the 1992-1996 period
were estimated using annual air and discharge measurements as independent variables. Accuracy
of model predictions for each year was determined by comparing independent observations of
daily water temperature (G. Smith, USFWS, unpublished data) collected about 10 km upstream
at BPNWR. Water temperatures averaged 0.8°C cooler there than at lower Browns Park in the
summers of 1994 and 1995. Therefore, that value was added to BPNWR observations in all
years to make comparisons with lower Browns Park model predictions realistic.
Another purpose of the lower Browns Park model was to predict water temperatures
under high (50 m3/s), moderate (37.5 m3/s), and low summer base flows (25 m3/s). This site was
chosen because it is upstream from where most native and endangered fishes were thought to
occur. In all scenarios, flow declined from high levels in early-June to 50 m3/s by 1 July and, in
the high base flow scenario, remained at that level for the remainder of the summer. In moderate
and low flow scenarios, target base flow was achieved by 15 July. Those base flow scenarios
were within the summer discharge range used to construct the model and represented realistic
operational scenarios for water levels discharged from Flaming Gorge Dam from 1992 to 1996.
Mean daily air temperature for the period of record at BPNWR was the other independent
variable. Predicted and observed water temperatures and discharge regimes for the Green River
at lower Browns Park were compared with similar observations for the unregulated Yampa River
where a reproducing population of Colorado pikeminnow existed (Bestgen et al. 1998).
Predicted water temperatures were compared among all three models to understand
temperature levels and warming rates of the Green River under different summer discharge
regimes. In those scenarios, air temperature was held at a constant 19.3°C, the mean daily
average from June through August over the period of record (N. Doesken, Dept. of Atmospheric
Science, Colorado State Univ., unpublished data).
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