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Last modified
7/14/2009 5:02:33 PM
Creation date
5/22/2009 4:57:14 PM
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UCREFRP
UCREFRP Catalog Number
8188
Author
Muth, R. T., et al.
Title
Flow and Temperature Recommendations for Endangered Fishes in the Green River Downstream of Flaming Forge Dam.
USFW Year
2000.
USFW - Doc Type
\
Copyright Material
NO
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<br />Final Report <br /> <br />3-14 <br /> <br />September 2000 <br /> <br />3.4.1 Seasonal Distribution of Green River Flows <br /> <br />Flow in the Green River is dominated by snowmelt; consequently, there was a great deal <br />of seasonal variability in the unregulated flow regime. To quantify how this variability has been <br />affected by regulation, a comparison was made between the monthly distribution of regulated and <br />unregulated flow in the three reaches; data used were from 1963 to 1996. These data are presented <br />in Figure 3.6, and the percentage change in mean monthly flow due to regulation is presented in <br />Table 3.4. <br /> <br />Regulation has resulted in a reduction of flows from April through July and an increase in <br />flows from August through March. Reach 1, whose flow is dominated by releases from Flaming <br />Gorge Dam, has been most affected. The effects of regulation have been reduced in Reaches 2 and <br />3, since intervening tributaries, especially the Yampa River, contribute flows whose seasonal <br />distributions have been less affected by regulation. Nevertheless, flow variability in the system has <br />been reduced in all three reaches. <br /> <br />3.4.2 Peak Flows in the Green River <br /> <br />Regulation has resulted in a substantial reduction in the magnitude of spring peak flows. <br />Before construction of Flaming Gorge Dam, median spring peak flows were about 330 m3/s <br />(Figure 3.7), but they were reduced to about 85 m3/s after the dam was built. Only five occurrences <br />of releases greater than 200 m3/s have occurred since construction of the dam was completed in 1962 <br />(1983, 1984, 1986, 1997, 1999). Daily time-series data for 1963 to 1996 were used4 to compare <br />measured regulated peak flows to estimated unregulated peak flows. For all but measured flows at <br />the Greendale gage, log Pearson ill distributions were created to enable comparisons of specific <br />exceedance periods. For flows at Greendale, effects of Flaming Gorge Dam preclude the use of a log <br />Pearson ill distribution. For these data, a distribution was created by ranking values. <br /> <br />The frequency of high peak flows has been reduced significantly by regulation (Figure 3.8). <br />The discrepancy between regulated and unregulated flows is greatest in Reach 1, with effects of <br />regulation diminishing downstream. Table 3.5 presents the same data, showing specific flow values <br />and recurrence intervals for the corresponding exceedance levels. At the Jensen gage, the median <br />peak flow is 669 m3/s without regulation and 448 m3/s with regulation. At the Green River gage, the <br />median peak flow has been reduced from 788 to 575 m3/s. The percent reduction in peak flow <br />between unregulated and regulated conditions is shown in Table 3.6. <br /> <br />4IdealIy, instantaneous peak flows would have been used in this analysis, but the simulation of unregulated <br />instantaneous peak flows is not feasible. However, the difference between daily average peak flows and instantaneous <br />peak flows is not great. From 1963 to 1996, the instantaneous peak flow at the Jensen gage was calculated to be only <br />3.8% higher than the daily average peak flow; consequently, daily average peaks adequately convey the character of <br />peak flows in the Green River basin. <br />
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