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Last modified
7/14/2009 5:02:34 PM
Creation date
5/20/2009 3:39:59 PM
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UCREFRP
UCREFRP Catalog Number
8251
Author
Rakowski, C. L. and J. C. Schmidt.
Title
The Geomorphic Basis of Colorado Squawfish Nursery Habitat in the Green River Near Ouray, Utah.
USFW Year
1996.
USFW - Doc Type
#93-1070,
Copyright Material
NO
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<br />Draft Final Completion Report to UDWR for Contract #93-1070, Amendment 3 <br /> <br />Base Flows <br /> <br /> <br />The summer base flows for the period between 1970 and 1990 were much greater than had occurred prior to <br /> <br /> <br />construction of Flaming Gorge Dam. Since darn closure, September typically has had the lowest mean monthly <br /> <br /> <br />discharge of the year (Fig. 3), although prior to dam closure, December and January typically had the lowest mean <br /> <br /> <br />monthly discharge of the year. Prior to dam closure, September base flows were typically less than 40 m3fs (Fig. 6). <br /> <br /> <br />After closure of Flaming Gorge Dam, base flows were as high as 85 m3fs and were never less than 55 m3fs between <br /> <br /> <br />1970 and 1990 (Fig. 6). After 1990 and the adoption of the Fmal Biological Opinion for the Operation of Flaming <br /> <br /> <br />Gorge, September base flows have been about 42 m3fs. These September flows are more similar to pre-dam <br /> <br /> <br />conditions. <br /> <br /> <br />Winter base flows (i.e., December, January, and February) have also increased since closure of Flaming Gorge <br /> <br />Dam. The 5-yr moving average of the mean monthly discharge for these three months is shown in Figure 7, Since the <br /> <br /> <br />closure of Flaming Gorge Dam, the average winter discharge has more than doubled (Fig. 3), and is greater than the <br /> <br /> <br />current recommended summer discharges (31 - 51 m3fs). The current flow recommendations establish target summer <br /> <br /> <br />low flows, but allow a much greater range of winter flows (between 22.7 and 133.1 m3fs). This large range of <br /> <br />discharges ignores the fact that overwinter habitat stability and availability are components of successful recruitment. <br /> <br />4 <br /> <br />Sediment Transport <br /> <br /> <br />Within the Green River basin. the sources of water and sediment do not coincide. Most of the water originates <br /> <br /> <br />in the mountainous headwater regions, whereas most of the sediment is contributed by the lower elevation semi-arid <br /> <br /> <br />regions (Iorns and others. 1965). While the peak flows that have the capacity to transport large quantities of sediment <br /> <br /> <br />are reduced by Flaming Gorge Dam, the sediment contributions to the Green River are not strongly regulated by the dam <br /> <br />because sediment-laden tributaries enter further downstream. Consequently, the Green River downstream from the <br /> <br /> <br />umegulated Yampa River is not a sediment-starved system like the Colorado River immediately below Glen Canyon <br /> <br />Dam. <br /> <br />Sediment load has been estimated using sediment rating curves and discharge records. Andrews (1986) <br />demonstrated that the sediment rating curve near Jensen. Utah. had not changed since the closure of Flaming Gorge <br />Dam, but that peak discharge and duration of large discharges had been significantly reduced. As a consequence, the <br />mean annual sediment discharge near Jensen. Utah. had decreased by 54 percent to 2.91x109 kg. Andrews (1986) <br />
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