Flow and Temperature Recommendations for Endangered Fishes in ...

Final Report 3-27 September 2000
Green and Duchesne Rivers. Like the Yampa River, the White River is not significantly regulated.
However, the yield of the White River basin is only about one third that of the Yampa River.
Both the Price and San Rafael Rivers originate in the Wasatch Plateau in the central part
of Utah. Each river flows southeast to join the Green River near Green River, Utah. Although these
two rivers are the largest tributaries in the 393-km area downstream of Ouray, Utah, their combined
contribution is only 4% to the entire flow of the Green River.
Scofield Reservoir in the Price River basin and Joe’s Valley Reservoir in the San Rafael
River basin regulate the flows of these two rivers. Peak flows (Table 3.9) generally occur in late
summer, either as a result of runoff from intense summer thunderstorms or releases from upstream
storage.
3.4.5 Stage-Flow Relationships and the Effect of Hydropower Operations on Daily
Fluctuations
Water-surface elevation (stage) is dependent on flow, but the nature of that relationship
varies along the river and is strongly influenced by channel morphology. Stage-flow relationships
at the Greendale, Jensen, and Green River gages are presented in Figure 3.13. This figure illustrates
the differences in the relationship at these different locations and the asymptotic nature of each
relationship; i.e., as flow increases, the relative incremental increase in stage lessens. Differences in
channel width and floodplain characteristics at each location are reflected in the shape of the curves
depicted in Figure 3.13. The river is considerably wider at the Jensen and Green River gages than
at Greendale; consequently, as flow increases at Jensen and Green River, the rate of stage change
is less than the rate at Greendale.
Variations in channel morphology along the river and tributary inputs serve to dampen flow
and stage fluctuations that result from hydropower operations at Flaming Gorge Dam. The degree
of attenuation of operations-induced fluctuations also depends on specific release parameters,
including the ramp rate (the rate of change from minimum and maximum flow expressed as m 3 /s/h),
minimum and maximum flow levels, and duration of peak releases. This dampening or attenuation
becomes greater at increasing distances from the dam until operations-induced fluctuations are no
longer detectable.
Operations-induced fluctuations in flow and stage are thought to be important to endangered
fishes because changes in these parameters can result in changes in the availability and quality of
low-velocity habitats (Hlohowskyj and Hayse 1995). Fluctuations have obvious adverse effects if
they are of sufficient magnitude and frequency to empty and fill important habitats on a daily basis.
Adverse effects at lower fluctuation levels could result if fluctuations significantly reduced water
temperatures and productivity within the habitat or caused fish to expend excess energy during
winter. These effects are discussed further in Chapter 4.