7752

• UCREFRP Catalog Number: 7752
• Author: Stanford, J. A.
• Title: Instream Flows to Assist the Recovery of Endangered Fishes of the Upper Colorado River Basin
• USFW Year: 1993.
• USFW - Doc Type: Review and Synthesis of Ecological Information, Issues, Methods and Rationale.
• Copyright Material: NO

Therefore, I support the recommendation in principle, but the historical baseline used to
derive mean monthly flows appears to be incorrect Depletions in the Yampa River currently are
ca. 110,000 cfs (Figure 7, Brendecke 1993), not 68,000 cfs. I also do not think it is appropriate to
use monthly means in such analyses because daily flow variation is a very important,~omponent of
river ecology. The daily flow duration curve for the period of record would more accurately reflect
the real baseline. Moreover, if natural seasonal and daily flow variations are vital to the fishes, then
the natural diel and daily flow variation observed in the Yampa River should provide a basis for
designing more benign flows in the regulated Green River.

Green River
Recommendations on the Green River were based on inferences from ecological studies of
the endangered fish, which I summarized above (not necessarily in support of the recommended
flows) and the backwater area to discharge relationship determined by Pucherelli et al. (1990). The
main intent of the peak flow recommendation by the U.S. Fish and Wildlife Service apparently was
to add volume to the peak flows derived from the Yampa River to create an annual spring peak
sufficient to flood and maintain connectivity of the channel to backwater environments and
floodplain wetlands in the alluvial reaches near Jensen and downstream.
Rationale for duration and amplitude of the spring peak was not given, except with regard to
constraints on releases at Flaming Gorge Dam (Le., only 4,000 cfs can be discharged through the
generators plus an additional 4,000 cfs can be passed through bypass or jet tubes without opening
flood gates). The fact that the Yampa and Green Rivers historically peaked at different times was
not clearly addressed, nor were the proposed ramping rates on the rising and falling limbs of the
hydro graph in either the context of the discharge to backwater area relationship of Pucherelli et al.
(1990) or the need to establish ecologically functional wetlands on the floodplain (e.g., flooded
bottomlands at Escalante Bottom). The 1992 spring flow~ followed the hydro graph recommended
in the Biological Opinion (Figure 17).

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