7423

• UCREFRP Catalog Number: 7423
• Author: U.S. Bureau of Reclamation.
• Title: Glen Canyon Environmental Studies Draft Report, September 1987.
• USFW Year: 1987.
• USFW - Doc Type: Washington, D.C.
• Copyright Material: NO

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Little Colorado River at its confluence with the
mainstem.

The GCES data indicate that current operations do not
appear to have a deleterious impact on the humpback
chub population in the Little Colorado River. Modified
operations might increase chub population size in this
area. However, there do not appear to be any op-
erational schemes that would increase the range of the
chub and therefore reduce its current dependence on the
small area of critical habitat in the mouth of the
Little Colorado River. The FWS is currently developing
a new biological opinion on the impact of Glen Canyon
Dam operations on downstream endangered species.

Our Understanding of the Relationships Between
Dam operations And Downstream Resources Is Not
Complete

The limited time available for the studies increases
the uncertainty of long-term predictions made from data
collected during the study. The coincidence of the
GCES with high flows that were not typical of pre-1983
releases limited our ability to determine the response
of resources to low and fluctuating flows. These high
releases required major changes in research design as
the studies were in progress. However, we believe that
the uncertainties in data and gaps in our knowledge
would not change the conclusions that dam operations
affect downstream resources and that modified
operations would better protect resources.

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