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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eliminated, the long period of maximum powerplant flows
under current operations. The resulting amount of sand
stored in the main channel would be less than under
current operations, making beaches more vulnerable to
erosion. Also, the change each year from low to high
flows would produce unstable beaches, and might result
in a higher rate of erosion than under current condi-
tions (See Appendix A, section V.)

Terrestrial vegetation and wildlife both would benefit
under the chub scenario when compared to current
operations, which include flooding. The major
long-term benefit to vegetation would be protection
from physical removal and substrate loss similar to
that which occurred following the flood releases in
1983, 1984, 1985, and 1986. However, possible
long-term loss of beaches could lead to some loss of
vegetation and wildlife populations.

Releases For COMMON NATIVE FISH Have Strong
Negative Effects On White-water Boating

The common native fish scenario (Figure VII-2) is based
on the evidence that the largest number of backwaters
are available at relatively low flows (5,000 cfs).
Therefore, low flows from June to August would increase
the availability of backwater habitats during the
vulnerable rearing period over those available under
current operations. The remaining water is evenly dis-
tributed from September through May. Preliminary
research has shown that flows of 5,000 cfs can triple
the number of available backwaters compared to flows of
28,000 cfs (Appendis B, Section V). It is possible
that a similar number of backwaters would be available
under flows higher than 5,000 cfs. Additional surveys
of backwater numbers at different flow levels are
needed to refine this scenario.

The number of backwaters is increased if low flows are
preceded by steady flows because sandbars deposited in
eddies show more topographic relief under these
conditions and more backwaters form when flows are
dropped (Appendix A, section II). Fluctuations
continually change the depth, temperature, and velocity
of backwaters, forcing larval fish to either move into
the mainstem river or be stranded and die.