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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flood, and much of the gain in sand at high
elevations will be temporary.

The floods of 1983 and 1984 caused loss of
area of camping beaches, especially in narrow
reaches. Because this loss occurred even
after the system had had almost 20 years to
store sand for resupply of beaches, we
conclude that floods occurring more than once
in 20 years will cause even greater loss of
beaches unless delivery of. sand from
tributaries is exceptionally high.

(3) Flood flows may be required to move very
coarse debris brought to the river by flows
in tributaries. A large tributary debris
flow, such as that which created Crystal
Rapid in 1966, could make navigation very
hazardous. LcLrge annual floods of the
pre-dam period adjusted these deposits, eas-
ing the constriction at rapids and making
them more navigable. The size and frequency
of flows needed to remove large, newly added
debris are not known. Evidence suggests that
flows of 90,000-300,000 cfs may be required
to maintain rapids at their pre-dam condition
of navigability. These flows may very well
be above the limits of releases that would
ever be made as part of planned operations at
Glen Canyon Dam.