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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sand at elevations above the 3l,500 cfs level if sand
is in sufficient supply, initiation of fluctuating
flows or lower steady flows after these floods will
cause loss of the newly-deposited sand throughout the
canyon. Loss will be greatest in narrow reaches,
where competition for campsites is keenest.
Redistribution of sand by fluctuating flow may reduce
the area and depth of backwaters. (See Appendix A,
Section II.)

IMPACT OF YEAR - ROUND FLUCTUATIONS
ON RESOURCES

CRITICAL RESOURCES
NOTive Trout Trout WW Terres.
Chub Fish Repro/Grow Fishi~ Booting Beoches Habitat
0 - v: - - - 0

Figure VI-7. Fluctuations have adverse impacts (-)
primarily on the aquatic resources and recreation.
They have no significant impact (0) on terrestrial
resources and chub, and benefit (+) trout growth.

Flood Releases Have Greatest Potential For
Long-Term And Irreversible Impacts

Of the operations evaluated, flooding has the greatest
potential to irreversibly impact the Colorado River in
Grand Canyon. Flooding was a natural and consistent
aspect of pre-dam flows. However, the large amounts
of sediment carried by pre-dam flows allowed renewal of
beaches and substrate for vegetation. Loss of beaches,
sand substrate, and marshes may be nearly irreversible