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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SECTION I: INTRODUCTION

Sediment is literally the foundation of the riparian
environment and recreation on the Colorado River in
Grand Canyon National Park (Grand Canyon) (Figure
A-I). Deposits of sand are substrate for the
terrestrial biological resources and are used by
boaters as campsites, lunch stops, and attraction
sites. Deposits of boulders form rapids, a highlight
of river recreation in Grand Canyon. Gravel bars are
used by some fish species for spawning.

Before initiation of the Glen Canyon Environmental
Studies (GCES), several researchers such as Laursen and
others (1976) and Howard and Dolan (1981) had studied
sediment transport and sand deposits in Grand Canyon.
The results of these previous studies initially
predicted that sand deposits would eventually be
depleted after completion of Glen Canyon Dam, but later
studies indicated that large scale erosion of sand
deposits had ceased by the late 1970s (Howard and Dolan
1981). Concern over the effect on camping beaches of
more recent flood releases, and the potential change in
operations of Glen Canyon Dam made possible by
improvement (Uprate and Rewind Program) of the
generators, required the undertaking of new studies.

Sediment-Dependent Resources

Sediment resources identified by researchers and
management agencies as those most important to
biological resources and to recreation were camping
beaches, sand which is substrate for vegetation,
backwaters in sand deposits which are used by juvenile
fish, and rapids. Although sand stored in main channel
pools is not in itself important to the biological
system or recreation, it is considered as a resource
in this study because of its indirect importance to
other resources.

Some narrow sand deposits which typically continuously
line the channel margin in wide reaches of Grand
Canyon, or discontinuously line the channel margin in
narrow reaches, are overgrown by vegetation and used by
wildlife. These deposits are called channel margin
deposits (Figure A-2). However, the largest and most
numerous sand deposits are located near debris fans
which form at the mouths of tributaries. At these
debris fans, the channel is typically narrower and
shallower than elsewhere, and large zones of
recirculating current (recirculation zones, Figure A-3)

A-5