7387

• UCREFRP Catalog Number: 7387
• Author: U.S. Bureau of Reclamation.
• Title: Glen Canyon Environmental Studies Executive Summaries of Technical Reports.
• USFW Year: 1988.
• USFW - Doc Type: \
• Copyright Material: NO

I Tributor1 debris fon

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clays in some of these formations aid in the initiation
of debris flows.

The magnitude and frequency of debris flows control the
hydraulics of the Colorado River in Grand Canyon
National Park. Debris flows from small tributaries
aggrade fans that typically force the river against the
opposite wall of the canyon (Figure 2). The ability of
small drainages, such as Monument Creek, to form
hydraulic controls (rapids) on one of the largest
rivers in the united states is hydrologically
significant. The debris fans also cause flow
separation zones conducive to deposition and storage of
sand on beaches. Reworking of debris fans by
discharges of the Colorado River creates secondary
riffles or rapids (Figure 2). Debris flows are the
source of large volumes of sand entering the river at
discrete points, although the debris flows occur
infrequently. Knowledge of the magnitude and
frequency of debris flows is necessary for any under-
standing or long-term estimates of sediment transport
in the Colorado River in Grand Canyon National Park.

KEY

2 Rapid controlled b1lorg. immobile
boulder,

3 Debris bar (synonymous wjth" island"
or "rock gard.n ")

4 Riffl. or rapid caused b1 debris bar

Figure 2. Geomorphic features of a typical rapid
controlled by debris flows on the Colorado River.

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