7378

• UCREFRP Catalog Number: 7378
• Author: Wydoski, R. S.
• Title: Potential Impacts of Alterations in Streamflow and Water Quality on Fish and Macroinvertebrates in the Upper Colorado River Basin.
• USFW Year: 1980.
• USFW - Doc Type: 77-147
• Copyright Material: YES

112

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Stream Channelization

average of eight times (range. 1.5-112 times) the wei~t of ~ame fish

Stream channels are altered for various reasons including highway

found in channelized sections. Invertebrates are s~ilarly affected by

construction. land reclamation. navigation. flood control. and others.

altered sections of streams. For example. the standing crop of inver-

These alterations are often solutions of single purpose problems which

tebrates was eight times greater in unaltered than in altered sections of

frequently result in the creation of other problems. Stream channeli-

the Missouri River.

zation is a form of alteration that involves straightening and reducing
the length of the original channel. thereby increasing the hydraulic

The basic problem is that little consideration is given to the hy-

draulic characteristics of a stream that are favorable to fish--the chan-

gradient and thus the water velocity. In addition. cover along the

nels are simply deepened and straightened to improve flow. In addition.

streambank is removed and pools are often converted into riffles or runs

the streambed gravel and rubble are used to build levees along the banks.

(Elser. 1968). Changes of this kind affect the habitat of both aquatic

and these levees destroy existing vegetation and thus cover. This method

and terrestrial organisms, After channelization. streambeds are known

is a poor approach to controlling high flows. since it increases down-

to remain unstable. somet~es for years. Substrate instability is be-

stream flooding. The existing hydraulic gradient should be preserved

lieved to be the most significant factor related to changes in fish and

when stream channels are relocated. This is especially ~portant with

invertebrate populations after channelization (Etnier. 1972).

regard to sedtment loads and transport (Platts and Megahan. 1975). Land-

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Downstream areas are often subjected to increased flooding and

use planning that involves the entire river system should be considered

so that a natural equilibrium of the hydraulic gradient can be maintained

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eutrophication as a result of these alterations. Flooding has been

shown to drastically reduce trout populations, particularly young-of-

(Goldman. 1973). As quantitative information becomes available for

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the-year. in various parts of the United States (Hoopes. 1975; Seegrist
and Gard, 1972). Shelford's ecological law of tolerance can be applied

assessing the effects of stream alterations, and for determining what

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alternatives are available. managers will be better able to make intelli-

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in this situation whereby a water velocity that is extremely high may be

gent decisions toward solving their problems.

as detrimental as when the streamflow is too low.

Most of the changes in streamflow due to stream channelization in

In the Intermountain West, most stream channelization studies have

the Upper Colorado River would occur in mountain streams because road

been conducted in Montana and Idaho. Altered stream channels in thir-

construction in the narrow canyons requires channeling, or in the flood-

the weight of game fish produced by unaltered channels (Peters and Alvord,
1964). Undisturbed sections of for~y-five Idaho streams contained an

plain of streams because of private reclamation or flood control projects.

Nevertheless, channelization continues to affect water flows and to dis-

teen Montana streams produced only one-fifth the number and one-seventh

rupt stream ecosystems in this region because of the many, although some-

t~es small, alterations made particularly by private landowners.

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