8141A

• UCREFRP Catalog Number: 8141A
• Author: Wydoski, R. S. and W. T. Helm.
• Title: Effects of Alterations to Low Gradient Reaches of Utah Streams.
• USFW Year: 1980.
• USFW - Doc Type: \
• Copyright Material: NO

SUMMARY AND CONCLUSIONS

. Erosion and deposition of streambed gravel were directly correlated with
the percentage of stream reach that was altered. The greatest erosion and
deposition resulted in reaches with a high proportion of alteration whereas
reaches with a lower proportion of alteration were less affected. Pools
occurred less frequently in bulldozed than in backhoe altered areas, although
this may have been due to stream characteristics rather than the type of
alteration. Shape and integrity of stream banks differed distinctly between the
two types of alteration. Banks were left relatively unchanged in shape during
dredging, except that in some places they were nearly covered with material
removed from the streambed. Some of the riparian vegetation survived. Stream
banks and riparian vegetation in bulldozed areas were eliminated, as banks
were either tapered back or completely covered, with no deep water left in
close proximity.

High stream flows in spring appeared to be required to maintain the depth
and frequency of pools. Normal spring flows through altered reaches removed
streambed materials deposited in pools by the alteration process, restoring
them to near pre-alteration depths. Although the location of pools may have
been changed somewhat as a result of channelization and subsequent restoration
by fluvial processes, the number of pools was essentially the same. Low
spring flows did not restore many altered pools, and left some pools in
unaltered areas shallower than usual. While about equal amounts of erosion
occurred during the low flows of fall and the high flows of spring in altered
stream reaches, most deposition occurred during the high flows in spring.

In all bulldozed sites the trout populations were not self-sustaining,
either because of few spawning adults or little recruitment and survival of age
o trout. No long term differences in growth rates were observed for trout in
altered or unaltered reaches.

During the study, dredging had less affect than bulldozing on survival of
age 0 fish, but there were indications that dredging would reduce spawning in
the future.

During low streamflows brown trout and whitefish used deep pools. Since
such pools were absent from severely channeled areas fish moved from these
altered areas into areas which contained pools, but returned when streamflows
were normal. Although the biomass and production of brown trout were adver-
sely affected by stream channel alterations. these measurements failed to show
that trout from severely channeled areas depend on more natural reaches for
survival during low streamflows and for recruitment of young.

Production of brown trout and mountain whitefish was directly related to
the proportion of a reach in pools, being highest in the reach with the most
pools and least in the reachwiththe fewest. Biomass followed this same
trend.

Growth of whitefish was faster in both altered and unaltered areas of the
Blacksmith Fork and Logan Rivers than has been reported in the literature for

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