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

No significant changes in alignment occurred in this reach, although there
were some changes in elevation of the stream bottom. Proceeding upstream from
station 0 for about 100 meters there was little change except for a modest
amount of deposition. A tree fell into the stream between 131 and 147, restrict-
ing channel width. The increased velocity caused down cutting from 115 to 131
and the channel constriction impounded water, causing deposition at 147.
Erosion of the east bank caused a shift at 196, where the maximum depth
increased. There was little change from 211 to 224, but erosion on both sides
of the stream caused down cutting at 238. Deposition decreased the depth of
a pool between 253 and 268, but from 285 to 361 there was no change (Figure 20).
Between 377 and 404 deposition occurred in mid-channel, while little change
took place from 417 to 433 and from 460 to 531 (Figure 20). Deposition decreas-
ed the depth from 433 to 460 and at 550. There was a decrease of 2.6 m in
average width in this reach between November, 1975 and July, 1976. This
difference is probably a consequence of irrigation diversion of water rather
than a change in stream channel, since the water level at the staff gauge down-
stream declined sharply about mid-June. Extensive irrigation use of stream
water usually begins in mid-May to early June. Since 1976 was a poor water year,
diversion decreased the flow more than it would normally, and caused the
decrease in average width.

The Blacksmith recently bulldozed site was altered by bulldozing in
November, 1971, when the stream was deepened and dikes built along each side of
the stream. Cross sections were surveyed between stations 0 and 381 in August,
1975. On September 6, 1975 the landowner altered the stream bed with a bull-
dozer between stations 81 and 351. Alteration was done to decrease bank erosion
by shifting the location of water current impingement on the bank from station
244 downstream to 229a, an area which had been fortified with railroad ties.
The channel was straiahtened between stations 91 and 184 to eliminate bank
erosion at 139. Afte; completion of the alterations, the stream was surveyed
from station 81 to 591 in September, 1975, and the entire study area was again
surveyed in June, 1976 (Figure 21).

Between 81 and 226 the river was straightened and the width increased an
average of 4.4 m by the alterations. The pool on the west (right) bank was
filled in and the river moved 4.6 m to the east (Figure 21). From 97 to 123
gravel was pushed to the west bank, moving the channel to the east an average
of 3.7 III (Figure 21). Gravel was pushed into the pool and against both banks
between 139 and 154, and into the pool between 169 and 229a. For about 60 m,
from 229b to 321, extensive gravel deposits were removed from mid-stream and
pushed against the west bank, reducing stream width by 3.4 m (Figure 21). This
shifted the thalweg to the center of the stream until it reached station 215.

During spring runoff in May, 1976, a tree fell into the river at 81,
causing development of a large pool extending from 97 downstream to 46. Erosion
along the west bank removed the gravel deposited during the alteration and
returned the channel to near the August, 1975 position (Figure ). Some mid-
channel erosion between 112 and 123 lowered the river bed in that area (Figure
21) while deposition raised the bed from 139 to 169. Along the west bank,
erosion returned the river to near its August, 1975 position from 184 to 229a.
However, from 229b to 321, where the river was narrowed by alteration, little
change took place (Figure 21). There was no change from 321 to 381 between

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