7632

• UCREFRP Catalog Number: 7632
• Author: Pucherelli, M. J., J. N. Halls and R. C. Clark.
• Title: Green River Channel Mapping Study, 1987.
• USFW Year: 1987.
• USFW - Doc Type: \
• Copyright Material: NO

4

All sites were slightly larger in channel area and width in 1986.
The channel area for all alluvial sites increased from 3,336 acres
in 1978 to 3,413 acres in 1986, an increase of 2.3 percent. An increase
of 77 acres in 41.8 river-miles equates to 1.8 acres per river-mile.
The channel area for nonalluvial sites changed from 2,275 acres in
1978 to 2,319 acres in 1986, a net increase of 1.9 percent. An increase
of 44 acres in 27.4 miles equates to 1.6 acres per river-mile. The
net change in average channel width from 1978 to 1986 ranged from a
gain of 30 feet for river-miles 142 to 131 to a gain of 7 feet for
river-miles 128.3 to 117. Average channel width for alluvial sites
changed from 659 feet in 1978 to 674 feet in 1986, a net increase of
2.3 percent. The average channel width for nona1luvial areas increased
from 684 feet in 1978 to 697 feet in 1986, a net increase of 1.9 percent.
The total river area increased by 120 acres (+2.1 percent) and channel
width increased from 669 to 683 feet (+2.1 percent).

The slight increase in channel width indicated by the 1986 data may
be attributed to flood incidents in the early 1980's. Increases in
alluvial sites channel width were slightly smaller than width increases
in nonalluvial areas.

Figure 2 graphs the channel width from 1963 to 1986. Although the
average river channel width decreased significantly from 1963 to 1974,
it is not of the same magnitude reported by Andrews (1986), which was
90 feet in this segment of the Green River. The slight river width
increase between 1978 and 1986 probably demonstrates the Green River's
response to flood episodes in 1983 and 1984. The very slight changes
in channel width from 1974 to 1978 indicate that the Green River channel
width is stabilizing from Split Mountain to Willow Creek.

It was observed that of the 357 acres of channel area lost between
1963 and 1974, 154 acres (43 percent) were related to increases in
number of islands, island size, and the loss of side channels previously
associated with islands that have increased in size to the point that
they have become part of the channel bank. In table 3, old islands
are islands that are now part of the channel bank, and old channels
are side channels that have been filled and are not part of the bank.
In general, the number of islands and their acreages increased from
1963 to 1974 when old islands and old side channels were included in
the calculations. The acreage of islands increased only slightly from
1974 to 1978. There was a relatively small decrease in island acreage
from 1978 to 1986, again reflecting the flooding which occurred in
1983 and 1984. Figure 3 illustrates the changes in vegetated islands
per river-mile. The largest change occurred from 1963 to 1974, as
expected (+12 percent), leveled off from 1974 to 1978, and decreased
slightly from 1978 to 1986. The increase in island acreages was approxi-
mately twice as large in nonalluvial areas than in alluvial areas.
Andrews (1986) also reported that the most significant process narrowing
the channel in this segment of the Green River occurred where a side
channel filled with bed material and the midchannel bar had become
attached to the bank.