1109

• UCREFRP Catalog Number: 1109
• Author: Pucherelli, M. J., R. C. Clark and J. N. Halls.
• Title: Green River Backwater Habitat Mapping Study, 1987
• USFW Year: 1987.
• USFW - Doc Type: Draft.
• Copyright Material: NO

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Backwaters were classified according to their position in the river
(bank and mid - channel). Bank backwaters occurred in sandbars or
cobblebars attached to the bank, and channel backwaters were associated
with sandbars or cobblebars in mid - channel. Bank and channel
backwaters were further classified according to area (square meters):

- <20
- >20<200
- >200<500
- >500<1000
- >1000

Tabular summaries for number and area of backwater types were produced
for each site. Additionally, because of their hydrologic similarities,
the Island Park, Jensen, and Ouray sites were also considered as a
total.

For statistical purposes, each site was divided into river miles
according to the appropriate river guides. Numbers and areas of
backwaters were calculated by river mile in order to determine a mean
and standard deviation for each site and combinations of sites. A
paired "t" test was employed to analyze differences among flows. A
standard regression analysis was used to describe the relationship
between flow and backwater numbers and area.

Results and Discussion

Island Park

Table 1 (Appendix A) presents the area (m2) of each class for each flow
at the Island Park site. An inverse relationship existed between flow
and area. Backwater area consistently increased as flow was decreased
from 5,260 cfs to 1,101 cfs. Two significant increases occurred:
backwater area increased from 8,575 m2 (2.1 ac) to 11,160 m2 (2.8 ac) or
a 30% change from 2,423 cfs to 1,773 cfs, and from 13,349 m2 (3.3 ac) to
20,070 m2 (5. 0 ac) or a 50% change from 1,430 cfs to 1,381 cfs.
Backwater area was maximized at 1,101 cfs (22,153 m2). Isolated pool
area generally increased as flow decreased; however, a significant
decrease occurred at 1,430 cfs. This decrease in isolated pools, as well
the large increase in backwater area from 1,430 cfs to 1,381 cfs, may be
attributed to the chronological order of these flows. Backwaters at
1,381 cfs and 1,101 cfs were allowed to form during a gradually
descending hydrograph. The 1,430 flow was obtained immediately after
the lowest flow of the season (approximately 1,000cfs - see Appendix B).
Furthermore, this flow was not allowed to stabilize and only occurred
for one day, which may have affected backwater and isolated pool
formation.

Table 2 (Appendix A) presents backwater number, size distribution, area,
and average backwater size for each flow at Island Park. The
relationship between flow and backwater number was not as clear as the
flow\area relationship; however, backwater numbers were maximized at
1,381 cfs and 1,101 cfs, with 56 and 52 backwaters, respectively. The
1,773 flow produced 45 backwaters, while the lowest number of backwaters