7762

• UCREFRP Catalog Number: 7762
• Author: Valdez, R. A. and B. R. Cowdell.
• Title: Annual Summary Report-1994, Effects of Flow Regulation and Ice Formation on Overwinter Nursery Habitat of Age-0 Colorado Squawfish in the Green River Below Flaming Gorge Dam.
• USFW Year: 1994.
• USFW - Doc Type: \
• Copyright Material: NO

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Site 2: Site 2 was a downstream oriented chute channel in Island Park (RM 329.7). This backwater had an
area of 550 m2 and a maximum depth of 2.0 ft. Conditions on February 2, included average surface
ice thicknesses of 0.5 ft with an average 0.9 ft of free water beneath. Site 2 could not be accessed
during the second trip, however it is our opinion that due to the general warming trend in February,
this backwater remained suitable habitat throughout the winter.

Site 3: Site 3 was a downstream oriented chute channel located in Rainbow Park (RM 327.3). This
backwater had an area of 1750 m2 with a maximum depth of 4.5 ft. This backwater had a slight flow-
through during the initial mapping in September, which steadily increased throughout the winter. By
February 24, the habitat was effectively a side channel with water velocities of approximately 1.0 ft/sec.
This area was determined to be unsuitable overwinter habitaL

Site 4: Site 4 was a small downstream scour channel located on a mid-channel sand bar in Rainbow Park
(RM 328.5). This backwater had an area of 110 m2 with a maximum depth of 1.3 ft. By February 24,
changes in channel morphology replaced this backwater with a uniform sandbar. No evidence of the
original habitat remained.

6.2.2 Reach 2

Reach 2 extended from the Split Mountain Campground (RM 319) to the Bonanza Bridge (RM 290). Eight
backwaters were sampled in Reach 2. River ice conditions included minimal shoreline ice formed the last
week of January with surface ice rarely extending more than a meter from shore. Frazil ice formed during the
first week of February. During this time frazil ice floated to the surface forming large mats which covered
most of the water surface in the Jensen area (see Franl Ice section). The river in Reach 2 was typically free
of frazil ice by 1400 hrs. Frazil ice formed again during the second week of February, however only small
amounts were noted with no significant accumulation on the surface. No ice jams were observed in Reach
2. Ice accumulations slowly decreased after peak formation the first week of February. Most ice was absent
by the last week of February.

Site 5: Site 5 was a downstream chute channel formed at the bottom of side channel below Chew Bridge (RM
314.7). This backwater had an area of 480 m2 and a maximum depth of 3.6 ft. This backwater had
a slight flow-through during the initial mapping, which persisted throughout the winter. Ice formation
was not substantial. Even with the slight flow, this area would have been suitable sheltering habitat
during the winter.

Site 6: Site 6 was a downstream scour channel located at below Chew Bridge (RM 314.7). This backwater
had an area of 390 m2 with a maximum depth of 1.9 ft. Surface ice formation was minimal, less than
0.1 ft. This area had a slight flow-through on February 23, but was considered suitable habitat during
the winter.

SIte 7: Site 7 was an upstream oriented eddy retum-channeI located just below Chew Bridge (RM 316.2).
This backwater had area of 200 m2 with a maximum depth of 3.0 ft. On February 3, several collapsed
ice lenses were noted creating an average surface ice thickness of 0.2 ft. These lenses of thin (0.05
ft) surface ice would form during the high daily flow then collapsed when water stage dropped. These
'lenses' would stack upon each other, forming a mosaic of irregular surface ice. By February 23, solid
ice had formed in the back third of the backwater, reducing area of usable habitat to 130 m2. Despite
the formation in ice lenses and reduction in habitat, this backwater was considered suitable habitat
during the winter.

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