8119

• UCREFRP Catalog Number: 8119
• Author: Valdez, R. A. and B. R. Cowdell.
• Title: Effects of Flow Regulation and Ice Formation on Overwinter Nursery Habitat and Survival of Age-0 Colorado Squawfish in the Green River Below Flaming Gorge Dam - Draft.
• USFW Year: 1996.
• USFW - Doc Type: Logan, Utah.
• Copyright Material: NO

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minimum daily air temperatures recorded near Jensen for winters 1986-87, 1987-88, 1993-94, and
1994-95.

Despite the lack ofan extensive ice cap in winter of 1993-94, frazil ice was observed on the Green
River during two periods; January 31- February 4 and February 13-16, 1994. During the first period,
frazil ice was mixed in the water column in the upper sections of the study area and through
Whirlpool and Split Mountain canyons. In the lower, slow water sections below Dinosaur National
Monument, frazil ice became suspended on the surface as large floating mats. These mats, termed
'lily-pad ice', were typically 1-3 m in diameter and 0.3-0.5 m thick, and are the precursor to surface
ice (Ashton 1980, 1983). This lily-pad ice was thick and covered most of the river surface in the
Jensen area. Frazil ice production during the second period, February 13-16, was not as extensive
. as the first period, and lily-pad ice" was not observed.

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Although ice formation on the Green River was not extensive in winter of 1993-94, ice jams were
observed on several occasions, particularly in the downstream reaches of the study area. These ice
jams were formed in the narrow portions of the channel, and were most common near the Chew
Bridge (RM 316.3) and the Ouray National Wildlife Refuge (i.e., Leota Bottom, RM 255.5-254.0;
Old Charlie Wash, RM 251.3-249.0). The ice jams were created by dislodged surface ice and lily-pad
ice transported from upstream. Jams formed in constricted areas of the channel often damming water
and diverting flow into high, dry channels. Ice jams persisted in the Ouray area throughout the month
of February breaking up February 28 - March 4.

5.2 Winter of 1994-95

5.2.1 Air and Water Temoerature
Air temperatures in the Umta Basin during the winter of 1994-95, as in 1993-94, were unusually
warm. Monthly maximum air temperatures near Jensen for December through March were 2.9 to
S.50C above normal, while monthly minima were 3.5 to 10.50C above normal (Figure 5).

Despite warmer air temperatures in 1994-95 than in the previous winter, ice formation was more
extensive and ice cap persistence was longer in 1994-95 (Figure 6). We attribute this greater
persistence ofice to lower monthly volumes of water in the Green River, and hence to a lower heat
budget. Monthly volumes released from Flaming Gorge Dam from November, 1994 through March,
1995 were only 40% to 75% of comparable monthly releases for 1993-94 (Tables 3, 4). The
temperature of the water released at the dam was approximately the same in both winters, and ranged
from about 90e in November to 40C in January. Water temperature at Green River in February
ranged from 0.62 to 3.660C.

5.2.2 Ice Formation
River ice formation on the Green River also varied longitudinally in winter of 1994-95. In reach 1,
ice conditions included minimal shoreline development the first week of December. Ice formation
peaked by the first week of January, with shoreline surface ice rarely extending more than 1 m from
shore. SmaIl amounts of frazil ice were observed the first week of January. Ice accumulations
quickly decreased through January, most mainchannel ice was gone by the first week of February.
No ice jams were observed in this reach. In reach 2, river ice began forming the first week of

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