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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5.1 Winter of 1993-94

5.1.1 Air and Water Temperature
Air temperatures in the Uinta Basin during the winter of 1993-94 were unusually warm. Monthly
maximum air temperatures near Jensen for December through March were 2.9 to 9.0oC above
normal, while monthly minima were 2.9 to 4.9oe above normal (Figure 5).

This mild winter resulted in slow cooling of water temperatures in the Green River and delayed ice
formation. Water temperatures at the USGS gage near Jensen did not reach freezing (OOC) until
February 2, 1994, and temperatures below l.Ooe lasted for only 4 days (Figure 6).

Diel temperatures of the Green River during the first ice measurement trip (January 31 - February 4)
typically ranged from -0.05 to 0.30oC. Water temperatures in each reach were similar with a range
of -0.05 to 0.320C in Reach 1, -0.10 to 0.38oe in Reach 2, and 0.4 to 0.50C in Reach 3. No
significant differences in water temperatures were noted between reaches.

5.1.2 Ice Formation
Ice formation on the Green River between Island Park and Ouray was not extensive in winter of
1993-94. In reach 1 (Island Park, RM 333 to Split Mountain Canyon, RM 327), there was minimal
shoreline ice that first formed the last week of January with surface ice rarely extending more than.
1 m from shore. Small amounts offrazil ice were observed the:first week of February and no ice jams
were observed in this reach. Ice accumulations slowly decreased after peak formation the first week
of February. Most ice was absent by the last week of February. In reach 2 (Split Mountain
Campground, RM 319 to the Bonanza Bridge, RM 290), river ice development was similar to reach
1, except that fra.zi1 ice fonnation was more extensive during the night and early morning.. The river
in reach 2 was typically free of frazil ice by mid-afternoon (about 1400 h). No ice jams were
observed in reach 2, and ice accumulations slowly decreased after peak formation the first week of
February. Most ice was absent by the last week of February.

In reach 3 (Bonanza Bridge, RM 290 to Ouray, RM 248), river ice conditions included large areas
of broken sur.tace and jam ice. Mats of jumbled, irregular surface ice, composed of compacted frazil
and dislodged shoreline ice moved into reach 3 from reach 2. This ice began jamming in constricted
portions of the channel the first week of February. Several jams dammed water, diverting flow into
high water channels.

Although shoreline ice was present in much of the region from early November to late February,
complete ice cover was rare. An ice cap formed on the river near Jensen beginning on the morning
of February 2, 1994, but persisted for only 5 days. In the upstream reaches of the study area (i.e.,
abov~ Jensen Bridge), the ice cap was mostly broken and jammed, while the ice cap in the lower
reaches was smooth and solid. Following the short period of cold temperatures that lead to this ice
development, air and water temperatures warmed steadily for the remainder of the winter and
precluded further development ofan ice cap. This period of ice formation was much shorter than
observed by Valdez and Masslich (1990) during the winters of 1986-87 and 1987-88. Figure 6
illustrates the beginning and duration of an ice cap, compared to river water temperatures and

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