9569

• UCREFRP Catalog Number: 9569
• Author: Valdez, R. A.
• Title: Synthesis of Winter Investigations of Endangered Fish in the Green River Below Flaming Gorge Dam.
• USFW Year: 1994.
• USFW - Doc Type: 18-11,
• Copyright Material: NO

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regimes. These contrasting conditions provided an excellent opportunity to examine fish

response to different winters under similar dam operation.

Winter 1 (1986.87). Higher than normal air temperatures in Winter 1 produced

above normal water temperatures near Jensen. Monthly maximum air temperatures for

December through March were from 0.7 to 4.10C above normal, while minimum

temperatures were 1.2 to 6.10C above normal. Monthly water temperatures were up to

2.30C warmer in February of Winter 1 than in Winter 2 (Figure 7). Higher releases from

Flaming Gorge Dam in Winter 1 also moderated river temperatures by delivering a larger

thermal mass to downstream areas.

Ice formation in Winter 1 was minimal and temporary, except for the lower 20 miles

(RM 270-250) of the study area, where surface ice persisted for about 3 weeks, from mid

to late January, 1987. This surface ice thickened to 3 to 5 cm, and was broken and

transported downstream by large mainstem fluctuations. Otherwise, surface ice persisted on

backwaters and along some shorelines from mid-January through February, 1987. These thin

ice layers extended from shorelines and backwaters in the morning, and usually melted as

the main channel warmed during the day. Jam ice was observed on the Green River for

only a short period in Winter 1, between mid-January and mid-February. Frazil ice was also

rare in Winter 1, forming at night during low temperatures, and melting from daytime solar

radiation. Although the Green River did not freeze above Jensen during Winter 1, the

Yampa River was frozen much of the winter. Breakup of the Yampa River contributed to

heavy ice flows in the Green River on March 9-10, 1987.