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SYNTHESIS OF GREEN RIVER AND YAMPA RIVER STUDIES
<br />Two recent investigations in the upper Colorado River basin described the effect of
<br />fluctuating IIows and ice dynamics on fish activity and habitat under winter conditions. Valdez and
<br />Masslich (1989) used radiotelemetry to describe movement and habitat use by adult Colorado
<br />squawfish and razorback suckers in the Green River, between Echo Park (RM 345), Colorado, and
<br />Ouray (RM 248), Utah, from December through March 1986-87 (Winter 1) and 1987-88 (Winter 2).
<br />Wick and Hawkins (1989) conducted a similar, concurrent investigation with radiotagged adult
<br />Colorado squawfish in the Yampa River, from Lily Park (RM 51) to Morgan Gulch (RM 105),
<br />Colorado (Figure 1). Locations cited in this report for the Green River are in river miles (RM) from
<br />it's confluence with the Colorado River in Canyonlands National Park, Utah. Yampa River locations
<br />are referenced by river mile from it's confluence with the Green River in Echo Park, Dinosaur
<br />National Monument, Colorado.
<br />River Hydrology And Ice Conditions
<br />Green River
<br />Hydrology
<br />Average and maximum flows of the Green River, and volume released from Flaming Gorge
<br />Dam, were higher the first year of the investigation, 1986-87. For the water year 1987 (October 1,
<br />1986 -September 30, 1987), average, maximum, and minimum daily discharges near Greendale (0.5
<br />miles below Flaming Gorge Dam) were 2,220; 4,030; and 742 cfs (63, 114, and 21 cros), respectively.
<br />For the water year 1988 (October 1, 1987 -September 30, 1988), average, maximum, and minimum
<br />daily discharges were 1,672; 3,280; and 860 cfs (47, 93, and 24 cros), respectively. Total volume
<br />released from the dam was 1,607,000 acre-feet in water year 1987, and 1,214,000 acre-feet in water
<br />year 1988 (USGS 1987, 1988).
<br />Releases during Winter 1 were generally higher than in Winter 2 (Figure 2). Average daily
<br />releases from Flaming Gorge Dam in Winter 1 ranged from a high of 3,619 cfs (103 cros) in
<br />December to a low of 1,285 cfs (36 cros) in March. Average daily releases in Winter 2 ranged from
<br />2,351 cfs (67 cros) in January to 1,308 cfs (37 cros) in March.
<br />Flows of the Green River near Jensen for 2 years preceding Flaming Gorge Dam (1960-62)
<br />and for 2 years of the investigation (1986-88) illustrate seasonal impact of the dam on the hydrograph
<br />in habitat occupied by the endangered fish species (Figure 3), located about 174 km downstream of
<br />the dam. In preimpoundment years, winter IIows from December through March, were characterized
<br />as the lowest of the year. These base flows were sometimes interrupted by spikes representing runoff
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