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DRAFT' February 25, 1998 0 situation reverses and the temperatures are controlled by the lower temperature, higher volume flow from the Green River. The temperature effects at Echo Park are displayed in Figure 4. From the confluence with the Yampa River at Echo Park, the Green River flows west into Whirlpool Canyon and then into Island and Rainbow Parks. The river in this reach slows down and spreads out, which allows the water increased exposure to a large channel and radiant solarenergy from the sun. Figure 4 displays the seasonal importance (as described by conditions in 1996) of this reach, which contributes significantly to the warming of the Green River. From Rainbow Park, the river drops into Split Mountain Canyon where the river is shaded by canyon walls and water velocities increase, water temperature is unchanged through this reach. The Green River enters the Uinta Basin near the U. S. Geological Survey gage at Jensen, Utah, where temperatures are monitored once daily. Through this broad alluvial area, the River spreads out into a large meandering channel and summer water temperature increases. This reach of the Green River is very biologically productive with warm temperatures and abundant nutrients. During the spring runoff in average and above-average years, water flows into overbank areas and warms. As these waters clear up, light penetration increases, primary production increases, and nutrient levels increase. As the warm water from the overbank areas drain back into the • water, the river gains nutrients. Air temperature (and hence water temperature) is influenced by cloud cover and storm fronts. Generally, the temperature effects of Flaming Gorge regulation can be detected at the Jensen gauge but not at the Green River, Utah gauge (Smith and Green, 1991). Reach 3 - Increasing Warming Trends The Duchesne and White Rivers join the Green River at the lower end of the alluvial reach just below the town of Ouray, Utah. Having traveled a shorter distance before emptying into the Green River, the Duchesne and White Rivers have not quite reached ambient air temperature, but do not appreciably change temperature in the Green River. Figures 4b and 4c appear to indicate that the temperature of the White River in July and August may be slightly lower than that of mainstem Green River. While Figures 4b and 4c show the temperature of the Green River dropping slightly, closer examination indicates that the location of the thermograph just below the mouth of the White River may reflect incomplete mixing of the White and Green Rivers which may tend to under estimate the temperature of the Green River at this location: Several kilometers below the White - Duchesne Rivers confluence, the Green River enters into the Desolation Canyon - Grays Canyon reach where the diurnal fluctuations in water temperature are moderated by warmth from the canyon walls radiating to the air and water at night. Below this reach, the Price River joins the Green River but does little to affect water temperatures of the Green River. The Price River has also reached ambient air temperature, and the flow of the Price has been depleted to a point where the River is more representative of an irrigation return flow 0 . 13