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With reduced peak flows, water temperatures are warming more quickly <br />during the spring runoff period in the Colorado River. The opposite <br />occurs in the Jensen area of the Green River with cold water from Flaming <br />Gorge Reservoir depressing temperatures during the summer. <br />Historic conditions on the Colorado River system no longer exist. <br />* Peak flows have been drastically reduced, altering the sediment trans- <br />port of the river system. Based on an analysis of long-term sediment <br />records collected by the USGS, approximately 1.6 million tons per year of <br />sand and smaller sized sediment accumulates between the Jensen and Ouray <br />gages on the Green River. The majority of this storage may occur within <br />the short reach between the White River confluence and the Ouray gage. <br />At the Green River, Utah, gage the sediment storage is approximately <br />2 million tons per year. These figures represent imbalance which is <br />normally indicative of moderate aggradation conditions. Thus, materials <br />entering the Green and Colorado Rivers via tributaries during runoff are <br />not efficiently flushed through the system. Sediment entering the rivers <br />is accumulating in sand bars and filling the main river channel. There <br />are now more silt/sand areas, braided channels, and aggradation of the <br />main river channel with a reduction of deep runs, clean gravel/rubble <br />areas, and the frequency and duration of overbank flows. A shallower, <br />wider, and warmer river has resulted which fluctuates less seasonally but <br />substantially more on a daily basis. These changes seem to benefit the <br />introduced (exotic) fishes while having detrimental effects on the <br />endemic endangered species. <br />Some sections of the Upper Colorado River Basin are impacted by <br />daily flow fluctuations as a result of power generation. The Upper Green <br />River is such an area where daily flow fluctuations are evident, espe- <br />cially under reduced flow conditions. The daily fluctuations during the <br />spawning and young-of-the-year (YOY) rearing period are having an impact <br />on both Colorado squawfish and humpback chub survival. The area of <br />impact of daily flow fluctuation is dependent upon the degree of flow <br />change and the base flow level. However, in the Upper Green River this <br />area of impact extends from Flaming Gorge Dam downstream beyond Ouray and <br />possibly as far as Sand Wash. <br /> <br />w <br />6