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1 <br />Stratigraphic analysis of channel change has been underway for the past 2 yrs, <br />primarily funded from other sources, but supplemented by this project. The most <br />recent progress reports for this project is attached. <br /> RESULTS <br /> Analyses are still underway, and the 1995 field season is necessary to confirm <br /> many of the observations obtained from aerial photographs. The following are <br /> preliminary results from data collection and analyses to date: <br /> 1. The magnitude of the annual peak discharge of the Green River upstream from <br /> the Yampa River has decreased about 60 percent from the 1923-62 period to the period <br /> following closure of Flaming Gorge Dam. At Jensen and Green River, UT, the changes <br />have b <br />b <br />25 <br />d <br />di <br />fl <br />d b <br />i <br />l <br />d <br />h <br />f <br />h <br /> een a <br />out <br />percent, <br />epen <br />ng on t <br />oo <br />e <br />ng eva <br />uate <br />. <br />e recurrence o <br />t <br />e <br /> Floods on the Yampa River <br />have been unchanged during the same periods(Table 1) <br /> , <br />2. The highest floods of this century occurred between in the early part of this <br /> century. Instanteous peak discharge at Green River, UT, exceeded 60,000 ft3/s in <br /> 1897, 1909, 1917, and1921 (Figure. 1). Peak flows at Greendale are estimated to <br /> have exceeded 20,000 ft3/s in 1899, 1918, and 1921 (Figure 2). These floods are <br /> unprecedented; the fact that floods of this magnitude do not occur at present may be <br /> related to climatic change and be unrelated to the existence of dams. The effects of these <br /> floods on habitat availability have not been evaluated; <br />Th <br />3 <br />b <br />d <br />h <br />G <br />d <br />l <br />d <br />1961 <br />d 1987 <br />Fi <br /> . <br />e <br />e <br />at t <br />e <br />reen <br />a <br />e gage aggra <br />an <br />( <br />gure <br />ed 0.3 ft between <br /> 3); <br />4. The bed at the Jensen gage has not changed in elevation since 1948 (Figure 4). <br />Speculation about channel degradation in the Razorback bar and Escalante Bottoms area is <br />not supported by these findings; <br />5. Degradation of about 0.3 ft of the channel bed at Ouray occurred between 1951 <br />and 1966 (Figure 5). It is unlikely that these changes are related to Flaming Gorge <br />Dam; <br /> 6. Prior to closure of Flaming Gorge Dam, the Green River near Greendale, UT, <br /> was covered by ice between 3 and 5 mths per year. The last year that ice cover was <br /> reported at this gage was 1958 (Figure 6). <br /> 7. Between the winters of 1946-47 and 1960-61, the average duration of ice <br /> cover was 3.6 mths near Jensen. Since that time, the duration has decreased to 0.8 <br /> mths. At Ouray, the average duration of ice cover was 3 mths between 1951 and 1965. <br /> 8. A new floodplain, in apparent equilibrium with reduced floods has developed in <br /> the Uinta Basin, especially in the Ouray National Wildlife Refuge. This floodplain is <br />