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Last modified
7/14/2009 5:02:36 PM
Creation date
5/22/2009 12:35:47 PM
Metadata
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UCREFRP
UCREFRP Catalog Number
9493
Author
Gaeuman, D., P. R. Wilcock and J. C. Schmidt.
Title
High Flow Requirements for Channel and Habitat Maintenance of the Lower Duchesne River between Randlett and Ouray, Utah.
USFW Year
2003.
USFW - Doc Type
\
Copyright Material
NO
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<br />FINAL REPORT, November 2003 <br />High-jlow Requirements for the Duchesne River <br /> <br />Changes in Stream Flow in the Study Area <br />Total annual runoff and flood magnitudes have been highly variable over the period of <br />record. The years with total annual runoff in the upper quartile of the measured record averaged <br />5.8 times the mean annual flow of the years with total annual runoff in the lowest quartile of the <br />distribution. The magnitudes of 1.5-year, 2-year, and 5-year floods, and the flows exceeded 10, <br />50, and 90 percent of the time are all at least five times greater in upper-quartile years than in <br />lower-quartile years. Wetter and drier years appear to cluster in the latter half of the 20th century, <br />when three relatively dry periods lasting roughly a decade were separated by two relatively wet <br />periods, each lasting about 5 years. <br />Mean annual runoff for water years 1972 through 2000, after the Bonneville Unit of the <br />Central Utah Project (CUP) began operations, declined by approximately 10 percent from the <br />mean annual runoff for the pre-project water years of 1943 through 1971. The impact ofthe <br />CUP is most pronounced during years with total annual flow in the lowest quartile of the record. <br />For these years, mean annual flow is 33 percent less since 1972 than for before 1972. The <br />frequencies and magnitudes of large discharges decreased less than the frequencies and <br />magnitudes of moderate discharges. The magnitudes of 1.5-year and 2-year floods and of the <br />flow exceeded 50 percent of the time decreased by more than 25 percent after 1972, while the <br />magnitude of the 5-year flood decreased by only about 5 percent. <br />A significant decline in stream flow through the study area occurred in the mid-1920s, as <br />determined from statistical extension of the hydrologic record. The total annual flow, magnitude <br />of floods, and the magnitude of flow of various durations all were much greater for the period <br />between 1912 and 1924 than for the period between 1925 and 2000. <br /> <br />Discharges Necessary to Access High Bars and Secondary Channels <br />One-dimensional hydraulic models developed at three detailed study sites indicate that <br />floods ranging from the 2-year to the 2.6-year events are required to initiate significant flow onto <br />high bar surfaces. The average discharge that inundates these surfaces is 4,000 ft3 Is. Somewhat <br />smaller magnitude events with discharges of approximately 3,000 fe/s and a recurrence interval <br />of 1.7 years are sufficient to produce flow into the main chute channels. Flows capable of <br />inundating the floodplains and higher bar ridges are larger than the 3.2-year flood and may be <br />approximated by the 6-year event. <br /> <br />xi <br />
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