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Last modified
7/14/2009 5:02:31 PM
Creation date
5/22/2009 4:39:17 PM
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UCREFRP
UCREFRP Catalog Number
7752
Author
Stanford, J. A.
Title
Instream Flows to Assist the Recovery of Endangered Fishes of the Upper Colorado River Basin
USFW Year
1993.
USFW - Doc Type
Review and Synthesis of Ecological Information, Issues, Methods and Rationale.
Copyright Material
NO
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<br />.. ," <br /> <br />Alteration of Flow, Temperature and Sediment Regimes <br />Regulation has reduced the spring peaks of the snowmelt-dominated rivers of the Upper <br />Colorado River Basin and increased the baseflows (see Figures in Stanford and Ward 1983, <br />Andrews 1986). Hydroelectric operations also have increased short-term (hourly! .daily) flow <br />variability (e.g., Figures 10-14). Note that extreme hourly variation may be masked by presentation <br />of flow as daily means (compare Figures 12 and 13 with August and September data in Figure 14). <br />Daily means are usually plotted in analyses of flow durations because hourly data are reduced to <br />daily means in the long term data bases for stream flows maintained by the U.S. Geological Swvey. <br />Rivers regulated by hypolimnial (bottom) release dams (e.g., Aspinall Units on Gunnison) <br />are cooler in the summer and warmer in winter for many miles downstream from the dam than was <br />the case before impoundment (Stanford and Ward 1983), although Flaming Gorge Dam was <br />retrofitted with a selective withdrawal system to ameliorate negative effects of cold temperatures on <br />fish growth downstream from the dam (Stanford and Ward 1986a). <br />Retention of sediments within impoundments such as Flaming Gorge and the Aspinall <br />Units has reduced suspended sediment concentrations and bedloads downstream from the dams. <br />Moreover, loss of peak flows has reduced the transport power of the river. Sediment discharges <br />from tributaries downstream from the point of regulation therefore are more persistent; alluvium <br />and colluvium entering the river channel are not moved downstream with predam efficiency <br />(personal obselVation in the Upper Colorado River Basin and documented in the Grand Canyon by <br />Dolan 1978 and others). Thus, riverine sediment budgets and channel elevations may change <br />dramatically after regulation. In the Green River, mean annual sediment discharge decreased by <br />54% at Jensen and 48% at Green River, 105 and 290 river miles downstream from Flaming Gorge <br />ReselVoir (Andrews 1986). A new quasi-equilibrium between sediment supply and transport has <br />been attained in the Green River (Lyons and Pucherelli 1992) resulting in a decrease in the bankfull <br />channel of 6% (Andrews 1986) to 10% (Lyons and PuchereIli 1992). Loss of channel area is <br />attributed to formation of new islands and increased island size and loss of side channels which <br /> <br />26 <br />
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