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WSP12656
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Last modified
1/26/2010 4:17:10 PM
Creation date
8/6/2007 1:52:23 PM
Metadata
Fields
Template:
Water Supply Protection
File Number
8220.101.10.B
Description
Colorado River - Water Projects - Glen Canyon Dam-Lake Powell - Glen Canyon TWG
State
CO
Basin
Colorado Mainstem
Water Division
5
Date
7/1/2004
Author
Schmidt - Topping - Grams - Goeking
Title
The Degraded Reach - Rate and Pattern of Bed and Bank Adjustment of the Colorado River in the 25 km Immediately Downstream from Glen Canyon Dam - 07-01-04
Water Supply Pro - Doc Type
Report/Study
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<br />002433 <br /> <br />evidence indicative of a long-term slight decrease in the pre-dam supply of fine-sediment <br />to the channel. <br />Williams and Wolman (1984) analyzed data compiled from river segments <br />downstream from large dams throughout the United States in an effort to formulate <br />general models describing downstream channel adjustment. They included the 10 <br />Reclamation monitoring cross-sections in Glen Canyon in their analysis of 287 cross- <br />sections from locations throughout the United States. Williams and Wolman (1984) <br />selected a subset of 114 cross-sections where degradation had occurred and these were <br />used in developing a statistical model that described the general pattern of bed erosion in <br />degrading reaches downstream from dams. They concluded that once degradation began, <br />the rate of continued degradation could be fit to either a logarithmic or hyperbolic <br />function, with time as the independent variable and bed elevation as the dependent <br />variable. This model well described the pattern of bed degradation for five of the Glen <br />Canyon cross-sections, but did not fit the remaining five. Thus, while a logarithmic rate <br />of decrease in bed elevation may fit many degrading cross-sections, there is a high degree <br />of variability that was not explained by a simple mathematical model. In this study, we <br />reanalyze all available data for Glen Canyon, looking at channel response at all measured <br />cross-sections for the period between 1956 and January 2000. <br />Effects of the operations of Glen Canyon Dam on channel-side alluvial deposits <br />have been extensively studied in reaches downstream from Lees Ferry (see reviews by <br />Webb et aI., 1999; Schmidt et aI., 2002). These studies have documented (1) no long- <br />term accumulation of sand on the bed since the 1980s, (2) net loss of sand from eddies <br />below the elevation inundated by flows of about 708 m3/s, (3) aggradation and <br />subsequent erosion of deposits formed during post-dam floods, and (4) net decrease in the <br />total area of eddy deposits since completion of Glen Canyon Dam. These studies have <br />not investigated changes to deposits in Glen Canyon. <br />Changes in sand storage have been monitored at one eddy-deposited sand bar in <br />Glen Canyon (Beus and Avery, 1992; Kaplinski et aI., 1995; Hazel et aI., 1999). This <br />sand bar, located 15 kIn downstream from the dam, was surveyed 39 times between July <br /> <br />13 <br />
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