River Resource Management in the Grand Canyon (1996) / Chapter Skim
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5 SEDIMENT AND GEOMORPHOLOGY
5 SEDIMENT AND GEOMORPHOLOGY
Pages 70-83
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From page 70... ...
. Amount of Sediment Is Not a Problem in the Grand Canyon There is adequate sediment, of which sand is the dominant constituent, entering the Colorado River below Glen Canyon Dam to maintain bars and beaches.
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From page 71... ...
A sand budget must be maintained that shows the amount and distribution of sand. As we will discuss later in this chapter, the critical reach for sand management is between the Paria and the Little Colorado rivers.
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From page 72... ...
Without inadvertent spills, as occurred in 1983, or deliberate flood flows, Glen Canyon Dam would cause the rapids to increase in size. Without flood flows, there would be no mechanism to remove the large material in the debris flows (Cooley et al., 1977; Dolan, 1981; Kieffer, 1987~.
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From page 73... ...
The BOR modeled sand movement by using the hydraulics developed by the water-routing model with calibration to sand discharge relationship at various control points in the canyon. The gauge below the Little Colorado River and the long-term gauge at Phantom Ranch (Bright Angel Creek)
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From page 74... ...
Coordination and Communication "Unfortunately, the critical linkage of sediment/water flow in the main channel was pursued predominantly as an exercise in its own right, largely divorced of concerns about sediment sources and sinks and with inadequate attention to modeled sediment movement to beaches, riparian habitats, and so on" (NRC, 1987, pp.
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From page 75... ...
Others, though more general, had direct bearing on it. The particular sediment-related suggestions were summarized as follows: "Future work by the Department of the Interior should seek to look for connections between research disciplines in the planning phases of the study, initiate studies of tributary processes because they are the main source of sediment in the Colorado River main stem, include in future hydrologic research empirical approaches es well as modeling approaches, link sediment studies to biological and hydrological monitoring and research, and institute geomorphic studies to supplement the hydraulic studies of the Colorado River system in the Grand Canyon" (NRC, 1987, p.
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From page 76... ...
. A steady flow of 15,200 cfs would carry about 550,000 tons of sand per year to the Little Colorado River, and some 1.13 million tons per year past Phantom Ranch and out of the canyon into Lake Mead (BOR, 1993, Appendix D)
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From page 77... ...
In particular, if the Little Colorado peak coincides with high flow from Glen Canyon Dam, a sizable peak of discharge and transport can occur. The most critical piece of information in the sand budget will be the amount of sand in the main channel between the Paria and the Little Col
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From page 78... ...
Knowlecige of the mechanism of eddy formation, the variation of the mechanism with discharge, and the process for transfer of suspended sand across the eddy fence (a vertical plane that clivides an eddy field from other parts of the channel flow that are moving in a downstream direction) into the eddy field (an area of flowing water where motion occurs in a circular fashion or in a reverse direction to the rest of the channel)
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From page 79... ...
The model is an improvement over the steady-state model of GOES 1, but it still is the weak link in the modeling needs for managing sand. USGS Effort on Eddy Modeling Eddy modeling is farther along than main channel modeling, although it was less well understood when GOES began.
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From page 80... ...
Linking of Sediment Modeling and Eddy Modeling At the present time, there still is a need for linking the main channel water and sand discharge with the eddy system and the growth of bars. The deficiency at this time appears to be more in the main channel sand modeling than in the eddy modeling.
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From page 81... ...
RECOMMENDATIONS GCES has improved our understanding of sand movement and storage below Glen Canyon Dam. GCES sponsored the development of a more physically based analysis of the sediment transport and the eddy circulation system of the Colorado River system.
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From page 82... ...
· Creation of a procedure for determining sand budgets in different parts of the canyon downstream from Glen Canyon Dam. Less emphasis should be placed on collection of qualitative geomorphic data and more on the understanding of sediment transport processes, especially through the use of quantitative, physically based models of the system.
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From page 83... ...
1994. Monitoring the Effects of Interim Flows from Glen Canyon Dam on Sand Bar Dynamics and Campsite Size in the Colorado River Corridor, Grand Canyon National Park, Arizona.
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