WSP01181

• File Number: 8220.101.10.D
• Description: Glen Canyon Dam/Lake Powell
• State: AZ
• Basin: Colorado Mainstem
• Date: 10/1/1994
• Title: Experimental High Discharge Release From Glen Canyon Dam Through Grand Canyon NP - Draft Work Plan
• Water Supply Pro - Doc Type: EIS

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essential for further refinement of the global model of water flow (S. M. Wiele and J. D, Smith,
A one- -3 dimensional unsteady model of discharge waves in the Colorado River through the
Grand Canyon, unpubl. U. S. Geological Survey manuscript). No determinations of bed
roughness have been made at high discharge (greater than 620 mJ/s) and such a roughness
parameter is necessary to accurately predict water surface elevations, wave attenuation, and
sediment transport.
Basic velocity and sediment transport data at gaging stations will provide essential
empirical data to be used in refining sediment rating curves, in calculating sediment budgets
within reaches, and in comparing model predictions of sediment transport actual values.
Predictions of the concentrations of suspended sediment and total transported load during the
flood will be compared with data collected during the flood.

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2. b, Eddy hydraulics and sediment transDOrt
The mechanics of flow circulation and sediment transport will be studied in detail at 5 to
7 eddies. Daily measurements will describe the net gain or loss of sediment during the preceding
day, changes in topography of the separation and reattachment bar and return current channel,
exchange rate of water between main channel and the eddy, and concentration of suspended
sediment in the main channel adjacent to the eddy: The surface-velocity field of the eddy will be
measured at least daily during the flood. Measurements will be analyzed to determine the rate of
sediment deposition over duration of the flood. adjustment of eddy bar topography, and
variations in mass-exchange rate as the eddy bar approaches its equilibrium configuration given
the discharge and suspended sand concentration in the main channel. The observed evolution of
bar topography will be used to evaluate a vertically averaged two-dimensional model of eddy
circulation.

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ECOLOGY

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Geomorphological proces~ control most of the development of appropriate habitat tor
wetland (marsh) and riparian species. Changes in the status of return current channels
(backwaters) that may fill with sediment allow establishment of marsh plants, but continued
filling will gradually raise the substrate levels and eliminate conditions suitable for these plants.
A clearer understanding of the circulation processes in eddies before and during high flows will
guide our understanding of bow sediment transport processes cause the formation and loss of
locations that become marshes and will allow testing of predictions on rates of scour and filling,
marsh habitat creation and loss, and marsh ecosystcln evolution.
Sediment deposits that support riparian vegetation also change constantly as a result of
variations in river discharge. Although riparian vegetation may help stabilize sediment deposits,
the energy of river flows is sufficient to alter substrate under riparian plants, often causing loss
of riparian communities. Sediment deposition processes also create new habitat for riparian
species. This along with limited post-dam discharges have allowed an extensive invasion of
previously scoured areas by both indigenous and nllD-indigenous riparian species. The
interrelationships between sediment transport and depositional processes, and riparian and

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