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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deposition. In addition, prediction of geomorphic effects of floods over a range of discharges
will come by an appropriate synthesis of modelling and field studies. Prior to this flood
experiment, models using controlled high flow data have been limited to 790 mJ/s (28,000
W/m). Some basic data with which to further calibrate models can be obtained during this
experimental flood. Geomorphic data will also we used in understanding the processes that
cause habitat changes for aquatic and riparian species, for example, development of return
current channels (backwaters).

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The following hypotheses will be tested by performing the experimental flood:

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Spatial Patterns of Bar Deoosition
Null hypothesis-
HO: There will be no net change in the number, size, shape, or location of
channel-margin alluvial deposits 1 yr after recession from this flood.
Alternative hypotheses -
HI: Following the flood, reattachment bars will resemble those described by Schmidt and
Graf(1990) as existing in Grand Canyon in the mid-1980's. Well defined eddy return
current channels will exist and their number and size will exceed the number and size of
such channels as they existed prior to the flood.
H2: There will be a net increase in the total nlDDber and size of alluvial deposits along
the river.

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The above mentioned alternate hypotheses are only general statements. Each alternative
could also be restated by individual suhreach and for other measurement periods (e.g. I
month after the flood, 6 months, 2 yr, etc.)

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Main channel hYdraulics and sediment transoorl
Null hypothesis-
HO: Sediment mass balance calculations and global models of hydraulics and sediment
transport successfully predict high discharge sediment transport. Eddy deposition
calculations and numerical modeling of eddy circulation successfully predict eddy
deposition rates.
Alternative hypotheses-
HI: Modeling does not predict river hydraulics and sediment transport. Eddy deposition
rates are not accurately predicted.

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The general method of this research will combine specific field measurements at
numerous field sites (e.g., gaging stations, long-term sand-bar survey sites, sites of recent debris
flows) with comprehensive river-length analysis of air photography. The scale of the river and
length of Grand Canyon preclude intensive study of all potential deposition sites. Field

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