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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INTRODUCllON

In spring 1995, an experimental flood is planned for release from Glen Canyon Dam into
the Colorado River through Grand Canyon. The purpose of this release is to (I) test the
hypothesis that fluviallandforrns, aquatic habitats, and terrestrial habitats characteristic of the
unregulated Colorado River will be restored by discharges substantially greater than powerplant
capacity and (2) provide the opportunity to measure essential geomorphic and ecologic processes
during flood passage and flood recession. Results of this experimental discharge will provide
information needed to devise an operational flow regime intended to maintain, manage and
protect the riparian and aquatic resources of the Colorado River in Grand Canyon National Park.
The planned flood is a part of the culmination ofa IO-yr research program funded by the
U. S. Bureau of Reclamation's Glen Canyon [Dam] Environmental Studies (GCES) program. and
sets the stage for a new phase of adaptive river management described in the recently released
draft environmental impact statement for Operations of Glen Canyon Darn (U. S. Bureau of
Reclamation, 1994). A substantial body of scientific research bas added to our knowledge of
processes typical of the unregulated Colorado River in Grand Canyon and changes that have
occurred in the river corridor caused by closure of Glen Canyon Dam in 1963. These studies
show that the unregulated river environment was dominated by landforms and habitats formed
and maintained by high-magnitude floods and that many of these flood-formed attributes have
been substantially altered since dam closure. The experimental flood represents a part of a
scientifically planned strategy of restoration these habitats.

FLOOD DESIGN
The proposed magnitude of the dam release is over approximately l,l9Om3/s (42,000
fills). This level of release is about 282 m3/s (10,000 fills) above power plant capacity and more
than 565 m3/s (20,000 fills) above the maximum discharge allowed under Interim Flows. A
discharge of this magnitude has not been achieved in the reaches above the Little Colorado River
since 1986. The anticipated duration of the high discharge phase of the event will be
approximately 7 days. This period is dictated, in part, by availability of water, and is believed to
be of sufficient length to produce the geomorphic changes anticipated from this flood
experiment and allow for development of tools (e.g., models) for addressing future flood
experiments and spills. As presently conceived, the flood will be preceded by 4 days of steady
flow at 226 m3/s (8,000 fills). The upramp rate to peale flow will be 71 m3/s (2,500 fills) per hour
and the downramp rate will be 42 mJ/s (1500 fillS) per hour. These ramp rates are not
operationally constrained, and have been established based on predictions and measurements of
attentuation of discharge waves (5. M Wiele and 1. D. Smith, A one dimensional unsteady
model of discharge waves in the Colorado River through the Grand Canyon, unpubl. U. S.
Geological Survey manuscript) and to reduce seepage erosion losses (Buhdh, unpubl. ms. 1992).
The flood recession will be to 226 mJ/s (8,000 fills) and held at that steady release for 4 days.
Thereafter, norrnallnterim Flows will resume.

Flood Desio Considerations
There are numerous considerations in identifying'the desired magnitude of the flood

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