WSP08242

• File Number: 8220.101.09
• Description: Glen Canyon Dam/Lake Powell
• State: AZ
• Basin: Colorado Mainstem
• Date: 1/1/1992
• Author: USDOI-BOR
• Title: Newsletter - Colorado River Studies Office - Vol.4
• Water Supply Pro - Doc Type: Publication

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demands in any month. Peak discharges under
existingnonnal operations would not exceed 31,500 ds.
Use of the full powerplant capacity (33,200 ds) would
be studied as a subalternative. Historically, minimum
flows allowable have been 1,000 ds from Labor Day
until Easter and 3,000 ds from Easter until Labor Day
(the recreation season).

Elements Potentially Added to Any
Alternative

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The following elements may potentially be applied to
any alternative to meet a need or to mitigate adverse
consequences of the alternative under analysis. It may
be operational or nonoperational, structural or
nonstructural. Elements will be added to alternatives
where logically appropriate to further meet the
objective of the alternative or if identified as a need
through the long-term monitoring program.
Mitigation measures also may be added as necessary.

Sand Pumping - Sand deposited in the Colorado River
channel could be pumped onto selected beaches, sand-
bars, or terrace deposits where a source of river channel
sand is readily available.

Beach Protection - Rock jetties or riprap lining could be
constructed to protect beaches at selected locations. All
structures would consist of native rock and vegetation
to blend with the natural environment. Because of
logistical constraints, only beaches within a few
hundred yards of a debris fan could be protected in this
manner.

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BeachjHabitat Building Flows - Special high releases
of from 6 to 14 days duration could be made to help
rebuild eroded beaches, increase terrestrial habitat, and
create and maintain rearing habitat for native fishes in
the Grand Canyon. High flow releases could be
scheduled to coincide when there are high
concentrations of sediment in the Colorado River
tributaries. Sand stored within channel pools and
eddies would provide the primary source of material.
Beach or habitat building flows would exceed the
normal operating range to deposit sand on the elevated
beaches. High flows build some beaches, while
eroding others; and the optimum discharge may have
to be determined experimentally. Since these special
releases would be scheduled after the channel pools
and eddies refill with sand, the special releases may be
scheduled only once in several years. Beach/habitat
building flows would be considered research flows;
and the effect on downstream resources would require
careful monitoring before, during, and after the event.

Reduced Flood Frequency - The large flood releases
caused by the high spring runoffs between 1983 and

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1986 caused significant degradation of the environment
by eroding many of the sand deposits within Glen and
Grand Canyons. Peak flows were over 90,000 ds'in
1983, and peak discharges ranged between 45,000 and
53,000 ds from 1984 to 1986. To reduce the frequency
and magnitude of spills, more space could be reserved
in Lake Powell to accommodate high spring runoff or
the height of the spillway could be raised to increase its
capacity, although no designated flood storage
currently exists in Lake Powell.

Multilevel Intake Structure - Preliminary studies
indicate that selective withdrawal structures Oll the
existing penstocks could permit water to be withdrawn
from selected reservoir levels to adjust downstream
river temperatures. Withdrawals could be adjusted on
a seasonal basis to meet ecological objectives such as
improving habitat for native fishes. The consequences
of multilevel releases on all facets of the environment
need to be further evaluated. Additional research and
analysis will be conducted to answer unresolved issues
as appropriate .under the adaptive management
program.

Power System Adjustments - For each alternative, the
Western Area Power Administration (Western) may
change the manner in which it markets energy and
capacity from Glen Canyon Dam. The Glen Canyon
Environmental Studies' Power Resources Committee is '
evaluating both a resource-based marketing plan and
fixed-levels for marketing energy and capacity from
Glen Canyon Dam. Western and its customers could
consider the following options for each alternative:

. Purchase power from alternate sources

. Build new power facilities

. Change transmission system capability

. Increase energy conservation

Adaptive Management - Adaptive Management is
considered to be an essential element of each
alternative--particularly the selected alternative. It
includes organized research and monitoring
coordinated by a multiagency resource managment
and review group that will evaluate the effectiveness of
the selected plan in meeting resource management
objectives.