8128

• UCREFRP Catalog Number: 8128
• Author: U.S. Bureau of Reclamation.
• Title: Operation of Glen Canyon Dam\
• USFW Year: 1995.
• Copyright Material: NO

Overview
This overview briefly describes the need, alternatives, and issues of the Glen Canyon
Dam Final Environmental Impact Statement. The summary provides greater detail.
This environmental impact statement (EIS) analyzes a range of alternative Glen Canyon
Dam operations designed to protect downstream resources and Native American interests
in Glen and Grand Canyons, as well as to produce hydropower.
Glen Canyon Dam-the key feature of the Colorado River Storage Project-was completed
by the Bureau of Reclamation in 1963 as a multipurpose facility. The purposes for which
the dam was constructed are set forth in the Colorado River Storage Project Act of 1956
and include, among others: regulating the flow of the Colorado River; water storage;
reclamation of and and semiarid lands; flood control; and hydroelectric power generation,
"... as an incident of the foregoing purposes."
The Colorado River is the main influence in the dynamic ecosystem of these canyons.
Glen Canyon Dam brought about fundamental changes in the river and predam ecosystem.
Sediment transport and supply have been reduced, and controlled volumes of cold, clear
water annually pass through Glen and Grand Canyons. Both native and non-native fish
that cannot tolerate these conditions have declined or disappeared from the canyon.
Other species and communities that were rare or nonexistent before the dam now abound.
Alternatives
None of the alternatives presented in this EIS can return the system to predam conditions.
However, this EIS considers nine alternate ways to operate the dam to reduce further
adverse impacts on or to enhance the valuable ecosystem components that remain or have
developed under postdam conditions. These alternatives propose changes in maximum
and minimum flows, daily flow fluctuations, and rate of change in fluctuations (ramp rate).
The alternatives would change the riverflows below the dam (also called discharges or
releases), which are measured in cubic feet per second. Annual or monthly volumes are
measured in acre-feet. '
The alternatives are variations of dam operations, ranging from unrestricted fluctuations
to steady flows. The impacts often vary only slightly among alternatives. The EIS team
and cooperating agencies considered the sum total of these sometimes subtle variations in
recommending the preferred alternative-the Modified Low Fluctuating Flow Alternative.
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