Status and Trends of Resources Below Glen Canyon Dam Update 2009

• Description: Status and Trends of Resources Below Glen Canyon Dam Update 2009 USGS
• State: CO
• Author: Hamill, John
• Title: Status and Trends of Resources Below Glen Canyon Dam Update 2009
• Water Supply Pro - Doc Type: News Article/Press Release

Status and Trends of Resources Below Glen Canyon Dam
Update -2009
The protection of resources
found in Glen Canyon National
Recreation Area and Grand Canyon
National Park, Arizona, emerged as
a significant public concern in the
decades following the completion of
Glen Canyon Dam in 1963. The dam,
which lies about 15 miles upstream
from the park, altered the Colorado
River's flow, temperature, and
sediment - carrying capacity, resulting
over time in beach erosion, expansion
of nonnative species, and losses
of native fish. During the 199ft, in
response to public concern, Congress
and the Department of the Interior
embarked on an ongoing effort to
reduce and address the effects of dam
operations on downstream resources.
In 2WA, the U.S. Geological Survey
produced a comprehensive report
entitled The State of the Colorado
River Ecosystem in Grand Canyon,"
which documented the condition
and trends of resources downstream
of Glen Canyon Dam from 1991 to
2W4. This fact sheet updates the
2W5 report to extend its findings to
include data published through April
2089 for key resources
Background
Congress passed the Grand Canyon Protec-
tion Act of 1992, which directs the Secretary
of the Interior to operate the dam "to protect,
mitigate adverse impacts to, and improve
values for which Grand Canyon National Park
and Glen Canyon National Recreation Area
were established...."
In response to the 1992 legislation and
an extensive environmental review, the
Secretary of the Interior signed a formal
decision in 1996 that altered historical flows
from the dam and established the Glen Can-
yon Dam Adaptive Management Program
(GCDAMP). Adaptive management, also
known as "learning by doing," is a process
U.S. Departmentofthe Interior
I c r- ....i..,. ;, 1 c......„.
A view of Marble Canyon (top) in Grand Canyon National Park, Arizona. Grand Canyon is home to a diverse
range of wildlife, including the endangered humpback chub (Gila cypha, lowerleft), and is a premier whitewa-
ter rafting (lower right) destination. The flow of Colorado River through the canyon is controlled by Glen Canyon
Dam. Federal efforts to protect natural, cultural, and recreational resources affected by the dam are ongoing.
for evaluating and revising management ac-
tions as new information becomes available.
The U.S. Geological Survey (USGS) Grand
Canyon Monitoring and Research Center is
responsible for the scientific monitoring and
research efforts of the program.
During the past 13 years, the modified
low fluctuating flow (MLFF) alternative
has governed dam operations. Under MLFF
operations, the historical range of daily flow
fluctuations and peak releases associated
with hydropower production from the dam
have been reduced. Additionally, in keeping
with the precepts of adaptive management,
the Department of the Interior implemented
a series of flow and nonflow experiments
intended to improve downstream resource
conditions. After more than a decade, two
questions remain: What are the effects of
Glen Canyon Dam operations on those re-
sources of concern? Are desired outcomes
being achieved? The current condition of
each key resource is summarized below and
in the table on the following pages.
USGS Fact Sheet 2009 -3633
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