Geoscience Reference
In-Depth Information
CHAPTER 26
The Glen Canyon Dam Adaptive
Management Program: Progress and
Immediate Challenges
John F. Hamill and Theodore S. Melis
Grand Canyon Monitoring and Research Center, U.S. Geological Survey, Flagstaff, USA
Introduction
ways. The most important have been: (i) altering
the hydrology by decreasing flow in spring but
increasing it during the summer and winter
(Topping
et al
., 2000a); (ii) greatly decreasing sand
supply to Grand Canyon, while also increasing
sand-transport capacity through nearly doubling
the median discharge during the 1990s (Topping
et al
., 2000a, b, 2003); and (iii) decreasing year-
round water temperature and virtually eliminating
seasonal water temperature variability (Vernieu
et al.,
2005). Since most of the sediment load of
the river is now deposited in Lake Powell, the
downstream tributaries, primarily the Paria and
Little Colorado Rivers, provide the Grand Canyon
with only about 16% of the pre-dam sand supply
(Wright
et al
., 2005). Water released from the
dam is also cold, with a post-construction average
temperature of 8
◦
C(Webb
et al
., 1999). The dam
has been blamed variously for narrowing rapids,
sediment erosion, invasive non-native riparian
vegetation and the loss of native fish (Webb
et al
.,
1999).
The international prominence of the Grand
Canyon, (a World Heritage Site), and public
concern about the impacts of the dam, resulted
in the Grand Canyon Protection Act (GCPA)
of 1992. The GCPA directs the Secretary of
the Interior to operate Glen Canyon Dam and
The Colorado River provides water for more than
27 million people in the western United States of
America. It provides habitat for unique assemblages
of fish and supports a variety of uses such
as agriculture, hydro-electric power generation,
various industries and a range of recreational
activities. There are 22 major reservoirs in the
Colorado River Basin (Pontius, 1997), including
Lake Powell, formed by the Glen Canyon Dam,
approximately 24 km upstream from the Grand
Canyon National Park (Figure 26.1). The lake holds
approximately 33 000 000 m
3
of water, while eight
hydro-electric generators on the dam produced
3.5 million megawatt hours of energy in 2007.
The management of the Colorado River and the
operation of Glen Canyon Dam are governed by a
complex series of laws, Supreme Court decrees and
operating principles; these are collectively known
as the 'Law of the River' (Adler, 2007). In general
terms, the Law of the River provides for the
equitable distribution and sharing of water among
the seven Colorado River Basin states - Arizona,
California, Colorado, Nevada, New Mexico, Utah,
and Wyoming.
Since it was completed in 1963, Glen Canyon
Dam has altered the Colorado River in several
