Grand Canyon & Glen Canyon Dam: The Basics
Shaped by the Colorado River over the last six million years, Grand
Canyon stretches 277 miles, is a mile deep and up to 18 miles wide.
It was declared a National Park in 1919 and a World Heritage Site
Human inhabitants of Grand Canyon have included sophisticated big-game
hunters of the Clovis and Folsom cultures 10,000 years ago, Desert
Archaic peoples from 6500 BC to 1 AD, and the farming culture of
the Basketmaker and Puebloan peoples until about 1275 AD. Today,
the Havasupai still live in Grand Canyon; the Navajo and Hualapai
Nations have land in the Canyon, and the Canyon contains sacred
sites revered by the Hopi and Zuni.
Dams and Grand Canyon
Hoover Dam flooded the lower 20 percent of Grand Canyon in 1941.
Upstream, 15 miles above Grand Canyon, Glen Canyon Dam stopped the
Colorado River's natural flow in 1963. In 1968, public opposition
defeated proposals to build Marble and Bridge Canyon dams, which
would have inundated much of Grand Canyon between Hoover and Glen
Sediment and Nutrients
Ninety-five percent of Grand Canyon's sediment and nutrients are
trapped behind Glen Canyon Dam. Organic materials mixed into this
sediment used to provide the fertilizer for the river ecosystem's
health. Instead, the Colorado River in Grand Canyon now runs clear
and cold, allowing the green alga cladophora to grow and replace
the natural warm-water food web. The absence of replenishing sediment
is also causing critical beach and sandbar habitat to disappear,
and undermining the stability of archaeological sites sacred to
the Canyon's native peoples.
The isolation of Grand Canyon's river habitat between Hoover Dam
downstream and Glen Canyon Dam upstream has inhibited migration
and genetic diversity among the native species still found in Grand
Today, water flowing through Glen Canyon Dam is extracted 200 feet
below the surface of Lake Powell reservoir, too low for the sun's
rays to penetrate. As a result, water entering Grand Canyon is a
near constant 47°F. By contrast, before the dam was built, water
temperatures ranged from near freezing in the winter to 80°F in
the summer. These warm water temperatures were critical to triggering
native fish reproduction and maintaining native insect populations.
Regulated flows currently keep the Colorado River in Grand Canyon
fluctuating daily between 8,000 and 20,000 cubic feet per second
(cfs). Before Glen Canyon Dam, flows in Grand Canyon fluctuated
seasonally from 3,000 to 90,000 cfs. Spring snow melt brought a
rushing torrent of water into the Canyon, transporting sediment,
building beaches, replenishing the nutrient base on the river's
shores and creating vital backwater habitat as the water receded.
Low flows were critical for warming water, juvenile fish survival,
and maintaining the food base.
River otters and muskrats are no longer found in Grand Canyon. Four
of the eight native Colorado River fish are gone, and two more are
struggling for survival. Native birds, lizards, frogs and many of
the Canyon's native insects are disappearing as well. In addition,
native vegetation along the river's high water zone is absent or
stunted due to the lack of nutrients and the invasion of competing
non-native plants species.
The river's altered chemistry, flow and temperature cycles have
created an artificial environment allowing non-native species to
dominate Grand Canyon's river corridor. Native plants and animals
must now compete with new alien species for habitat and food. These
changes run contrary to the mission of the National Park Service,
which is to preserve the parks' natural integrity.
Current management of Glen Canyon Dam runs counter to the intent
of several federal laws, including: the Grand Canyon Protection
Act, Endangered Species Act, Archaeological and Historic Preservation
Act, and National Park Service Organic Act.
More than $100 million has been invested in failed efforts to reverse
the demise of Grand Canyon's river ecosystem. Efforts will continue
to fail unless all natural processes are restored: river flow, water
temperature, and sediment and nutrient inputs. The simplest solution
is to decommission Glen Canyon Dam.