Glen Canyon Dam

Glen Canyon Dam
Glen Canyon Dam on 19 June 2005
Official name	Glen Canyon Dam
Impounds	Colorado River
Locale	Page, Arizona, USA
Length	1,560 feet (475 m)
Height	710 feet (216 m)
Width (at base)	300 feet (91 m)
Construction began	1956
Opening date	1966
Reservoir information
Creates	Lake Powell
Power generation information
Turbines	8 116MW Francis turbines
Installed capacity	1300 MW
Maximum capacity	451 MW
Annual generation	3.209 billion kilowatt-hours
Bridge information
Carries	US 89
Maintained by	Bureau of Reclamation

The Glen Canyon Dam is a dam on the Colorado River at Page, Arizona, USA. It provides water storage for the arid southwestern United States, to generate electricity for the region's growing population, and to provide water recreation opportunities. The dam generates an average of 451 megawatts, 6% of the total electricity generated in Arizona and 13% of that generated in Utah where most of Lake Powell resides, which amounts to a total carbon dioxide savings of over 5 million metric tons,^[1] although it has a maximum capacity of 1300 megawatts.^[2] Damming the river flooded Glen Canyon and created a large reservoir called Lake Powell.

Completed in 1964, Glen Canyon Dam bridge is 1,560 ft (475.5 m) long and 700 feet (213 m) above the Colorado River. It is the 4th highest bridge in the United States. Before it and the downstream Navajo Bridge were built, it was a 192-mile (309 km) drive to the other side of the canyon.

Just downstream from the dam is an arch bridge that carries U.S. Route 89. Also nearby is the 2280 megawatt, coal-fired Navajo Generating Station.

Despite continuing opposition from many environmental groups, the dam, Lake Powell, and the Glen Canyon National Recreation Area remain popular tourist destinations. Continued population growth in the western and southwestern United States places more demands on the system of dams and reservoirs on the Colorado River for water, power, and recreational purposes, which are important to the infrastructures and economies of the western United States.^[3]

History

The dam is part of the Colorado River Storage Project for the Upper Colorado Basin. It is located about 4.5 miles (7.2 km) south of the border between Utah and Arizona. According to the U.S. Bureau of Reclamation who operates the dam, "The project furnishes the long-time regulatory storage needed to permit States in the upper basin to meet their flow obligation at Lees Ferry, Arizona, (as defined in the Colorado River Compact) and still use their apportioned water."^[4]

Construction of the dam began in 1956 by the industrial conglomerate, Merritt-Chapman & Scott. Although the dam was not dedicated until 1966, it was able to begin blocking the flow of the river in 1963.

Environmental opposition to dam site

The Sierra Club and other environmental organizations opposed the original plan for damming the Colorado River, including the construction farther upstream of the Echo Park Dam, which would have inundated part of Dinosaur National Monument. When the plan was modified, however, the Sierra Club dropped its objection to the Glen Canyon Dam. Its then Executive Director, David Brower, later called this decision one of the biggest mistakes of his career:

"Glen Canyon died, and I was partly responsible for its needless death. Neither you nor I, nor anyone else, knew it well enough to insist that at all costs it should endure. When we began to find out, it was too late." ^[5]

Continued opposition

In subsequent years the dam has continued to inspire deeply felt opposition. Eco-novelist and essayist Edward Abbey railed against the dam, and considered Glen Canyon the "living heart" of the Colorado River. In his 1975 novel, The Monkey Wrench Gang, the protagonists view the dam as an abomination, and fantasize about blowing it up. On March 21, 1981, Abbey was among the onlookers as a small group of Earth First! activists unfurled a 300-foot (91 m)-long, tapered sheet of black plastic from the top of the dam, making it look as though a gigantic crack had opened in the concrete.^[6]

Since 1996, the Sierra Club has called for increasing the release of water, so that a more natural flow of the river can be restored and Lake Powell can be gradually drained.

Thirty-one years after the dam's completion, Senator Barry Goldwater of Arizona, who originally supported the project, stated in an interview that he would be happier without the lake and expressed regret for voting in favor of its construction.^[7]

Important events in 1983, 1984

Aerial photo of the dam. White line marks waterlevels in 1983, 1984.

The winter of 1982-1983 provided a deep snowpack over much of the watershed behind the dam. This was followed by an exceptionally wet early spring. In May, there was a quick rise in temperatures. All of these factors combined to create perfect conditions for maximum runoff in the Colorado River basin. By early June, the river was rapidly filling Lake Powell. By late June, even with the powerhouse running at full flow capacity and opening bypass jet tubes (for a total flow of 44,000 cfs (1,246 m³/s)), the sustained inflow of over 100,000 cfs (2,832 m³/s) required using the spillways for the first time. Because this was the first test of the spillways, the spillways were shutdown after a few days of operation and were inspected for damage. This inspection showed serious damage from cavitation had already begun. Because the spillways are essential for dam safety, engineers decided to use the left spillway primarily, and keep the right spillway in reserve. The right spillway would only be used if the left spillway became too damaged to handle the required spill volume. To facilitate this mode of operation, an additional 8 feet (2.44 m) of freeboard was immediately added to the spillway gates. This modification prevented water from flowing over the top of the gates, effectively giving Lake Powell more storage capacity, and allowing control of spillway flow volume. This tactic proved effective and the flood was contained, with the high water level rising to within approximately 6 feet (1.8 m) of the dam's crest.

The spillway flows were controlled to 20,000 cfs (566 m³/s) for the left side and 4,000 cfs (113 m³/s) for the right side. Even with the reduced flow levels, there were various indications that the spillway tunnels were being damaged by the flow, including breakdown of the "rooster tail" at the outflow works, and finally a noticeable red color present in the spillway output. After about six weeks of operation, the spillway gates were closed in early August. The tunnels were immediately inspected for damage, and the investigation confirmed that they had sustained serious damage from the high velocity flow, with the left side receiving the most damage. Typically, the tunnel lining had been seriously damaged and/or penetrated for hundreds of feet. In the left tunnel, in the area where maximum damage was sustained, 75% of the conduit's overall circumference was destroyed. This exposed the underlying soft sandstone layer to the high velocity flow and allowed significant erosion beyond the conduit's channel. This included a large hole approximately 35 feet (11 m) deep by 150 feet (46 m) in length.^[8] The followup investigation showed that the damage from cavitation could be reduced by installing an anti-cavitation system similar to the system first used on Montana's Yellowtail Dam. The repairs were completed on a short schedule to be ready in time for the 1984 runoff season. However, the spillways were not used in 1984, except for a short spillway test to verify that the design modification worked as expected.^[9] Passing this test was crucial, because a working spillway is an essential requirement for safe dam operation and it provided the necessary confirmation that the reservoir's operational rules were safe and prudent.

Structure, operations, and reservoir water allocations

Structure

Glen Canyon Dam and Bridge

The Glen Canyon Dam is 710 feet (216 m) high.^[10] The concrete arch dam has a crest length of 1,560 feet (475 m) and contains 4,901,000 cubic yards (3,747,000 m³) of concrete.^[10] The dam is 25 feet (8 m) wide at the crest and 300 feet (91 m) wide at the maximum base.^[10] Its height above the Colorado River is 583 feet (178 m).

Operations

The Hydroelectric plant under the dam

The Glen Canyon hydroelectric powerplant, at the toe of the dam, consists of eight 155,500-horsepower (116,000 kW) Francis turbines. Total nameplate generating capacity for the powerplant is 1,296,000 kilowatts. Eight penstocks through the dam convey water to the turbines.

The dam's hydroelectric plant generated 3.209 billion kilowatt-hours (11.55 PJ) of electricity in 2005.

Runner on display at Glen Canyon Dam.

High volume flows are now periodically released to assist in re-arrangement of river beaches in the canyon, deemed necessary to prevent overgrowth of exotic plant species such as tamarisk and balance the needs of the human population with that of the environment.

Water allocation

Upstream face with control gates for two internal spillways (at left) and eight generators

California, Arizona, Nevada, and New Mexico receive about 8.2 million acre-feet (10.1 km³) of water each year from the Glen Canyon Dam. About 85% of the water goes to irrigation projects, and the rest is diverted to urban areas.^[11]

Environmental impacts

Because of the dam, there has not been the periodic flooding that would wash away and renew sand banks along the portion of the Colorado River that transits the Grand Canyon. Because of the stability of the sand banks, several non-native species of plants became established, adversely affecting the native wildlife.

An environmental impact statement was completed in 1995, which concluded that some effort needed to be made to re-enact flooding events on the river.^[12] Public hearings were held in Salt Lake City, Denver, Phoenix, Flagstaff, Los Angeles, San Francisco, and Washington, D.C. More than 17,000 comments were received during the scoping period, reflecting national attention and the interest of people in the Western States. In accordance with the findings, a controlled flood was held in late March and early April 1996.

The controlled floods appear to have had a beneficial effect upon the downstream ecosystem. However, the results of an experimental flood in early 2005 were mixed. New beaches were built for the rafting industry and the natural sandbars that species in the area depend on were partially restored.

In 2006, the Bureau of Reclamation announced plans to develop another Environmental Impact Statement (EIS) on the implementation of a long-term experimental plan for operational activities at Glen Canyon Dam and other management actions on the Colorado River. The EIS continues efforts of the Glen Canyon Dam Adaptive Management Program created to protect resources downstream of Glen Canyon Dam, including the Grand Canyon, through adaptive management and experimentation.

This EIS process implements the provisions of the settlement agreement recently executed between the United States and the Center for Biological Diversity and other environmental groups in the Center for Biodiversity et al. v. Kempthorne litigation regarding the operation of Glen Canyon Dam. In conformance with the National Environmental Policy Act, this EIS effort will include public involvement and scoping and will consider a range of options and evaluate their ability to address scientific understanding and resource protection objectives.

In 1996, the Bureau of Reclamation found that 8% of the river's flow, almost 1,000,000 acre feet (1.2×10⁹ m³) worth hundreds of millions of dollars annually, disappears between the inflow to Lake Powell and the dam, due to a combination of evaporation and loss into the banks.^[13]

See also

• Risks to the Glen Canyon Dam

References

External links

Wikimedia Commons has media related to: Glen Canyon Dam

• Glen Canyon National Recreation Area
• Glen Canyon Dam page from the Bureau of Reclamation
• Images of Glen Canyon before it was flooded
• Article by David Brower on restoring Glen Canyon
• The Glen Canyon Institute
• 1995 Glen Canyon EIS
• New Environmental Impact Assessment of the Glen Canyon Dam (2006)

Coordinates: 36°56′14″N 111°29′04″W / 36.93712°N 111.484355°W / 36.93712; -111.484355