Lake Powell, formed by the dam, extends 186 mi (299 km) upstream into S Utah. The lake was named after the American explorer John W. Powell, who mapped and named the canyon in 1870. This lake is the nucleus of the Glen Canyon National Recreation Area (see National Parks and Monuments, table). Downstream is the Glen Canyon Bridge, 1,271 ft (387 m) long and 700 ft (213 m) high, one of the world's longest and highest steel-arch bridges.

Glen Canyon Dam is a dam on the Colorado River at Page, Arizona, USA, operated by the United States Bureau of Reclamation. The purpose of the dam is to provide water storage for the arid southwestern United States, and to generate electricity for the region's growing population. Damming the river flooded Glen Canyon and created a large reservoir called Lake Powell. 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.

History

The dam is part of the Colorado River Storage Project for the Upper Colorado Basin. It is located about south of the border between Utah and Arizona. According to the Bureau of Reclamation, "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.

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.

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." (From the 1963 Sierra Club book, The Place No One Knew, edited by Brower)

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 -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.

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.

Despite 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.

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.

Structure and operations

The Glen Canyon Dam is 710-feet (216-m) high. The concrete arch dam has a crest length of and contains 4,901,000 cubic yards (3,747,000 m³) of concrete. The dam is wide at the crest and wide at the maximum base. Its height above the Colorado River is .

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. Average residential per-capita electrical usage in Arizona in 2001 was 4,937 kilowatt-hours ; per these statistics, the plant generates enough electricity to supply about 650,000 persons in the region with household power.

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.

Environmental impacts

Owing to this 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. 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 a million acre feet 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.

References

External links

• 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)