Glen Canyon Dam is a concrete arch-gravity dam in the southwestern United States, located on the Colorado River in northern Arizona, near the city of Page. The 710-foot-high (220 m) dam was built by the Bureau of Reclamation (USBR) from 1956 to 1966 and forms Lake Powell, one of the largest man-made reservoirs in the U.S. with a capacity of more than 25 million acre-feet (31 km3). The dam is named for Glen Canyon, a series of deep sandstone gorges now flooded by the reservoir; Lake Powell is named for John Wesley Powell, who in 1869 led the first expedition to traverse the Colorado River's Grand Canyon by boat. Glen Canyon and Lake Powell are managed by the Department of the Interior within Glen Canyon National Recreation Area. A dam in Glen Canyon was studied as early as 1924, but these plans were initially dropped in favor of the Hoover Dam (completed in 1936) which was located in the Black Canyon. By the 1950s, due to rapid population growth in the seven U.S. and two Mexican states comprising the Colorado River Basin, the Bureau of Reclamation deemed the construction of additional reservoirs necessary. The Glen Canyon Dam remains a central issue for modern environmentalist movements. Beginning in the late 1990s, the Sierra Club and other organizations renewed the call to drain Lake Powell and dismantle the dam. Since first filling to capacity in 1980, Lake Powell water levels have fluctuated greatly depending on water demand and annual runoff. The operation of Glen Canyon Dam helps ensure an equitable distribution of water between the states of the Upper Colorado River Basin (Colorado, Wyoming, and most of New Mexico and Utah) and the Lower Basin (California, Nevada and most of Arizona). During years of drought, Glen Canyon guarantees a water delivery to the Lower Basin states, without the need for rationing in the Upper Basin. In wet years, it captures extra runoff for future use. The dam is also a major source of hydroelectricity, averaging over 4 billion kilowatt hours per year. The long and winding Lake Powell, known for its scenic beauty and recreational opportunities including houseboating, fishing and water skiing, attracts millions of tourists each year to the Glen Canyon National Recreation Area. In addition to its flooding of the scenic Glen Canyon, the dam's economic justification was questioned by some critics. It became "a catalyst for the modern environmental movement," and was one of the last dams of its size to be built in the United States. The dam has been criticized for the large evaporative losses from Lake Powell and its impact on the ecology of the Grand Canyon, which lies downstream; environmental groups continue to advocate for the dam's removal. Water managers and utilities state that the dam is a major source of renewable energy and provides a buffer for severe droughts.
Background
The need for a dam The Colorado River is the single largest source of water in the southwestern United States and northwest Mexico; before massive dam projects tamed the river in the 20th century, its flow was far from dependable. Annual discharge from the Colorado River and its tributaries ranges from 4 to 22 million acre-feet (4.9 to 27.1 km3), and 10-year averages may fluctuate as much as 1 million acre-feet (1.2 km3). Flooding, and the river's enormous silt or sediment load, created problems for settlements in the Lower Colorado River Valley and navigation on the lower portion of the river. During droughts, there was too little water available for irrigation. In 1904, the Colorado River was accidentally redirected after it damaged a canal gate in Mexico, causing the river to flood part of California's Imperial Valley and create the Salton Sea. After this catastrophe, California and Arizona began to call for a dam to control the tempestuous river.
… excerpt ends here. Continue reading the full article.
