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 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 . 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.Needham, p. 202 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.Martin, p. 3 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 , and 10-year averages may fluctuate as much as . 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.Reisner, p. 123 After this catastrophe, California and Arizona began to call for a dam to control the tempestuous river.Martin, p. 21
In 1922, six U.S. states signed the Colorado River Compact to officially allocate the flow of the Colorado River and its tributaries. Each half of the Colorado River Basin—the Upper Basin, comprising Colorado, New Mexico, Utah and Wyoming—and the Lower Basin, with California and Nevada—was allotted of water annually, and Treaty relating to the utilization of waters of the Colorado and Tijuana Rivers and of the Rio Grande was signed in 1944 allocating to Mexico. The third lower basin state, Arizona, did not ratify the Compact until 1944 because it was concerned that California might seek to appropriate a portion of its share before it could be put to use.Martin, pp. 25–29
The total, , was based on only thirty years of streamflow records starting in the late 1890s. It was believed to represent the annual flow as measured at Lee's Ferry, Arizona (the official dividing point of the upper and lower basins), downstream of present-day Glen Canyon Dam. As it turned out, the early 20th century was one of the wettest periods in the last 800 years. The dependable natural flow past Lees Ferry is now believed to be about .
The general consensus among inhabitants of the Colorado River basin and government officials was that a high dam had to be built on the Colorado to control floods and provide carry-over water storage for times of drought.Stevens, pp. 15–18 Possible locations for this dam were debated for years, and the Bureau of Reclamation's first study for a dam at Glen Canyon was made in 1924, in addition to studies for locations at Black and Boulder Canyons lower on the Colorado, below Grand Canyon.Rogers, p. 9 These studies found that the lower Colorado sites had stronger foundation rock which might result in less reservoir seepage. The Glen Canyon site was so remote that delivering supplies and transporting workers there would be infeasible at the time. The first Glen Canyon proposal lay upstream of the Lee's Ferry dividing line, and would be considered the Upper Basin's water. With its substantial Congressional clout, California refused to allow the "virtual faucets" of a Colorado River dam "to be built in what amounted to hostile territory."Martin, p. 28
With the Glen Canyon site out of the question, the initial need for a reservoir was realized in 1936 with the completion of Hoover Dam in Black Canyon, storing in the mammoth reservoir of Lake Mead. It was not able to weather the worst floods or droughts, and was filling with sediment at a rate that would render it useless in a few hundred years. But most importantly, Hoover only controlled the lower portion of the river. The Upper Basin states, whose rivers remained undammed, had no way to ensure they could fulfill their delivery obligation to the Lower Basin states while retaining enough water for their own use. Without storage reservoirs of their own, the Upper Basin states risked a "call" on the Colorado River during drought years: they would be forced to use less water in order to keep the river flowing to Lake Mead and California, the state with the most senior water rights.
Colorado River Storage Project
To provide water for the Upper Basin and ensure delivery to the Lower Basin, the Bureau of Reclamation proposed the Colorado River Storage Project, which would consist of a dam on the Colorado River at Glen Canyon, several dams on the Gunnison River and San Juan River, and a pair of dams to be built on the Green River, the Colorado's major upper tributary, at Echo Park and Split Mountain.Martin, p. 54 The 1956 Colorado River Storage Project Act authorized the purposes of "regulating the flow of the Colorado River, storing water for beneficial consumptive use, providing for reclamation of arid and semi-arid lands, providing flood control, and generating hydropower."
The proposal for Glen Canyon Dam was most vocally supported by the state of Arizona, which wished to get Colorado River water to Phoenix and Tucson, located hundreds of miles away from the Colorado in the center of the state. Glen Canyon Dam would regulate river flow between Lee's Ferry and Lake Mead, where the Colorado drops some , allowing the future construction of two additional hydroelectric dams, at Marble Canyon and Bridge Canyon. These two dams would be partially inside Grand Canyon National Park. Glen, Marble and Bridge together would provide the power necessary to pump water to where it was needed in central Arizona. In 1963, Arizona's congressional delegation proposed these dams as part of the Central Arizona Project to accomplish these goals. The state of California opposed the project, as it would eliminate the "surplus" water in the Colorado (really the Upper Basin's yet unused supplies) it had gotten accustomed to using.Martin, p. 56
The Bureau of Reclamation recognized a more serious problem. Construction of the Storage Project, and allowing the Upper Basin to develop its water supplies, would tip the whole Colorado River system toward a structural water deficit since the Colorado River's average flow is less than what was apportioned in the 1922 Compact. The USBR predicted that by 2030 the annual water supply for the Lower Basin would fall by twenty-five percent, to . To make up for this deficit, the USBR incorporated these proposals with the "Pacific Southwest Water Plan" on January 21, 1964, in which power sales from Glen, Marble and Bridge (often called "cash register dams") would be used to fund a diversion of water from the wetter Pacific Northwest to the Colorado Basin. In addition to the proposed diversion of the Trinity River in Northern California, Marc Reisner wrote in Cadillac Desert that "in the Pacific Northwest there was a lot of suspicion that the Pacific Southwest Water Plan was merely a smokescreen for a much larger plan, long a gleam in the Colorado Basin's eye, to tap the Columbia River."Reisner, p. 273–275
Environmental concerns
The Echo Park dam would be inside the federally protected Dinosaur National Monument and would submerge of scenic canyons – a move that alarmed environmentalists. The environmental organization Sierra Club, led by David Brower, was the most vocal opponent of Echo Park Dam, and fought a protracted battle against the Bureau of Reclamation, on the basis that "building the dam would not only destroy a unique wilderness area, but would set a terrible precedent for exploiting resources in America's national parks and monuments".Billington, Jackson and Melosi, p. 398
The Bureau of Reclamation favored the Echo Park site over Glen Canyon, because its narrow canyons and high elevation (more than , as compared to at Glen Canyon) would lead to less evaporation. It said that building Echo Park Dam and a "low" Glen Canyon Dam would save of water per year over a "high" Glen Canyon Dam (which was ultimately the version to be built). While studying the figures, Brower discovered that the difference should be no more than .Harvey, p. 193 Although it is unclear whether the discrepancy was due to a miscalculation or intentional manipulation, Brower said "it would be a great mistake [to rely on the Bureau's figures] when they cannot add, subtract, multiply and divide."
In the face of public scrutiny, and wishing to avoid more questions about the Colorado River Storage Project as a whole, the Bureau of Reclamation dropped the Echo Park proposal in 1954. Even as construction began on the other dams, the drama of the Echo Park debate had shifted the American public's perception on big government projects and their environmental consequences.Gahan and Rowley, p. 698 Echo Park was considered a victory for the American environmental movement, but it only happened in exchange for a dam upstream at Flaming Gorge, and increasing the size of the proposed dam at Glen Canyon to replace the storage that would have been provided by Echo Park.Billington and Jackson, p. 337 A common misconception is that the environmentalists were given a choice between damming Echo Park and damming Glen Canyon, but the USBR "had always planned to build a dam at Glen Canyon, regardless of the outcome of the Echo Park debate".Rogers, p. 13