page_title: Glen Canyon Dam
section_title: Filling Lake Powell
hierarchical_section_title: Glen Canyon Dam / Construction / Filling Lake Powell
caption_attribution_description: English: Aerial view of the Glen Canyon Dam, 1965, US Bureau of Reclamation.
context_page_description: Glen Canyon Dam is a concrete arch-gravity dam on the Colorado River in northern Arizona, United States, near the town of Page. The 710-foot high dam was built by the U.S. Bureau of Reclamation from 1956 to 1966 and forms Lake Powell, one of the largest man-made reservoirs in the U.S. with a capacity of 27 million acre feet. 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's Grand Canyon by boat.
  A dam in Glen Canyon was studied as early as 1924, but these plans were initially dropped in favor of the Hoover Dam 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. Contrary to popular belief, Lake Powell was not the result of negotiations over the controversial damming of the Green River within Dinosaur National Monument at Echo Park; the Echo Park Dam proposal was abandoned due to nationwide citizen pressure on Congress to do so.
context_section_description: With a capacity equal to almost two years' annual flow of the Colorado River, engineers were aware that Lake Powell would be difficult to fill, but more problems were encountered than expected. The original plan was to fill Lake Powell to 3,490 feet (1,060 m) above sea level, the minimum level necessary to generate hydroelectric power by late 1964, after which water would be released down to Lake Mead, with only the excess stored in Lake Powell. However, the spring runoff in 1963 was the lowest on record in ten years. By the beginning of 1964, Lake Powell had barely reached half the target level, and Lake Mead had seen a sharp decline. In March, Secretary of the Interior Stewart Udall ordered the filling halted and extra releases made to Lake Mead, to the consternation of the Upper Basin states. In May, Udall changed his mind yet again to lower releases, gambling that the spring runoff would be enough to raise Powell to minimum power pool by autumn, by which time power releases could begin, to prevent Lake Mead from falling below its minimum power pool. That gamble paid off, with Lake Powell barely inching over the 3,490-foot (1,060 m) mark on August 16, 1964.
  It took more than 17 years for Lake Powell to finally reach its full elevation of 3,700 feet (1,100 m) above sea level, which it crossed on June 22, 1980. One of the main reasons for this slow rise, in addition to the need to meet obligations to the Lower Basin, was the leakage of vast amounts of water into the porous Navajo Sandstone aquifer. Between 1963 and 1969, as much as 655,000 acre feet (0.808 km³) leaked into the reservoir banks each year. Conversely, some of this "bank storage" flows back into the reservoir as springs and seeps when Lake Powell is low. Exactly how much of this water has potential to return to the reservoir, and how much "disappears" into the ground, is subject to debate.
  The Bureau of Reclamation projected that once Lake Powell filled, the total bank storage would stabilize at approximately 6 million acre feet (7.4 km³), and henceforth would fluctuate depending on water levels in the reservoir. The actual loss was 13.4 million acre feet (16.5 km³), twice the initial prediction, but river flow data indicates that further leakage after 1980 has been negligible. However, according to a 2013 study by hydrologist Thomas Myers for the Glen Canyon Institute, the reservoir continues to lose about 380,000 acre feet (0.47 km³) each year due to leakage. According to USBR data for water year 2015 (a year when Lake Powell did not experience a significant overall gain or loss in volume), Lake Powell lost a total of 368,000 acre feet (0.454 km³) to evaporation and only 8,000 acre feet (0.0099 km³) to leakage.
caption: Lake Powell filling underway, 1965
exif: {}