page_title: Glen Canyon Dam
section_title: Dam and spillways
hierarchical_section_title: Glen Canyon Dam / Design / Dam and spillways
caption_attribution_description: English: Glen Canyon — with Glen Canyon Dam, Glen Canyon substation, Lake Powell, and the bridge, in northern Arizona.
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: Glen Canyon's overall design was based on that of Hoover Dam – a massive concrete arch-gravity structure anchored in solid bedrock – with several significant changes. The engineers wanted the dam to rely predominantly on its arch shape to carry the tremendous pressure of the impounded water into the canyon walls instead of depending on the sheer weight of the structure to hold the reservoir back, as had been done at Hoover. However, the foundation rock at Glen Canyon consists of porous sandstone prone to spalling, in contrast to the stronger granite at the Hoover Dam site, forcing the Glen Canyon design to follow more conservative lines by greatly thickening the abutments, thus increasing the surface area through which the weight of dam and reservoir would be transmitted to the rock and relieving the pressure per square inch on the highly breakable cliffs.
  The Glen Canyon Dam is 710 feet (220 m) high from the foundations and stands 583 feet (178 m) above the Colorado River. The crest of the dam is 1,560 feet (480 m) long and 25 feet (7.6 m) wide, while the maximum thickness of the base is 300 feet (91 m). The elevation at the crest is 3,715 feet (1,132 m), and the elevation of the Colorado River below the dam is 3,132 feet (955 m). In total, the dam contains 5,370,000 cubic yards (4,110,000 m³) of concrete and 28,900,000 pounds (13,100,000 kg) of reinforcing steel. The hydroelectric power station and river outlet works are located at the foot of the dam. The outlet works consist of four 96-inch (240 cm) diameter pipes, each controlled by a ring gate and hollow-jet valve. The discharge capacity of the river outlet works is 15,000 cubic feet per second (420 m³/s).
  The two spillway tunnels are excavated through the canyon walls on each side of the dam. Twin radial gates, each 40 feet (12 m) wide and 52.5 feet (16.0 m) high, control the flow of water into the spillways. Together, the spillways can pass up to 208,000 cubic feet per second (5,900 m³/s). The tunnels required 132,000 cubic yards (101,000 m³) of excavation and another 110,000 cubic yards (84,000 m³) of concrete lining. The circular, concrete-lined spillway tunnels plunge at a 55-degree angle, reducing in diameter from 48 to 41 feet (15 to 12 m), until they intersect with the old river diversion tunnels at sharp elbow joints before returning to the Colorado River. This was done as a cost-saving measure, but resulted in the destruction of both spillways during the 1983 flood releases. The repairs, in which air slots were installed to prevent cavitation shock waves, cost about $15 million.
caption: An aerial view of Glen Canyon Dam from upstream, showing the spillways to lower left and right, the Glen Canyon Bridge and the electric switchyard to the right of the bridge.
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