Marble Canyon Dam

Marble Canyon Dam
Location of the proposed Marble Canyon Dam in the western United States, lower site
Country	United States
Location	Coconino County, Arizona
Coordinates	36°25′2.5″N 111°52′06.75″W / 36.417361°N 111.8685417°W / 36.417361; -111.8685417Coordinates: 36°25′2.5″N 111°52′06.75″W / 36.417361°N 111.8685417°W / 36.417361; -111.8685417
Status	Proposed
Construction cost	$238 million (est.)
Owner(s)	U.S. Bureau of Reclamation
Dam and spillways
Impounds	Colorado River
Height	310 ft (94 m)
Reservoir
Creates	Marble Canyon Reservoir
Total capacity	363,000 acre·ft (0.448 km3)
Normal elevation	3,140 ft (960 m)
Power station
Installed capacity	600 MW
Annual generation	2.31 billion KWh

The Marble Canyon Dam, also known as the Redwall Dam, was a proposed dam on the Colorado River in Arizona. The dam was intended to impound a relatively small reservoir in the central portion of Marble Canyon to develop hydroelectric power. Plans centered on two sites between miles 30 and 40 in the canyon. At one point a 38-mile (61 km) tunnel was proposed to a site just outside Grand Canyon National Park to develop the site's full power generation potential, reducing the Colorado River to a trickle through the park.

Although first proposed in the 1920s to generate hydroelectricity, work did not begin until the dam was incorporated as part of the U.S. Bureau of Reclamation (USBR)'s Pacific Southwest Water Plan in the 1940s for its Central Arizona component. Together with Bridge Canyon Dam, located at the lower end of the Grand Canyon, it would have provided the hydroelectric power necessary to lift Colorado River water from Lake Havasu to central Arizona's farms and cities, including Phoenix and Tucson. The two dams would have operated as "cash register" facilities to provide funds for future reclamation projects through the sale of cheap hydropower.

After a series of studies and site investigations, the dam was abandoned as a project in order to facilitate legislation creating the Central Arizona Project. The dam sites were incorporated into Marble Canyon National Monument in 1968, which was absorbed into Grand Canyon National Park in 1975.

First proposed in the 1940s by the United States Bureau of Reclamation, the location in Marble Canyon was regarded as one of the most remote and difficult-to-access dam sites in the United States, about 2,500 feet (760 m) below the rim of the canyon. The proposed dam was of moderate size, about 310 feet (94 m) high, using a thin-arch concrete design and retaining about 363,000 acre-feet. To keep the small reservoir free of silt, silt retention dams were needed on the tributary canyons. The retention dam in Paria Canyon was planned to be 380 feet (120 m) tall, and only 70 feet (21 m) wide at the base and 120 feet (37 m) wide at the crest, retaining 100 years of silt deposits. Despite these measures, the Marble Canyon reservoir was projected to have a lifespan of 104 years before filling with silt.