Wednesday, January 23, 2008

Megastructures - Hoover Dam

History Construction of Hoover Dam began in 1931, and the last concrete was poured in 1935 , two years ahead of schedule. President Franklin D. Roosevelt dedicated the dam on September 30,1935. The power plant structures were completed in 1936, and the first generator began commercial operation in October of that year. The 17th and final generator went into commercial operation in 1961.

Hoover Dam was without precedent, the greatest dam constructed in its day. An arch-gravity structure rising 726 feet above bedrock, Hoover is still the Western Hemisphere's highest concrete dam. It is 660 feet thick at its base, 45 feet thick at its crest, and stretches 1,244 feet across the Black Canyon. There are 4.4 million cubic yards of concrete in the dam, power plant and related structures.

Hoover Dam pioneered the Bureau of Reclamation's efforts in multiple-purpose water resources development. The dam controls floods while it stores water for irrigation, municipal, and industrial uses. The dam also provides hydroelectric power generation, recreation and fish and wildlife habitat.

Dam Benefits

Colorado River water irrigates more than a million acres of land in the U.S., and nearly half a million acres in Mexico. The water helps meet the municipal and industrial needs of over 14 million people. As it passes through Hoover's turbines, the water generates low-cost hydroelectric power for use in Nevada, Arizona and California. About 4 billion kilowatt-hours of energy, enough for 500,000 homes, are generated annually:

Irrigation & Storage

Water that was once muddy is now sparkling clear in reservoirs and in stretches of the Colorado River. Hoover and other dams on the Colorado have tamed the turbulent flow, creating clean bodies of water that provide recreation for more than 10 million people each year. These waters have also provided habitats for fish and wildlife in areas that were once nearly barren.

Colorado River water stored behind Hoover Dam irrigates some of America's richest farmlands. Valley and mesa lands in the warm desert climate along the river grow a wide variety of fruits, vegetables and other non-surplus crops throughout the year. Major irrigation projects, which benefit from Hoover's control and regulation of the Colorado River, include the Palo Verde Valley, the Colorado River Indian Reservation, the Yuma and Gila projects in Arizona, and the Imperial and Coachella valleys in California.

By regulating the Colorado River, Hoover Dam assures a steady flow of municipal and industrial water to Los Angeles, San Diego and other cities in the Southwest. Phoenix, Arizona was added to the list when the Central Arizona Project began delivering water in 1985. The Tucson area began to receive project water in 1991. Several agriculture users, a number of smaller cities, and an Indian community between Phoenix and Tucson also benefit from the water availability.

Part of the hydroelectric energy generated at Hoover and Parker dams helps pump water along the Colorado River Aqueduct. The 242-mile-long aqueduct has an annual capacity of 1.212 million acre-feet (1 billion gallons) of water a day. Five pumping stations lift the water 1,617 feet over the mountains between the Colorado River and the coastal plain.

Homes and industries in the Las Vegas metropolitan area receive Colorado River water from Lake Mead through the Robert B. Griffith Water Project, which was completed in 1982.

Hydroelectric Power

Hydroelectric power is created as water rushes through turbines that activate generators. When the water has completed its task, it flows on unchanged to serve other needs. The electricity produced is clean, nonpolluting and, unlike many other forms of energy, renewable.

Through the sale of power and water, a major portion of the money used to construct Reclamation projects is returned to the Federal Treasury. Hoover Dam's approximate $175 million cost was repaid over a 50-year period, with interest. Hoover Dam and power plant revenues from the sale of water and power have repaid approximately $260 million, including interest, to the Federal Treasury, principally from 50-year power contracts that ended May 31, 1987. Several contingencies, including $25 million allocated to flood control, will be repaid with interest over the 30-year contract period which began June 1, 1987.

Water is released from Lake Mead through similar sets of diversion works in both walls of Black Canyon. The water, drawn through the intake towers, flows through pipes called penstocks, to the power plants. The penstocks also can be used to discharge water directly from the reservoir to the river below the dam. The spillways were tested in 1941 and not used again until the record high flows of 1983.

Vital Statistics
Hoover Dam
Height: 726.4 feet (221.28 meters)
Crest Length: 1,244 feet(379.2 meters)
Top Thickness: 45 feet (13.7 meters)
Bottom Thickness: 660 feet (201.2 meters)
Composition: 3.25 million cubic yards
(2.5 million cubic meters) of concrete.
The Reservoir (Lake Mead)
Length: When full 110 miles
Shoreline: 550 miles
Capacity: 28,537,000 acre-feet , including dead storage
Maximum depth: 500 feet
Area: 157,900 acres
Elevation: 1221.4 feet

1 comment:

BigWalls said...

And we'll never know who built it ;)