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U.S. Department of the Interior
Hoover Dam is the highest and third largest concrete dam in the United States. The dam, powerplant, and high-voltage switchyards are located in the Black Canyon of the Colorado River on the Arizona-Nevada state line. Lake Mead, the reservoir behind the dam, can hold the average two-year flow of the Colorado River. Hoover Dam's authorized purposes are: first, river regulation, improvement of navigation, and flood control; second, delivery of stored water for irrigation and other domestic uses; and third, power generation. Lake Mead also provides outstanding outdoor, water-based recreation opportunities, and is home to a myriad of wildlife.
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Waters of the Colorado River are impounded by Hoover Dam. This water is released when needed to meet downstream demands for irrigation or domestic water, or when the dam is being operated under flood control criteria. The water is released at a time and in a way to meet the water delivery need, and to maximize other benefits, including power generation. Irrigation water is provided to numerous Reclamation projects in the lower Colorado River Basin, including the Imperial Irrigation District and Coachella Valley Water District (through the All-American Canal system); the Gila, Yuma, and Yuma Auxiliary Projects; the Palo Verde Project near Blythe, CA, the Colorado River Indian Reservation, and the Central Arizona Project. A dependable supply of water for domestic purposes also is provided to the semiarid southern California coastal region, to central and southern Arizona, and to southern Nevada. The water for southern California is diverted at Lake Havasu and transported through the Metropolitan Water District`s Colorado River Aqueduct to the district`s area of use. The water for Arizona is also diverted from Lake Havasu, by the Central Arizona Project aqueduct, and transported into the State`s interior. Southern Nevada withdraws its water from Lake Mead through the Robert B. Griffith (formerly Southern Nevada Water) Project.
Hoover Dam and Lake Mead
Hoover Dam, about 35 miles southeast of Las Vegas, Nevada, is a concrete thick-arch structure, 726.4 feet high and 1,244 feet long at the crest. The dam contains about 3,250,000 cubic yards of concrete; total concrete in the dam and appurtenant works is 4,400,000 cubic yards. The reservoir behind the dam, Lake Mead, had an original total storage capacity of 32,471,000 acre-feet. Following completion of a sedimentation survey conducted in 1963-64, it was calculated that the total storage capacity had been reduced to 27,377,000 acre-feet, which includes 1.5 million acre-feet of space reserved exclusively for flood control.
To bypass and control the river during construction, four 50-foot-diameter, concrete-lined tunnels were constructed through the canyon walls, two on each side of the river. The tunnels averaged about 4,000 feet in length. When no longer needed for diversion purposes, the upstream tunnel entrances were closed by huge steel gates, and concrete plugs were placed near the midpoint of each tunnel. The downstream sections were incorporated into the dam's spillway and outlet works features. A total of 315,000 cubic yards of concrete was used to line the diversion tunnels.
There are two drum-gate controlled channel spillways, one on each side of the canyon. Each spillway discharges through an inclined, concrete-lined tunnel that connects with the remaining portion of the original outer diversion tunnel downstream from the tunnel plug. The crest of each spillway is surmounted by three piers that divide the crest into four 100-foot sections, each equipped with a 16- by 100-foot drum gate. The spillway capacity at reservoir elevation 1229.0 with the gates in the raised position is 64,800 cubic feet per second. At surface elevation 1229.0 with the gates lowered, the design capacity of the spillways is 400,000 cubic feet per second.
Four combination penstock and outlet units are provided, each originating at one of the four intake towers upstream from the dam, and installed in a tunnel back of the dam abutments. The penstock and outlet units originating at the upstream intake towers are installed in the inner pair of the four tunnels originally used for river diversion. The two penstock and outlet units originating at the downstream intake towers are installed in tunnels located about 170 feet above the lower units. Beyond the penstock outlets, each downstream unit branches into outlet pipes which terminate in the Arizona and Nevada canyon-wall valve houses.
The capacity of the canyon-wall and tunnel-plug outlets at reservoir water surface elevation 1225.0 is 52,600 cubic feet per second. The total release capacity through the canyon wall outlet works, tunnel plug outlet works, and generating units, is 100,600 cubic feet per second.
The powerplant is located at the toe of the dam, with wings that extend downstream 650 feet along each canyon wall. The turbines are designed to operate at heads ranging from 420 to 590 feet. The final generating unit, N-8, was installed at Hoover Dam in 1961, giving the dam a total of 17 commercial generating units. Installation of Unit N-8 brought the powerplant's rated capacity to 1,850,000 horsepower. Two station-service units, rated at 3,500 horsepower each, increased the plant total to 1,857,000 horsepower. In terms of electrical energy, the total rated capacity for the plant was 1,344,800 kilowatts, including the two station-service units, rated at 2,400 kilowatts each, at the end of 1961. Between 1982 and 1993, the 17 commercial generating units were uprated with new turbines, and new transformers and breakers were installed, raising the plant's capacity to its current levels of 2,991,000 horsepower and 2,074,000 kilowatts
The dam, powerplant and all appurtenant facilities are owned, operated, and maintained by the Bureau of Reclamation, as are the transformer and switching facilities. Prior to 1987, the powerplant, transformer and switching facilities were operated and maintained by the Los Angeles Department of Water and Power, and the Southern California Edison Co.
Through the treaty concluding the Mexican War in 1849 and the Gadsden Purchase of 1853, the United States acquired the territories of New Mexico, Arizona, and California. Discovery of gold in California in 1849 brought hordes of adventurers westward. They crossed the Colorado River near Yuma, Arizona, and at Needles, California. In 1857, Lieutenant J. C. Ives traveled 400 miles up the river by boat from the Gulf of California to Black Canyon, present site of Hoover Dam. He reported the region to be valueless.
In 1869, Major J. W. Powell of the Geological Survey succeeded in leading a river expedition down the canyon of the Colorado. The expedition traveled from Green River in Utah to the Virgin River in Nevada - through more than a thousand miles of unknown rapids and treacherous canyons.
Investigations
In 1875, a route was mapped for a canal to irrigate southern California`s rich but arid land. Construction of the canal began about 20 years later, and in 1901 the first water from the Colorado River flowed through the Imperial Canal into the Imperial Valley.
The river, annually fed by melting snows in the Rocky Mountains, typically swelled to a raging flood in the spring, then dried to a trickle in the late summer and fall, so crops were frequently destroyed. Farmers built levees to keep out the river, but, even when the levees held, crops withered and died when the river ran too low to be diverted into the canals.
In 1905, a disastrous flood burst the banks of the river, and it flowed for nearly two years into the Salton Sink in the Imperial Valley, creating what is now known as the Salton Sea. The river was eventually turned back into its original channel, but the continuing threats of floods remained.
Faced with constantly recurring cycles of flood and drought, residents of the Southwest appealed to the then-Reclamation Service to solve the problem. Engineers began extensive studies of the river in search of a feasible plan for its control. In 1918, a plan was conceived for regulation of the river by building a single dam of unprecedented height in Boulder Canyon, about eight miles upstream of the dam's eventual location. The Colorado River Compact, signed at Santa Fe, New Mexico, on November 24, 1922, cleared the way for construction of the dam by allocating most of the river`s estimated flow between the upper and lower basins of the river and providing for later division of what was thought to be water excess to these allocations.
The project was authorized by the Boulder Canyon Project Act of December 21, 1928 (45 Stat. 1057), subject to the terms of the Colorado River Compact. The act authorized the construction of a dam and powerplant in either Boulder or Black Canyon, and the All-American Canal System in southern California. The Boulder Canyon Project Adjustment Act (54 Stat. 774), dated July 19, 1940, provided for certain changes in the original plan.
On October 1, 1977, in conformance with Public Law 95-91 (Department of Energy Organization Act of August 4, 1977), the power marketing function (including transmission lines and attendant facilities) of the Bureau of Reclamation was transferred to the Department of Energy. However, operation and maintenance of the Federal hydroelectric generating plants along the Colorado River remained under the Bureau of Reclamation's jurisdiction. Effective October 9, 1977, administration of the Boulder Canyon Project (Hoover Dam) and portions of the Parker-Davis Project were combined into one operational unit, now called the Lower Colorado Dams Project.
On August 17, 1984, Congress passed the Hoover Power Plant Act of 1984. This act authorized an increase in the capacity of the existing generating equipment at the Hoover Dam power plant, and the improvement of parking, visitor facilities, and roadways and other facilities to contribute to the safety and sufficiency of visitor access to Hoover Dam and Powerplant.
The Boulder Canyon Project is characterized by the extraordinary. The height and base thickness of the dam, the size of the power units, the dimensions of the fusion-welded plate-steel pipes, the novel system of artificially cooling the concrete, the speed and coordination of construction, and other major features of the project were without precedent for their time. The magnitude of the construction introduced many new problems and intensified many usual ones, requiring investigations of an extensive and diversified character to ensure structures representing the utmost in efficiency, safety, and economy of construction and operation. Construction was begun in Black Canyon in 1931 and the dam was dedicated on September 30, 1935. The first generator of the powerhouse was in full operation on October 26, 1936. The last generator went into operation on December 1, 1961. In 1962, the construction railroad spur from Boulder City, Nevada., to the dam was sold and removed.
Little changed at the dam until construction of new visitor facilities at Hoover Dam was initiated in 1986. The initial items of work included relocation of two existing electric transmission towers and realignment of a small portion of the highway on the Nevada side of the dam. Construction was halted in 1988 because of a lack of funding, but resumed again in 1989 with the excavation of a new elevator shaft in the Nevada canyon wall. Construction of the visitor building and parking garage was initiated in 1991, and the new facilities - the visitor center, parking structure, and a new penstock viewing platform - were opened to the public on June 21, 1995.
The project assures a dependable water supply to irrigate more than 2 million acres of land in southern California and southwestern Arizona, and over 400,000 acres in Mexico. These irrigated lands supply large amounts of produce and other agricultural products for the Nation`s markets.
Hoover Dam helps ensure a dependable water supply for municipal, industrial and other domestic uses in southern Nevada, Arizona and southern California. More than 20 million people and numerous industries in these three states receive Colorado River water that was stored by Hoover Dam.
Surrounded by rugged mountains and canyon walls, Hoover Dam and Lake Mead are outstanding scenic and recreation attractions. More than one million people a year now take guided tours of Hoover Dam, and more than nine million people visit the Lake Mead National Recreation Area annually. LMNRA, which includes Lakes Mead and Mohave (formed by Davis Dam), is administered by the National Park Service. LMNRA was America's first designated national recreation area. National Park Service concessionaires provide lodging, boats for hire, and sightseeing boat trips on the lake as well as through Black Canyon below the dam. Other popular activities are camping, picnicking, swimming, boating, water skiing, and year-round fishing for striped bass, large-mouth bass and other game fish. A large part of the area is open to hunting.
Hoover Dam is also a major tourism site. Guided tours of the dam have been provided by the Bureau of Reclamation since 1936, with only a brief hiatus during World War II and following the attacks of September 11, 2001. Prior to 1995, physical limitations at the dam restricted the number of guided tours to about 750,000 people a year. New visitor facilities opened at the dam in June 1995 make it possible for a million or more people annually to take a guided tour of the dam and powerplant.
For specific information about any of these recreation sites, click on the name below:
Hoover Dam on Recreation.govHoover Dam Tours WebsiteLake Mead National Recreation Area on Recreation.govLake Mead National Recreation Area
Hydroelectric Power
Hoover Dam is one of the world`s largest producers of electric power, generating, on average, four billion kilowatt-hours of firm hydroelectric energy annually. This energy played a vital role in the production of airplanes and other equipment during World War II, and it also was instrumental in development of industrial expansion in the Southwest.
Firm power generated at Hoover Dam is provided to 15 contractors in the States of California, Arizona and Nevada under contracts that were signed in 1987, and will expire in 2017. The approximate percentage of firm power delivered to each state is: Nevada, 23.4 percent; Arizona 19 percent; and California, 57.6 percent.
Hoover Dam has virtually ended the possibility of devastating floods striking the lower reaches of the river as they did prior to project construction. The benefits from controlling floods are reflected in the $25 million of the project cost that was allocated by the Congress to flood control. Since 1950, benefits realized from flood control operations on the mainstem of the Colorado River are estimated at $1.26 billion.
