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Hoover Dam is a testimony to a country\'s ability to construct monolithic projects in the midst of adverse conditions. Built during the Depression; thousands of men and their families came to Black Canyon to tame the Colorado River. It took less than 5 years, in a harsh and barren land, to build the largest dam of its time. Now, more than 60 years later, Hoover Dam still stands as a world-renowned structure. The dam is a National Historic Landmark and has been rated by the American Society of Civil Engineers as one of America\'s Seven Modern Civil Engineering Wonders.
A Hoover Dam History
The High-Scalers
Millions of years of weather eroded the canyon walls. Water froze in cracks and crevices, splitting the rock. Before construction could begin on the dam, this loose rock had to be removed. Special men were required for the job, men called \"high-scalers.\"
Their job was to climb down the canyon walls on ropes. Here they worked with jackhammers and dynamite to strip away the loose rock. The men who chose to do this work came from many backgrounds. Some were former sailors, some circus acrobats, some were American Indians. All of them were agile men, unafraid to swing out over empty space on slender ropes.
It was hard and dangerous work, perhaps the most physically demanding work on the entire project. Laden with tools and water bags, the men would descend the canyon walls. Jackhammer drills were lowered to them, and powder holes were drilled into the rock. The jackhammers weighed 44 lbs. and had to be maneuvered into position by hand Once the holes had been drilled into the rock, they were loaded with dynamite. After the shot, broken rocks sometimes had to be levered free using crowbars.
Moving about on the cliffs was difficult and dangerous. Live air hoses, electrical lines, bundles of drill steel festooned the cliffs. The scalers had to carefully pick their way through the resulting maze. The danger from falling rocks and dropped tools was extreme. The most common cause of death during the building of the dam was being hit by falling objects. The men began making improvised hard hats for themselves by coating cloth hats with coal tar. These \"hard-boiled hats\" were extremely effective. Several men were hit by falling rocks so hard that their jaws were broken by the impact, yet they did not receive skull fractures. Because of these \"hard-boiled hats,\" men survived accidents which would otherwise have killed them. The Six Companies contracted for commercially made hard hats and issued them to every man on the project. The use of hard hats was encouraged, and deaths from falling objects were reduced.
The risk and high visibility of the job lent it a certain status which appealed to some types of men. When the foremen weren\'t looking, they would swing out from the cliffs and perform stunts for the workers below. Contests were held to see who could swing out the farthest, the highest, or who could perform the best stunts.
It wasn\'t all done for fun and games, though. For several weeks, scaler Louis \"The Human Pendulum\" Fagan transported a crew of shifters around a projecting boulder on the Arizona side. The man to be transferred would wrap his legs around Fagan\'s waist, grasp the rope, and with a mighty leap, they would sail out into the air and swing around the boulder. Fagan then returned for the next man in the crew. This acrobatic commute was accomplished twice a day until the job was finished.
Perhaps the most famous feat any of the high scalers ever performed was a daring midair rescue. Burl R. Rutledge, a Bureau of Reclamation engineer, fell from the canyon rim. Twenty-five feet below, high scaler Oliver Cowan heard Rutledge slip. Without a moment\'s hesitation, he swung himself out and seized Rutledge\'s leg. A few seconds later, high scaler Arnold Parks swung over and pinned Rutledge\'s body to the canyon wall. The scalers held Rutledge until a line was dropped and secured around him and the shaken engineer was pulled, unharmed, to safety.
Hoover Dam - How It All Works
Hoover Dam is a part of the Bureau of Reclamations\'s multipurpose projects on the Colorado River. These projects control floods; they store water for irrigation, municipal, and industrial use; and they provide generation of hydroelectric power, recreation, and fish and wildlife habitat.
Lake Mead, with a storage capacity of 28,537,000 acre-feet, is the largest man-made lake in the United States.
The Hoover Dam Power Plant has 17 large generators and has a rated capacity of more then 2,000 megawatts.
Through the sale of power and water, the Bureau of Reclamation has been able to return to the Federal Treasury the cost of its operations on the Colorado River.
The Dam
Hoover Dam is a concrete arch-gravity type, in which the water load is carried by both gravity action and horizontal arch action. The first concrete for the dam was placed on June 6, 1933, and the last concrete was placed in the dam on May 29, 1935.
The dam was built in blocks or vertical columns varying in size from about 60 feet square at the upstream face of the dam to about 25 feet square at the downstream face. Adjacent columns were locked together by a system of vertical keys on the radial joints and horizontal keys on the circumferential joints. Concrete placement in any one block was limited to 5 feet in 72 hours. After the concrete was cooled, a cement and water mixture called grout was forced into the spaces created between the columns by the contraction of the cooled concrete to form a monolithic (one piece) structure.
Hoover Dam contains three and one-quarter million cubic yards of concrete. There are 4,360,000 cubic yards of concrete in the dam, powerplant, and appurtenant works. This much concrete would build a monument 100 feet square and 2-1/2 miles high; would rise higher than the Empire State Building (which is 1,250 feet) if placed on an ordinary city block; or would pave a standard highway, 16 feet wide, from San Francisco to New York City.
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Related Topics
Hoover Dam Statistics
The Reservoir
At elevation 1221.4, Lake Mead contains 28,537,000 acre-feet. An acre-foot is the amount of water required to cover 1 acre to a depth of 1 foot, or approximately 326,000 gallons. The reservoir will store the entire average flow of the river for 2 years. That is enough water to cover the State of Pennsylvania to a depth of one foot.
Lake Mead extends approximately 110 miles upstream toward the Grand Canyon. It also extends about 35 miles up the Virgin River. The width varies from several hundred feet in the canyons to a maximum of 8 miles. The reservoir covers about 157,900 acres or 247 square miles.
Recreation, although a by-product, constitutes a major use of the lakes and controlled flows created by Hoover and other dams on the lower Colorado River today. Lake Mead is one of America\'s most popular recreation areas, with a 12-month season that attracts more than 9 million visitors each year for swimming, boating, skiing, and fishing. The lake and surrounding area are administered by the National Park Service as part of the Lake Mead National Recreation Area, which also includes Lake Mohave downstream from Hoover Dam.
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Related Topics
Colorado River Basin Map
The Power Plant
There are 17 main turbines in Hoover Powerplant. The original turbines were all replaced through an uprating program between 1986 and 1993. With a rated capacity of 2,991,000 horsepower, and two station-service units rated at 3,500 horsepower each, for a plant total of 2,998,000 horsepower, the plant has a nameplate capacity of 2,074,000 kilowatts. This includes the two station-service units, which are rated at 2,400 kilowatts each.
Hoover Dam provides generation of low-cost hydroelectric power for use in Nevada, Arizona, and California. Hoover Dam alone generates more than 4 billion kilowatt-hours a year - enough to serve 1.3 million people. From 1939 to 1949, Hoover Powerplant was the world\'s largest hydroelectric installation; with an installed capacity of 2.08 million kilowatts, it is still one of the country\'s largest.
Hoover Dam\'s $165 million cost has been repaid, with interest, to the Federal Treasury through the sale of its power. Hoover Dam energy is marketed by the Western Area Power Administration to 15 entities in Arizona, California, and Nevada under contracts which expire in 2017. Most of this power, 56 percent, goes to southern California users; Arizona contractors receive 19 percent, and Nevada users get 25 percent. The revenues from the sale of this power now pay for the dam\'s operation and maintenance. The power contractors also paid for the uprating of the powerplant\'s nameplate capacity from 1.3 million to over 2.0 million kilowatts.
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Related Topics
Hydroelectric Generators
Dam Dimensions
. Height - 726.4.feet (221.3 meters)
. Length at Crest - 1,244 feet (379.2 meters)
. Width at Top - 45 feet (13.7 meters)
. Width at Base - 660 feet (201.2 meters)
. Weight - 6.6 million tons Reservoir Statistics
. Capacity - 28,537,000 acre-feet (35,200,000,000 cubic meters)
. Length - 110 miles (177 kilometers)
. Shoreline - 550 miles (885 kilometers)
. Max Depth - 500 feet (152 meters)
. Surface Area - 157,000 acres (63,900 hectares)
Quantities of Materials Used in Project
. Concrete - 4.440,000 cubic yards
. Explosives - 6,500,000 pounds
. Plate Steel and Outlet Pipes - 88,000,000 pounds
. Pipe and Fittings - 6,700,00 pounds (840 miles)
. Reinforcement Steel - 45,000,000 pounds Concrete Mix Proportions
. Cement - 1.00 part
. Sand - 2.45 parts
. Fine Gravel - 1.75 parts
. Intermediate Gravel - 1.46 parts
. Coarse Gravel - 1.66 parts
. Cobbles (3 to 9 inch) - 2.18 parts
. Water - 0.54 parts
Hydroelectric Generators
The Hoover Dam Powerplant is arranged in two wings, 650 feet in length, one on each side of the river. There are nine main generator units on the Arizona side of the river and eight on the Nevada side. The larger of these units each have a generating output of 133 megawatts. There are two in-house generators capable of generating 2,400 kilowatts each. The total rated capacity of the plant is 2,074 megawatts.
Hydroelectric Generators
The primary parts of a generating unit are:
The Exciter
The Rotor
The Stator
The Shaft
The Turbines
The exciter sends an electric current to the rotor, a large electromagnet, charging it with a magnetic field. The rotor spins inside the stator, a tightly wound coil of wire. The moving magnetic field causes an electric current to move through the stator. This current, at 16,500 volts, leaves the generator and is then carried to the transformers where it is \'stepped up\' to 230,000 volts for transmission. The rotor is propelled by a shaft connected to turbines. Water falling through penstocks connected to the reservoir supplies the energy to spin the turbines.
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