The Story of Hoover
Dam
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 onequarter 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.
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.
Related Topics
Colorado River Basin
Map
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 12month 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.
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-
Related Topics
Hydroelectric
Generators
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.
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
(35,200,000,00
0 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
Mix
Proportions
•
•
•
•
•
•
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
•
•
•
•
•
•
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.