Sigma Xi, The Scientific Research SocietyEngineering Hoov

Sigma Xi, The Scientific Research Society
Engineering: Hoover Dam
Author(s): Henry Petroski
Reviewed work(s):
Source: American Scientist, Vol. 81, No. 6 (November-
December 1993), pp. 517-521
Published by: Sigma Xi, The Scientific Research Society
Stable URL: http://www.jstor.org/stable/29775051 .
Accessed: 06/01/2013 08:28
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Hoover Dam
Henry Petroski
Everything seems to move slowly at Hoover
Dam. Long lines of cars, buses and trucks in
low gear wind along the two-lane road
down one steep side of Black Canyon and up the
other. The lines stop frequently as carloads of
tourists crane their necks at the grandeur of the
site, and drivers search for a parking space
among the tiers of overlooks. For all the conges?
tion, few motorists seem impatient or interested
in searching maps for alternate routes. Everyone
driving in this vicinity must know that U.S. High?
way 95, which arcs along the crest of the dam, is
the only road across the Colorado River between
Davis Dam, over 50 miles to the south, and Nava
jo Bridge, over 150 miles to the east.
Pedestrians move about the top of the dam at a
snail's pace in the desert heat, crisscrossing the

crest over which, by design, no water has ever
flowed. Several thousand tourists may visit
Hoover Dam on a summer day, most of them
standing in long lines to board the large elevator
that takes them, 20 at a time, 600 feet down into
the inner workings of the dam. Many come from
Las Vegas, 35 miles to the northwest. Even there,
amid all the noise and neon, a visit to Hoover
Dam is hawked as one of the area's must-do
things. The pitch may be engineering achieve?
ment as awesome entertainment, but few who
visit the works at Black Canyon seem disappoint?
ed by the decided calmness and harmony of it all.
Just as the Mississippi River wreaked havoc in
the Midwest last summer, so the Colorado River
used to be alternately a blessing and a bane for
the Southwest. Although the Colorado seemed a
potential source of water for irrigation in rich but
arid regions such as Arizona and southern Cali?
fornia, it did not provide a consistent supply of
water. It often flooded low-lying lands in the
spring and early summer and then slowed to a
trickle during late summer and early fall. When?
ever crops, cattle and Californians were not
awash, they went thirsty.
Two promising regions with rich alluvial soil
were the Colorado Desert and the below-sea-lev?

el Salton Sink. Near the turn of the century they
were renamed Imperial Valley by land developers
who promised through their California Develop?
ment Company (CDC) to supply enough water
from the Colorado to make the otherwise arid
land attractive. For a few years the scheme
worked and the region was booming, but soon
the CDC's irrigation canal silted up and, in the
face of lawsuits from landowners, a new way to
divert the Colorado's water had to be found
quickly. A hastily engineered scheme?one that
also blunted the impact of the newly formed Bu?
reau of Reclamation's charge that CDC had mo?
nopolized the water supply?brought water up
from Mexico. That worked fine at first, but in 1905
so much water came down the Colorado in
spring and fall floods that the river changed its
course and flowed into the Salton Sink, which
then became the inland Salton Sea. Lost crops,
lost topsoil and a lost irrigation system amount?
ing to millions of dollars presented a disastrous
prospect for Imperial Valley. It was two years be?
fore the Colorado was put back on course, but the
root problems associated with both exploitation
of and protection from the river remained.
The great amount of silt carried southward by
the Colorado kept raising the river's channel, and
so required constant maintenance of the protec?

tive levees and other components of the irriga?
tion system, much of which was located in Mexi?
co. Problems with getting work crews back and
forth across the border led eventually to support
for a new canal located entirely on American soil.
It was in such a climate that a young lawyer
named Phil Swing, supported by southern-Cali?
fornia water interests, was sent in 1917 to repre?
sent them in Congress and to promote the idea of
an "All-American Canal."
Swing's effectiveness led quickly to the intro?
duction of legislation, but the proposal was de?
feated largely because of the opposition of Arthur
Powell Davis, a 40-year veteran of government
service who knew about as much about the Col?
orado River basin as anyone. Davis, nephew of
the Colorado canyon's explorer, John Wesley
Powell, had served as chief hydrographer when a
Panama Canal route was under investigation and
as an engineer with the U.S. Reclamation Service
since its origins in 1902. The driving force behind
the design and construction of many dams and ir?
rigation canals, he was director of the Reclama?
tion Service when the All-American Canal bill
1993 November-December
Henry Petroski is the Aleksandar S. Vesic Professor and chair?
man of the Department of Civil and Environmental Engineering
at Duke University, Durham, NC 27706.

Figure 1. Hoover Dam photographed in 1990. (All photographs
courtesy of the Bureau of Reclamation.)
came before the Congress. He argued successfully
for that bill's defeat in 1919 so that a more com?
prehensive and long-range plan for the Colorado
might be explored first.
A Grand Plan
Years earlier, as a supervising engineer in the
Reclamation Service, Davis had thought about a
grand plan for the entire drainage system of the
Colorado. According to Joseph Stevens, who sub?
titled his telling of the story of Hoover Dam "an
American adventure," Davis's scheme was to be
"an undertaking to rival or even surpass in scale
and importance the construction of the Panama
Canal." Congressman Swing went further and
added the Pyramids, the Great Wall of China and
Solomon's temple to the list of feats of engineer?
ing that were less complicated than what came to
be known as the Boulder Dam Project. Congress
agreed that the great problem of the Colorado
basin should be studied by the Interior Depart?
ment, and its secretary, Albert Fall, assigned the
task to Davis's organization. The Fall-Davis Re?

port, issued in 1922, "contained an exhaustive hy
drological and geological profile of the Colorado
River and its canyons," but most attention was
drawn to its recommendation that the govern?
ment erect "at or near Boulder Canyon" a large
dam, which could generate power to repay in
time the construction expense.
Seven states?Arizona, California, Colorado,
New Mexico, Nevada, Utah and Wyoming?
would be affected by the larger plan, and they
would first have to reach an agreement about their
respective claims to water. Conferences were held,
with the federal government represented by the
Secretary of Commerce, Herbert Hoover, whom
Phil Swing claimed to have had a part in suggest?
ing as a "neutral" member of the Colorado River
Commission. It was Hoover who evidently broke
an impasse over state-by-state allocations by
proposing the establishment of Upper and Lower
Colorado River Basins, and this led all but one of
the states to agreement. According to Hoover, "a
blunderbuss of a governor in Arizona, who knew
nothing of engineering, bellowed that it would
'rob Arizona of its birthright/" After an amend?
ment required ratification by only six of the seven
affected states, the Colorado River Compact was
accomplished late in 1922.
A Boulder Canyon Project Act was introduced in

1923 by Congressman Swing and California Sena?
tor Hiram Johnson, and it became the focus of bitter
debate inside and outside of Washington. The pub?
lisher of The Los Angeles Times, Harry Chandler, was
concerned about future irrigation for the almost one
million acres he owned just south of the Imperial
Valley in Mexico. On the other hand, William Ran?
dolph Hearst of San Francisco, Chandler's Califor?
nia newspaper rival, favored the bill. The saga of
518 American Scientist, Volume 81
the Swing-Johnson legislation's debate through sev?
eral sessions of Congress has been written about in
detail, mostly from Congressman Swing's perspec?
tive, by Beverley Moeller. The legislative struggle fi?
nally came to an end when President Calvin
Coolidge signed the bill into law in December 1928.
Even before the first Swing-Johnson bill was in?
troduced, the Reclamation Service had begun de?
tailed explorations of possible dam sites. When the
Fell-Davis report was written, the choices had been
narrowed down to five possible sites in Boulder
Canyon and two sites about 20 miles downstream

in Black Canyon. Boulder Canyon's foundation
was already known to be granite, a preferred rock,
whereas Black Canyon's was volcanic tuff (com?
pacted ash), so Davis used the language "at or near
Boulder Canyon" in the report. Further investiga?
tion, however, revealed that the lower site at Black
Canyon was indeed the best of the lot. Among oth?
er factors, there was less jointing and faulting, less
silt and debris to be removed, easier prospects for
tunneling and a narrower gorge that equated to a
need for less concrete. Furthermore, beds of sand
and gravel for use in the concrete were located
nearby, the potential reservoir was larger and
nearby Las Vegas provided comparatively easy ac?
cess to the canyon.
Designing the Dam
In addition to a site for the dam, the details of the
design itself had to be specified. As with all engi?
neering structures, judgment was employed to ar?
rive at initial alternative geometries, which were
then subjected to successively more-refined de?
grees of analysis until a final design emerged.
About 30 geometries were investigated at the
Denver office of the Bureau of Reclamation, as the
Service had been renamed, and its engineers sub
jected the hypothesized dams to analyses of
stresses, including those that would result from

the cooling and contraction of the concrete as it
cured. As was customary in the days before digi?
tal computers, models (rubber and plaster, in this
case) were employed to guide and check theory
and hand calculations. Initial specifications called
for stresses no higher than 30 tons per square foot
anywhere in the dam. In the end this proved to be
difficult to meet, and stresses up to 40 tons per
square foot were allowed in the final design. This
is equivalent to about 550 pounds per square
inch, which is well below the compressive
strength of even common concrete, thus provid?
ing a considerable factor of safety against the pos?
sibility that the dam would fail by being crushed
under its own weight or under the pressure of
water it had to resist.
Although similar in vertical cross section to a
gravity dam (one whose sheer weight prevents it
from being tipped over or pushed downstream
by the water), Hoover Dam acts principally as an
arch dam, transferring the pressure of the water
behind it to the walls of the canyon, which act
like abutments. The great height of the dam,
about 725 feet above bedrock, and the consequent
weight of the concrete, requires its transverse pro?
file to spread like a gravity dam from 45 feet at
the crest to 660 feet at the base. The structural in?
tegrity of the dam was a matter of some debate
when the plans were first revealed by Elwood

Mead, then Commissioner of Reclamation, in a
1930 article in Civil Engineering.
Mead outlined succinctly some "extraordinary
problems met in design" in a paragraph that
showed a sensitivity to scale effects and design
philosophy that were essential to producing a
successful outcome:
In designing a dam more than 700 ft. in
height, stress factors become very important,
which in the design of dams of nominal size
are comparatively insignificant. Possible errors
in basic design assumptions must be carefully
studied and checked; the physical properties
and volumetric changes of so great a mass of
concrete must be carefully deteirnined; prima?
ry stresses caused by the weight of the materi?
als and the horizontal water pressure must be
accurately calculated, as well as secondary
stresses due to all possible causes.
Mead did not elaborate on such technical mat?
ters, however, and soon an article by M. H. Gerry,
Jr., a consulting engineer from San Francisco, ap
Figure 2. Boulder City, shown in 1934, housed the construction
workers.
1993 November-December 519

^^^^
Figure 3. Hoover Dam under construction in December, 1933,
reveal?
ing the interlocking cells.
peared in Civil Engineering, challenging the safety
and stability of the dam. Letters challenging the
challenger followed, and about a year after Com?
missioner Mead's article, Harald M. Westergaard, a
stmctural-engmeering professor at the University
of Illinois and consultant to the Bureau, published
"Safety of Hoover Dam," in which he discounted
Gerry's misinterpretation of structural principles
and declared that, "It is the business of the struc?
tural engineer to imagine each undesirable thing
that might happen to the structure and provide
against that." Westergaard and the Bureau engi?
neers had felt they had done just that before Mead
transmitted to the Secretary of the Interior specifi?
cations and drawings for the dam, power plant
and appurtenant works. These were approved in
late 1930, and construction bids were invited.
Building the Dam
In his memorandum of December 15,1930, trans?
mitting dam specifications, Mead reminded the

Secretary of the Interior that the Depression had
created very great "pressure for action on this
matter, as a means of finriishing employment and
encouraging a revival of business." The specifi?
cations spelled out various conditions that were
related to these economic concerns, including that
employment preference be given to ex-service?
men and citizens and that, specifically, "no Mon?
golian labor shall be employed." Other non-tech?
nical conditions required that Boulder City be
created 23 miles southeast of Las Vegas and close
to the canyon as a construction camp site. Al?
though bid specifications stated that buildings
erected in Boulder City were to have "a reason?
ably attractive appearance and no unpainted
shanties or tar paper shacks will be permitted/'
and even though there was much to be admired
in the planning and construction of the town, 60
years later Stevens would relate many stories of
shameful working conditions at Black Canyon.
Bids were due in Denver on March 4,1931, but
few construction companies had the experience
or resources, including the five-million-dollar
bond, required to compete. The successful bid?
ding scheme was put together by a group named

for the task, Six Companies, Inc. It comprised:
Utah Construction Co., Pacific Bridge Co., Kaiser
Paving Co., MacDonald-Kahn Construction Co.,
Morrison-Knudsen Co. and J. F. Shea Co. Each of
the partner firms naturally had its own expertise,
and Morrison-Knudsen included "America's
foremost dam builder," Frank T. Crowe.
A 1905 civil-engineering graduate of the Uni?
versity of Maine, Crowe had gained cutting-edge
experience in building high, concrete dams while
he worked for the Bureau of Reclamation. After al?
most 20 years in the field, he was offered and took
a desk job as general superintendent of construc?
tion for the Bureau, but he quit after a year to join
the Morrison-Knudsen Company so that he could
once again engage directly in dam building. It was
Crowe who spearheaded the effort to come up
with a bid figure for the Boulder Canyon Project,
and he presented it to Six Companies representa?
tives at a meeting early in February at the Engi?
neers Club of San Francisco. When the bids were
opened in Denver the next month, Six Companies'
low bid of just under $49 million was within five
hundredths of one percent of the price tag esti?
mated by engineers at the Bureau of Reclamation.
The contract remained, until World War II, the
largest ever awarded by the government.
In order to build the dam proper, the river had
to be diverted through tunnels driven through

the canyon walls. An upstream diversion dam,
which had to be built between the annual floods,
and a downstream coffer dam would keep the
construction site dry. After the main dam was
completed, most of the diversion tunnels would
be blocked off, but some parts would be incorpo?
rated into the system of penstocks that would
feed the turbines in the hydroelectric power plant.
After about two years, the river bottom had been
cleared to bedrock, and the first forms to receive
concrete were erected. The pouring of concrete
began on June 6, 1933, and continued day and
night over the next two years. Three million cubic
yards of concrete, from two specially built mixing
plants, were distributed among cube-like cells
that interlock in the completed dam. Cooling
pipes embedded five feet apart throughout the
concrete carried away the heat of hydration; oth?
erwise, the dam would still be cooling down and
developing cracks as the concrete contracted. The
completed dam was turned over to the govern?

ment on March 1, 1936, more than two years
ahead of schedule, and energy began to be pro?
duced by the power plant that fall.
The dam was dedicated on September 30,1935,
by President Franklin D. Roosevelt. First to speak at
the ceremony was his Secretary of the Interior,
Harold Ickes, who, after repeatedly referring to the
structure as Boulder Dam, declared, "This great en?
gineering achievement should not carry the name
of any living man but, on the contrary, should be
baptized with a designation as bold and character?
istic and imagination stirring as the dam itself." He
was implying that the dam should not be named
after Hoover, who was, of course, still alive. Ickes
had in fact reopened a debate over the name of the
dam that went back to an earlier dedication cere?
mony, one that acknowledged Congress's first ap?
propriations for the entire Boulder Canyon Project
with the driving of a spike of Nevada silver for the
rail line that was to connect the construction site
with the Union Pacific Railroad in Las Vegas. At
that ceremony, Ray Wilbur, the Secretary of the In?
terior under President Hoover, who signed the bill,
had asserted, to the surprise of many in attendance,
"I have the honor to name this dam after a great
engineer who really started this greatest project of
all times, the Hoover Dam."
From the beginning, then, the name of the dam

was a contentious and confusing issue. In 1939,
the American Society of Civil Engineers (ASCE)
readopted Hoover Dam for use in society publi?
cations, pointing to correspondence between Sec?
retary Ickes and Attorney General Homer Cum
mings. Cummings declared the name Hoover
Dam to be official, because of its use in the appro?
priations bill and government contracts for the
dam, as opposed to the collective Boulder
Canyon Project, which included also the power
plant and appurtenant works. In 1947, the Re?
publican 80th Congress, called "do-nothing" by
President Harry Truman, passed legislation rein?
stating the name Hoover Dam. Whatever its
name, more than 27 million people have visited
the dam over the years, and there appears to be
general agreement with a plaque?placed near
the center of the crest by the ASCE in 1955?de?
claring the dam to be one of the country's Seven
Modern Civil Engineering Wonders.
Bibliography
Bureau of Reclamation. 1930. Hoover Dam, Power Plant and
Ap?
purtenant Works: Specifications, Schedule, and Drawings.
Wash?

ington, D.C.: United States Department of the Interior.
Hoover, Herbert. 1952. Memoirs: The Cabinet and the Presi?
dency, 1920-1933. New York: Macmillan.
Mead, Elwood. 1930. Hoover Dam. Civil Engineering Octo?
ber: 3-8.
Moeller, Beverley Bowen. 1971. Phil Swing and Boulder Dam.
Berkeley: University of California Press.
Stevens, Joseph E. 1988. Hoover Dam: An American Adven?
ture. Norman: University of Oklahoma Press.
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Contentsp. 517p. 518p. 519p. 520p. [521]Issue Table of
ContentsAmerican Scientist, Vol. 81, No. 6 (November-
December 1993), pp. 506-616Front MatterLetters to the Editors
[pp. 507-509]Computing Science: Balanced on a Pencil Point
[pp. 510-516]Engineering: Hoover Dam [pp. 517-
521]Marginalia: Northern Exposures [pp. 522-525]SCIENCE
OBSERVERNO STOCK IN SMALLPOX VIRUS? [pp. 526-
527]WHAT MAKES PERMAFROST PERMANENT? [pp. 527-
528]SPIRAL HEARTBREAK [pp. 528-529]Recent Animal
Extinctions: Recipes for Disaster [pp. 530-541]Ethical Problems
in Academic Research [pp. 542-553]Directed Evolution
Reconsidered [pp. 554-561]Theory of Moves [pp. 562-570]The
Crisis in Russian Physics [pp. 571-579]The Scientists'
BookshelfScience Books for Young Readers [pp. 580-
588]Physical SciencesReview: untitled [pp. 589-589]Review:
untitled [pp. 589-590]Review: untitled [pp. 590-590]Review:
untitled [pp. 590-591]Earth SciencesReview: untitled [pp. 591-

592]Review: untitled [pp. 592-592]Life SciencesReview:
untitled [pp. 595-596]Behavioral SciencesReview: untitled [pp.
596-598]Review: untitled [pp. 598-598]Review: untitled [pp.
598-599]Mathematics and Computer SciencesReview: untitled
[pp. 599-599]Review: untitled [pp. 599-600]Engineering and
Applied SciencesReview: untitled [pp. 600-600]Review:
untitled [pp. 600-601]Science History, Philosophy and
PolicyReview: untitled [pp. 601-602]Review: untitled [pp. 602-
602]Sigma Xi National Lecturers, 1994—1995 [pp. 603-
611]Sigma Xi Today: NOVEMBER 1993 · VOLUME 2,
NUMBER 3 [pp. 613-616]Back Matter
Sigma Xi, The Scientific Research Society
Engineering: Hoover Dam
Author(s): Henry Petroski
Reviewed work(s):
Source: American Scientist, Vol. 81, No. 6 (November-
December 1993), pp. 517-521
Published by: Sigma Xi, The Scientific Research Society
Stable URL: http://www.jstor.org/stable/29775051 .
Accessed: 06/01/2013 08:28
Your use of the JSTOR archive indicates your acceptance of the
Terms & Conditions of Use, available at .
.
JSTOR is a not-for-profit service that helps scholars,
researchers, and students discover, use, and build upon a wide
range of
content in a trusted digital archive. We use information

technology and tools to increase productivity and facilitate new
forms
of scholarship. For more information about JSTOR, please
contact [email protected]
.
Sigma Xi, The Scientific Research Society is collaborating with
JSTOR to digitize, preserve and extend access
to American Scientist.
http://www.jstor.org
http://www.jstor.org/action/showPublisher?publisherCode=sigm
axi
http://www.jstor.org/stable/29775051?origin=JSTOR-pdf
Hoover Dam
Henry Petroski
Everything seems to move slowly at Hoover
Dam. Long lines of cars, buses and trucks in
low gear wind along the two-lane road
down one steep side of Black Canyon and up the
other. The lines stop frequently as carloads of
tourists crane their necks at the grandeur of the
site, and drivers search for a parking space
among the tiers of overlooks. For all the conges?

tion, few motorists seem impatient or interested
in searching maps for alternate routes. Everyone
driving in this vicinity must know that U.S. High?
way 95, which arcs along the crest of the dam, is
the only road across the Colorado River between
Davis Dam, over 50 miles to the south, and Nava
jo Bridge, over 150 miles to the east.
Pedestrians move about the top of the dam at a
snail's pace in the desert heat, crisscrossing the
crest over which, by design, no water has ever
flowed. Several thousand tourists may visit
Hoover Dam on a summer day, most of them
standing in long lines to board the large elevator
that takes them, 20 at a time, 600 feet down into
the inner workings of the dam. Many come from
Las Vegas, 35 miles to the northwest. Even there,
amid all the noise and neon, a visit to Hoover
Dam is hawked as one of the area's must-do
things. The pitch may be engineering achieve?
ment as awesome entertainment, but few who
visit the works at Black Canyon seem disappoint?
ed by the decided calmness and harmony of it all.
Just as the Mississippi River wreaked havoc in
the Midwest last summer, so the Colorado River
used to be alternately a blessing and a bane for
the Southwest. Although the Colorado seemed a
potential source of water for irrigation in rich but
arid regions such as Arizona and southern Cali?

fornia, it did not provide a consistent supply of
water. It often flooded low-lying lands in the
spring and early summer and then slowed to a
trickle during late summer and early fall. When?
ever crops, cattle and Californians were not
awash, they went thirsty.
Two promising regions with rich alluvial soil
were the Colorado Desert and the below-sea-lev?
el Salton Sink. Near the turn of the century they
were renamed Imperial Valley by land developers
who promised through their California Develop?
ment Company (CDC) to supply enough water
from the Colorado to make the otherwise arid
land attractive. For a few years the scheme
worked and the region was booming, but soon
the CDC's irrigation canal silted up and, in the
face of lawsuits from landowners, a new way to
divert the Colorado's water had to be found
quickly. A hastily engineered scheme?one that
also blunted the impact of the newly formed Bu?
reau of Reclamation's charge that CDC had mo?
nopolized the water supply?brought water up
from Mexico. That worked fine at first, but in 1905
so much water came down the Colorado in
spring and fall floods that the river changed its
course and flowed into the Salton Sink, which
then became the inland Salton Sea. Lost crops,

lost topsoil and a lost irrigation system amount?
ing to millions of dollars presented a disastrous
prospect for Imperial Valley. It was two years be?
fore the Colorado was put back on course, but the
root problems associated with both exploitation
of and protection from the river remained.
The great amount of silt carried southward by
the Colorado kept raising the river's channel, and
so required constant maintenance of the protec?
tive levees and other components of the irriga?
tion system, much of which was located in Mexi?
co. Problems with getting work crews back and
forth across the border led eventually to support
for a new canal located entirely on American soil.
It was in such a climate that a young lawyer
named Phil Swing, supported by southern-Cali?
fornia water interests, was sent in 1917 to repre?
sent them in Congress and to promote the idea of
an "All-American Canal."
Swing's effectiveness led quickly to the intro?
duction of legislation, but the proposal was de?
feated largely because of the opposition of Arthur
Powell Davis, a 40-year veteran of government
service who knew about as much about the Col?
orado River basin as anyone. Davis, nephew of
the Colorado canyon's explorer, John Wesley
Powell, had served as chief hydrographer when a
Panama Canal route was under investigation and
as an engineer with the U.S. Reclamation Service
since its origins in 1902. The driving force behind
the design and construction of many dams and ir?

rigation canals, he was director of the Reclama?
tion Service when the All-American Canal bill
1993 November-December
Henry Petroski is the Aleksandar S. Vesic Professor and chair?
man of the Department of Civil and Environmental Engineering
at Duke University, Durham, NC 27706.
Figure 1. Hoover Dam photographed in 1990. (All photographs
courtesy of the Bureau of Reclamation.)
came before the Congress. He argued successfully
for that bill's defeat in 1919 so that a more com?
prehensive and long-range plan for the Colorado
might be explored first.
A Grand Plan
Years earlier, as a supervising engineer in the
Reclamation Service, Davis had thought about a
grand plan for the entire drainage system of the
Colorado. According to Joseph Stevens, who sub?
titled his telling of the story of Hoover Dam "an
American adventure," Davis's scheme was to be

"an undertaking to rival or even surpass in scale
and importance the construction of the Panama
Canal." Congressman Swing went further and
added the Pyramids, the Great Wall of China and
Solomon's temple to the list of feats of engineer?
ing that were less complicated than what came to
be known as the Boulder Dam Project. Congress
agreed that the great problem of the Colorado
basin should be studied by the Interior Depart?
ment, and its secretary, Albert Fall, assigned the
task to Davis's organization. The Fall-Davis Re?
port, issued in 1922, "contained an exhaustive hy
drological and geological profile of the Colorado
River and its canyons," but most attention was
drawn to its recommendation that the govern?
ment erect "at or near Boulder Canyon" a large
dam, which could generate power to repay in
time the construction expense.
Seven states?Arizona, California, Colorado,
New Mexico, Nevada, Utah and Wyoming?
would be affected by the larger plan, and they
would first have to reach an agreement about their
respective claims to water. Conferences were held,
with the federal government represented by the
Secretary of Commerce, Herbert Hoover, whom
Phil Swing claimed to have had a part in suggest?
ing as a "neutral" member of the Colorado River
Commission. It was Hoover who evidently broke
an impasse over state-by-state allocations by
proposing the establishment of Upper and Lower
Colorado River Basins, and this led all but one of

the states to agreement. According to Hoover, "a
blunderbuss of a governor in Arizona, who knew
nothing of engineering, bellowed that it would
'rob Arizona of its birthright/" After an amend?
ment required ratification by only six of the seven
affected states, the Colorado River Compact was
accomplished late in 1922.
A Boulder Canyon Project Act was introduced in
1923 by Congressman Swing and California Sena?
tor Hiram Johnson, and it became the focus of bitter
debate inside and outside of Washington. The pub?
lisher of The Los Angeles Times, Harry Chandler, was
concerned about future irrigation for the almost one
million acres he owned just south of the Imperial
Valley in Mexico. On the other hand, William Ran?
dolph Hearst of San Francisco, Chandler's Califor?
nia newspaper rival, favored the bill. The saga of
the Swing-Johnson legislation's debate through sev?
eral sessions of Congress has been written about in
detail, mostly from Congressman Swing's perspec?
tive, by Beverley Moeller. The legislative struggle fi?

nally came to an end when President Calvin
Coolidge signed the bill into law in December 1928.
Even before the first Swing-Johnson bill was in?
troduced, the Reclamation Service had begun de?
tailed explorations of possible dam sites. When the
Fell-Davis report was written, the choices had been
narrowed down to five possible sites in Boulder
Canyon and two sites about 20 miles downstream
in Black Canyon. Boulder Canyon's foundation
was already known to be granite, a preferred rock,
whereas Black Canyon's was volcanic tuff (com?
pacted ash), so Davis used the language "at or near
Boulder Canyon" in the report. Further investiga?
tion, however, revealed that the lower site at Black
Canyon was indeed the best of the lot. Among oth?
er factors, there was less jointing and faulting, less
silt and debris to be removed, easier prospects for
tunneling and a narrower gorge that equated to a
need for less concrete. Furthermore, beds of sand
and gravel for use in the concrete were located
nearby, the potential reservoir was larger and
nearby Las Vegas provided comparatively easy ac?
cess to the canyon.
Designing the Dam
In addition to a site for the dam, the details of the

design itself had to be specified. As with all engi?
neering structures, judgment was employed to ar?
rive at initial alternative geometries, which were
then subjected to successively more-refined de?
grees of analysis until a final design emerged.
About 30 geometries were investigated at the
Denver office of the Bureau of Reclamation, as the
Service had been renamed, and its engineers sub
jected the hypothesized dams to analyses of
stresses, including those that would result from
the cooling and contraction of the concrete as it
cured. As was customary in the days before digi?
tal computers, models (rubber and plaster, in this
case) were employed to guide and check theory
and hand calculations. Initial specifications called
for stresses no higher than 30 tons per square foot
anywhere in the dam. In the end this proved to be
difficult to meet, and stresses up to 40 tons per
square foot were allowed in the final design. This
is equivalent to about 550 pounds per square
inch, which is well below the compressive
strength of even common concrete, thus provid?
ing a considerable factor of safety against the pos?
sibility that the dam would fail by being crushed
under its own weight or under the pressure of
water it had to resist.
Although similar in vertical cross section to a
gravity dam (one whose sheer weight prevents it
from being tipped over or pushed downstream

by the water), Hoover Dam acts principally as an
arch dam, transferring the pressure of the water
behind it to the walls of the canyon, which act
like abutments. The great height of the dam,
about 725 feet above bedrock, and the consequent
weight of the concrete, requires its transverse pro?
file to spread like a gravity dam from 45 feet at
the crest to 660 feet at the base. The structural in?
tegrity of the dam was a matter of some debate
when the plans were first revealed by Elwood
Mead, then Commissioner of Reclamation, in a
1930 article in Civil Engineering.
Mead outlined succinctly some "extraordinary
problems met in design" in a paragraph that
showed a sensitivity to scale effects and design
philosophy that were essential to producing a
successful outcome:
In designing a dam more than 700 ft. in
height, stress factors become very important,
which in the design of dams of nominal size
are comparatively insignificant. Possible errors
in basic design assumptions must be carefully
studied and checked; the physical properties
and volumetric changes of so great a mass of
concrete must be carefully deteirnined; prima?
ry stresses caused by the weight of the materi?
als and the horizontal water pressure must be
accurately calculated, as well as secondary
stresses due to all possible causes.

Mead did not elaborate on such technical mat?
ters, however, and soon an article by M. H. Gerry,
Jr., a consulting engineer from San Francisco, ap
Figure 2. Boulder City, shown in 1934, housed the construction
workers.
1993 November-December 519
^^^^
Figure 3. Hoover Dam under construction in December, 1933,
reveal?
ing the interlocking cells.
peared in Civil Engineering, challenging the safety
and stability of the dam. Letters challenging the
challenger followed, and about a year after Com?
missioner Mead's article, Harald M. Westergaard, a
stmctural-engmeering professor at the University
of Illinois and consultant to the Bureau, published
"Safety of Hoover Dam," in which he discounted
Gerry's misinterpretation of structural principles
and declared that, "It is the business of the struc?
tural engineer to imagine each undesirable thing

that might happen to the structure and provide
against that." Westergaard and the Bureau engi?
neers had felt they had done just that before Mead
transmitted to the Secretary of the Interior specifi?
cations and drawings for the dam, power plant
and appurtenant works. These were approved in
late 1930, and construction bids were invited.
Building the Dam
In his memorandum of December 15,1930, trans?
mitting dam specifications, Mead reminded the
Secretary of the Interior that the Depression had
created very great "pressure for action on this
matter, as a means of finriishing employment and
encouraging a revival of business." The specifi?
cations spelled out various conditions that were
related to these economic concerns, including that
employment preference be given to ex-service?
men and citizens and that, specifically, "no Mon?
golian labor shall be employed." Other non-tech?
nical conditions required that Boulder City be
created 23 miles southeast of Las Vegas and close
to the canyon as a construction camp site. Al?
though bid specifications stated that buildings
erected in Boulder City were to have "a reason?
ably attractive appearance and no unpainted
shanties or tar paper shacks will be permitted/'

and even though there was much to be admired
in the planning and construction of the town, 60
years later Stevens would relate many stories of
shameful working conditions at Black Canyon.
Bids were due in Denver on March 4,1931, but
few construction companies had the experience
or resources, including the five-million-dollar
bond, required to compete. The successful bid?
ding scheme was put together by a group named
for the task, Six Companies, Inc. It comprised:
Utah Construction Co., Pacific Bridge Co., Kaiser
Paving Co., MacDonald-Kahn Construction Co.,
Morrison-Knudsen Co. and J. F. Shea Co. Each of
the partner firms naturally had its own expertise,
and Morrison-Knudsen included "America's
foremost dam builder," Frank T. Crowe.
A 1905 civil-engineering graduate of the Uni?
versity of Maine, Crowe had gained cutting-edge
experience in building high, concrete dams while
he worked for the Bureau of Reclamation. After al?
most 20 years in the field, he was offered and took
a desk job as general superintendent of construc?
tion for the Bureau, but he quit after a year to join
the Morrison-Knudsen Company so that he could
once again engage directly in dam building. It was
Crowe who spearheaded the effort to come up
with a bid figure for the Boulder Canyon Project,
and he presented it to Six Companies representa?
tives at a meeting early in February at the Engi?

neers Club of San Francisco. When the bids were
opened in Denver the next month, Six Companies'
low bid of just under $49 million was within five
hundredths of one percent of the price tag esti?
mated by engineers at the Bureau of Reclamation.
The contract remained, until World War II, the
largest ever awarded by the government.
In order to build the dam proper, the river had
to be diverted through tunnels driven through
the canyon walls. An upstream diversion dam,
which had to be built between the annual floods,
and a downstream coffer dam would keep the
construction site dry. After the main dam was
completed, most of the diversion tunnels would
be blocked off, but some parts would be incorpo?
rated into the system of penstocks that would
feed the turbines in the hydroelectric power plant.
After about two years, the river bottom had been
cleared to bedrock, and the first forms to receive
concrete were erected. The pouring of concrete
began on June 6, 1933, and continued day and
night over the next two years. Three million cubic
yards of concrete, from two specially built mixing
plants, were distributed among cube-like cells
that interlock in the completed dam. Cooling
pipes embedded five feet apart throughout the
concrete carried away the heat of hydration; oth?
erwise, the dam would still be cooling down and

developing cracks as the concrete contracted. The
completed dam was turned over to the govern?
ment on March 1, 1936, more than two years
ahead of schedule, and energy began to be pro?
duced by the power plant that fall.
The dam was dedicated on September 30,1935,
by President Franklin D. Roosevelt. First to speak at
the ceremony was his Secretary of the Interior,
Harold Ickes, who, after repeatedly referring to the
structure as Boulder Dam, declared, "This great en?
gineering achievement should not carry the name
of any living man but, on the contrary, should be
baptized with a designation as bold and character?
istic and imagination stirring as the dam itself." He
was implying that the dam should not be named
after Hoover, who was, of course, still alive. Ickes
had in fact reopened a debate over the name of the
dam that went back to an earlier dedication cere?
mony, one that acknowledged Congress's first ap?
propriations for the entire Boulder Canyon Project

with the driving of a spike of Nevada silver for the
rail line that was to connect the construction site
with the Union Pacific Railroad in Las Vegas. At
that ceremony, Ray Wilbur, the Secretary of the In?
terior under President Hoover, who signed the bill,
had asserted, to the surprise of many in attendance,
"I have the honor to name this dam after a great
engineer who really started this greatest project of
all times, the Hoover Dam."
From the beginning, then, the name of the dam
was a contentious and confusing issue. In 1939,
the American Society of Civil Engineers (ASCE)
readopted Hoover Dam for use in society publi?
cations, pointing to correspondence between Sec?
retary Ickes and Attorney General Homer Cum
mings. Cummings declared the name Hoover
Dam to be official, because of its use in the appro?
priations bill and government contracts for the
dam, as opposed to the collective Boulder
Canyon Project, which included also the power
plant and appurtenant works. In 1947, the Re?
publican 80th Congress, called "do-nothing" by
President Harry Truman, passed legislation rein?
stating the name Hoover Dam. Whatever its
name, more than 27 million people have visited
the dam over the years, and there appears to be
general agreement with a plaque?placed near

the center of the crest by the ASCE in 1955?de?
claring the dam to be one of the country's Seven
Modern Civil Engineering Wonders.
Bibliography
Bureau of Reclamation. 1930. Hoover Dam, Power Plant and
Ap?
purtenant Works: Specifications, Schedule, and Drawings.
Wash?
ington, D.C.: United States Department of the Interior.
Hoover, Herbert. 1952. Memoirs: The Cabinet and the Presi?
dency, 1920-1933. New York: Macmillan.
Mead, Elwood. 1930. Hoover Dam. Civil Engineering Octo?
ber: 3-8.
Moeller, Beverley Bowen. 1971. Phil Swing and Boulder Dam.
Berkeley: University of California Press.
Stevens, Joseph E. 1988. Hoover Dam: An American Adven?
ture. Norman: University of Oklahoma Press.
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Contentsp. 517p. 518p. 519p. 520p. [521]Issue Table of
ContentsAmerican Scientist, Vol. 81, No. 6 (November-
December 1993), pp. 506-616Front MatterLetters to the Editors
[pp. 507-509]Computing Science: Balanced on a Pencil Point
[pp. 510-516]Engineering: Hoover Dam [pp. 517-

521]Marginalia: Northern Exposures [pp. 522-525]SCIENCE
OBSERVERNO STOCK IN SMALLPOX VIRUS? [pp. 526-
527]WHAT MAKES PERMAFROST PERMANENT? [pp. 527-
528]SPIRAL HEARTBREAK [pp. 528-529]Recent Animal
Extinctions: Recipes for Disaster [pp. 530-541]Ethical Problems
in Academic Research [pp. 542-553]Directed Evolution
Reconsidered [pp. 554-561]Theory of Moves [pp. 562-570]The
Crisis in Russian Physics [pp. 571-579]The Scientists'
BookshelfScience Books for Young Readers [pp. 580-
588]Physical SciencesReview: untitled [pp. 589-589]Review:
untitled [pp. 590-591]Earth SciencesReview: untitled [pp. 591-
592]Review: untitled [pp. 592-592]Life SciencesReview:
untitled [pp. 595-596]Behavioral SciencesReview: untitled [pp.
596-598]Review: untitled [pp. 598-598]Review: untitled [pp.
598-599]Mathematics and Computer SciencesReview: untitled
[pp. 599-599]Review: untitled [pp. 599-600]Engineering and
Applied SciencesReview: untitled [pp. 600-600]Review:
untitled [pp. 600-601]Science History, Philosophy and
PolicyReview: untitled [pp. 601-602]Review: untitled [pp. 602-
602]Sigma Xi National Lecturers, 1994—1995 [pp. 603-
611]Sigma Xi Today: NOVEMBER 1993 · VOLUME 2,
NUMBER 3 [pp. 613-616]Back Matter

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