Hoover Dam

Hoover Dam

Overview

Hoover Dam, once known as Boulder Dam, is a concrete arch-gravity dam
Arch-gravity dam
An arch-gravity dam, curved-gravity dam or arched dam is a dam with the characteristics of both an arch dam and a gravity dam. It is a dam that curves upstream in a narrowing curve that directs most of the water against the canyon rock walls, providing the force to compress the dam...

 in the Black Canyon
Black Canyon of the Colorado
The Black Canyon of the Colorado is the canyon on the Colorado River where Hoover Dam was built. The canyon is located on the Colorado River at the state line between Nevada and Arizona. The western wall of the gorge is in the El Dorado Mountains, and the eastern wall is in the Black Mountains of...

 of the Colorado River, on the border between the US states of Arizona
Arizona
Arizona ; is a state located in the southwestern region of the United States. It is also part of the western United States and the mountain west. The capital and largest city is Phoenix...

 and Nevada
Nevada
Nevada is a state in the western, mountain west, and southwestern regions of the United States. With an area of and a population of about 2.7 million, it is the 7th-largest and 35th-most populous state. Over two-thirds of Nevada's people live in the Las Vegas metropolitan area, which contains its...

. It was constructed between 1931 and 1936 during the Great Depression
Great Depression
The Great Depression was a severe worldwide economic depression in the decade preceding World War II. The timing of the Great Depression varied across nations, but in most countries it started in about 1929 and lasted until the late 1930s or early 1940s...

 and was dedicated on September 30, 1935, by President Franklin Roosevelt. Its construction was the result of a massive effort involving thousands of workers, and cost over one hundred lives.
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Hoover Dam, once known as Boulder Dam, is a concrete arch-gravity dam
Arch-gravity dam
An arch-gravity dam, curved-gravity dam or arched dam is a dam with the characteristics of both an arch dam and a gravity dam. It is a dam that curves upstream in a narrowing curve that directs most of the water against the canyon rock walls, providing the force to compress the dam...

 in the Black Canyon
Black Canyon of the Colorado
The Black Canyon of the Colorado is the canyon on the Colorado River where Hoover Dam was built. The canyon is located on the Colorado River at the state line between Nevada and Arizona. The western wall of the gorge is in the El Dorado Mountains, and the eastern wall is in the Black Mountains of...

 of the Colorado River, on the border between the US states of Arizona
Arizona
Arizona ; is a state located in the southwestern region of the United States. It is also part of the western United States and the mountain west. The capital and largest city is Phoenix...

 and Nevada
Nevada
Nevada is a state in the western, mountain west, and southwestern regions of the United States. With an area of and a population of about 2.7 million, it is the 7th-largest and 35th-most populous state. Over two-thirds of Nevada's people live in the Las Vegas metropolitan area, which contains its...

. It was constructed between 1931 and 1936 during the Great Depression
Great Depression
The Great Depression was a severe worldwide economic depression in the decade preceding World War II. The timing of the Great Depression varied across nations, but in most countries it started in about 1929 and lasted until the late 1930s or early 1940s...

 and was dedicated on September 30, 1935, by President Franklin Roosevelt. Its construction was the result of a massive effort involving thousands of workers, and cost over one hundred lives. The dam was controversially named in honor of President
President of the United States
The President of the United States of America is the head of state and head of government of the United States. The president leads the executive branch of the federal government and is the commander-in-chief of the United States Armed Forces....

 Herbert Hoover
Herbert Hoover
Herbert Clark Hoover was the 31st President of the United States . Hoover was originally a professional mining engineer and author. As the United States Secretary of Commerce in the 1920s under Presidents Warren Harding and Calvin Coolidge, he promoted partnerships between government and business...

.

Since about 1900, the Black Canyon and nearby Boulder Canyon had been investigated for their potential to support a dam that would control floods, provide irrigation water and produce hydroelectric power. In 1928, Congress authorized the project. The winning bid to build the dam was submitted by a consortium called Six Companies, Inc., which began construction on the dam in early 1931. Such a large concrete structure had never been built before, and some of the techniques were unproven. The torrid summer weather and the lack of facilities near the site also presented difficulties. Nevertheless, Six Companies turned over the dam to the federal government on March 1, 1936, more than two years ahead of schedule.

Hoover Dam impounds Lake Mead
Lake Mead
Lake Mead is the largest reservoir in the United States. It is located on the Colorado River about southeast of Las Vegas, Nevada, in the states of Nevada and Arizona. Formed by water impounded by the Hoover Dam, it extends behind the dam, holding approximately of water.-History:The lake was...

, and is located near Boulder City, Nevada
Boulder City, Nevada
Boulder City is a city in Clark County, Nevada, United States. It is approximately from the City of Las Vegas. As of the 2010 census the population of Boulder City was 15,023.Boulder City is one of only two cities in Nevada that prohibit gambling....

, a municipality originally constructed for workers on the construction project, about 25 mi (40.2 km) southeast of Las Vegas, Nevada
Las Vegas, Nevada
Las Vegas is the most populous city in the U.S. state of Nevada and is also the county seat of Clark County, Nevada. Las Vegas is an internationally renowned major resort city for gambling, shopping, and fine dining. The city bills itself as The Entertainment Capital of the World, and is famous...

. The dam's generators provide power for public and private utilities in Nevada, Arizona, and California. Hoover Dam is a major tourist attraction; nearly a million people tour the dam each year. Heavily travelled U.S. 93 ran along the dam's crest until October 2010, when the Hoover Dam Bypass
Hoover Dam Bypass
The Mike O'Callaghan – Pat Tillman Memorial Bridge, the key component to the Hoover Dam Bypass project, was the first concrete-steel composite arch bridge built in the United States, and it incorporates the longest concrete arch bridge in the Western Hemisphere. Opened on October 19, 2010,...

 opened.

Search for resources


As the United States developed the Southwest, the Colorado River was seen as a potential source of irrigation water. An initial attempt at diverting the river for irrigation purposes occurred in the late 1890s, when land speculator William Beatty built the Alamo Canal
Alamo Canal
The Alamo Canal was a long waterway that connected the Colorado River to the head of the Alamo River. The canal was constructed to provide irrigation to the Imperial Valley. A small portion of the canal was located in the United States but the majority of the canal was located in Mexico...

 just north of the Mexican border; the canal dipped into Mexico before running to a desolate area Beatty named the Imperial Valley
Imperial Valley
The Imperial Valley is an agricultural area of Southern California's Imperial County. It is located in southeastern Southern California, centered around the city of El Centro. Locally, the terms "Imperial Valley" and "Imperial County" are used synonymously. The Valley is bordered between the...

. Though water from the Imperial Canal allowed for the widespread settlement of the valley, the canal proved expensive to maintain. After a catastrophic breach that caused the Colorado River to fill the Salton Sea
Salton Sea
The Salton Sea is a shallow, saline, endorheic rift lake located directly on the San Andreas Fault, predominantly in California's Imperial Valley. The lake occupies the lowest elevations of the Salton Sink in the Colorado Desert of Imperial and Riverside counties in Southern California. Like Death...

, the Southern Pacific Railroad
Southern Pacific Railroad
The Southern Pacific Transportation Company , earlier Southern Pacific Railroad and Southern Pacific Company, and usually simply called the Southern Pacific or Espee, was an American railroad....

 spent $3 million in 1906–07 to stabilize the waterway, an amount it hoped vainly would be reimbursed by the Federal Government. Even after the waterway was stabilized, it proved unsatisfactory because of constant disputes with landowners on the Mexican side of the border.


As the technology of electric power transmission
Electric power transmission
Electric-power transmission is the bulk transfer of electrical energy, from generating power plants to Electrical substations located near demand centers...

 improved, the Lower Colorado
Lower Colorado River Valley
The Lower Colorado River Valley is the river region of the lower Colorado River of the southwestern United States in North America that rises in the Rocky Mountains and has its outlet at the Colorado River Delta in the northern Sea of Cortez in northwestern Mexico, between the states of Baja...

 was considered for its hydroelectric-power potential. In 1902, the Edison Electric Company of Los Angeles
Southern California Edison
Southern California Edison , the largest subsidiary of Edison International , is the primary electricity supply company for much of Southern California, USA. It provides 14 million people with electricity...

 surveyed the river in the hope of building a 40 feet (12.2 m) rock dam which could generate 10000 hp. However, at the time, the limit of transmission of electric power was 80 miles (128.7 km), and there were few customers (mostly mines) within that limit. Edison allowed land options it held on the river to lapse—including an option for what became the site of Hoover Dam.

In the following years, the Bureau of Reclamation, known as the Reclamation Service at the time, also considered the Lower Colorado as the site of a dam. Service chief Arthur Powell Davis proposed using dynamite to collapse the walls of Boulder Canyon, 20 miles (32.2 km) north of the eventual dam site, into the river. The river would carry off the smaller pieces of debris, and a dam would be built incorporating the remaining rubble. In 1922, after considering it for several years, the Reclamation Service finally rejected the proposal, citing doubts about the unproven technique and questions as to whether it would in fact save money.

Planning and agreements



In 1922, the Reclamation Service presented a report calling for the development of a dam on the Colorado for flood control and electric power generation. The report was principally authored by Davis, and was called the Fall-Davis report after Interior Secretary Albert Fall. The Fall-Davis report cited use of the Colorado River as a federal concern, because the river's basin covered several states, and the river eventually entered Mexico. Though the Fall-Davis report called for a dam "at or near Boulder Canyon", the Reclamation Service (which was renamed the Bureau of Reclamation the following year) found that canyon unsuitable. One potential site at Boulder Canyon was bisected by a geologic fault
Geologic fault
In geology, a fault is a planar fracture or discontinuity in a volume of rock, across which there has been significant displacement along the fractures as a result of earth movement. Large faults within the Earth's crust result from the action of tectonic forces...

; two others were so narrow there was no space for a construction camp at the bottom of the canyon or for a spillway. The Service investigated Black Canyon and found it ideal; a railway could be laid from the railhead in Las Vegas to the top of the dam site. Despite the site change, the dam project was referred to as the "Boulder Canyon Project".

With little guidance on water allocation from the Supreme Court
Supreme Court of the United States
The Supreme Court of the United States is the highest court in the United States. It has ultimate appellate jurisdiction over all state and federal courts, and original jurisdiction over a small range of cases...

, proponents of the dam feared endless litigation. A Colorado attorney proposed that the seven states (California, Nevada, Arizona, Utah, New Mexico, Colorado and Wyoming) which fell within the river's basin form an interstate compact
Interstate compact
An interstate compact is an agreement between two or more states of the United States of America. Article I, Section 10 of the United States Constitution provides that "no state shall enter into an agreement or compact with another state" without the consent of Congress...

, with the approval of Congress. Such compacts were authorized by Article I of the United States Constitution but had never been concluded among more than two states. In 1922, representatives of seven states met with then Secretary of Commerce
United States Secretary of Commerce
The United States Secretary of Commerce is the head of the United States Department of Commerce concerned with business and industry; the Department states its mission to be "to foster, promote, and develop the foreign and domestic commerce"...

 Herbert Hoover
Herbert Hoover
Herbert Clark Hoover was the 31st President of the United States . Hoover was originally a professional mining engineer and author. As the United States Secretary of Commerce in the 1920s under Presidents Warren Harding and Calvin Coolidge, he promoted partnerships between government and business...

. Initial talks produced no result, but when the Supreme Court handed down the Wyoming v. Colorado
Wyoming v. Colorado
Wyoming v. Colorado is a set of court cases, all dealing with water distribution from the Laramie River. Petition for rehearing was granted which revised the original decision. A motion to dismiss was later denied....

decision undermining the claims of the upstream states, they became anxious to reach an agreement. The resulting Colorado River Compact
Colorado River Compact
The Colorado River Compact is a 1922 agreement among seven U.S. states in the basin of the Colorado River in the American Southwest governing the allocation of the water rights to the river's water among the parties of the interstate compact...

 was signed on November 24, 1922.

Legislation to authorize the dam was introduced repeatedly by Representative Phil Swing
Phil Swing
Philip David "Phil" Swing is a former American Republican politician from Imperial County, California.-Biography:...

 (R-Calif.) and Senator Hiram Johnson
Hiram Johnson
Hiram Warren Johnson was a leading American progressive and later isolationist politician from California; he served as the 23rd Governor from 1911 to 1917, and as a United States Senator from 1917 to 1945.-Early life:...

 (R-Calif.), but representatives from other parts of the country considered the project as hugely expensive and one that would mostly benefit California. The 1927 Mississippi flood made Midwestern and Southern congressmen and senators more sympathetic toward the dam project. On March 13, 1928, the failure of the St. Francis Dam
St. Francis Dam
The St. Francis Dam was a concrete gravity-arch dam, designed to create a reservoir as a storage point of the Los Angeles Aqueduct. It was located 40 miles northwest of Los Angeles, California, near the present city of Santa Clarita....

, constructed by the city of Los Angeles, caused a disastrous flood that killed hundreds of people. As that dam was an arch-gravity type, as was proposed for the Black Canyon dam, dam opponents claimed that the Black Canyon dam's safety could not be guaranteed. Congress authorized a board of engineers to review plans for the proposed dam. The Colorado River Board found the project feasible, but warned that should the dam fail, every downstream Colorado River community would be destroyed, and that the river might change course and empty into the Salton Sea. The Board cautioned: "To avoid such possibilities, the proposed dam should be constructed on conservative if not ultra-conservative lines."

On December 21, 1928 President Coolidge
Calvin Coolidge
John Calvin Coolidge, Jr. was the 30th President of the United States . A Republican lawyer from Vermont, Coolidge worked his way up the ladder of Massachusetts state politics, eventually becoming governor of that state...

 signed the bill authorizing the dam. The Boulder Canyon Project Act appropriated $165 million for the Hoover Dam along with the downstream Imperial Dam
Imperial Dam
The Imperial Diversion Dam is a concrete slab and buttress, ogee weir structure across the California/Arizona border, northeast of Yuma. Completed in the 1938, the dam retains the waters of the Colorado River into the Imperial Reservoir before desilting and diversion into the All-American Canal,...

 and All-American Canal
All-American Canal
The All-American Canal is an long aqueduct, located in southeastern California. It conveys water from the Colorado River into the Imperial Valley and to nine cities. It is the Imperial Valley's only water source, and replaced the Alamo Canal, which was located mostly in Mexico...

, a replacement for Beatty's canal entirely on the U.S. side of the border. It also permitted the compact to go into effect when at least six of the seven states approved it. This occurred on March 6, 1929 with Utah's ratification; Arizona did not approve it until 1944.

Design, preparation and contracting



Even before Congress approved the Boulder Canyon Project, the Bureau of Reclamation was considering what kind of dam should be used. Officials eventually decided on a massive concrete arch-gravity dam
Arch-gravity dam
An arch-gravity dam, curved-gravity dam or arched dam is a dam with the characteristics of both an arch dam and a gravity dam. It is a dam that curves upstream in a narrowing curve that directs most of the water against the canyon rock walls, providing the force to compress the dam...

, the design of which was overseen by the Bureau's chief design engineer John L. Savage
John L. Savage
John Lucian Savage was an American civil engineer. He is best known for supervising the design and construction of the Hoover Dam, Shasta Dam and Grand Coulee Dam in the United States along with surveying for the future Three Gorges Dam in China...

. The monolithic dam would be thick at the bottom and thin near the top, and would present a convex face towards the water above the dam. The curving arch of the dam would transmit the water's force into the abutments, in this case the rock walls of the canyon. The wedge-shaped dam would be 660 ft (201.2 m) thick at the bottom, narrowing to 45 ft (13.7 m) at the top, leaving room for a highway connecting Nevada and Arizona.

On January 10, 1931, the Bureau made the bid documents available to interested parties, at five dollars a copy. The government was to provide the materials; but the contractor was to prepare the site and build the dam. The dam was described in minute detail, covering 100 pages of text and 76 drawings. A $2 million bid bond
Bid bond
A bid bond is issued as part of a bidding process by the surety to the project owner, to guarantee that the winning bidder will undertake the contract under the terms at which they bid....

 was to accompany each bid; the winner would have to post a $5 million performance bond
Performance bond
A performance bond is a surety bond issued by an insurance company or a bank to guarantee satisfactory completion of a project by a contractor.A job requiring a payment & performance bond will usually require a bid bond, to bid the job...

. The contractor had seven years to build the dam, or penalties would ensue.

The Wattis Brothers, heads of the Utah Construction Company
Utah Construction Company
The Utah Construction Company was a construction company founded by Edmund Orson Wattis, Jr, Warren L. Wattis and William. H. Wattis in 1900.-History:...

, were interested in bidding on the project, but lacked the money for the performance bond. They lacked sufficient resources even in combination with their longtime partners, Morrison-Knudsen, which employed the nation's leading dam builder, Frank Crowe
Frank Crowe
Francis Trenholm Crowe was the chief engineer of the Hoover Dam. During that time, he was the superintendent of Six Companies, the construction company that oversaw the construction project....

. They formed a joint venture to bid for the project with Pacific Bridge Company of Portland, Oregon
Portland, Oregon
Portland is a city located in the Pacific Northwest, near the confluence of the Willamette and Columbia rivers in the U.S. state of Oregon. As of the 2010 Census, it had a population of 583,776, making it the 29th most populous city in the United States...

; Henry J. Kaiser
Henry J. Kaiser
Henry John Kaiser was an American industrialist who became known as the father of modern American shipbuilding. He established the Kaiser Shipyard which built Liberty ships during World War II, after which he formed Kaiser Aluminum and Kaiser Steel. Kaiser organized Kaiser Permanente health care...

 & W. A. Bechtel Company of San Francisco; MacDonald & Kahn Ltd. of Los Angeles; and the J.F. Shea Company of Portland, Oregon. The joint venture was called Six Companies, Inc.—Bechtel and Kaiser were considered one company for purposes of the name. The name was descriptive and was an inside joke among the San Franciscans in the bid—"Six Companies" was a Chinese benevolent association in the city. There were three valid bids, and Six Companies' bid of $48,890,955 was the lowest, within $24,000 of the confidential government estimate of what the dam would cost to build, and five million dollars less than the next lowest bid.

The city of Las Vegas had lobbied hard to be the headquarters for the dam construction, closing its many speakeasies
Speakeasy
A speakeasy, also called a blind pig or blind tiger, is an establishment that illegally sells alcoholic beverages. Such establishments came into prominence in the United States during the period known as Prohibition...

 when the decision maker, Secretary of the Interior Ray Wilbur came to town. Instead, Wilbur announced in early 1930 that a model city was to be built in the desert near the dam site. This town became known as Boulder City, Nevada
Boulder City, Nevada
Boulder City is a city in Clark County, Nevada, United States. It is approximately from the City of Las Vegas. As of the 2010 census the population of Boulder City was 15,023.Boulder City is one of only two cities in Nevada that prohibit gambling....

. Construction of a rail line joining Las Vegas and the dam site began in September 1930.

Labor force



Soon after the dam was authorized, increasing numbers of unemployed converged on southern Nevada. Las Vegas, then a small city of some 5,000, saw between 10,000 and 20,000 unemployed descend on it. A government camp was established for surveyors and other personnel near the dam site; this soon became surrounded by a squatters' camp. Known as McKeeversville, the camp was home to men hoping for work on the project, together with their families. Another camp, on the flats along the Colorado River, was officially called Williamsville, but was known to its inhabitants as Ragtown. Once construction began, Six Companies hired large numbers of workers, with more than 3,000 on the payroll by 1932 and with employment peaking at 5,251 in July 1934. "Mongolian" (Chinese) labor was forbidden by the construction contract, while the number of blacks employed by Six Companies never exceeded thirty, mostly lowest-pay-scale laborers in a segregated crew, who were issued separate water buckets.

As part of the contract, Six Companies, Inc. was to build Boulder City to house the workers. The original timetable called for Boulder City to be built before the dam project began, but President Hoover ordered work on the dam to begin in March 1931 rather than in October. The company built bunkhouses, attached to the canyon wall, to house 480 single men at what became known as River Camp. Workers with families were left to provide their own accommodations until Boulder City could be completed, and many lived in Ragtown. The site of Hoover Dam endures extremely hot weather, but the summer of 1931 was especially torrid, with the daytime high averaging 119.9 °F (48.8 °C). Sixteen workers and other riverbank residents died of heat prostration between June 25 and July 26.
The Industrial Workers of the World
Industrial Workers of the World
The Industrial Workers of the World is an international union. At its peak in 1923, the organization claimed some 100,000 members in good standing, and could marshal the support of perhaps 300,000 workers. Its membership declined dramatically after a 1924 split brought on by internal conflict...

 (IWW or "Wobblies"), though much reduced from their heyday as militant labor organizers in the early years of the century, hoped to unionize the Six Companies workers, by capitalizing on their discontent. They sent eleven organizers, several of whom were arrested by Las Vegas police. On August 7, 1931, the company cut wages for all tunnel workers. Although the workers sent away the organizers, not wanting to be associated with the "Wobblies", they formed a committee to represent them with the company. The committee drew up a list of demands that evening and presented them to Crowe the following morning. He was noncommittal. The workers hoped that Crowe, the general superintendent of the job, would be sympathetic; instead he gave a scathing interview to a newspaper, describing the workers as "malcontents".

On the morning of the 9th, Crowe met with the committee and told them that management refused their demands, was stopping all work, and was laying off the entire work force, except for a few office workers and carpenters. The workers were given until 5 p.m. to vacate the premises. Concerned that a violent confrontation was imminent, most workers took their paychecks and left for Las Vegas to await developments. Two days later, the remainder were talked into leaving by law enforcement. On August 13, the company began hiring workers again, and two days later, the strike was called off. While the workers received none of their demands, the company guaranteed there would be no further reductions in wages. Living conditions began to improve as the first residents moved into Boulder City in late 1931.

A second labor action took place in July 1935, as construction on the dam wound down. When a Six Companies manager altered working times to force workers to take lunch on their own time, workers responded with a strike. Emboldened by Crowe's reversal of the lunch decree, workers raised their demands to include a $1 per day raise. The company agreed to ask the Federal government to supplement the pay, but no money was forthcoming from Washington. The strike ended.

River diversion



Before the dam could be built, the Colorado River needed to be diverted away from the construction site. To accomplish this, four diversion tunnels were driven through the canyon walls, two on the Nevada side and two on the Arizona side. These tunnels were 56 feet (17.1 m) in diameter. Their combined length was nearly 16,000 ft or more than 3 mi (5 km). The contract required these tunnels to be completed by October 1, 1933, with a $3,000 per day fine to be assessed for any delay. To meet the deadline, Six Companies had to complete work by early 1933, since only in late fall and winter was the water level in the river low enough to safely divert.

Tunneling began at the lower portals of the Nevada tunnels in May 1931. Shortly afterward, work began on two similar tunnels in the Arizona canyon wall. In March 1932, work began on lining the tunnels with concrete. First the base, or invert, was poured. Gantry crane
Gantry crane
Gantry cranes, bridge cranes, and overhead cranes, are all types of cranes which lift objects by a hoist which is fitted in a hoist trolley and can move horizontally on a rail or pair of rails fitted under a beam...

s, running on rails through the entire length of each tunnel were used to place the concrete. The sidewalls were poured next. Movable sections of steel forms were used for the sidewalls. Finally, using pneumatic guns, the overheads were filled in. The concrete lining is 3 ft (0.9144 m) thick, reducing the finished tunnel diameter to 50 ft (15.2 m). The river was diverted into the two Arizona tunnels (the Nevada tunnels were kept in reserve for high water) on November 13, 1932. This was done by exploding a temporary cofferdam
Cofferdam
A cofferdam is a temporary enclosure built within, or in pairs across, a body of water and constructed to allow the enclosed area to be pumped out, creating a dry work environment for the major work to proceed...

 protecting the Arizona tunnels while at the same time dumping rubble into the river until its natural course was blocked.

Following the completion of the dam, the entrances to the two outer diversion tunnels were sealed at the opening and half way through the tunnels with large concrete plugs. The downstream halves of the tunnels following the inner plugs are now the main bodies of the spillway tunnels.

Groundworks, rock clearance and grout curtain


To protect the construction site from the Colorado River and to facilitate the river's diversion, two cofferdams were constructed. Work on the upper cofferdam began in September 1932, even though the river had not yet been diverted. The cofferdams were designed to protect against the possibility of the river flooding a site at which two thousand men might be at work, and their specifications were covered in the bid documents in nearly as much detail as the dam itself. The upper cofferdam was 96 ft (29.3 m) high, and 750 feet (228.6 m) thick at its base—thicker than the dam itself. It contained 650000 cubic yards (496,960.7 m³) of material.
Once the cofferdams were in place and the construction site was drained of water, excavation for the dam foundation began. For the dam to rest on solid rock, it was necessary to remove accumulated erosion soils
Fluvial
Fluvial is used in geography and Earth science to refer to the processes associated with rivers and streams and the deposits and landforms created by them...

 and other loose materials in the riverbed until sound bedrock was reached. Work on the foundation excavations was completed in June 1933. During this excavation, approximately 1500000 cubic yards (1,146,832.3 m³) of material was removed. Since the dam was an arch-gravity type, the side-walls of the canyon would bear the force of the impounded lake. Therefore the side-walls were excavated too, to reach virgin rock as weathered rock might provide pathways for water seepage.

The men who removed this rock were called "high scalers". While suspended from the top of the canyon with ropes, high-scalers climbed down the canyon walls and removed the loose rock with jackhammers and dynamite
Dynamite
Dynamite is an explosive material based on nitroglycerin, initially using diatomaceous earth , or another absorbent substance such as powdered shells, clay, sawdust, or wood pulp. Dynamites using organic materials such as sawdust are less stable and such use has been generally discontinued...

. Falling objects were the most common cause of death on the dam site; the high scalers' work thus helped ensure worker safety. One high scaler was able to save life in a more direct manner: when a government inspector lost his grip on a safety line and began tumbling down a slope towards almost certain death, a high scaler was able to intercept him and pull him into the air. The construction site had, even then, become a magnet for tourists; the high scalers were prime attractions and showed off for the watchers. The high scalers received considerable media attention, with one worker dubbed the "Human Pendulum" for swinging co-workers (and, at other times, cases of dynamite) across the canyon. To protect themselves against falling objects, some high scalers took cloth hats and dipped them in tar, allowing them to harden. When workers wearing such headgear were struck hard enough to inflict broken jaws, but sustained no skull damage, Six Companies ordered thousands of what initially were called "hard boiled hats" (later hard hat
Hard hat
A hard hat is a type of helmet predominantly used in workplace environments, such as construction sites, to protect the head from injury by falling objects, impact with other objects, debris, bad weather and electric shock. Inside the helmet is a suspension that spreads the helmet's weight over the...

s) and strongly encouraged their use.

The cleared, underlying rock foundation of the dam site was reinforced with grout, called a grout curtain
Grout curtain
Grout curtains are barriers that protect a dam from seepage and can be used in initial construction or repair. Additionally, they can be used to strengthen foundations and contain spills.-Characteristics:...

. Holes were driven into the walls and base of the canyon, as deep as 150 feet (45.7 m) into the rock, and any cavities encountered were to be filled with grout. This was done to stabilize the rock, to prevent water from seeping past the dam through the canyon rock, and to limit "uplift"—upward pressure from water seeping under the dam. The workers were under severe time constraints due to the beginning of the concrete pour, and when they encountered hot springs or cavities too large to readily fill, they moved on without resolving the problem. A total of 58 of the 393 holes were incompletely filled. After the dam was completed and the lake began to fill, large numbers of significant leaks into the dam caused the Bureau of Reclamation to look into the situation. It found that the work had been incompletely done, and was based on less than a full understanding of the canyon's geology. New holes were drilled from inspection galleries inside the dam into the surrounding bedrock. It took nine years (1938–47) under relative secrecy, to complete the supplemental grout curtain.

Concrete



The first concrete was poured into the dam on June 6, 1933, 18 months ahead of schedule. Since concrete heats and contracts
Thermal expansion
Thermal expansion is the tendency of matter to change in volume in response to a change in temperature.When a substance is heated, its particles begin moving more and thus usually maintain a greater average separation. Materials which contract with increasing temperature are rare; this effect is...

 as it cures, the potential for uneven cooling and contraction of the concrete posed a serious problem. Bureau of Reclamation engineers calculated that if the dam was built in a single continuous pour, the concrete would take 125 years to cool and the resulting stresses would cause the dam to crack and crumble. Instead, the ground where the dam was to rise was marked with rectangles, and concrete blocks in columns were poured, some as large as 50 feet (15.2 m) square and 5 feet (1.5 m) high. Each five-foot form contained a series of 1 inches (2.5 cm) steel pipes through which first cool river water, then ice-cold water from a refrigeration
Refrigeration
Refrigeration is a process in which work is done to move heat from one location to another. This work is traditionally done by mechanical work, but can also be done by magnetism, laser or other means...

 plant was run. Once an individual block had cured and had stopped contracting, the pipes were filled with grout. Grout was also used to fill the hairline spaces between columns, which were grooved to increase the strength of the joins.

The concrete was delivered in huge steel buckets 7 feet (2.1 m) high and almost 7 feet (2.1 m) in diameter—Crowe was awarded two patents for their design. These buckets, which weighed 20 short tons (18.1 t) when full, were filled at two massive concrete plants on the Nevada side, and were delivered to the site in special railcars
Railroad car
A railroad car or railway vehicle , also known as a bogie in Indian English, is a vehicle on a rail transport system that is used for the carrying of cargo or passengers. Cars can be coupled together into a train and hauled by one or more locomotives...

. The buckets were then suspended from aerial cableways, which were used to deliver the bucket to a specific column. As the required grade of aggregate
Construction Aggregate
Construction aggregate, or simply "aggregate", is a broad category of coarse particulate material used in construction, including sand, gravel, crushed stone, slag, recycled concrete and geosynthetic aggregates. Aggregates are the most mined material in the world...

 in the concrete differed depending on placement in the dam (from pea-sized gravel to 9 inch (230 mm) stones), it was vital that the bucket be maneuvered to the proper column. Once the bottom of the bucket opened up, disgorging 8 cubic yards (6.1 m³) of concrete, a team of men worked it throughout the form. Although there are myths that men were caught in the pour and are entombed in the dam to this day, each bucket only deepened the concrete in a form by an inch, and Six Companies engineers would not have permitted a flaw caused by the presence of a human body.

A total of 3250000 cubic yards (2,484,803.3 m³) of concrete was used in the dam before concrete pouring ceased on May 29, 1935. In addition, 1110000 cubic yards (848,655.9 m³) were used in the power plant and other works. More than 582 miles (936.6 km) of cooling pipes were placed within the concrete. Overall, there is enough concrete in the dam to pave a two-lane highway from San Francisco to New York. Concrete cores were removed from the dam for testing in 1995; they showed that "Hoover Dam's concrete has continued to slowly gain strength" and the dam is composed of a "durable concrete having a compressive strength exceeding the range typically found in normal mass concrete". Hoover Dam concrete is not subject to Alkali-Silica Reaction (ASR) as the Hoover Dam builders happened to use nonreactive aggregate, unlike that at downstream Parker Dam
Parker Dam
Parker Dam is a concrete arch-gravity dam that crosses the Colorado River downstream of Hoover Dam. Built between 1934 and 1938 by the Bureau of Reclamation, it is high, of which are below the riverbed, making it "the deepest dam in the world". The dam's primary functions are to create a...

, where ASR has caused measurable deterioration.

Dedication and completion



With most work finished on the dam itself (the powerhouse remained uncompleted), a formal dedication ceremony was arranged for September 30, 1935, to coincide with a western tour being made by President Franklin Roosevelt. The morning of the dedication, it was moved forward three hours from 2 p.m. Pacific time to 11 a.m.; this was done because Secretary of the Interior
United States Secretary of the Interior
The United States Secretary of the Interior is the head of the United States Department of the Interior.The US Department of the Interior should not be confused with the concept of Ministries of the Interior as used in other countries...

 Harold L. Ickes
Harold L. Ickes
Harold LeClair Ickes was a United States administrator and politician. He served as United States Secretary of the Interior for 13 years, from 1933 to 1946, the longest tenure of anyone to hold the office, and the second longest serving Cabinet member in U.S. history next to James Wilson. Ickes...

 had reserved a radio slot for the President for 2 p.m. but officials did not realize until the day of the ceremony that the slot was for 2 p.m. Eastern Time. Despite the change in the ceremony time, and temperatures of 102 °F (38.9 °C), 10,000 people were present for the President's speech in which he avoided mentioning the name of former President Hoover, who was not invited to the ceremony. To mark the occasion, a three-cent stamp was issued by the United States Post Office Department
United States Post Office Department
The Post Office Department was the name of the United States Postal Service when it was a Cabinet department. It was headed by the Postmaster General....

—bearing the name "Boulder Dam", the official name of the dam between 1933 and 1947. After the ceremony, Roosevelt made the first visit by any American President to Las Vegas.

Most work had been completed by the dedication, and Six Companies negotiated with the government through late 1935 and early 1936 to settle all claims and arrange for the formal transfer of the dam to the Federal Government. The parties came to an agreement and on March 1, 1936, Secretary Ickes formally accepted the dam on behalf of the government. Six Companies was not required to complete work on one item, a concrete plug for one of the bypass tunnels, as the tunnel had to be used to take in irrigation water until the powerhouse went into operation.

Construction deaths


There were 112 deaths associated with the construction of the dam. Included in that total was J. G. Tierney, a surveyor who drowned on December 20, 1922, while looking for an ideal spot for the dam. He is generally counted as the first man to die in the construction of Hoover Dam. His son, Patrick W. Tierney, was the last man to die working on the dam's construction, 13 years to the day later. Ninety-six of the deaths occurred during construction at the site. Of the 112 fatalities, 91 were Six Companies employees, three were BOR employees, and one was a visitor to the site, with the remainder employees of various contractors not part of Six Companies.

Not included in the official fatalities number were deaths that were recorded as pneumonia
Pneumonia
Pneumonia is an inflammatory condition of the lung—especially affecting the microscopic air sacs —associated with fever, chest symptoms, and a lack of air space on a chest X-ray. Pneumonia is typically caused by an infection but there are a number of other causes...

. Workers alleged that this diagnosis was a cover for death from carbon monoxide
Carbon monoxide
Carbon monoxide , also called carbonous oxide, is a colorless, odorless, and tasteless gas that is slightly lighter than air. It is highly toxic to humans and animals in higher quantities, although it is also produced in normal animal metabolism in low quantities, and is thought to have some normal...

 poisoning, brought on by the use of gasoline-fueled vehicles in the diversion tunnels, and a classification used by Six Companies to avoid paying compensation claims. The site's diversion tunnels frequently reached 140 °F (60 °C), enveloped in thick plumes of vehicle exhaust gases. A total of 42 workers were recorded as having died from pneumonia; none were listed as having died from carbon monoxide poisoning. No deaths of non-workers from pneumonia were recorded in Boulder City during the construction period.

Architectural style



The initial plans for the facade of the dam, the power plant, the outlet tunnels and ornaments clashed with the modern look of an arch dam. The Bureau of Reclamation, more concerned with the dam's functionality, adorned it with a Gothic
Gothic architecture
Gothic architecture is a style of architecture that flourished during the high and late medieval period. It evolved from Romanesque architecture and was succeeded by Renaissance architecture....

-inspired balustrade
Baluster
A baluster is a moulded shaft, square or of lathe-turned form, one of various forms of spindle in woodwork, made of stone or wood and sometimes of metal, standing on a unifying footing, and supporting the coping of a parapet or the handrail of a staircase. Multiplied in this way, they form a...

 and eagle statues. This initial design was criticized by many as being too plain and unremarkable for a project of such immense scale, so Los Angeles-based architect Gordon B. Kaufmann
Gordon Kaufmann
Gordon Kaufmann was an English born American architect mostly known for his work on the Hoover Dam. He arrived in California in 1914 and during his early career he did much work in the Mediterranean Revival Style which had become popular at that time.He was also the initial architect for Scripps...

, then the supervising architect to the Bureau of Reclamation, was brought in to redesign the exteriors. Kaufmann greatly streamlined the design, and applied an elegant Art Deco
Art Deco
Art deco , or deco, is an eclectic artistic and design style that began in Paris in the 1920s and flourished internationally throughout the 1930s, into the World War II era. The style influenced all areas of design, including architecture and interior design, industrial design, fashion and...

 style to the entire project. He designed sculptured turrets rising seamlessly from the dam face and clock faces on the intake towers set for the time in Nevada and Arizona — the two states are in different time zones, but as Arizona does not observe Daylight Saving Time
Daylight saving time
Daylight saving time —also summer time in several countries including in British English and European official terminology —is the practice of temporarily advancing clocks during the summertime so that afternoons have more daylight and mornings have less...

, the clocks display the same time for more than half the year.

At Kaufmann’s request, Denver artist Allen Tupper True
Allen Tupper True
Allen Tupper True was an American illustrator, easel painter and muralist who specialized in depicting the American West.-Biography:...

 was hired to handle the design and decoration of the walls and floors of the new dam. True's design scheme incorporated motifs of the Navajo
Navajo people
The Navajo of the Southwestern United States are the largest single federally recognized tribe of the United States of America. The Navajo Nation has 300,048 enrolled tribal members. The Navajo Nation constitutes an independent governmental body which manages the Navajo Indian reservation in the...

 and Pueblo
Pueblo
Pueblo is a term used to describe modern communities of Native Americans in the Southwestern United States of America. The first Spanish explorers of the Southwest used this term to describe the communities housed in apartment-like structures built of stone, adobe mud, and other local material...

 tribes of the region. Although some initially were opposed to these designs, True was given the go-ahead and was officially appointed consulting artist. With the assistance of the National Laboratory of Anthropology, True researched authentic decorative motifs from Indian sand paintings, textiles, baskets and ceramics. The images and colors are based on Native American visions of rain, lightning, water, clouds, and local animals — lizards, serpents, birds — and on the Southwestern landscape of stepped mesas. In these works, which are integrated into the walkways and interior halls of the dam, True also reflected on the machinery of the operation, making the symbolic patterns appear both ancient and modern.
With the agreement of Kaufmann and the engineers, True also devised an innovative color coding for the pipes and machinery, which was implemented throughout all BOR projects. True’s consulting artist job lasted through 1942; it was extended so he could complete design work for the Parker
Parker Dam
Parker Dam is a concrete arch-gravity dam that crosses the Colorado River downstream of Hoover Dam. Built between 1934 and 1938 by the Bureau of Reclamation, it is high, of which are below the riverbed, making it "the deepest dam in the world". The dam's primary functions are to create a...

, Shasta
Shasta Dam
Shasta Dam is an arch dam across the Sacramento River in the northern part of the U.S. state of California, at the north end of the Sacramento Valley. The dam mainly serves long-term water storage and flood control in its reservoir, Shasta Lake, and also generates hydroelectric power...

 and Grand Coulee
Grand Coulee Dam
Grand Coulee Dam is a gravity dam on the Columbia River in the U.S. state of Washington built to produce hydroelectric power and provide irrigation. It was constructed between 1933 and 1942, originally with two power plants. A third power station was completed in 1974 to increase its energy...

 dams and power plants. True’s work on the Hoover Dam was humorously referred to in a poem published in The New Yorker
The New Yorker
The New Yorker is an American magazine of reportage, commentary, criticism, essays, fiction, satire, cartoons and poetry published by Condé Nast...

, part of which read, “lose the spark, and justify the dream; but also worthy of remark will be the color scheme”.

Complementing Kaufmann and True's work, the Norwegian-born, naturalized American sculptor Oskar J.W. Hansen designed many of the sculptures on and around the dam. His works include the monument of dedication plaza, a plaque to memorialize the workers killed and the bas-reliefs
Relief
Relief is a sculptural technique. The term relief is from the Latin verb levo, to raise. To create a sculpture in relief is thus to give the impression that the sculpted material has been raised above the background plane...

 on the elevator towers. In his words, Hansen wanted his work to express "the immutable calm of intellectual resolution, and the enormous power of trained physical strength, equally enthroned in placid triumph of scientific accomplishment", because "[t]he building of Hoover Dam belongs to the sagas of the daring." Hansen's dedication plaza, on the Nevada abutment, contains a sculpture of two winged figures flanking a flagpole. Surrounding the base of the monument is a terrazzo
Terrazzo
Terrazzo is a composite material poured in place or precast, which is used for floor and wall treatments. It consists of marble, quartz, granite, glass or other suitable chips, sprinkled or unsprinkled, and poured with a binder that is cementitious, chemical or a combination of both...

 floor embedded with a "star map". The map depicts the Northern Hemisphere sky at the moment of President Roosevelt's dedication of the dam. This is intended to help future astronomers, if necessary, calculate the exact date of dedication. The 30 feet (9.1 m) high bronze figures, dubbed "Winged Figures of the Republic", were each formed in a continuous pour. To put such large bronzes into position without marring the highly polished bronze surface, they were placed on ice and guided into position as the ice melted. Hansen's bas-relief on the Nevada elevator tower depicts the benefits of the dam: flood control, navigation, irrigation, water storage, and power. The bas-relief on the Arizona elevator depicts, in his words, "the visages of those Indian tribes who have inhabited mountains and plains from ages distant."

Power plant and water demands



Excavation for the powerhouse was carried out simultaneously with the excavation for the dam foundation and abutments. A U-shaped structure located at the downstream toe of the dam, its excavation was completed in late 1933 with the first concrete placed in November 1933. Filling of Lake Mead began February 1, 1935 even before the last of the concrete was poured that May. The powerhouse was one of the projects uncompleted at the time of the formal dedication on September 30, 1935—a crew of 500 men remained after the dedication to finish it and other structures. To make the powerhouse roof bombproof, it was constructed of layers of concrete, rock, and steel with a total thickness of about 3.5 feet (1.1 m), topped with layers of sand and tar.

In the latter half of 1936, water levels in Lake Mead were high enough to permit power generation, and the first three generators, all on the Nevada side, began operating. In March 1937, one more Nevada generator went online and the first Arizona generator by August. By September 1939, four more generators were operating and the dam's power plant became the largest hydroelectricity facility in the world. The final generator was not placed in service until 1961, bringing the maximum generating capacity to 1345 megawatts at the time. Original plans called for 16 large generators, eight on each side of the river, but two smaller generators were installed instead of one large one on the Arizona side for a total of 17. The smaller generators were used to serve smaller municipalities at a time when the output of each generator was dedicated to a single municipality, before the dam's total power output was placed on the grid and made arbitrarily distributable. The present contracts for the sale of electricity expire in 2017.

Before water from Lake Mead reaches the turbines, it enters the intake towers and enters four gradually narrowing penstock
Penstock
A penstock is a sluice or gate or intake structure that controls water flow, or an enclosed pipe that delivers water to hydraulic turbines and sewerage systems. It is a term that has been inherited from the technology of wooden watermills....

s which funnel the water down towards the powerhouse. The intakes provide a maximum hydraulic head
Hydraulic head
Hydraulic head or piezometric head is a specific measurement of water pressure above a geodetic datum. It is usually measured as a water surface elevation, expressed in units of length, at the entrance of a piezometer...

 (water pressure) of 590 ft (179.8 m) as the water reaches a speed of about 85 mph (136.8 km/h). The entire flow of the Colorado River passes through the turbine
Francis turbine
The Francis turbine is a type of water turbine that was developed by James B. Francis in Lowell, Massachusetts. It is an inward-flow reaction turbine that combines radial and axial flow concepts....

s. The spillways and outlet works
Outlet works
A set of outlet works is a device used to release and regulate water flow from a dam. Such devices usually consist of one or more pipes or tunnels through the embankment of the dam, directing water usually under high pressure to the river downstream...

 (jet-flow gates) are rarely used. The jet-flow gates, located in concrete structures 180 feet (54.9 m) above the river and at river level, may be used to divert water around the dam in emergency or flood conditions, but have never done so, and in practice are only used to drain water from the penstocks for maintenance. Following an uprating project from 1986 to 1993, the total gross power rating for the plant, including two 2.4 megawatt electric generators that power Hoover Dam's own operations is a maximum capacity of 2080 megawatts. The annual generation of Hoover Dam varies. The maximum net generation was 10.348 TWh in 1984, and the minimum since 1940 was 2.648 TWh in 1956. The average has been about 4.2 TWh/year.

Control of water was the primary concern in the building of the dam. Power generation has allowed the dam project to be self sustaining: proceeds from the sale of power repaid the 50-year construction loan, and those revenues also finance the multi-million dollar yearly maintenance budget. Power is generated in step with and only with the release of water in response to downstream water demands. Lake Mead and downstream releases from the dam provide water for both municipal
Water supply
Water supply is the provision of water by public utilities, commercial organisations, community endeavours or by individuals, usually via a system of pumps and pipes...

 and irrigation
Irrigation
Irrigation may be defined as the science of artificial application of water to the land or soil. It is used to assist in the growing of agricultural crops, maintenance of landscapes, and revegetation of disturbed soils in dry areas and during periods of inadequate rainfall...

 uses. Water released from the Hoover Dam eventually reaches the All-American Canal
All-American Canal
The All-American Canal is an long aqueduct, located in southeastern California. It conveys water from the Colorado River into the Imperial Valley and to nine cities. It is the Imperial Valley's only water source, and replaced the Alamo Canal, which was located mostly in Mexico...

 for the irrigation of over 1000000 acres (404,686 ha) of land. Water from the lake serves 8 million people in Arizona, Nevada and California.

Spillways



The dam is protected against over-topping by two spillways. The spillway entrances are located behind each dam abutment, running roughly parallel to the canyon walls. The spillway entrance arrangement forms a classic side-flow weir
Weir
A weir is a small overflow dam used to alter the flow characteristics of a river or stream. In most cases weirs take the form of a barrier across the river that causes water to pool behind the structure , but allows water to flow over the top...

 with each spillway containing four 100 ft (30.5 m) long and 16 ft (4.9 m) high steel drum gates. Each gate weighs 5000000 pounds (2,267,961.9 kg) and can be operated manually or automatically. Gates are raised and lowered depending upon water levels in the reservoir and flood conditions. The gates cannot completely stop water from entering the spillways but can help maintain an extra 16 ft (4.9 m) of lake level.
Water flowing over the spillways drops sharply into 600 ft (182.9 m) long, 50 ft (15.2 m) wide spillway tunnels before connecting to the outer diversion tunnels, and reentering the main river channel below the dam. This complex spillway entrance arrangement combined with the approximate 700 ft (213.4 m) elevation drop from the top of the reservoir to the river below was a difficult engineering problem and posed several design challenges. Each spillway's capacity of 200000 ft3/s was empirically verified in post construction tests in 1941.

The large spillway tunnels have only been used twice. In addition to testing in 1941, the spillways were used because of flooding in 1983. Both times, in inspecting the tunnels after the spillways were used, engineers found major damage to the concrete linings and underlying rock. The 1941 damage was attributed to a slight misalignment of the tunnel invert (or base), which caused cavitation
Cavitation
Cavitation is the formation and then immediate implosion of cavities in a liquidi.e. small liquid-free zones that are the consequence of forces acting upon the liquid...

, a phenomenon in fast-flowing liquids in which vapor bubbles collapse with explosive force. In response to this finding, the tunnels were patched with special heavy-duty concrete and the surface of the concrete was polished mirror-smooth. The spillways were modified in 1947 by adding flip buckets, which both slow the water and decrease the spillway's effective capacity, in an attempt to eliminate conditions thought to have contributed to the 1941 damage. The 1983 damage, also due to cavitation, led to the installation of aerators in the spillways. Tests at Grand Coulee Dam
Grand Coulee Dam
Grand Coulee Dam is a gravity dam on the Columbia River in the U.S. state of Washington built to produce hydroelectric power and provide irrigation. It was constructed between 1933 and 1942, originally with two power plants. A third power station was completed in 1974 to increase its energy...

 showed that the technique worked, in principle.

Roadway and tourism



There are two lanes for automobile traffic across the top of the dam, which formerly served as the Colorado River crossing for U.S. Route 93
U.S. Route 93
U.S. Route 93 is a major north–south United States highway in the western United States. The southern terminus is at U.S. Route 60 in Wickenburg, Arizona. The northern terminus is at the Canadian border north of Eureka in Lincoln County, Montana, where the roadway continues into Roosville,...

. In the wake of the September 11, 2001 terrorist attacks
September 11, 2001 attacks
The September 11 attacks The September 11 attacks The September 11 attacks (also referred to as September 11, September 11th or 9/119/11 is pronounced "nine eleven". The slash is not part of the pronunciation...

, authorities expressed security concerns and the Hoover Dam Bypass
Hoover Dam Bypass
The Mike O'Callaghan – Pat Tillman Memorial Bridge, the key component to the Hoover Dam Bypass project, was the first concrete-steel composite arch bridge built in the United States, and it incorporates the longest concrete arch bridge in the Western Hemisphere. Opened on October 19, 2010,...

 project was expedited. Pending the completion of the bypass, restricted traffic was permitted over Hoover Dam. Some types of vehicles were inspected prior to crossing the dam while semi-trailer truck
Semi-trailer truck
A semi-trailer truck, also known as a semi, tractor-trailer, or articulated truck or articulated lorry, is an articulated vehicle consisting of a towing engine , and a semi-trailer A semi-trailer truck, also known as a semi, tractor-trailer, or (in the United Kingdom and Ireland) articulated truck...

s, bus
Bus
A bus is a road vehicle designed to carry passengers. Buses can have a capacity as high as 300 passengers. The most common type of bus is the single-decker bus, with larger loads carried by double-decker buses and articulated buses, and smaller loads carried by midibuses and minibuses; coaches are...

es carrying luggage, and enclosed-box truck
Box truck
A box truck, also known as a cube truck, cube van, bob truck, box van, or straight truck, is a truck with a cuboid-shaped cargo area.-Road vehicles:...

s over 40 feet (12.2 m) long were not allowed on the dam at all, and were diverted to U.S. Route 95
U.S. Route 95 in Nevada
In the U.S. state of Nevada, U.S. Route 95 is a major U.S. highway traversing the state from north to south directly through Las Vegas and providing connections to both Carson City and Reno...

 or Nevada State Routes 163
Nevada State Route 163
State Route 163 , often referred to as the Laughlin Highway, is a state highway in southern Clark County, Nevada. The route connects the town of Laughlin to the rest of the state via U.S. Route 95 ....

/68. The four-lane Hoover Dam Bypass opened on October 19, 2010. It includes a composite steel and concrete arch bridge
Arch bridge
An arch bridge is a bridge with abutments at each end shaped as a curved arch. Arch bridges work by transferring the weight of the bridge and its loads partially into a horizontal thrust restrained by the abutments at either side...

, the Mike O'Callaghan – Pat Tillman Memorial Bridge, 1500 ft (457.2 m) downstream from the dam.
With the opening of the bypass, through traffic is no longer allowed across Hoover Dam, though dam visitors are allowed to use the existing roadway to approach from the Nevada side and cross to parking lots and other facilities on the Arizona side.

Hoover Dam opened for tours in 1937, after its completion, but on December 7, 1941, was closed to the public for the duration of World War II, during which only authorized traffic, in convoys, was permitted. It reopened September 2, 1945, and by 1953, annual attendance had risen to 448,081. The dam closed on November 25, 1963 and March 31, 1969, days of mourning in remembrance of Presidents Kennedy
John F. Kennedy
John Fitzgerald "Jack" Kennedy , often referred to by his initials JFK, was the 35th President of the United States, serving from 1961 until his assassination in 1963....

 and Eisenhower. In 1995, a new visitor's center was built, and the following year, visits exceeded one million for the first time. The dam closed again to the public on September 11, 2001; modified tours were resumed in December and a new "Discovery Tour" was added the following year. Today, nearly a million people per year take the tours of the dam offered by the Bureau of Reclamation. Increased security concerns by the government have led to most of the interior structure being inaccessible to tourists. As a result, few of True's decorations can be seen any longer by visitors.

Environmental impact



The changes in water use caused by Hoover Dam's construction has had a large impact on the Colorado River Delta
Colorado River Delta
The Colorado River Delta is the region where the Colorado River flows into the Gulf of California . The delta is part of a larger geologic region called the Salton Trough. Historically, the interaction of the river’s flow and the ocean’s tide created a dynamic environment, supporting freshwater,...

. The construction of the dam has been credited as causing the decline of this estuarine ecosystem
Ecosystem
An ecosystem is a biological environment consisting of all the organisms living in a particular area, as well as all the nonliving , physical components of the environment with which the organisms interact, such as air, soil, water and sunlight....

. For six years, after the construction of the dam and while Lake Mead filled, virtually no water reached the mouth of the river. The delta's estuary, which once had a freshwater-saltwater mixing zone stretching 40 miles (64.4 km) south of the river's mouth, was turned into an inverse estuary where the level of salinity
Salinity
Salinity is the saltiness or dissolved salt content of a body of water. It is a general term used to describe the levels of different salts such as sodium chloride, magnesium and calcium sulfates, and bicarbonates...

 was higher close to the river's mouth.

The Colorado River had experienced natural flooding before the construction of the Hoover Dam. The dam eliminated the natural flooding, which imperiled many species adapted to the flooding, including both plants and animals.
The construction of the dam devastated the populations of native fish in the river downstream from the dam. Four species of fish native to the Colorado River, the Bonytail chub
Bonytail chub
The bonytail chub or bonytail, Gila elegans, is a cyprinid freshwater fish native to the Colorado River of Arizona, California, Colorado, Nevada and Utah in the southwestern United States...

, Colorado pikeminnow
Colorado pikeminnow
The Colorado pikeminnow Ptychocheilus lucius is the largest cyprinid fish of North America and one of the largest in the world, with reports of individuals up to 6 ft long and weighing over 100 pounds...

, Humpback chub
Humpback chub
The humpback chub Gila cypha, is a federally protected fish that lived originally in fast waters of the Colorado River system in the United States. This species takes its name from the prominent hump between the head and dorsal fin, which is thought to direct the flow of water over the body and...

, and Razorback sucker
Razorback sucker
The razorback sucker, Xyrauchen texanus, is an endangered fresh water sucker of rivers in the Colorado River drainage of western North America.-Description:...

, are currently listed as endangered
Endangered species
An endangered species is a population of organisms which is at risk of becoming extinct because it is either few in numbers, or threatened by changing environmental or predation parameters...

.

Naming controversy


During the years of lobbying leading up to the passage of legislation authorizing the dam in 1928, the dam was generally referred to by the press as "Boulder Dam" or "Boulder Canyon Dam", notwithstanding the fact that the proposed site had been shifted to Black Canyon. The Boulder Canyon Project Act of 1928 (BCPA) never mentions a proposed name or title for the dam. The BCPA merely allows the government to "construct, operate, and maintain a dam and incidental works in the main stream of the Colorado River at Black Canyon or Boulder Canyon".

When Secretary Wilbur spoke at the ceremony starting the building of the railway between Las Vegas and the dam site on September 17, 1930, he named the dam "Hoover Dam", citing a tradition of naming dams after Presidents, though none had been so honored during their terms of office. Wilbur justified his choice on the ground that Hoover was "the great engineer whose vision and persistence ... has done so much to make [the dam] possible". One writer complained in response that "the Great Engineer had quickly drained, ditched, and dammed the country".

After Hoover's election defeat and the accession of the Roosevelt administration, Secretary Ickes ordered on May 13, 1933 that the dam be referred to as "Boulder Dam". Ickes stated that Wilbur had been imprudent in naming the structure after a sitting president, that Congress had never ratified his choice, and that it had long been referred to as Boulder Dam. When Ickes spoke at the dedication ceremony on September 30, 1935, he was determined, as he recorded in his diary, "to try to nail down for good and all the name Boulder Dam". At one point in the speech, he spoke the words "Boulder Dam" five times within thirty seconds. Further, he suggested that if the dam were to be named after any one person, it should be for California Senator Hiram Johnson
Hiram Johnson
Hiram Warren Johnson was a leading American progressive and later isolationist politician from California; he served as the 23rd Governor from 1911 to 1917, and as a United States Senator from 1917 to 1945.-Early life:...

, a lead sponsor of the authorizing legislation. Roosevelt also referred to the dam as Boulder Dam, and the Republican-leaning Los Angeles Times
Los Angeles Times
The Los Angeles Times is a daily newspaper published in Los Angeles, California, since 1881. It was the second-largest metropolitan newspaper in circulation in the United States in 2008 and the fourth most widely distributed newspaper in the country....

, which at the time of Ickes' name change had run an editorial cartoon showing Ickes ineffectively chipping away at an enormous sign "HOOVER DAM", reran it showing Roosevelt reinforcing Ickes, but having no greater success.

In the following years, the name "Boulder Dam" failed to fully take hold, with many Americans using the two names interchangeably and mapmakers divided as to what name should be printed. Memories of the Great Depression
Great Depression
The Great Depression was a severe worldwide economic depression in the decade preceding World War II. The timing of the Great Depression varied across nations, but in most countries it started in about 1929 and lasted until the late 1930s or early 1940s...

 faded, and Hoover to some extent rehabilitated himself through good works during and after World War II. In 1947, a bill passed both Houses of Congress unanimously restoring the name to "Hoover Dam". Ickes, who was by then a private citizen, opposed the change, stating, "I didn't know Hoover was that small a man to take credit for something he had nothing to do with."

Power distribution


Power from the dam's powerhouse was originally sold pursuant to a fifty-year contract which terminated in 1987. When the contracts ended, the Bureau of Reclamation assumed control of the powerplant from the Los Angeles Department of Water and Power and Southern California Edison Co. The contracts were renegotiated and implemented for a 30-year period, and will expire in 2017. On October 3, 2011, the United States House of Representatives
United States House of Representatives
The United States House of Representatives is one of the two Houses of the United States Congress, the bicameral legislature which also includes the Senate.The composition and powers of the House are established in Article One of the Constitution...

 passed a bill which would, if enacted, extend the current power allocations until 2067. A similar bill awaits action in the Senate
United States Senate
The United States Senate is the upper house of the bicameral legislature of the United States, and together with the United States House of Representatives comprises the United States Congress. The composition and powers of the Senate are established in Article One of the U.S. Constitution. Each...

. The congressional action follows an agreement among the dam's larger allocation holders to form a 100 MWh pool of electricity to be offered to Native American tribes, electricity cooperative
Cooperative
A cooperative is a business organization owned and operated by a group of individuals for their mutual benefit...

s, and other new customers. The Bureau of Reclamation reports that the energy generated is allocated as follows:
AreaPercentage
Metropolitan Water District of Southern California
Metropolitan Water District of Southern California
The Metropolitan Water District of Southern California is the largest supplier of treated water in the US. The name is usually shortened to the "Metropolitan Water District" or simply "MWD". It is a cooperative of 14 cities and 12 municipal water districts that indirectly provides water to 18...

28.53%
State of Nevada
Nevada
Nevada is a state in the western, mountain west, and southwestern regions of the United States. With an area of and a population of about 2.7 million, it is the 7th-largest and 35th-most populous state. Over two-thirds of Nevada's people live in the Las Vegas metropolitan area, which contains its...

23.37%
State of Arizona
Arizona
Arizona ; is a state located in the southwestern region of the United States. It is also part of the western United States and the mountain west. The capital and largest city is Phoenix...

18.95%
Los Angeles, California
Los Angeles Department of Water and Power
The Los Angeles Department of Water and Power is the largest municipal utility in the United States, serving over four million residents. It was founded in 1902 to supply water and electricity to residents and businesses in Los Angeles and surrounding communities...

15.42%
Southern California Edison Company 5.54%
Boulder City, Nevada
Boulder City, Nevada
Boulder City is a city in Clark County, Nevada, United States. It is approximately from the City of Las Vegas. As of the 2010 census the population of Boulder City was 15,023.Boulder City is one of only two cities in Nevada that prohibit gambling....

1.77%
Glendale, California
Glendale, California
Glendale is a city in Los Angeles County, California, United States. As of the 2010 Census, the city population is 191,719, down from 194,973 at the 2000 census. making it the third largest city in Los Angeles County and the 22nd largest city in the state of California...

1.59%
Pasadena, California
Pasadena, California
Pasadena is a city in Los Angeles County, California, United States. Although famous for hosting the annual Rose Bowl football game and Tournament of Roses Parade, Pasadena is the home to many scientific and cultural institutions, including the California Institute of Technology , the Jet...

1.36%
Anaheim, California
Anaheim, California
Anaheim is a city in Orange County, California. As of the 2010 United States Census, the city population was about 365,463, making it the most populated city in Orange County, the 10th most-populated city in California, and ranked 54th in the United States...

1.15%
Riverside, California
Riverside, California
Riverside is a city in Riverside County, California, United States, and the county seat of the eponymous county. Named for its location beside the Santa Ana River, it is the largest city in the Riverside-San Bernardino-Ontario metropolitan area of Southern California, 4th largest inland California...

0.86%
Vernon, California
Vernon, California
Vernon is a city five miles south of downtown Los Angeles, California. The population was 112 at the 2010 United States Census, the smallest of any incorporated city in the state....

0.62%
Burbank, California
Burbank, California
Burbank is a city in Los Angeles County in Southern California, United States, north of downtown Los Angeles. The estimated population in 2010 was 103,340....

0.59%
Azusa, California
Azusa, California
Azusa is a city in Los Angeles County, California, United States. The population was 46,361 at the 2010 census, up from 44,712 at the 2000 census. Though sometimes assumed to be a compaction of the phrase "everything from A to Z in the USA" from an old Jack Benny joke, the place name "Azusa"...

0.11%
Colton, California
Colton, California
Colton is a city in San Bernardino County, California, United States. The city is located in the Inland Empire region of the state and is approximately 57 miles east of Los Angeles. The population of Colton is 52,154 according to the 2010 census, up from 47,662 at the 2000 census.Colton is the...

0.09%
Banning, California
Banning, California
-2010:The 2010 United States Census reported that Banning had a population of 29,603. The population density was 1,281.6 people per square mile . The racial makeup of Banning was 19,164 White, 2,165 African American, 641 Native American, 1,549 Asian, 39 Pacific Islander, 4,604 from other...

0.04%

See also


  • Hoover Dam Police
    Hoover Dam Police
    The Hoover Dam Police, officially the Bureau of Reclamation Police, is a federal security police force, stationed at Hoover Dam southeast of Las Vegas, Nevada. Reclamation Police Officers are stationed only at Hoover Dam. Hoover Dam was both listed on the National Register of Historic Places in...

  • List of largest hydroelectric power stations
  • Ralph Luther Criswell
    Ralph Luther Criswell
    Ralph Luther Criswell , first a Socialist and then a Republican, was a member of the Los Angeles City Council for ten years in the early 20th Century...

    , lobbyist on behalf of the dam

External links