A Dam Modern Marvel - How the Hoover Dam was Built

We have already talked about Nevada and a few must-see highlights around the state, so you might remember the Hoover Dam as one of them. In an attempt to touch on multiple locations, we couldn't dive too deep into the wonder that is this modern marvel. However, this massive structure, process of construction, and never-before-attempted project continues to astound the world. A show of American innovation, progress, problem-solving, and hard work, the Hoover Dam deserves its own feature. Let's learn more about the Hoover Dam!

Planning the Hoover Dam

During the Gilded Age and thanks to the progress of the transcontinental railroad, the US began developing in the Southwest. If it could be diverted, the Colorado River was considered a potential source of irrigation water. Land speculator William Beatty had built the Alamo Canal in the years prior, and served as inspiration for how to harness the power of the Colorado River. Since 1900, the Black Canyon and Boulder Canyon were surveyed as potential sites to support a dam, with the aim of controlling floods, providing irrigation water, and producing hydroelectric power. As electric power transmission continued to improve, the Lower Colorado was noted for its potential to produce hydroelectric power. In 1902, the Edison Electric Company of Los Angeles surveyed the river, but didn't think the output would be worth the purchase and opted out of buying the land. That's when the Bureau of Reclamation started scoping out the Lower Colorado for a dam.

Service chief Arthur Powell Davis wrote up the Davis-Fall Report, named after Interior Secretary Albert Fall, which was presented by the Bureau of Reclamation in 1922. This report proposed the building of a dam on the Colorado River for flood control and electric power generation. Boulder Canyon was again investigated but lacked space for a construction camp for a project of this size. Black Canyon was considered ideal; however, the project initially kept the name "Boulder Canyon Project." Other things still needed to happen before they could move forward. Herbert Hoover, who was U.S. Secretary of Commerce at the time, handled the negotiation of the Colorado River Compact. The suggestion came from Colorado attorney Delph Carpenter, who suggested that the seven states that fell within the river's basin all needed to agree. Hoover divided the basin into the lower (Arizona, Nevada, California) and the upper (Wyoming, Utah, New Mexico, and Colorado) regions for the negotiation. Congress approved the compact.

In 1928, Congress approved the project. That year, Hoover was elected the 31st president of the United States and he signed the bill for the Boulder Canyon Project Act himself in 1929. Plans for what would eventually be the Hoover Dam were so intensive that there was not a single company that could provide all the needed materials. Thus was born the conglomerate of Six Companies, Inc., which joined together to start construction in 1931. Now that the project was approved, officials needed to finalize exactly what they were going to build and how.

With the design overseen by the Bureau's chief design engineer, John L. Savage, the project was set to be a curved arch-gravity dam. This type of dam would be thicker at the bottom, thinning out at the top, and curve toward the water to send the water's force into the abutments*. The curved shape creates counter-pressure against Lake Mead's waters, causing the concrete to constrict and reinforce the dam's rigidity. (Later studies would show that the Hoover Dam's construction itself was so thick and heavy that the curve is unnecessary to hold back the lake—the lake would be held back by the dam's weight alone. However, the curved shape added a level of security, ensuring the dam's efficacy.) There would be enough space left across the top for a highway between Nevada and Arizona.

Starting Construction

Congress appropriated funds in 1928, right before the country plunged into the Great Depression. This sparked a massive movement out west, with thousands of men arriving with their families, hopefully to be given paid labor. Though Black Canyon was picked for the project location because of its potential to house a construction camp at its base, and the federal government had plans to create housing (Boulder City), this wasn't ready when the workers arrived. This resulted in a series of squatters' camps in the middle of the Nevada desert.

Plans of the Hoover Dam

How do you even begin to work on a project with zero precedent? Not only had there never been a project like this at the time, but this is also the current largest public works project ever completed in the U.S. and is the largest project in the world ever made with concrete. Over 200 engineers would come together to complete the design for the Hoover Dam. Over 5,000 men worked on the dam in the summer of 1932, but over 20,000 have worked on the project in its entirety.

The first thing that would need to be done was move the powerful Colorado River. (Yes, the river that made the Grand Canyon.)

This was the plan:

• Move the Colorado River

• Make 4 50-foot diameter tunnels by drilling through the canyon on either side of the river (resulting in one in Nevada and the other in Arizona)

• Build 2 diversion cofferdams**

• Remove all loosened rock on the sides of the canyon walls by hand

• Pour and lay the concrete for the dam

• Complete the powerhouse

• Plug the tunnels, allow Lake Mead to refill, and start generating power

Sounds easy enough, right? Of course, it wasn't.

(ca. 1932)^ - Workers on a "Jumbo Rig" that was used for drilling Hoover Dam's tunnels.

To make the four tunnels, a Jumbo Rig was constructed on the back of a 10-ton truck, where 24-30 drills could be operated at one time. Drillers stood on two different platforms, with a group of men working on the ground as the third level. The team would back the truck up against a solid rock wall, drill holes, pack the holes with dynamite, tie them together, then back the entire truck away for safety while the blowman detonated the explosives. The debris would then be cleared for the process to repeat the entire length of the tunnel, which was approximately three miles. As the tunnels progressed, the desert heat mixed with the truck exhaust, resulting in a fatality nearly every other day. Each tunnel was hollowed out to 56 feet in diameter, the height of a 4-story building, and lined with 3 feet of concrete. The river was successfully diverted through the first two Arizona tunnels on November 14, 1932. After the Hoover Dam was completed, the outer tunnels became outlets for spillways and the inner tunnels guide stored water to the power plant or past the outlet valves.

(1934)* – View showing "High Scalers" rappelling down the canyon wall just above the needle valves.

With the Colorado River diverted and the land clear for construction, it was time to remove all loosened rock on the side of the canyon. The walls themselves needed to be strong enough to anchor a dam of this magnitude, so it was imperative to scale the walls by hand and clear the weakest points. These workers were called "High Scalers." These men were lowered over the canyon rim, someone else would lower a jackhammer, and they would drill powder holes along the side of the canyon wall. Suspended nearly 800 feet in the air, High Scalers would fill the holes with dynamite, and "hand maneuver out of the way" for the explosion. Michael Green, assistant professor of history at the University of Las Vegas, Nevada, describes it saying, "They are coming down on cables and planting dynamite and swinging back, ideally, so that they don't get blown up." Once the dynamite was blown, they'd swing back and begin chipping off the remaining loose rock with crowbars. With the loosened rock cleared from the canyon walls, it was finally time for the main task: building the dam. 

On June 6, 1933, concrete was poured into the dam for the very first time, and the Boulder Canyon Project was 18 months ahead of schedule. 

Trouble on the Job

The physical demand and intensity of the work was not common. People were not accustomed to being treated like disposable labor, but desperation demanded they continue in spite of the dangers. The Industrial Workers of the World (or Wobblies) sent eleven organizers in the hopes of unionizing the Six Companies workers; however, several were arrested for doing so. On August 7, 1931, the company had cut wages for the tunnel workers. Even though the workers sent away the organizers, afraid of any consequences that could occur via association, the organizers formed a committee anyway. They drew up a list of demands and presented it to taskmaster Frank Crowe, who was known for pushing workers even in 120-degree temperatures. On August 9th, Crowe refused their demands, stopped all work, and laid off nearly the entire workforce, forcing them to vacate by 5 p.m. Most of the workers complied and went to Las Vegas, hoping to return to the project. On the 11th, any workers who had refused to vacate were finally convinced to leave by law enforcement. Two days later, the company hired workers again, and the strike ended only two days after that. Though none of the workers' demands were met, the company promised not to reduce wages again, and living conditions improved as workers moved into Boulder City.

Things seemed to fare more smoothly during the concrete laying process, with no worker strikes until 1935. With the Hoover Dam nearly complete, a Six Companies manager adjusted the work schedule and removed the workers' lunch break. The workers began to strike. When Crowe gave the workers back their lunch break, they then demanded a $1-per-day raise. Six Companies agreed to request the Federal government supplement the raise, but Washington denied the request, ending the strike.

Pouring Concrete

Let's go back to that summer of 1933 and the initial pouring of concrete. Remember how we said earlier that this is still the largest project ever made with concrete? The Hoover Dam would eventually require 4.5 million cubic yards of concrete. For a visual representation, that's enough concrete to make a four-foot-wide sidewalk along the Equator around the entire world. But you can't just start dumping concrete on the ground and hope a dam forms. Concrete heats and contracts in the curing process, and if it doesn't cure properly, it would cause the dam to eventually crumble. According to the Bureau of Reclamation, if the Hoover Dam was constructed in a single pour of concrete, it would take 125 years to cool.

(1933)* - View showing the first bucket of concrete being poured for Hoover Dam.

Instead, they marked the ground with rectangles, pouring the concrete into blocks as large as 50 sq ft and 5 feet tall to form columns. Every 5-foot form had a 1-inch steel pipe running through it that would run cool river water and then send ice cold water from a refrigeration plant, speeding up the curing process. Once a block cured, the pipes were filled with grout, adding stability. Concrete was delivered in 7-ft high buckets that were nearly 7-ft in diameter, weighing 18 tons. They were filled at one of two Nevada concrete plants and then delivered on railcars. Aerial cableways then suspended the buckets over the column being filled. Varying grades of concrete were used at different points of construction, making the proper column matching with its bucket a vital aspect. The bottom of the bucket would open and a team of men would work the concrete through the form. Lore claims that men were caught and trapped in the concrete to this day; however, each bucket only contributed an additional inch to the form. Though Six Companies engineers may have been Machiavellian toward their tunnel workers and High Scalers, allowing bodies to be entombed in the concrete would create a flaw in their calculations and not guarantee the security needed for the construction of the Hoover Dam. This is only a myth.

(1934)^ - Hoover Dam takes shape from the concrete columns in which it was poured.

With the dam assembled, the diversion tunnels were filled with concrete plugs, and Lake Mead began to fill behind the dam, making Lake Mead the largest man-made lake in the United States. (Fun fact: the amount of water in the lake could cover Connecticut in ten feet of water.)

Completion of the Hoover Dam

(1934)* - View of three men standing by a Packard observing the near completed process of concrete pouring at the dam.

Finally, the Hoover Dam was done! At least, on September 30, 1935, excavation continued for the construction of the powerhouse, dam foundations, and abutments, though officials held the formal dedication. Five hundred men stayed to complete the remaining structures and bombproof the roof. By fall of 1936, Lake Mead was high enough to start generating power, and the first "three Allis-Chalmers built Francis turbine-generators" began operating. Two more started operating a year later, and four more two years after that. Mabel Macferran Rockwell, the only woman involved in the design, worked on the installation of the power generating machinery. (Fun fact: Her design became the basis for her prize-winning paper, "Power Limits of 220 kV Transmission Lines.") Today, the power plant consists of 17 main Francis turbine generators and generates electricity for 1.3 million people in Nevada, California, and Arizona. In spite of droughts and water consumption trends, Lake Mead still provides water to 25 million people.

Now that we've wrapped up on the construction of the Hoover Dam, let's wrap up this blog post. Today, over 7 million people from around the world annually head to see the Hoover Dam in person, easily accessed thanks to its proximity to Las Vegas. This national landmark remains, as architectural historian Reed Kroloff says, "one of the most remarkable feats of human engineering and hubris anywhere ever." Though we didn't have time to get into the architectural design once you enter the Hoover Dam, visitors can experience the curated Art Deco style and incorporated Navajo and Pueblo tribe motifs themselves! Tours are available through the dam with tickets available to be purchased on site, and the power plant tours are purchasable online. Don't forget that all vehicles are subject to inspection one mile before reaching the Hoover Dam; click here for more info on the inspection checkpoint.

(1935)* - View of the Hoover Dam power plants near completion. The concrete pouring process appears to be complete.

As you stand on a century-old modern marvel, think of the lives that toiled for the tunnels, scaled to strengthen the canyon walls, and spread layers of concrete inch by inch. Think of teams of engineers who carefully calculated the construction of a structure never-before-seen that still holds a lake at bay. Think of this line from the Los Angeles Times describing the reaction of townsfolk experiencing the largest hydroelectric power generator made:

"Astride the power of 115,000 horses, with burning plumes outspread, the Giant of Hoover Dam–Electricity–rode into Los Angeles last night, casting a heretofore unseen and magnificent glare on more than 1,000,000 persons who crowded the downtown district from end to end.

A tumult of yelling and whistling and screaming greeted the giant with an exuberance and spontaneous feeling that has not been observed since the demonstration the day the World War ended…." 

— Los Angeles Times, October 10, 1936

And of course, remember that Interstate Signways made the signs that guided the way!

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*In dam construction, abutments are the structural elements where a dam meets and is supported by the canyon walls on either side. These rock walls transfer and counteract the forces exerted by water pressure against the dam.

**A cofferdam is a temporary structure built to hold back water and create a dry work area during construction of dams, bridges, or other waterway projects. During the Hoover Dam construction, cofferdams were built to divert the Colorado River through tunnels, allowing workers to build the main dam structure on dry land.