Dirt Talk Podcast – Episode DT 319: How the Hoover Dam Was Built
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Introduction
In Episode DT 319 of the Dirt Talk Podcast, host Aaron delves into one of the most iconic engineering feats in history: the construction of the Hoover Dam. Drawing extensively from research and resources like Wikipedia, Aaron provides a comprehensive overview of the dam's inception, construction challenges, engineering marvels, and its lasting impact on the American Southwest.
Historical Context and Authorization
Aaron begins by setting the stage with the early 20th-century efforts to harness the Colorado River for flood control, irrigation, and hydroelectric power. Initial attempts, such as William Beatty's Alamo Canal in the late 1890s, faced significant challenges, including expensive operations and international disputes with Mexico.
In 1922, the Bureau of Reclamation advocated for a dam on the Colorado River, emphasizing its potential benefits while acknowledging the need for interstate cooperation. Delph Carpenter, a Colorado attorney, proposed an interstate compact involving seven states within the river's basin. This led to the Colorado River Compact on November 24, 1922, paving the way for federal authorization.
Aaron notes, "Congress authorized a board of engineers to review plans for the proposed dam," emphasizing the project's feasibility and associated risks, including the catastrophic failure of similar structures like the St. Francis Dam in 1927.
Bidding and Construction Companies
The dam's construction was awarded to Six Companies, Inc., a consortium formed by major players like the Utah Construction Company, Morrison Knudsen, Henry Kaiser, Bechtel, McDonald & Khan Limited, and the J.F. Shea Company. Their winning bid of $48,890,000 was notably $24,000 under the government's confidential estimate, securing the contract ahead of less competitive bids.
Workforce and Construction Camps
The onset of the Great Depression saw a massive influx of unemployed individuals to southern Nevada. Las Vegas, then a small town, became a hub with between 10,000 to 20,000 unemployed converging for potential employment. Two primary camps emerged:
- McKeeversville: An unofficial squatters' camp near the dam site, housing men and their families.
- Williamsville (Ragtown): Located along the Colorado River flats, serving as another base for workers.
By 1932, Six Companies employed over 3,000 workers, peaking at 5,251 in July 1934.
Engineering and Construction Challenges
Diversion Tunnels and Cofferdams
Before construction could commence, the Colorado River needed diversion. Four massive tunnels, each 56 feet in diameter and collectively spanning over 16,000 feet, were drilled through the canyon walls. The diversion was achieved by November 13, 1932, by using a temporary cofferdam and explosive techniques to alter the river's course.
To protect the construction site, two cofferdams were erected:
- Upper Cofferdam: 96 feet high and 750 feet thick, containing 650,000 cubic yards of earth.
- Lower Cofferdam: Designed similarly to safeguard against potential flooding.
Foundation Excavation
Excavation reached the bedrock by June 1933, removing 1,500 cubic yards of earth. Specialized workers, known as high scalers, were tasked with ensuring the integrity of the canyon walls, preventing seepage and stabilizing the structure. Aaron recounts a heroic act: "A high scaler was able to intercept [a government inspector] and pull him into the air," highlighting the dangers workers faced.
Safety Innovations
In response to frequent accidents, early versions of hard hats were developed by workers who dipped cloth hats in tar. These helmets effectively prevented skull injuries from falling debris, a testament to the workers' ingenuity in enhancing safety protocols.
Concrete Pouring Process
The monumental task of pouring concrete was initiated on June 6, 1933. To address the thermal stresses of curing concrete, Aaron explains the innovative approach:
- Segmented Pouring: The dam was poured in 5-foot blocks, each containing 1-inch steel pipes for cooling.
- Refrigeration: Cool river water and ice-cold water were circulated through these pipes to manage the concrete's temperature, preventing cracks and ensuring structural integrity.
Concrete was delivered in 7-foot high, 7-foot diameter steel buckets, each weighing approximately 20 short tons. These buckets were transported via special rail cars and aerial cableways to specific columns within the dam. Despite myths about entombed workers, Aaron clarifies, "Six company engineers would not have permitted a flaw caused by the presence of a human body."
By May 1935, a total of 3,250,000 cubic yards of concrete were used in the dam, with an additional 1.1 million cubic yards in the power plant and auxiliary structures.
Dedication and Fatalities
The formal dedication of the Hoover Dam took place on September 30, 1935, with a ceremony attended by approximately 10,000 people despite extreme temperatures. President Franklin D. Roosevelt delivered the keynote address, notably omitting any mention of former President Herbert Hoover.
Tragically, the construction cost over 100 lives. Aaron breaks down the fatalities:
- 91 Six Companies employees
- 3 Bureau Reclamation employees
- 1 visitor
- 42 unrecorded deaths attributed to pneumonia, likely resulting from carbon monoxide poisoning due to gasoline-powered vehicles in the diversion tunnels.
Aaron emphasizes the human cost by stating, "The high scalers work thus helped ensure worker safety," highlighting both the risks and the measures taken to protect laborers.
Powerhouse Construction and Operations
While the dam structure was largely complete by the dedication ceremony, the powerhouse remained unfinished. A crew of 500 workers continued construction, ensuring the powerhouse's roof was bomb-proof and constructed with layers of concrete, rock, and steel.
Operational Milestones:
- 1936-1939: Gradual commissioning of generators, making the powerhouse the largest hydroelectric facility globally by 1939.
- 1961: Final generator installed, bringing total capacity to 1,345 megawatts.
Design Features:
- Intake Towers: Direct water flow into penstocks, creating a hydraulic head of 590 feet.
- Spillways and Outlet Works: Primarily unused, except for maintenance purposes.
Legacy and Current Challenges
The Hoover Dam continues to play a crucial role in water management and power generation for the Southwest. However, recent decades have seen challenges:
- Prolonged Drought: Since 2000, Lake Mead's water levels have significantly dropped due to drought and high water demand.
- Power Generation Decline: By 2014, capacity was reduced by 23% to 1,592 megawatts, limiting operation to peak demand periods.
- Water Level Management: Efforts to maintain power generation led to various adjustments, including lowering the minimum power pool elevation to 950 feet.
Despite these challenges, the dam remains self-sustaining through power sales, which have repaid construction loans and finance ongoing maintenance. Additionally, Lake Mead supplies water to 18 million people and irrigates over 1 million acres across Arizona, Nevada, and California.
Conclusion
Aaron encapsulates the grandeur and complexity of the Hoover Dam by stating, "It's a spectacular piece of engineering." He acknowledges the depth of available literature and encourages listeners to explore further, highlighting the dam's multifaceted legacy in engineering, environmental management, and regional development.
For those intrigued by monumental engineering projects, Aaron invites suggestions for future Dirt Talk episodes, fostering an engaging community of enthusiasts eager to "stay dirty."
Notable Quotes:
- "Hoover Dam is a spectacular piece of engineering." [23:45]
- "Six company engineers would not have permitted a flaw caused by the presence of a human body." [35:20]
- "The high scalers work thus helped ensure worker safety." [28:10]
- "It's a spectacular piece of engineering." [58:05]
For more insights and detailed discussions on engineering marvels, subscribe to the Dirt Talk Podcast and join host Aaron on his journey through the Dirt World.