Outside of China, the United States is the most-dammed country on the planet. Counting only dams taller than fifty feet high, the U.S. has some 5,000 dams that range from giant hydroelectric dams such as the Grand Coulee in Washington State to flood control dams in the southeast and dams that provide water for irrigation in California. Overall the United States has as many as 2.5 million dams of one sort or another. The design and construction of many of these dams took place between 1930 and 1975. This 45 years period is known as the golden age of dam building, starting with the construction of the Hoover Dam beginning in 1931. By the 1970s the golden age of dam construction began to come to an end with increased concerns of the impacts of dams on their surroundings. To better understand this time period I will look at the construction of Hoover Dam during the 1930’s followed by an examination many of today’s arguments for and against dams [i].
The need for a dam on the Colorado River was known decades before construction actually began due to the numerous destructive floods of the Colorado River. A need for water and electricity was also discovered to help with the development of the West. But there were many factors standing in the way such a large-scale construction project. Finally, in 1927 a bill detailing the project passed in Congress. Many construction companies began to look over the proposals but most agreed that the plan was too ambitious, too difficult, the project site was too unforgiving, and that the technology was not available to build a dam of that size[ii].
Hoover Dam is located in the Black Canyon, on the Colorado River, about thirty miles southeast of Las Vegas, Nevada. Construction on the dam began on April 20th by newly formed Six Companies Incorporated, a conglomeration of half a dozen smaller construction companies. Since the dam was located in such a remote location roads and railways had to be built to bring the workers and materials to the site. Boulder City, a camp was also built to house the thousands of workers. Before the construction of Hoover Dam even began Six Companies, Inc. had received over 2,400 job applications and more than 12,000 letters of inquiry from job seekers. Many men arrived with all of their possessions and their families ready to begin a new life in the desert. Many of these people were forced to wait and live in tent communities and shantytowns around Las Vegas. This created very poor living conditions where more than 25 workers and family members died of heat prostration between June and July of 1931. Fortunately the U.S. government anticipated this problem and had already created plans to build a modern city, known as Boulder City, to house the workers and their families near the site of Hoover Dam. To the surprise of both the government and Six Companies, Inc. Boulder City turned into a community. Churches, a school, a newspaper, and a library were all built in Boulder City making it a model community [iii].
Before construction of the actual dam could take place the Colorado River first had to be diverted, this was done by tunneling four huge diversion tunnels through the bedrock of Black Canyon. These tunnels were 56 feet in diameter, 4,000 feet long, and resulted in 1,500,000 cubic yards of rock to be excavated. In November 1932, the tunnels were completed and a temporary cofferdam was constructed which pushed the river into the diversion tunnels. For the next two years the Colorado River flowed through these four diversion tunnels while the construction on the actual dam was performed2.
The next activity necessary for the construction of the dam was to chip away at the canyon walls to provide the dam a smooth surface for the dam walls to adhere to. The canyon floor was dredged down to bedrock so the construction of the dam footers and the dam itself could begin. On June 6, 1933 the first bucket of concrete was placed at Hoover Dam. Over the next two years 3,250,000 cubic yards of concrete, enough to pace a sixteen-foot wide highway from San Francisco to New York were placed in the dam. The concrete was produced at a completely automated plant, which produced 24 cubic yards of concrete every three and a half minutes. The concrete was then transported to the dam by an elaborate network of aerial cableways that carried the four and eight cubic yard concrete buckets to the dam site every 78 seconds2.
One big problem encountered was that the heat produced by the curing concrete would be so great that would take 125 years to cool and the resulting stresses would have caused the dam to crack and crumble away. This was alleviated by instead of the dam being a single block of concrete; the dam was built as a series of individual columns. Trapezoidal in shape, the columns rose in five-foot lifts. This helped the heat dissipate but to help the concrete properly cool each form also contained cooling coils of 1" thin-walled steel pipe. When the concrete was first poured, river water was circulated through these pipes. Once the concrete had received a first initial cooling, chilled water from a refrigeration plant on the lower cofferdam was circulated through the coils to finish the cooling. As each block was cooled, the pipes of the cooling coils were cut off and pressure grouted at 300 psi by pneumatic grout guns2.
On February 1, 1935 some of the diversion tunnels were blocked allowing the Colorado River to begin backing up created Lake Mead. Lake Mead, the reservoir created by the Hoover Dam is the largest man-made lake in the United States, 115 miles long, 10 miles wide, and 500 feet deep. Lake Mead contains 28,537,000 acre-feet. An acre-foot is the amount of water required to cover 1 acre to a depth of 1 foot, or approximately 326,000 gallons. The reservoir will store the entire average flow of the river for 2 years. That is enough water to cover the State of Pennsylvania to a depth of one foot 2.
During the construction of the dam there were many other problems presented. Due to the construction’s fast pace, extreme weather conditions, and poor jobsite safety many workers were injured and killed. Many times workers were killed and due to the fast pace they were left where they died because they could not be saved, work could not be stopped to care for them. In the end 112 people were killed during the thirteen years of geological tests and construction 4.
Another problem was that the workers were paid very poorly and their rights were often neglected. These workers worked seven days a week with only two optional unpaid vacation days a year, July 4th and Christmas. The workers were also exposed to temperatures over 120 degrees during the summer and temperatures well below freezing in the winter, carbon monoxide poisoning, dehydration, heat prostration, and electrocution. To top off this list of almost inhumane working conditions the workers had little leverage to lobby for changes. Since the construction took place during the Great Depression there was an almost limitless pool of workers to choose from. If some workers began to complain about these conditions new workers who were willing to combat these conditions could quickly replace them. Workers finally reached a breaking point during the summer of 1931. On August 7, Six Companies reassigned a number of the diversion tunnel workers to lower paying jobs. Within hours of this reassignment, the entire work force went on strike. The workers list of grievances included clean water and flush toilets be provided, that ice water be readily available to workers, and that Six Companies obey all mining laws issued by the States of Nevada and Arizona. These grievances were taken to Six Companies and were rejected by Frank Crowe, the dam’s project manager, and all of his bosses with Six Companies. The striking workers then made a final effort by appealing to the U.S. Secretary of Labor, William Doak, to intervene on their behalf. He refused, and the workers then voted to return to work. This vote was influenced by the fear that they might not get their jobs back. After the workers returned, Six Companies stood by its pay cut, but promised it would be the last. They also made efforts to improve work conditions by providing additional lighting and water; the construction of Boulder City was sped up [iv].
Hoover Dam was finally completed eleven months before its scheduled completion date in 1935 at a cost of $108,000,000 all of which was repaid with interest in fifty years under he contracts created for the sale of the power created by the dam. At the time Hoover Dam was the largest dam ever built, the most expensive public project ever attempted, and at over 6.6 million tons, the first man-made structure to exceed the masonry mass of the Great Pyramid of Giza. The dam stands sixty stories or 726.5 feet tall, twice as tall as the Statue of Liberty, and is two football fields wide at the bottom. The dam’s power plant contains 17 main turbines which at the time were the largest generators and turbines ever installed in the United States. These turbines were all replaced during an upgrading program that took place between 1986 and 1993. The turbines in place today can produce a total of 2,998,000 horsepower and 2,074,000 kilowatts of electricity and is still one of the country’s largest. The powerhouse produces over four billion kilowatt-hours a year, which is used in Nevada, Arizona, and California 2.
The construction of Hoover Dam took place during the Great Depression. The construction of Hoover Dam was not just another construction project; it stood for the hope of the future and the ability of man to change nature. It created jobs for thousands of people who found themselves out of work due to the depression and showed the continuation of westward expansion. Today the dam still stands as a great icon representing more than just the hard work of thousands. It created a great pride in Americans whose pride took a great hit from the Great Depression. Many of the lessons learned during the construction of the dam could be applied all over the world, it was can be considered as the “Big One” that taught Americans how to think bigger and reach higher. It also created a great construction company and a large pool of skilled workers that were able to conquer many other large scales construction projects in the West including the Bonneville Dam, the Grand Coulee Dam, the foundations for the Golden Gate and Bay bridges, numerous canals, tunnels, factories, shipyards, pipelines, and refineries. It also helped give worker’s right and their safety more importance3.
Hoover Dam also created much needed flood control along the Colorado River, which has saved many farms and cities from flood damage. By providing a source of water for irrigation the dam has turned the once barren desert land on the banks of the Colorado River into fertile farming areas that in the past would struggle through times of drought and water shortages. The dam also provides Southern California and Las Vegas with a constant source of much needed water and electricity, this electricity lights up downtown Los Angeles, Las Vegas, and one hundred other cities. The electricity created at Hoover Dam also helped the mass construction of ships and planes that were used in World War II to defeat Hitler. Hoover Dam and Lake Mead also provide Nevada and Arizona millions of dollars from the tourism this great engineering feat draws5.
After the success of the Hoover Dam construction a large movement to “tame nature” was created many other dams were built across the United States. “Dam it all” became the cry of many of the nations engineers as the United States began to industrialize, establish inland ports, settle the West, and control flooding. This mentality is shown in a 1965 Bureau of Reclamation booklet that said, “Man serves God. But Nature serves Man”. This ideology continued for almost fifty years until many engineers began to realize that their monuments to the industrial age were not as permanent as the once believed. This began with a proposal that at one time would have been unthinkable, but today many groups are calling for the dismantling of many of the United State’s dams 6.
The reason for this push is that during the golden age of dam building engineers did not always take into account the environmental impact the construction of a dam would have. A 1990 survey of the World Bank, the financer of many of the world’s dams, hydroelectric dam projects shows that 58% were planned and built without any consideration of the downstream impacts the dams would have 7. The World Commission on Dams estimates that 67% of all dams have a negative environmental impact 8. Another reason is that many of the dams built only were designed for a fifty-year life. In the “1998 Report Card for America’s Infrastructure” performed by the American Society of Civil Engineers, ASCE, concluded that 25% of U.S. dams are more than fifty-years old and by 2020 that figure will reach 85%. Citing age, abandonment, and lack of funding for repairs, ASCE grave dams an overall grade of “D” 9.
Other factors cited by groups pushing for the removal of dams are that they effect water quality, reduce species diversity, destroy natural wetlands, impede the progress of salmon and other fish, create more flood damage, and poor irrigation practices. By damming a river the water level is usually lowered. The reduced flow of the river creates lower water levels downstream and during times of draught the reservoir water level also drops. This lower water level leads to stagnant water and higher water temperatures, which lower the quality of the water. This altering of the river’s water level and effects the species diversity located along the river. Also when the dam is completed and the reservoir begins to be filled many the habitats of many species is forever changed. Many species are able to survive under these conditions but others either die off or are forced to relocate 10 (2,3,6). This also changes the natural wetlands surrounding these rivers. These reservoirs dams create will flood out natural wetlands while downstream the same kinds of habitats will suffer from lack of water. Worldwide, the flooded valleys they occupy have forced at least 30 million people to abandon their homes since the 1930s. When China finishes its Three Gorges Dam on the Yangtze in 2009, for example, the project will flood an area with 1,208 historic sites, and displace nearly two million people 5. 90% of California’s natural wetlands have been lost to development and the wetlands created by dams are not comparable to what was there before the river’s obstruction 8.
Many dams located on the Snake and Columbia Rivers, including the Grand Coulee Dam and Bonneville Dam stand in the of salmon who traverse these rivers while migrating to the Pacific Ocean to reproduce. This has a significant effect on fisheries disrupting migratory fish patterns and spawning habits 10. These fish are now forced to travel through the dam’s turbines and thousands of fish each year do not survive this. Many of them are battered by the spinning metal blades of the turbines’ housings or torn apart by the rough motion of the rushing water 1. Many of these dams have reduced or wiped out the grand salmon runs. The Lewis and Clark expedition in 1805 spotted “emence quantities” of thrashing silver fish “jumping very think” on the Columbia River. Now on the same stretch of river eleven dams control every twitch of the water level with only a few adjustments to help migrating salmon negotiate the fish ladders and the turbines 10. The estimated cost of these loses on salmon fisheries between 1960 and 1980 is $6.5 billion 5. Salmon are protected under the Endangered Species Act, which may lead to the removal of many of these dams 10.
Many flood control dams do not necessarily reduce flood damage many times they increase it, shown by the statement “Floods are an act of God. Flood damage results from acts of men” 6. Flood-control dams tempt people to live closer to rivers. So when a catastrophic flood overwhelms the dam system, as happened along the Mississippi in 1993 and 2001, the damage is far greater than if people had given the river a respectfully wide berth like they would if there was no flood control devices in place 10. Now when there is flood damage taxpayers foot most of the bill in the form of disaster relief and subsidized federal insurance 6. Before the government began bailing out flood victim, and before dams and levees promised protection from floods most people steered clear of floodplains. Because the risk was so great no one built permanent structures on floodplains 6. Annual flood damage to property has almost tripled in constant dollars since 1951 and currently average $3 billion a year 6.
Similar to the increased trust in flood-controlled rivers, dams also create poor irrigation practices. Since there is a plentiful cheap water supply for irrigation created by dams many farmers use relatively wasteful watering techniques instead of more efficient methods 10. Many reservoirs in the west loose significant amounts of water to evaporation and seepage into banks. With water becoming the west’s most valuable resource, the average 1 million acre-feet, an acre-foot would approximately cover a football field with one foot of water; of water lost each year at Lake Powell is a cost few can justify.
After building a dam in the African Sahel, an area routinely hit hard by drought and famine. Many hoped for economic benefits but they still have not materialized more than ten years later. But valley fisheries were devastated forcing people to truck in fish from the cost and there have been many incidents of bilharzias, diarrheal diseases, and malaria increased and surprisingly, nutrition has not improved as expected 5. In 1999 bulldozers ripped open the 917-foot wide Edwards Dam, which blocked the Kennebec River in Maine for 162 years. This increased the population of fish like sturgeon, striped bass, Atlantic salmon, and alewives. The water quality has gotten cleaner, drawing more people animals, birds, and plants back to the river’s banks10. The Woolen Dam on the Milwaukee River in Wisconsin was torn down due to poor water quality. The water was so shallow that it warmed up significantly in the summer and caused large algae blooms. The dam was removed and now some of the land previously occupied by the reservoir has been turned into soccer and baseball fields, as well as open green space. Additionally the river has been repopulated and now supports a variety of species of sport fish9.
Even though there are many negative effects of dams and many examples of how the removal of dams improves the environment there are many people and arguments on why dams should remain. Some of these factors are that the reservoirs created by dams are important to birds, they do not affect salmon and other fish, as many people believe, they are necessary for development, they are important for irrigation, they prevent floods, and produce environmentally clean energy. The reservoirs created by dams are very important to birds. Birds use them for stopovers on their migratory paths and as permanent reservoirs. Such reservoirs tends to have a less diverse bird population than natural lakes, but they make up 8% of all internationally important wetlands and the removal of these reservoirs could ruin the bird’s present habitat. It is sometimes better to leave an existing dam in place to preserve the species that remain because there is no guarantee that the original species will return 8.
Not all salmon in the Snake and Columbia rivers take turbine rides on their way to the sea. The U.S. Army Corps of Engineers have built spillways, bypass channels, and “fish friendly” turbines that help fish travel past the dams. Other salmon are scooped up by barges and trucks and dumped back into the water downstream of the dams. 20% of the young salmon in the two rivers end up in the turbines and only one in ten die at each dam 1. The latest scientific data shows that the Snake River dams and their fish bypass systems pass 96-98% of all salmon safely. 80% of salmon are safely bypassed around the dams through fish ladders, screens, and fish transportation, which helps them bypass the dams entirely. The fish mortality rate on the Snake River is only 6% and today there are more fish going downstream and the water is cooler than before there were dams built on the Snake and Columbia Rivers. The rapids and the times of low water levels in the rivers kill many fish before they reach the dams. In the past before dams controlled these rivers many salmon were found dead from the intense rapids and from beating themselves against rocks while trying to navigate the river 11.
Without dams development in many areas is almost impossible. Two prerequisites for the development of a nation or community are energy and water. But since in many areas these resources are very scarce dams are necessary to provide these resources. Due to this dams have become almost synonymous with development 10. City planners in Las Vegas claim that the water and electricity provided by the Hoover Dam is necessary to support the 4,000 new residents who flock to their city each month and to feed the city’s unique infrastructure, which consists of many huge hotels, and casinos that need large amount of electricity to operate 6.
Dams also help support farmers who irrigate their lands with water from their reservoirs, shipping companies, which transport grain and good in the still waters, and unions that support the jobs that these dams create. One-third of all food produced comes from irrigated lands. This irrigation is the only way to meet the projected future food needs. It is expected that 80% of food production will come from irrigated lands by 2025. Irrigation accounts for over 75% of water consumption in the United States and almost 90% in other countries worldwide. Reservoirs also provide drinking water, while smoothing out the high and low water level created during cycles of flooding and drought during the rainy seasons and then release the water stored in times of shortage10.
Many dams also have hydroelectric plants associated with them. These plants produce power without contributing to the greenhouse effect like many other power sources do. Dams create about 20% of the world’s electricity and 7% of all energy. Hydroelectric dams also attract industry and jobs. Energy prices in hydro-rich regions are 30% to 50% lower than the national average10. Dams also stimulate local economies by supporting a variety of outdoor recreational activities including camping, hiking, boating, fishing, and swimming12.
Overall each and every dam and river is different and when deciding if dam breaching or dam removal is appropriate, many different factors need to be looked at. These include the environmental impacts of the dam, the environmental impacts of the breaching, the opposition to breaching, the engineering of how it will be done, the recreational and socioeconomic impacts of the dam, the impacts of removal, and the economic costs.
[i] Davy, Emma. “Robofish” Current Science March 2, 2001: 10.
5 Robbins, Elaine. “Damning Dams.” E Jan 1999: 14.
6 Franklin, Chris. “Let the Colorado River run free.” Earth Island Journal Spring 1997: 23.
8 “Not so fast; Eliminating dams; Why dams can be green.” The Economist March 3, 2001: 4.
9 Wade, Beth. “Bringing down the dams.” American City and County June 1999: 20.
10 “Knocking down dams – A good year for alewives.” The Economist July 29, 2000: 32.
12 McMahon, Richard Jr. “Let’s not damn the dams.” The Business Journal January 28, 2000: 47.