Overview
Dams have been built with the intention to improve human quality of life by diverting water for power, navigation, and flood control, but have also resulted in human health concerns and environmental problems. Dams benefit people by providing usable, reliable water sources. In the once swampy San Joaquin Valley, Calif., they have created an area that now provides a quarter of America’s food supply. Hydroelectric dams provide 13% of the total power generation in the United States which prevents over 200 million tons of carbon dioxide emissions. They make 70% of the power generated in Latin America. However, dam projects can produce greenhouse gases by flooding areas and increasing the rate of decomposition, emitting carbon dioxide and methane. A UN commission was set up in 1997 to monitor and evaluate impacts of current, existing and future dams (both positive and negative).
The one thing that remains clear is that the need for energy and water will not go away.
Is it Worth a Dam?
In 1936, the first mega-dam, the Hoover Dam, was built on the Colorado River in Black Canyon, near what was then the little town of Las Vegas, Nevada. Standing 221 m high, three times the size of the Statue of Liberty, it was the largest dam in the world. Its massive concrete walls held back the waters of Lake Mead, a 160-km-long body of water heavy enough to bend the earth’s crust. Nine more large dams diverted the Colorado River’s water into Arizona, Nevada, and southern California, fueling the growth of major cities and helping to turn the arid West into a lush and lucrative garden.
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Shifting points of reference . Once the biggest dam on earth, the Hoover Dam, built in 1936, now appears unremarkable compared to some of the world’s more recently built mega-dams.
Photo credit: United States Bureau of Reclamation
The Colorado dams were part of a dam-building fever that encompassed the globe. Dams harnessed the world’s major rivers, including the Danube, the Nile, the Zambezi, the Yangtze, and the Ganges. Like Indian Prime Minister Jawaharlal Nehru, post-colonial leaders saw them as the new “temples of development,” monuments to a nationalistic vision of modernization and unlimited growth, and vigorously promoted their construction. By 1989, the Hoover Dam was only 15th in the list of the world’s largest dams.
According to Patrick McCully, campaigns director of the Berkeley, California-based International Rivers Network, over 800,000 dams have been constructed worldwide for drinking water, flood control, hydropower, irrigation, navigation, and water storage. But since the 1950s, the peak of the big dam era, perceptions of dams and dam building have changed. Once symbols of development, dams today symbolize, for some critics, not progress but environmental and social devastation. The benefits and detriments of dams have locked opponents and proponents in hot debate.
Decisions on dam building, once the province of governments and bureaucracies, are becoming a public process involving many stakeholders with different priorities. All stakeholders need a clear understanding of the possible benefits and potential consequences of dams, as well as alternatives to dams, if they are to achieve a rational, sustainable solution.
Dams and Civilization
Farmers and rulers have been impounding water for millennia. Eight thousand years ago, the Sumerians built an irrigation-based civilization between the Tigris and Euphrates rivers, then lost it to the salinization that now plagues some 20% of Iraq’s arable territory. By the first century BC, low dams had been built in the Mediterranean, the Middle East, Central America, and China. Limited technology kept their height down: a fifth-century Sri Lankan dam, 34 m high, was the world’s highest for a millennium.
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In the interest of fish . Many dams, such as the Bonneville Dam, incorporate fish hatcheries (above, lower right) into their design.
Photo credit: United States Army Corps of Engineers, Portland District
The age of hydropower and large dams emerged following the development of the turbine in 1832. By the turn of the century, hydro plants were operating in the United States, Italy, and Norway. Improvements in turbine design ushered in the mega-dam boom in the 1930s. As dam-building technology spread, fairly autonomous government agencies like the Bureau of Reclamation and the U.S. Army Corps of Engineers, and river management agencies like the Tennessee Valley Authority (TVA), became the model for water management authorities worldwide.
Today, most of the world’s large rivers are dammed. Of large rivers in the United States, only one–the Yellowstone–flows freely along its 1,000-km length. Worldwide, some 40,000 “large” dams (over 15 m high, according to the International Commission on Large Dams) and about 800,000 smaller ones have been constructed. According to McCully, the dams impound a total of over 400,000 km 2 of reservoirs–the area of California–with an estimated capacity of as much as 10,000 km 3 , five times the volume of all river water.
The Dam-busters’ Debate
The original purposes of dams were to improve human quality of life by providing drinking water and to support economic growth by diverting water for power, navigation, flood control, and irrigation. In many ways, dams have succeeded. For example, the fields of Western farmers feed the United States and many other parts of the world, and India’s irrigation systems have enabled that country to be self-sufficient in food production since 1974. In addition, in many parts of the world dams have helped to remedy life-threatening problems such as poverty from lack of economic development, famine as a result of drought, devastation from floods, and continued disease from lack of potable water supplies.
But the adverse effects of river impoundments–disruption of ecosystems, decline of fish stocks, forced resettlements, and disease–have of late made dams symbols of corporate and governmental hubris. In his 1993 book Desert Cadillac (the basis for a 1997 public television series of the same name), author Marc Reisner charges that dam-building agencies like the Bureau of Reclamation and the U.S. Army Corps of Engineers “greened” the U.S. West, with often disastrous ecological and social results. “We can’t imagine how dependent we’ve become on the liberties we’ve taken with the natural order,” Reisner states in the TV series.
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Opponents of dams, so-called “dam-busters,” charge that government agencies, utilities, and international loan agencies such as the World Bank have created a network that fosters irresponsible and self-serving decisions when it comes to dam building. “When I studied engineering, dam building was presented as a rational process, but most dam building is driven by greed, or a dictator who wants a project,” says Bill Jobin, an engineering consultant with Blue Nile, an environmental and engineering consulting company in Dolores, Colorado. Jobin criticizes governments and lending agencies for “compartmentalization,” or failing to consider the full range of consequences, including human health and environmental costs, in deciding whether to build a particular dam. He says this leads to “bad” dams–dams that ignore high environmental or human costs–being built despite their predicted consequences. Referring to the fact that the World Bank recently pulled out of a number of dam-building agreements because of environmental and social costs, he says, “With the World Bank’s stance, you’d think they’d know the score. But when it gets down to the loan officer, he just says, ‘let’s go.'”
Some critics charge that many of the promised benefits of dams built during the first part of the century have not materialized, often because the engineering and planning studies supporting such dam projects were seriously flawed, if not contrived, according to Sam Flaim, an economist and engineering consultant based in Golden, Colorado. “The benefits of dams for flood control and navigation were exaggerated by bureaucracies who were in the business of getting dams built,” Flaim says. “[Dams] were widely perceived as beneficial, and those benefits are now being questioned. Also, what was once perceived as a benefit–interruption of natural stream flows–is now perceived as a cost.” Flaim adds, “Dams achieved exactly what the planners and engineers intended–interrupting large annual changes in stream flows so water would be available all year. Now we look at those realized intentions as negative consequences. But there have been unforeseen benefits in the environment, too: an increase in food and habitat for raptors, trout fisheries. Dams are here now; the issue is how to use them.”
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Dam-busters, proponents say, must remember that, without the economic and social benefits that dams provide, much development would be impossible. “You have to think of the benefits of dams in monetary terms,” says Earl Eiker, chief of hydraulics at the U.S. Army Corps of Engineers. “If you’re going to have sustainable development, you can’t leave the environment totally pristine. This is a trade-off that we must accept, though impacts on the environment can and should be minimized. But without water resources development, this country wouldn’t be what it is today. We all like to know that we will have water when we turn on the taps, or lights when we flip the switch.”
It is impractical and poor strategy to oppose all dams on principal. “Dam opponents make a serious mistake when they don’t raise the right issues, and distinguish between different types of dams,” says Robert Tillman, senior environmental specialist for Africa at the World Bank. “There are more good dams than bad ones. The bad dams are the shallow ones that flood large areas of land, or that produce relatively little power. It’s in the tropics that these dams are associated with diseases like schistosomiasis and malaria; these are not a problem in temperate areas. We also need to revisit the definition of large dams: you can’t call a 10-meter dam large when you have 190-meter dams. And with proper mitigation, dam sites can be improved.”
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