DAMS

Dams, barriers to alter flowing bodies of water, are among the most ancient and powerful examples of the proclivity of humans to alter nature for their own benefit. (Dams are also a type of construction shared with other animals, that is, beavers.) Before the advent of written history, dams were already being built to provide water storage and irrigation. An earthen dam in the Orontes Valley in Syria was ancient when visited by the Greek geographer Strabo around the beginning of the Common Era. The oldest large dam of which traces survive today is at Sadd-el-Kafara, near Cairo. Ninety-eight meters long, there are indications that it was intended to stand 125 meters high. It is estimated that this structure was built around 2500 b.c.e.

Dam Engineering

Despite their ubiquity and importance, dams are a stepchild of traditional engineering. Premodern treatises on construction such as Vitruvius's De architectura (first century b.c.e.) do not mention dams, although Roman dam achievements were not to be matched for 1,500 years. The scientific engineering of dams begins in the 1800s and was one of the early achievements of civil engineering as it replaced trial-and-error intuition with empirical rules of thumb for dam design.

In terms of function, dams primarily supply water for irrigation or urban use, or serve as sources of power. In conjunction with closely related structures called dikes, dams may also protect from flooding and/or facilitate transportation by creating navigable bodies of water such as canals.

In terms of design, dams are of two basic types: earth- or rock-filled gravity embankment dams and masonry or concrete dams. The former take the general shape of a large-based equilateral triangle with sloping embankments facing both upstream and downstream; the latter have more the shape of a right-angle triangle with a perpendicular upstream face and a sloping downstream face.

It was not until the mid-1800s that French engineers designed the first dams using scientific procedures to determine such issues as the slope of repose for embankments. At the same time engineers began to consider the geological structures on which various types of dams might rest and to analyze the internal stresses of masonry and concrete dams. Such analyses promoted the design of arch dams, in which a vertical upstream face is given a convex horizontal curve to help transfer forces from the impounded water into the walls of a canyon. The engineering of auxiliary structures such as spillways, locks, and power conversion systems also became part of dam design.

Progressive demands for water and power together with advances in dam engineering led in the first half of the twentieth century to what may be called the golden age of dam construction. But the second half of the twentieth century witnessed a technical reassessment of dam engineering in terms of safety and ecology, social and natural.

Dam Debates

For most of human history, dams were conceived and built with an eye only to the task to be accomplished, such as water storage, irrigation, or more recently, promotion of tourism, and without much concern for other implications, such as the impact on local populations or the environment. Of all major rivers in the United States, only the Salmon and Yellowstone are without dams. Half of the American wetlands that existed in 1790 have been flooded and destroyed by dam projects—up to 80 percent in river states such as Missouri, where one-third of all the water in the Missouri River is stored behind dams.

At the same time some experts argue that dams are often inefficient mechanisms for water storage, spreading water out over large areas in hot, dry desert climates where it evaporates. As much as 8 percent of Colorado River water may be lost to evaporation behind the Glen Canyon Dam in northern Arizona. Dams, by promoting water use, also contribute to the eventual depletion of aquifers.

In the modern world dams nevertheless continue to be seen as important symbols of human domination of the environment, sometimes outweighing all other issues. China's Three Gorges Dam, which will flood thousands of acres of agricultural land and displace more than one million people, is nevertheless viewed by the Chinese government as a powerful symbol of mastery and progress.

DAM SAFETY AND FAILURES. Like other huge, complex human technology projects, dams can fail if ill-designed or negligently maintained. The most famous failure in the United States was that of the South Fork Dam in Johnstown, Pennsylvania, in May 1889. Over the years, successive owners of the dam made dangerous modifications, eliminating outlet pipes, reducing its height, and narrowing the spillway. During an unprecedented rainfall, the water rose 3 meters (10 feet) above the usual lake level, breaking the dam and inundating Johnstown, with the loss of almost 3,000 lives.

RELOCATING PEOPLE. Dam projects have often involved the removal of the populations least able to defend themselves politically. Most often the groups forced to relocate are poor members of minority groups, subsisting on small-scale agriculture.

In June 1957 Congress voted the creation of Kinzua Dam in western New York, flooding half of a Seneca Indian reservation. More than 500 Seneca were forcibly moved in the dead of winter to trailer camps. Without access to hunting grounds, and denied compensation for their homes, these already poor individuals were, according to the sociologist Joy A. Bilharz (1998), driven into greater poverty, which lasted for decades.

Organized political opposition to large dam projects was pioneered in India, where in the late 1940s important projects backed by the prime minister, Jawaharlal Nehru, made little provision for the relocation of affected villages. Large demonstrations and other opposition increased the costs unacceptably, causing the government to back away from some of these projects.

ENVIRONMENTAL CONCERNS. During the twentieth century, the environmental movement advanced the argument that natural beauty was a factor to be taken into account in dam construction. John Muir led an early campaign against the O'Shaughnessy Dam in Yosemite National Park's Hetch Hetchy Valley on the grounds that it would destroy a unique environment. Later came the related idea that wild species themselves had interests worthy of protection, interests that might be harmed by dam construction. Environmentalists went to court to end construction of the Tellico Dam on the Little Tennessee River, on the grounds that it would destroy the remaining population of snail darters, an endangered fish. In response, federal courts halted construction of a dam already 80 percent completed. In 1978 the U.S. Supreme Court affirmed the court order halting construction, stating that the Endangered Species Act unambiguously bars projects that threaten the continued existence of a listed species. Congress, however, later passed legislation exempting Tellico from the Endangered Species Act, and the dam was completed.

Egypt's Aswan High Dam has been argued to have caused an environmental disaster, starving the Mediterranean of nutrients, making croplands excessively salty, and creating a reservoir in one of the highest evaporation zones on Earth.

DAM REMOVALS. Because of changing views of the utility of dams and the relative importance of environmental considerations, more than 500 dam removal projects were undertaken in the United States during the last decades of the twentieth century. The first dam removed for purely environmental reasons was the Quaker Neck Dam on the Neuse River in North Carolina. Built in 1952 to provide cooling water for a steam-driven electrical generating plant owned by Carolina Power & Light Company, the dam prevented shad from migrating upstream. The shad catch, 318,000 kilograms (700,000 pounds) in 1951, was only 11,400 kilograms (25,000 pounds) by 1996.

Carolina Power & Light was glad to get rid of Quaker Neck. The dam was expensive to maintain and also created litter and liability problems. Instead of the dam, a canal between two channels of the river now provides cooling water. More than 1,600 kilometers (1,000 miles) of local rivers have since been reopened to fish.

As the political and psychological importance of dams has faded and other considerations have come to the fore, Americans have stopped building dams. Since the mid-1970s, there has not been a single major dam construction project commenced in the United States.

JONATHAN WALLACE

SEE ALSO Bridges;Environmental Ethics;Three Gorges Dam;Water.

BIBLIOGRAPHY

Bilharz, Joy A. (1998). The Allegany Senecas and Kinzua Dam: Forced Relocation through Two Generations. Lincoln: University of Nebraska Press. Examines impacts on the Seneca nation of forced relocation to accommodate the Kinzua Dam project.

Devine, Robert S. (1995). "The Trouble with Dams." Atlantic Monthly 276(2): 64–74. Influential article arguing that most dams serve no significant purpose.

Goldsmith, Edward, and Nicholas Hildyard. (1984). The Social and Environmental Effects of Large Dams. San Francisco: Sierra Club Books. Representative of arguments critically reassessing dams during the last half of the twentieth century.

Jackson, Donald C. (1995). Building the Ultimate Dam: John S. Eastwood and the Control of Water in the West. Lawrence: University Press of Kansas. A biography of Eastwood (1857–1924), who from 1906 until his death designed more than sixty dam projects in the western United States, that stresses the psychological attractiveness of the multiple arch dam.

Jackson, Donald C., ed. (1997). Dams. Brookfield, VT: Ashgate. Collects seventeen previously published articles highlighting technical and social developments.

Khagram, Sanjeev. (2004). Dams and Development: Transnational Struggles for Water and Power. Ithaca, NY: Cornell University Press.

Levy, Matthys, and Mario Salvadori. (2002). Why Buildings Fall Down, rev. edition. New York: Norton. Analyzes dam collapses from a structural engineering standpoint.

Petersen, Shannon. (2002). Acting for Endangered Species: The Statutory Ark. Lawrence: University Press of Kansas. Contains an account of the snail darter and Tellico Dam.

Schnitter, Nicholas J. (1994). A History of Dams: The Useful Pyramids. Rotterdam, Netherlands: A. A. Balkema. A technical history with some comments on social context that takes its subtitle from the praise of dams by the Roman Sextus Julius Frontinus (c. 35–c. 103 c.e.).

Smith, Norman. (1971). A History of Dams. London: Peter Davies. The first general history of dams.

World Commission on Dams. (2000). Dams and Development: A New Framework for Decision-Making. London: Earthscan. A report that grew out of a 1997 World Bank workshop, arguing for a critical assessment of large-scale dam projects in terms of technical, economic, environmental, and social impacts.