Dams are a monumental presence on the American landscape. They divert and restrain mighty rivers that have run for millennia. They impound vast artificial lakes. Water from dams has turned deserts into orchards, slaked the thirst of millions of metropolitan citizens, and powered wartime production from the Southeast to the Northwest; but dams have also prevented salmon from spawning, flooded forests and fields, displaced populations, and required graves to be exhumed. It is not surprising, then, that dam building inspires powerful emotions.
Most people, when asked about American dams, think of one of the massive federal projects built between the 1930s and the 1970s, such as Hoover Dam or the Grand Coulee. Yet according to the National Research Council, there are over 2.5 million dams in the United States, most of which are small, privately owned structures. 1 Only a very small number — six thousand, to be precise — are large dams over 50 feet high, and only a small portion of these have been built by the federal government. 2 It is a bit daunting, then, to present a picture of dams across America. Which dams should one talk about? The most typical or the most exceptional ones? The structurally innovative, politically contentious, or newsworthy ones? The exemplary, influential, or precedent-setting ones?
Histories of engineering talk about dams in superlatives. They are the longest, highest, or most massive; they have the biggest reservoir or the highest head drop (distance from the reservoir surface to the powerhouse), or they were made with the least or the most amount of material. They were the first or the latest to set records in any of these ways. Dams imply a kind of engineering Olympics, a measure of people against nature. Like that other great technological achievement, the skyscraper, one can always build a bigger dam. Certainly, the biggest dams in the United States were colossal undertakings that took years to complete. The architectural critic Lewis Mumford called them “democratic pyramids” and compared them to the greatest constructions of antiquity. 3 The cultural historian David Nye suggests that because dams inspire feelings of awe, they engender national pride. 4 If newspaper coverage is any measure, this would certainly seem to be the case with the dams that span the great rivers of the country, like Hoover Dam across the Colorado, the Grand Coulee Dam across the Columbia, and Fort Peck Dam across the Missouri.
But the history of dam design is a history of invention and development that proceeded by trial and error in some cases, and by calculation and engineering in others. It is an iterative process in which each new design incorporates lessons from an earlier, similar dam. Dam design has to take into account precedents, engineering science, and the specific circumstances of site and construction process — such as whether the labor force is large or small, whether the ground conditions are solid or porous, and whether it is easy or difficult to get construction materials to the site.
In social terms, dams have always held the promise of using technology to harness nature for the benefit of people. This dream is perhaps best exemplified by the dams of the Tennessee Valley Authority. Yet today, dams are a much-maligned, even vilified, presence in the country’s western landscapes. They are criticized as destroyers of animal habitats, usurpers of native lands, boondoggles for land speculators, or subsidies for wealthy farmers. Yet ranchers, farmers, industrialists, unions, municipalities, states, and federal agencies have all, over the years, vied energetically for federal support in dam building, because dams require a huge mobilization of capital, manpower, and resources. And they have similarly huge effects, both desirable and collateral.