Over the past 100 years, the United States led the world in dam building—blocking and harnessing rivers for a variety of purposes, including hydropower, irrigation, flood control, and water storage. The US Army Corps of Engineers (Army Corps) has catalogued approximately 75,000 dams greater than six feet tall along the waterways of the United States—and at least tens of thousands of smaller dams plug our rivers across the country. (The National Research Council estimates that the number of US dams is over 2.5 million). US Secretary of the Interior Bruce Babbitt recently observed, “that means we have been building, on average, one large dam a day, every single day, since the Declaration of Independence.”
Few human actions have more significant impacts on a river system than the presence of a dam. As a result, dams occupy a central role in the debate about protecting and restoring our river resources. Many of the major environmental campaigns in the United States, and around the world, have revolved around efforts to fight construction of large dams. Hetch Hetchy, Marble Gorge, Bridge Canyon, Tellico, and Three Gorges are all examples of pivotal campaigns focused on the environmental, economic, and societal costs and benefits associated with building a new dam.
A less known page in the history of rivers is the large number of dams that have been removed. Relatively little attention has been paid to the hundreds of smaller dams that have been torn down and the thousands of miles of free flowing rivers that have been restored. For decades dam removal has been an accepted approach for dam owners to deal with unsafe, unwanted, or obsolete dams. The decision to remove a dam is not as radical an idea as some today may suggest; dams are removed all the time, by a variety of entities, for a variety of reasons. Just as for any building or other human construction, dams have finite lifetimes and are often removed when they become obsolete or dangerous.
Although dams can provide important societal benefits, dams also cause negative impacts to rivers, wildlife, and sometimes local communities. Some dams no longer provide any benefits, while continuing to harm the river. Others have significant negative impacts that outweigh the dam’s benefits. Still others simply are so old and/or unsafe that they cost too much money to maintain. In these situations, dam removal has been demonstrated to be a reasonable option to eliminate negative impacts and safety concerns.