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Let it Flow – The Case for Dam Removal

The damming of streams and rivers has its roots in early human civilization. From the earliest settlements, humans have diverted and stored water for a variety of uses. Today, there are more than 85,000 dams in the United States, serving a variety of functions, including flood prevention, water diversion and recreation. Dams play a significant role in the nation’s water supply and many large urban areas are supplied with water blocked by dams. Hydroelectric power from dams provides approximately 7 percent of electricity in the United States. About two-thirds of all dams are privately owned, and state and local governments own most of the remainder.

Although in the past dams were viewed as being almost entirely beneficial, today’s view of dams is more balanced, recognizing both the positive and negative effects.  Impounding and diverting water for upstream users modifies local habitats, affects plants and animals, and influences the lives of those who live downstream.  Dams can also present safety and economic risks due to the possibility of dam failure.  While the risks associated with aging dams are typically of low probability, the consequences are high.  Although dam failures are infrequent, the risk of failure increases with the age of the dam.

The first half of the twentieth century was the heyday of dam construction in the United States, peaking in the 1960s and decreasing significantly in the second half of the twentieth century and beginning of the twenty-first.  This means that America’s dams are aging.  The average age of a dam in the United States is more than 50 years old, and a small but significant number are a century old or more.  Many older dams no longer function as originally intended.  The dam structures may be in a state of disrepair, or the reservoirs created by the dams may have naturally filled in with sediment.

Currently, tens of thousands of dams are aging beyond their expected lifespans, with the possibility of attendant safety, environmental, and other problems.  Managing aging dams is quickly becoming a principal focus of dam engineering, made more challenging by the fact that existing dams represent different generations of design standards and construction practices.

Nationally, the number of high-risk dams is increasing.  In its Report Card for America’s Infrastructure, the American Society of Civil Engineers gave the nation’s dams a D grade.  It would cost an estimated $16 billion to repair the country’s most critical dams, and additional funding is needed for inspections and enforcement of safety programs.  Lack of funding for dam repair is a significant problem, particularly for privately owned dams.  The responsibility for dam upkeep and repair lies largely with the owners, many of whom cannot afford the costs.  Obtaining funding assistance, whether through government or private sources, can be difficult.

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One thought on “Let it Flow – The Case for Dam Removal

  1. A good article about the value of dam removal and the numerous issues and challenges involved. Another option that has been successful is the partial removal or modification of an existing dam (usually a low-head structure less than 10-12ft in height) to allow fish pasage and recreational boating access without the need for portaging. The first in-stream urban dam modifiaction for recreational boating was completed at Denver’s Confluence Park in 1975, and numerous similar projects have been completed throughout the U.S. Modification can be done to an abandoned existing dam, or to a structure that still provides service, such as water diversion, grade control, etc, without impact to the dam’s operation. This can be an option where onjections are raised (often by waterfront residents) regarding total dam removal and the loss or reduction of waterfront area. While the mulitple benefits are similar to total dam removal (fish and boat passage, riparian and wildlife habitat enhancement, etc), an additional benefit can be the creation of safer conditions for boaters, as often low-head dams have dangerous, life-threatening “keeper” hydraulic conditions that gives them the reputation of being “killing machines”.

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