Why are some dams being removed?
There has been a growing movement to remove dams where the costs – including environmental, safety, and socio-cultural impacts – outweigh the benefits – including hydropower, flood control, irrigation, or recreation – or where the dam no longer serves any useful purpose. The goal of removal can be multi-faceted, including restoring flows for fish and wildlife, reinstating the natural sediment and nutrient flow, eliminating safety risks, restoring opportunities for recreation, and saving taxpayer money. (AR)
How are dams removed?
Because dams and rivers vary greatly, physical removal strategies and techniques may also vary on a case by case basis. (AR)
How many dams have been removed to date?
According to American Rivers, 1,578 dams have been removed over the past 100 years in this country. AR is still in the process of gathering this data, so that figure continues to increase as more information becomes available. You can view an interactive map of all known U.S. dam removals. (AR)
Who decides that dams should be removed?
The decision to remove a dam is made by varying entities, depending on the regulatory oversight of the dam. In most cases, the dam owner itself is the decision-maker, often deciding that the costs of continuing to operate and maintain the dam are more than removing the dam. State dam safety offices can often order a dam to be removed if there are major safety concerns. State fish and wildlife offices are also often involved in the decision-making, particularly when the goals of the project include restoration of habitat for migratory and resident aquatic species. If the dam in question is a hydropower facility, the Federal Energy Regulatory Commission can order a hydropower dam under their jurisdiction to be removed for both environmental and safety reasons. (AR)
How can the benefits of a dam be replaced when it is removed?
While dams serve a number of human needs, society has developed ways to address many of these needs without dams. For instance, flood control can often be accomplished more effectively and for less money by restoring wetlands, maintaining riparian buffers, or moving people out of the floodplain. Updating antiquated irrigation systems and replacing inappropriate crops can dramatically reduce the need for dams and reservoirs in the arid West. Rather than plugging rivers with multiple hydropower dams, a cheaper and less environmentally harmful solution is to use existing energy efficiency technologies. For example, the three megawatts of power lost in the removal of the Edwards Dam, on the Kennebec River in Maine, can be replaced simply by replacing 75,000 light bulbs with energy efficient bulbs. Many dams that have been removed no longer had any beneficial use or that use was very limited. (AR)
What are the potential downsides to dam removal?
Dam removal does result in fundamental changes to the local environment. The reservoir will be eliminated, and with it the flat-water habitat that had been created. Wetlands surrounding the reservoir may also be drained, although new wetlands are often created both in the newly restored river reach above the former dam site and in the river below. Sediment that collects behind a dam, sometimes over hundreds of years, may contain toxics such as pcbs, dioxide, and heavy metals. Removal of these toxic materials is often extremely expensive, and the threat of re-suspending these toxic-laden sediments in the process of dam removal has the potential to damage downstream water quality and threaten the health of fish and wildlife and water users. These impacts, however, can be prevented through proper removal techniques. (AR)
Short term impacts of the dam removal itself can include increased water turbidity and sediment buildup downstream from releasing large amounts of sediment from the reservoir, and water quality impacts from sudden releases of water and changes in temperature. It has been demonstrated that these short-term impacts are greatly outweighed by the quick recovery of the system and the long-term benefits that result. (AR)
Will there be an increase in flooding?
This would only be a concern if the dam actually provides flood control, however, this is true for only a very small percentage of dams. Flood control dams are fairly easy to recognize because they tend to have fluctuating water levels, and relatively low water levels except during flood events. It is important to note that dams can actually increase the risk of flooding both downstream and upstream of the dam, due to dam disrepair and/or misoperation. (NHDES)
In heavy rainfall or flooding, some dams are designed to hold back some of the water flowing downstream, protecting people and property downstream from higher water. This naturally results in higher water upstream of the dam, but auxiliary spillways are designed to pass excess flood waters downstream. However, most dams in the state are not designed to function as flood control structures. They are “run of the river” dams designed to hold relatively stable water levels in the impoundment. Flood situations can sometimes exceed the capabilities of either type dam, resulting in a failure and a more drastic and sudden flooding of downstream property. Constant maintenance of dams, and awareness of dam operators is essential to protecting the public in flood situations. (AR)
Does the dam have historical value?
Part of the dam removal planning process is to assess the project’s potential to impact historical resources. In accordance with the National Historic Preservation Act, the State Historic Preservation Office must be consulted about the project as early as possible in the project planning process. They may recommend further study to determine the historic value of the site, based on both archaeological and architectural criteria. At some project sites the dam’s historic contributions are honored with interpretive signs, recovered mill stones and other information. In other cases, when a dam is historically significant, dam removal may not be appropriate and other alternatives may need to be considered. (NHDES)