page_title: Dam removal
section_title: Methods of removal
hierarchical_section_title: Dam removal / Methods of removal
caption_attribution_description: English: Here five notches can be seen as the 210 ft high Glines Canyon Dam was removed over the course of over a year.
context_page_description: Dam removal is the process of demolishing a dam, leaving a river to flow freely. It is undertaken for a variety of reasons that include environmental rehabilitation, structural weakness and maintenance expense.
  All dams negatively affect the aquatic environments of rivers that they are located on, but those effects are often negated by the stated purpose of the dam, whether it is hydroelectric power, flood control, or other functions. When the negative environmental effects outweigh the benefits, a dam may be considered for removal. This happened on the Elwha River in Olympic National Park in Washington when extraordinarily rich salmon habitat was being disrupted by an out-dated hydroelectric plant. Before dams were built on the Elwha River, 400,000 salmon returned each year to spawn, but that number dropped to fewer than 3,000 after dams were put up. Once the hydroelectric power generating capacities of the dams had outlived their useful lives, the importance of this salmon habitat necessitated the removal of the dams on the Elwha River.
  Dam failure is another threat that can lead to the removal of dams.
context_section_description: There are several ways dams can be removed and the chosen method will depend on many factors. The size and type of the dam, the amount of sediment behind the dam, the aquatic environment below the dam, who owns the dam and what their priorities are, and the timeframe of dam removal are all factors that affect how the dam will be removed. Removal is costly no matter what and expenses typically rise when greater weight is given to environmental concerns. Fortunately, the cost of dam removal is usually shared by multiple stakeholders such as the dam owner and either the federal, state or local government. Four of the most common dam removal methods are described below.
  Sediment management is a driving force in all of them. A common problem for dams is how sediment carried naturally by the river is deposited in the reservoir and eventually fills it up with silt. This excess sediment reduces the hydroelectric generating capacity of a reservoir, changes the river channel downstream, traps nutrient-rich sediment behind the dam, and can put a dangerous amount of pressure on the dam itself. Oftentimes the sediment stored in a reservoir is good for the riparian corridor below the dam, can rebuild fish habitat, provide nutrients, and add onto a beach or estuary. Other times, the sediment can increase the turbidity of the river harming fish, scour the landscape, and bury infrastructure.
  Sediment can be tested before it is released to determine if it will be harmful to the landscape below the dam. Dam removal can have adverse consequences if this is not done. For example, when the Fort Edward Dam on the Hudson River was removed in the 1970s, PCBs in the sediment were released, affecting human and wildlife health downstream.
caption: Here five notches can be seen at the Glines Canyon Dam as it was removed in a multi-year process.
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