Dam removal

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Dam removal is the process of demolishing a dam, returning water flow to the river^[1]. Arguments for dam removal consider whether their negative effects outweigh their benefits. The benefits of dams include hydropower production, flood control, irrigation, and navigation. Negative effects of dams include environmental degradation, such as reduced primary productivity, loss of biodiversity, and declines in native species; some negative effects worsen as dams age, like structural weakness, reduced safety, sediment accumulation, and high maintenance expense. The rate of dam removals in the United States has increased over time^[1][2], in part driven by dam age. As of 1996, 5,000 large dams around the world were more than 50 years old. In 2020, 85% percent of dams in the United States are more than 50 years old.^[3] In the United States roughly 900 dams were removed between 1990 and 2015, and by 2015, the rate was 50 to 60 per year.^[2] France and Canada have also completed significant removal projects.^[4] Japan's first removal, of the Arase Dam on the Kuma River, began in 2012 and was completed in 2017.^[5] A number of major dam removal projects have been motivated by environmental goals, particularly restoration of river habitat, native fish, and unique geomorphological features. For example, fish restoration motivated the Elwha Ecosystem Restoration and the dam removal on the river Allier,^[6] while recovery of both native fish and of travertine deposition motivated the restoration of Fossil Creek.^[7]