Dam removal

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. Sometimes the fear of failure is due to seismic activity or the placement of the dam. Additionally, the older the dam is, the more likely it is to fail. Around the world, a growing number of 20th-century dam construction projects are reaching the end of their design lives: as of 1996, 5,000 large dams around the world were more than 50 years old.[1] By 2020, in the United States alone, 85% percent of the country’s dams will have exceeded that 50 year threshold.

Finally, economic reasons often provide a convincing reason to remove a dam. The cost of keeping outdated hydroelectric equipment running decades after it was installed or upgrading dam safety systems may not be worth it. Additionally, population centers and industrial facilities that demanded hydropower decades ago can move and leave the dam without a purpose.

Since around 2000, most major dam removal projects, and the largest single project, the $350M removal of two Olympic Peninsula dams as part of the Elwha Ecosystem Restoration, have been driven by restoration of river habitat and fish passages. Inspired by the Elwha project, a French group called SOS Loire Vivante successfully lobbied for the removal of two dams in the Upper Loire Valley, and the re-engineering of a 1941 hydroelectric dam on the Allier River to restore habitat for Atlantic salmon.

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Wikipedia