Removing dams is an effective way to restore rivers, save dam owners and taxpayers money, revitalise riverside communities and improve public safety, the report published by American Rivers, Friends of the Earth, and Trout Unlimited claims.

The report, Dam Removal Success Stories: Restoring Rivers through Selective Removal of Dams that Don’t Make Sense, which examines the history and benefits of dam removal in the US, documents more than 465 dams that have been removed across the country and includes 25 detailed case studies of dam removal success stories.

“As society’s needs continue to change, more and more dam owners are seeing removal as the best approach for dealing with old, unsafe or uneconomical dams,” said Sara Johnson, Trout Unlimited’s Director of Volunteer Operations and small dams expert. “Selective removal of dams is a cost-effective river restoration tool that can be a ‘win-win-win’ situation-for dam owners, for fish, and for the local community.”

There are approximately 75,000 dams over six feet tall on rivers across the US, and tens of thousands of smaller dams. Dams have a variety of negative impacts on rivers, including: blocked or slowed flows; reduced river levels; blocked or inhibited fish passage; obstructed movement of nutrients, gravel, and woody debris; altered water temperature; lower levels of dissolved oxygen; limited public access to the river; and harm to the natural character of the landscape.

The dams highlighted in the report were removed because their negative effect on rivers and riverside communities outweighed their benefits. Many of the dams blocked fish migration and degraded water quality. Many were old, abandoned and unsafe.

“Contrary to popular belief, dam removal is not new and radical,” added Bowman, of American Rivers. “This report shows that for decades dam removal has been an accepted approach for dam owners and communities to deal with unsafe, unwanted, or obsolete dams.”

The report found that in many instances, removing a dam restored natural features such as waterfalls, rapids and fish runs. Such ecological improvements can lead to improvements in fish and wildlife habitat and water quality and to economic benefits for riverside communities. In each of the 25 case studies presented in the report, new opportunities for tourism, boating, and fishing arose when a free-flowing river was restored.

States with the most recorded removals include Wisconsin (73 dams), California (47 dams), Ohio (39 dams), Pennsylvania (38 dams), and Tennessee (25 dams). All types of dams have been removed, from water supply to hydroelectric, flood control to recreation. Earthfill dams, concrete arch dams, gravity dams, masonry dams, and timber crib dams have all been taken out. Removed dams have been publicly owned, privately owned, and abandoned dams.

The average height of the removed dams was approximately 21 feet (6.4m). More than 40 dams were 40 feet (12.2m) or taller that have been taken out, including four dams that were 120 feet (36.6m)or taller.

The average length was approximately 224 feet(68.2m). The majority of dam removals identified occurred in the 1980s (92 dams) and 1990s (177 dams). The earliest recorded removal was completed in 1912. The year in which there were the most removals was 1998, when 29 dams were removed.

The research identified three primary reasons for removing a dam:

  • to resolve environmental problems, such as restoring a river’s damaged ecosystem and rebuilding depleted fish and wildlife populations
  • to address public safety concerns over an ageing and deteriorating dam
  • to deal with economic issues – for instance when the dam had ceased to be cost-effective

The removal of a dam was found to result in any combination of the following benefits:

  • return of fish and wildlife: for example, following the removal of four small dams and 12 unscreened water diversions, 20,000 chinnook salmon returned to spawn in Butte Creek, in California’s Sacramento Valley, compared with fourteen counted in the creek in 1987. The reliability and amount of water available for waterfowl and farming also increased. On Florida’s Chipola River, 61 fish species were found after the Dead Lakes Dam was removed, compared with only 34 found before
  • economic benefits: for example, removing the Woolen Mills Dam from Wisconsin’s Milwaukee River (at a cost of $86,000) was cheaper than repairing or replacing the dam (estimated cost, $3.3 million). In addition, the dam removal helped stimulate the leisure industry in the area
  • elimination of public safety hazards: for example, in 1990, the 86-year old Bluebird Dam was removed from Colorado’s Ouzel Creek to eliminate the danger that the dam would fail and cause a flood.

Removal is not appropriate for all, or even most, of the nation’s dams, the report found. However, the operation of dams could be improved to minimise their environmental and societal impacts, while still providing their intended benefits. Nevertheless, for some dams, the impacts outweigh its benefits: in such cases, dam removal is a reasonable and viable option, the report concludes.

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