||The examples and perspective in this article deal primarily with the United States and do not represent a worldwide view of the subject. (December 2010)|
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Dam removal is the process of removing out-dated, dangerous, or ecologically damaging dams from river systems. There are thousands of out-dated dams in the United States that were built in the 18th and 19th centuries, as well as many more recent ones that have caused such great ecological damage, that they are proposed for removal.
Catastrophic dam failures such the 1977 Kelly Barnes Dam, killing 39 students, faculty and staff of the college, the 1976 Teton Dam failure in Idaho, the 1928 St. Francis Dam failure in California, and the 1889 Johnstown Flood remind people of the dangers dams can present. The largest catastrophic failure of a dam was the 1975 Banqiao Dam disaster that killed 26,000 people immediately, resulted in 145,000 dying of disease later, and displacing 11,000,000 residents.
Purposes and effects of dams
Many of the dams in the eastern US were built for water diversion, agriculture, factory watermills, and other purposes that are no longer useful. Because of the age of these dams, over time the risk for catastrophic failure increases. In addition, many of these dams block anadromous fish runs, such as Atlantic salmon and American shad, and prevent important sediments from reaching estuaries.
Many dams in the western US were built for agricultural water diversion in the arid country, with hydroelectric power generation being a very significant side benefit. Among the largest of these water diversion projects is the Columbia Basin Project, which diverts water at the Grand Coulee Dam. The Bureau of Reclamation manages many of these water diversion projects.
Dams in the Pacific Northwest and California block passage for anadromous fish species such as Pacific Salmon and steelhead. Fish ladders and other passage facilities have been largely ineffective in mitigating the negative effects on salmon populations. Bonneville Power Administration manages electricity on 11 dams on the Columbia River and 4 on the Snake River, which were built by the Army Corps of Engineers.
In the Desert Southwest, dams can change the nature of the river ecosystem. In the particular case of the Glen Canyon Dam, the originally warm, sediment-filled, muddy water, instead runs cold and clear through the Grand Canyon, which has significant impacts on the downstream ecosystems. Three native fish species have become extinct in the Grand Canyon and others are endangered since the dam was completed, including humpback chub and razorback sucker.
Some dam projects, such as those on the Salt River Project in Arizona, eliminate the flow of the river downstream, by diverting the flow into the Arizona Canal system for use in agriculture and urban usage, such that only a dry channel or arroyo heads out across the desert.
While the need for clean, alternative energy sources are important, with so many considerations involved, sometimes it makes sense to evaluate whether the benefits of dams outweigh the costs of safety concerns, ecosystem functions, and management expenses.
Dam removal projects in the United States
- 1973 - Lewiston Dam, South Fork Clearwater River, Idaho – The 39 ft (12 m) dam was built in 1927 as a hydroelectric facility, but lacked fish ladders. Upon completion of the Lower Granite Dam and its reservoir, the lack of gradient on the river made it obsolete. Its removal improved salmon runs on the river.
- 1997 - Marie Dorian Dam, Walla Walla River, Oregon – The 8 ft (2.4 m) dam blocked passage to Pacific Salmon and steelhead into the Blue Mountains from the Columbia Basin.
- 1999 - Edwards Dam, Kennebec River, Maine – Built in 1837, the 24 ft (7.3 m) dam blocked access to Atlantic Salmon and American Shad. This was a landmark case in which a U.S. federal agency, the Federal Energy Regulatory Commission, required the decommissioning and removal of a dam against the operator's wishes.
- 2004 - Embrey Dam, Rappahannock River, Virginia - The 22-foot-tall, 770-foot-long, 1910 hydroelectric Embrey Dam was blown up with 600 tons of explosives by the U.S. Army Corps of Engineers on February 23, 2004. The aim of removal was to re-open miles of spawning grounds to aid populations of American Shad, herring, catadromous American eel, and other species. The historical character of the Ambursen-type reinforced concrete structure required a parallel documentation and (partial) preservation project by industrial archeologists. In 2008 longtime U.S. Senator from Virginia John Warner described the removal of Embrey Dam as the "proudest achievement in his legislative career."
- 2004 - Cuddebackville Dam, Neversink River, New York - Built in two portions dating from the 1820s (for water diversion into a canal) and 1915 (for hydroelectric power), the dam had been abandoned since 1945. The dam was removed in October 2004 by the U.S. Army Corps of Engineers, in a novel partnership with the Nature Conservancy, to benefit the aquatic life in the area, specifically the Dwarf Wedge Mussel and the American Shad.
- 2007 - Marmot Dam, Sandy River, Oregon – The removal of this 50 ft (15 m) dam by Portland General Electric has been extremely successful at improving access for Pacific Salmon and steelhead to the upper Sandy River watershed up into the Mount Hood Wilderness.
- 2009 - Savage Rapids Dam, Rogue River, Oregon – Built for agricultural water diversion, it was removed by the Bureau of Reclamation due to its out-dated facilities and non-functioning fish ladders that prevented fish migration past the dam.
- 2011 - Condit Dam, White Salmon River, Washington – The 123 ft (37 m) dam blocked access for Pacific Salmon and steelhead runs on 33 miles (53 km) of river. PacifiCorp proposed to remove the dam, rather than paying for fish passage upgrades. Removal was proposed in 2006, but actions from Skamania and Klickitat counties held up the process. In fall 2008, salmon were trucked up above to dam to allow them to spawn higher up the river. In October 2011, PacifiCorp contractors used explosives to blow a 15-foot (4.6 m) hole in the dam to drain its reservoir and allow young salmon to enter the Columbia River and head to sea.
- 2012 - Elwha and Glines Canyon Dams, Elwha River, Washington – The largest dam removal project in history is the Elwha Ecosystem Restoration project on the Olympic Peninsula of Washington. In 2012, the 108 ft (33 m) Elwha Dam and the 210 ft (64 m) Glines Canyon Dam will be removed to restore stocks of Pacific Salmon and trout species to the Elwha River watershed. The removal of these blockades will allow migratory salmon to travel past the dams and upriver, an event that has not occurred since the dams' creation in 1913. Salmon reintroduction will allow for marine nutrients to return to the upper river beds as the salmon end their life cycles, providing a valuable research opportunity for interested parties.
Dams which have been discussed for removal
Lower Snake River Dams
The lower four Snake River dams including the 100 ft (30 m) Lower Granite Dam, 98 ft (30 m) Little Goose Dam, 100 ft (30 m) Lower Monumental Dam, and 100 ft (30 m) Ice Harbor Dam. These dams, built by the United States Army Corps of Engineers, serve as hydroelectric power sources as well as ensuring agricultural barge traffic navigation to Lewiston, Idaho.
The lower four dams on the Snake River have collected large amounts of sediment. In fact, 3 million cubic yards of sediments are deposited each year. To combat this trend, cities like Lewiston, Idaho and many others along the Snake River have built a system of levees maintained by the Army Corps of Engineers. The levees in Lewiston were designed to leave five feet between water levels and the top of the levees. Today, there is only up to two feet remaining. As water levels continue to rise, either some of the dams must be removed or dredged, or the levees will continue to grow. The Corps admits that the amount of sediment in the riverbed is too great for dredging to be effective, and Lewiston community leaders are worried that higher levees will further cut the town off from its rivers.
The 100 ft (30 m) Rindge Dam on Malibu Creek in the Santa Monica Mountains of California was built in 1924 and today is completely filled with sediment, making it obsolete. Malibu Creek once supported the southernmost steelhead population in the world. But today, steelhead no longer occupy the creek.
Klamath River Dams
Four dams on the Klamath River including the John C. Boyle, Copco No. 1, Copco No. 2, and Iron Gate dams. These dams are operated by PacifiCorp and are up for relicensing. In addition to blocking salmon runs, the reservoirs that form behind the dams built up extremely high levels of toxic algal blooms.
On September 29, 2009, a tentative agreement was reached to remove the four dams; if the plan proceeds they will be dismantled starting in 2020.
Glen Canyon Dam
The 710 ft (220 m) Glen Canyon Dam has been proposed for removal because of the negative effects it has on the water quality and riparian habitat of the Colorado River in Grand Canyon National Park. In addition, the reservoir impounded behind it, Lake Powell has filled all of the canyons for up to 160 miles (260 km) above the dam. This lake, while providing recreational opportunities, has eliminated more than 160 miles (260 km) of habitat for endangered Colorado River fish species. The reservoir also loses more than 6 percent of the total annual flow of the Colorado River to evaporation and seepage. Advocates of dam removal also cite these losses of stored water as reason to decommission the dam. If it were to be removed, it would dwarf any dam removal project in history.
- Dennen, Rusty (9/23/2008). "Rapids to be named for John Warner".
- Barker, E. (2007, February 16). Corps of engineers gets earful about sediment problems. Lewiston Tribune.
- "Why Restore Wild Salmon?" Save Our Wild Salmon. Retrieved 18 May 2011. <http://www.wildsalmon.org/index.php?option=com_content&view=article&id=94&Itemid=62>.
- Fimrite, P. Deal to raze 4 Klamath dams. San Francisco Chronicle 30 September 2009.
- "Why Glen Canyon?". Glen Canyon Institute. Retrieved 15 February 2013.
|Wikisource has the text of the 1911 Encyclopædia Britannica article Dams.|
- Elwha River Dam Removal Study
- Dam Removal Success Stories:Restoring Rivers through Selective Removal of Dams that Don't Make Sense
- Portland General Electric Marmot Dam
- Army Corps of Engineers Dam Removal Page
- Friends of the Earth River Restoration Page
- Natural Resources Council of Maine Kennebec River Restoration
- Spot.us - Story: The Story Behind the World's Biggest Dam Removal - Rough Water