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D am removal

Explore the history, effects, and reasons for dam removal, highlighted by case studies such as Elwha Dam in Washington and Marmot Dam in Oregon. Learn about the ecological impact, sediment transport, and implications of dam removal.

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D am removal

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  1. Dam removal Thanks to Sarah Lewis at the Forest Science Labs from Oregon State U for some of the slides and images in this presentation Sara Mitchell Geomorphology College of the Holy Cross Worcester, Massachusetts Worcester Consolidated Street Railway (Mass Electric) dam, Blackstone River

  2. Outline • History of dam building • Effects of dams • Why are dams coming down? • A few examples Elwha Dam, Olympic National Park, WA

  3. History of dam building in US Moore State Park, Paxton, MA (1700s) Hoover Dam, Arizona (1935) Range of ages, variety of purposes, different effects

  4. Mill dams Walter and Merritts, 2008

  5. Source: World Commission on Dams Hiroshi Ishidaira  Yamanashi University 13,382dams

  6. U.S. Dams Built and Removed per decade since 1900 1990-2000 Sources: National Inventory of Dams (2000) American Rivers (2000)

  7. Effects of dams • Hydrology • Sediment • Ecology Chinook salmon

  8. Effects on hydrology depend on purpose of dam Hydroelectric: flow depends on power needs Flood control: goal to fill reservoir in dry times and release slowly in wet times Reregulating dam: constructed below a hydroelectric dam, purpose is to return flows to a more natural pattern Many small dams do not control flow at all

  9. Sediment transport • Balance between sediment supply and ability of flow to move it • Decrease sediment supply but keep flow the same, channel bottom coarsens or erodes • Decrease flow but keep sediment supply the same, channel aggrades with fine sediment • Decrease both, then it depends on the balance Why is sediment important?

  10. Upstream: Sediment Trapping Cougar Reservoir, SF McKenzie River

  11. ~ 750,000 m3 of sediment 46 m 14 m Marmot Dam on the Sandy River, OR Entire reservoir filled in with sediment What happens if you trap all this sediment on the landscape?

  12. Downstream: Textural coarsening Clackamas River

  13. Downstream: Incision / bed degradation Arno River at Empoli

  14. Downstream: Coastal erosion

  15. Ecology • Change from flowing stream to lake upstream • Inundate riparian (streamside) corridor • Blocks fish passage • Changes sediment regime • Changes flow • Annual pattern • Temperature • Existence at all of flow • People are reassessing value of dams Colorado Squawfish

  16. The emerging issue of dam removal – why now? Threatened and endangered species River restoration Aging dams/dam safety Policy windows (i.e., FERC relicensing) Liability Deregulation of energy industry Symbolism

  17. FERC re-licensing • Federal Energy Regulatory Commission • Every 30-50 years • Dams must meet today’s regulations • Safety • Fish passage • Cost-benefit • Would it cost more to update the dam than to remove it?

  18. Dam safety • Taum Sauk reservoir failure, Missouri (2005)

  19. Percentage of Dams over 50 years Old Source: National Inventory of Dams, Aug. 2000

  20. Percentage of Dams over 50 years Old by 2020 Source: National Inventory of Dams, Aug. 2000

  21. Coupled upstream downstream problem Geomorphic issues Upstream Rate of removal, evolution of upstream deposit Release of contaminated sediments Downstream Rates of transport, propagation, and evolution of sediment wave; effects on channel morphology graphics by Shannon Hayes

  22. Dam removal sediment releases 108 Glines Canyon 107 Marmot Condit 106 Embrey Savage Rapids Edwards 105 Milltown Reservoir sediment (m3) Big Rapids 104 historic small dam removals 103 102 2008 2012 2009 2009 2012

  23. A few examples • Milltown Dam, Clark Fork River, Montana • Marmot Dam, Sandy River, Oregon • Elwha and Glines Canyon dams, Elwha River, Washington • Merrimack Village Dam, Merrimack River, New Hampshire

  24. Milltown Dam, Montana Slide from Andrew Wilcox, University of Montana (2008)

  25. Marmot Dam, Sandy River, Oregon ~ 750,000 m3 of sediment 46 m 14 m Hydroelectric dam, entire reservoir filled in with sediment One of largest dams removed to date

  26. Video of Marmot Dam removal • http://www.opb.org/programs/ofg/segments/view/1651 • Nice enthusiasm shown by Gordon Grant (USFS hydrologist/ geomorphologist)

  27. Elwha River, Washington • Largest dam removal project(s) to date • Fish passage • Multi-year project (dams are now down) • 19 million m3 of sediment trapped http://pubs.usgs.gov/fs/2011/3097/

  28. Elwha Dam Glines Canyon Dam Can also find videos of removal online

  29. Removal of the Merrimack Village Dam, New Hampshire Originally built in 1730s, became a safety hazard, not used Taken down in 2008 to improve fish habitat (NOAA “Open Rivers” program) Photos from NOAA

  30. There is probably a dam near you • This map layer portrays major dams of the United States. The map layer was created by extracting dams 50 feet or more in height, or with a normal storage capacity of 5,000 acre-feet or more, or with a maximum storage capacity of 25,000 acre-feet or more, from the 79,777 dams in the U.S. Army Corps of Engineers National Inventory of Dams. http://geocommons.com/overlays/13139

  31. Possible talking points • Release of contaminated sediments • Watersheds as a complex system which dams disrupt in multiple ways • Dam safety • $$$ • Is restoring fish habitat realistic? • Is it wise to lose a carbon neutral energy source in order to restore fish habitat? • Newspaper articles, local river advocacy groups, municipalities Hydropower dams on Columbia River

  32. Ideas for incorporating this topic in the classroom • Research history of dams in your area • Get involved in a local dam removal project: observe before and after • Debate the pros and cons for dam removal • …?

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