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Clearinghouse for Dam Removal Information (CDRI)

Clearinghouse for Dam Removal Information (CDRI)

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The Brownsville Dam Removal

The Brownsville Dam was constructed in the 1880s as a summer diversion structure for a local woolen mill in the forested and agricultural Calapooia River watershed of the Willamette Valley, Oregon. The small dam, 33.5m (110ft) in width, raised the level of the Calapooia River by 1.8m (6ft) during the high-flow season extending from October to May. During summer months, removable flashboards were installed, raising the river level to 3.4m (11ft) above its historic elevation. The Calapooia Watershed Council coordinated removal of the Brownsville Dam in the summer of 2007 to improve passage for steelhead and spring Chinook, which are listed on the National Endangered Species Act (ESA). To advance the science of dam removal, researchers from Oregon State University, directed by Dr. Desiree Tullos, characterized the changes to sediment dynamics, channel morphology, aquatic communities, and human social networks that have occurred over the course of the removal.

Brownsville Dam before removal, August 2007 (left) and immediately after removal, September 2007 (right).

Uncharacteristic Results

Biophysical Monitoring

At the time of removal, local stakeholders were concerned that the sediment release following dam removal would result in a decline in quality of downstream aquatic habitat. However, detailed analyses of baseline conditions suggested that the coarse gravel stored in the reservoir was in fact likely to improve habitat complexity in the sediment-deficient reaches below the dam. One year after dam removal, monitoring data from reaches below the dam and reference reaches upstream confirmed that median particle sizes in riffles and bars below the dam had increased as the channel substrate shifted from hardpan to become dominated by coarse gravel. Sediment evacuated from the reservoir deposited into bar features, increasing bar area in the reach downstream by nearly 600% and, contrary to conventional wisdom of dam removal, percentages of fine materials in riffles and bars decreased.

Social Impact Assessment

To characterize the socioeconomic impact of the Brownsville dam removal, a research group of social scientists, led by Dr. Denise Lach of Oregon State University, interviewed approximately 30 community members from the various stakeholder groups involved in the community decision-making process. From the interviews, the a priori template design from the existing literature on social impacts has been expanded).

Brownsville Dam one month removal, October 2007 (left) and 13 months after removal, October 2008 (right).

Learning from the Brownsville Dam Removal

Baseline Data Collection

Baseline data documents pre-removal conditions, but may also direct formulation of research hypotheses and allow for prioritized monitoring plans. At Brownsville, baseline data collection informed simple predictive models regarding how and when sediment would move and where channel changes were likely to be detected. This information allowed researchers to target monitoring within anticipated response reaches, and to focus broad conceptual models to create detailed study hypotheses based upon spatially explicit data.

Model Evolution

The outcomes of the Brownsville dam removal were somewhat contradictory to results predicted by the current conceptual models of dam removal that constitute the underpinnings of many effectiveness monitoring studies. The results of the Brownsville dam removal provides an example as to why monitoring data should be used to constantly evaluate and validate conceptual models to enhance learning as the science and practice of dam removal progresses.

For more information and results, read the Brownsville dam reports.

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Other Useful Reports

Dam Removal Success Stories
Friends of the Earth, American Rivers, and Trout Unlimited (1999) detail 26 dam removals – 25 of which are successful projects and one of which is not.
Dam Removal: A Citizen's Guide to Restoring Rivers
River Alliance of Wisconsin and Trout Unlimited (2000) provide a step-by-step process for those interested in pursuing dam removal as a river restoration tool.
Dam Removal: A New Option for a New Century
Aspen Institute (2002) offer policy recommendations based on a two-year multi-disciplinary dialogue among 26 experts in river and dam management.
Exploring Dam Removal: A Decision-Making Guide
American Rivers and Trout Unlimited (2002) discuss if a dam is a good candidate for removal based on ecology, economics, society, and engineering.
Stream Barrier Monitoring Guide
Gulf of Maine Council on the Marine Environment (2007) presents a standardized framework for monitoring ecological changes.
Bioscience v. 52(8): A Special Section on Dam Removal and River Restoration
Various articles and authors (2002) explore scientific and social aspects of dam removal.
Last modified: 10/7/2014 8:50 AM by S. Cronin

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