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Dam Removal

Dams in the Hudson WatershedBy identifying and supporting the removal of dams that are at risk of failure and are barriers to fish passage, the Hudson River Estuary Program and its partners promote ecosystem functioning and habitat connectivity while reducing threats to human safety and property.

 

Many dams in the Eastern U.S. are falling into disrepair, yet still creating barriers to fish passage. With over a 1000 dams in the Hudson River Estuary Watershed, there is a great opportunity to improve ecosystem and community health by identifying and removing those barriers that pose the greatest risks to both.

 

Barrier removal success story

Alewives in the Wynants Kill
Alewives in the Wynants Kill

Habitat for migratory fish, such as herring and American eel, has been substantially reduced by barriers in Hudson River tributaries. In the City of Troy, the first barrier to fish was removed on the Wynants Kill in early May, and in less than 5 days, alewives had retaken the tributary as spawning habitat for the first time in 85 years. The City of Troy got a tributary restoration grant from the NYSDEC Hudson River Estuary Program and removed the barrier, reconnecting over a quarter mile of spawning habitat for herring, and improving habitat for many other species including American eel. This barrier had been identified by WRI staff as a critical barrier to migratory and resident fish, as well as many other aquatic and riparian organisms.  Watch videos of the herring run here Alewives in the Wynants Kill and Alewives and the concrete channel of the Wynants Kill.

Research

The New York State Water Resources Institute and the Hudson River Estuary Program have supported studies to inform local decision making around the potential pros and cons of dam removal. Weiming Wu of Clarkson University characterized the volume of erodible sediments and their contaminant concentration behind the Bingham Mills Dam on Roeliff Jansen Kill and Burden Pond Dam on Wynants Kill Creek. Patrick Sullivan of Cornell University is conducting ongoing monitoring at dam sites throughout the Hudson River Estuary Watershed, through a 2017 funded project entitled "Hudson Tributary Dam Removal."

At a broader scale, Christina Tonitto and Susan Riha of Cornell University conducted a review of dams removed in the last two decades throughout the United States, and summarized the lessons learned from these cases into six recommendations:

  1. Engage stakeholders to inform watershed residents of the economic, ecological, and safety considerations for dam removal.
  2. Streamline planning through policy changes. For example, the creation of standardized guidelines for dam removal, state-specific resources to assist communities looking to undertake dam removal, or a dam removal-specific permitting process.
  3. Monitor pre- and post-dam removal in both the impounded and a control reach to understand how removal impacts physical, chemical, and biological characteristics.
  4. Expect aquatic organism population recovery to vary. If the dam primarily limited habitat, recovery may take years to decades and never fully occur. If the dam primarily limited migration, recovery may occur within a year. Expect rapid vegetation colonization in the dewatered impoundment.
  5. Expect chemical changes to vary with dam size and sediment storage. In small dam systems, removal may result in little chemical change. In dams with significant sediment storage, there is a risk of resuspended industrial contamination or nutrient enrichment. Pre-removal sediment analysis is recommended if contamination may be an issue.
  6. Prioritize predicting post-removal hydrologic flows, using a program such as HEC-RAS.

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