Dams and Impoundments Impact of Dams on the Rancocas Creek watershed

Across the United States, 2.5 million dams of all sizes block and harness rivers.  Most of them are quite small. Of those 2.5 million dams, only 80,000 are more than six feet high.

Dams serve a wide range of purposes, such as providing hydroelectric power, water supply, and irrigation, supporting recreation and shipping, and managing flood control.  Many dams have become integral to the identity of their communities.

Beneficial functions notwithstanding, dams produce severe negative impacts on the rivers they harness.  Dams alter a river’s chemical, physical, and biological processes.  Over the past two decades these negative impacts have become more obvious, but the environmental costs of dams have only recently captured scientific attention.

  • Dams cause the build-up of sediment.  They block free-flowing water and impede the river’s flushing function, as well as the transport of nutrients and sediment downstream.
  • Dams fragment rivers and block the natural movement of fish and other aquatic species.
  • Dams contribute to, and sometimes are the sole cause of, many species becoming threatened, endangered, or extinct.  Prime dam sites often are prime fish spawning sites.
  • Dams alter water temperatures, dissolve oxygen levels, and produce turbidity and salinity, both upstream and downstream of the structure.

RP and Dams

The Rancocas Creek watershed and system is typical of rivers and tributaries in South Jersey  What was once a free-flowing river system is now interrupted by dams on both the main stem and the tributaries.

State and national inventories record numnerous dams in the Rancocas Creek watershed

As the dams in the watershed age and require investment for repairs, an increasing number of communities, dam owners, and government agencies will face decisions on what to do about dams. The decision to remove or rehabilitate a dam involves many considerations, as do the decisions about what methods to use to restore a free-flowing stream.  Such considerations include dam safety, environmental impact (i.e. possible toxins in the accumulated sediment behind the dam), and economic issues.

Concerned community leaders and citizens have worked together to remove dams and restore reaches of streams in the watershed throughout the United States.  In the Rancocas Creek watershed we are analyzing dams and associated impoundments.

  • restore more than 100 miles of a freshwater ecosystem;
  • expand viable habitat for sensitive species including North America’s most endangered animal, freshwater mussels; and
  • support local economies in riverfront communities through improved water quality and enhanced recreation opportunities.

Learn more

  • See the dam program page to learn more about specific actions that others are doing about dams.  It maybe feasible to model some type of dam program here  in the RCW (Rancocas Creek Waterhed).
  • To learn more about the issues surrounding Dams and climate contact Rancocas Pathways.

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