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Fish Passage Options
Many fish species migrate hundreds of miles between suitable habitats in oceans and streams. Structures placed across a stream can have dramatic impacts on the movements of fish within a stream.
Channel spanning structures such as dams and weirs are barriers to fish passage. These structures block channels and make areas of habitat inaccessible to aquatic organisms. Many options exist for enhancing fish passage in these situations.
Restoring fish passage by installing fishways or removing barriers provides immediate improvement in and recovery of fish populations, as well as the restoration of aquatic habitat. Some options for enhancing fish passage in the Brandywine River include the following.
 | Dam Notching
Notching involves the partial removal of a dam. The notch creates a bypass to enhance fish passage. Dam notching allows the structure to remain intact or be removed later. Notching a dam is done gradually to ensure the release of sediment stored above the dam does not adversely impact water quality downstream. |
 | Denil Fishway
Denil fishways use a series of symmetrical baffles to redirect the flow of water, causing fish to swim around a barrier. Like railway switchbacks, these "fish ladders" can accommodate steep grades and require limited for construction. The image at left shows a dam in Rock Creek Park in Washington, DC with a concealed fishway to enhance the aesthetics. |
 | Rock Ramp
Rock ramps use boulders or timbers to create pools and small falls resembling natural habitat features. Due to the length of channels needed for rock ramps, such structures are appropriate for short barriers. The diagram at left shows a dam converted to a rock ramp that mimics a natural channel. |
Before dam removal | Dam Removal
The removal of a dam restores fish migration and provides habitat for juvenile fish. Dam removal is the least expensive option for enhancing fish passage, requiring no maintenance and enabling the maximum possible fish passage. The images at left show the Cuddebackville dam on New York's Neversink River - a tributary of the Delaware River where efforts are also underway to restore American shadÑbefore and after removal. |
After dam removal | |
For more information send email to emc@brandywine.org, call 610-388-2700, or write to Environmental Management Center, Brandywine Conservancy, P.O. Box 141, Chadds Ford, PA 19317
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