Use of Nature-Like Fishways for Improving Diadromous Fish Passage at Northeast U.S. Dam Removal Sites

Pro-active dam removals are steadily increasing in number as an evolving paradigm and viable practice for providing diadromous fishes with access to spawning and rearing habitats.  To date, most dam removal sites in the Northeast U.S. are defunct, low-head, run-of-the-river structures but which pose complete barriers or greatly inhibit passage by native fishes such as river herring and American shad.  While removal is often viewed as a straightforward solution to restoring fish passage and other ecological services, many of these dam removal sites pose physical challenges to efficient fish passage. In particular, the presence of in-river bedrock on which or near where the dam was built, as well as the accumulation of substantial sediment volume stored within the impoundment, and the presence of upstream infrastructure and wetland communities that have ecological succeeded in response to the impoundment hydrology, pose challenges to these fish passage projects.  Nature-like fishways are now well used in the hybridization of the dam removal practice to help improve upon fish passage efficiency.  While the placement of rock as new in-river grade controls is perceived by some as creating new structures that pose a risk of failure, improvements in engineering practices combined with designs taking into account fish swimming performance and behaviors are being applied in the construction of nature-like fishways.  A number of nature-like fishways have been completed in the Northeast over the last 5+ years some of which passage performance has been documented and evaluated.  Conversely, more of these sites are still under review and evaluation, and some completed projects have provided valuable learning experiences for improving upon designs for both project sustainability and fish passage efficiency. This presentation will summarize the nature-like fishway projects in the Northeast in which NOAA’s Restoration Center has been involved through funding and technical assistance.  Discussion will focus on several Northeast projects that should help to serve as examples in improving on design practices for increasing diadromous fish passage efficiency at nature-like fishway sites. These learning experiences are being applied in the development of an East Coast diadromous fish passage manual that when released, is expected to serve restoration practitioners as a valuable source for passage design criteria and engineering practices for nature-like fishway construction and performance monitoring.