Through funding made available by the U.S. Department of Energy, Alden conducted a series of studies to evaluate and optimize the design and operation of two modular and scalable fish bypass systems developed specifically to provide safe downstream passage of silver American Eels at hydropower projects. The goal of the studies was to address the need for biologically effective and less expensive downstream fish passage technologies for silver eels. The studies were developed specifically for this fish species and life stage due to population declines in many areas of its range and the potential for mortality to occur if eels migrating to the marine environment to spawn are entrained through hydro turbines during their journey to the sea. The large size and unique behaviors of silver eels have made it difficult for dam owners to implement downstream passage measures that are both biologically and cost effective, resulting in a need for new innovative technologies.

The studies conducted by Alden included a laboratory evaluation of the biological performance of the two bypass systems, a field evaluation of biological performance conducted with full-scale bypass systems installed at the intake of a small hydro project in New Hampshire, CFD modeling of the laboratory flume and field evaluation site, and a desktop assessment of the potential for application of each technology at hydro projects within the known range of American Eel and the expected benefits (i.e., biological and economic). Few organizations have the capabilities to conduct this array of technical studies, but Alden’s scientists and engineers have been using various combinations of these approaches and methods to develop and evaluate state-of-the-art fish passage and protection systems for nearly 50 years.

Assistance with the performance and completion of these studies was provided by Lakeside Engineering (bypass design and installation) and Blue Leaf Environmental (DIDSON acoustic camera and 3D acoustic telemetry services).


Evaluation of bypass performance with silver eels happened in both controlled laboratory settings and at a small hydro project to determine the bypass efficiency and behavioral responses, so as to optimize design and operation of the bypass systems.

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