Juvenile alwife passing through Natel Energy’s Restoration Hydro Turbine had a 98.2% immediate and 100% delayed survival rate, a new study published in the North American Journal of Fisheries Management shows. The results support the equally positive results of additional scientific studies Natel has conducted with third-party scientific partners on fish survival through its turbine technology.
Commonly known as shad or river herring, alewife are an anadromous species native to the east coast of North America. Alewife are born in freshwater habitats and then migrate downstream as juveniles to spend their adult lives in the ocean. Like many other types of fish on the Atlantic coast, a single alewife might encounter multiple hydropower sites as it attempts to migrate from the river to the ocean.
Current best practice for managing downstream passage of fish through hydropower sites is fish exclusion, usually with screens, and directing them around the turbines, often toward a dedicated bypass. Exclusion methods, are sometimes inadequate and many fish, particularly juvenile fish, are able to pass through even fine screens, and enter turbines. Approximately 1 in 5 fish die when passing through a conventional hydropower turbine, said Natel.
Natel’s alewife study was designed to quantify the survival rate of juvenile fish through a novel hydro turbine specifically designed for safe fish passage. The study was conducted in 2021 with Kleinschmidt Associates at the Freedom Falls Hydropower Project, a small, 35kW plant located at a refurbished historical mill dam on Sandy Stream.
Natel Energy engineers release juvenile alewives (herring) into the mouth of the penstock through a turbine injector temporarily installed at the Freedom Falls Hydro Plant. The fish will pass from here through the Restoration Hydro Turbine
For the test, 484 alewives (Alosa pseudoharengus) measuring 87-132mm (3-5 in) in length were used. The fish were passed through a .55 m (1.8ft) Natel Restoration Hydro Turbine (RHT).
“The results of this study underscore the opportunity this new turbine technology presents to all those involved in hydropower, including regulators, operators and non-governmental organizations,” said Natel co-founder and Chief Technology Officer Abe Schneider. “We’re confident that we can continue to invest in the immense renewable benefits of hydropower in a way that does not compromise the preservation and well-being of aquatic life through the use of fish-safe turbine technology.”
The RHT’s design is distinct from a conventional hydro turbine in four major ways, each of which is designed to reduce the likelihood that a fish will be struck by a turbine blade and/or to reduce the likelihood that fish impacted by the blade will be harmed. First, the RHT’s runner blades have very thick leading edges, and there are fewer blades than in a conventional turbine. The RHT’s runner blades are also swept forward from the hub to the tips, in order to direct the fish to pass through the turbine closer to the hub, where blade speeds are lower. Finally, the RHT has a minimal gap between the runner and turbine housing, eliminating the risk of fish being caught between the runner and the housing.
The results of the juvenile alewife study are reinforced by the results of additional scientific studies Natel has conducted with third-party scientific partners, including the Pacific Northwest National Laboratory and Alden Laboratory. The parallel studies affirm an average of greater than 99% safe passage of other fish species, sizes, and life stages, including American eel and rainbow trout, through the fish-safe Restoration Hydro Turbine.