Natel Energy reports that a new study published in the North American Journal of Fisheries Management shows a 98.2% immediate and 100% delayed survival rate for juvenile alewife passing through its Restoration Hydro Turbine (RHT).
Natel said these results support its hypothesis that a modern style of hydro turbine can improve fish survival outcomes without compromising hydraulic efficiency and without the use of screens or bypasses. By using fish-safe turbines, hydropower can combat climate change and reverse biodiversity loss.
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 and migrate downstream as juveniles to spend their adult lives in the ocean. An 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 exclusion — preventing fish from entering the turbines, usually with screens, and directing them around the turbines, often toward a dedicated bypass. However, many fish, particularly juveniles, are able to pass through even fine screens and enter turbines. About one in five fish die when passing through a conventional hydropower turbine. Standard compact turbines have many thin, fast-moving blades that can injure or kill fish, and the environmental benefit that those turbines provide in renewable energy is often offset by the blow they deal to aquatic biodiversity, Natel said.
Natel’s alewife study was designed to quantify the survival rate of juvenile fish through the RHT turbine, specifically designed for safe fish passage. The study was conducted in 2021 with Kleinschmidt Associates at the 35 kW Freedom Falls Hydropower Project located at a refurbished historical mill dam on Sandy Stream. A total of 484 alewives measuring 87 mm to 132 mm (3 in to 5 in) long were used for the test. The fish were passed through a 0.55 m (1.8 ft) Natel 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 ways, Natel said. 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 swept forward from the hub to the tips to direct the fish to pass 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 there.
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 RHT.
