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Hydropower is a valuable renewable energy source, but its effects on the downstream passage of many riverine fish species are not well understood. Turbines that are designed to function as safe downstream passage routes for fish are being developed with the goal of mitigating the effects of hydropower operations on the environment. In this paper, we present the results of a study conducted with the juvenile life stage of the Alewife Alosa pseudoharengus, a major migratory species on the Atlantic coast of North America. The test was conducted at a small hydropower plant located in Freedom, Maine, with a single Restoration Hydro Turbine (RHT) operating under 7.5 m of gross head. Groups of 140-170 fish were released into the intake of a 55-cm-diameter RHT and were recaptured with a specialized trap at the turbine discharge outlet. The combined immediate and 48-h survival rates (AE95% CI) for all treatments, corrected for control mortality, were 98.2 AE 2.0% and 100.0 AE 6.6%, respectively. The passage of Alewives through the runner region of the turbine was also captured with high-speed video. The results of the study demonstrate that the RHT, which is designed for fish safety, is an effective way to pass juvenile alosines downstream at hydropower facilities.

Objective: Study the effects of downstream passage through a novel turbine designed for fish safety, the Restoration Hydro Turbine (RHT), on American Eels Anguilla rostrata in a recirculating turbine test facility.Methods: A 55-cm-diameter RHT was operated under 10 m of hydraulic head and 667 revolutions/min. In total, 131 eels were passed through the turbine and 43 eels were used as experimental controls (length = 33.9-65.5 cm). High-speed video of passage through the runner region was captured for 89% of turbine-passed eels, and injury and behavioral effects were recorded immediately before and after passage, as well as after a 48-h holding period. A subset of 37 eels was additionally examined with X-ray imaging for internal injuries. Result:The 48-h survival rate for both treatment and control groups was 100%, with no major internal or external injuries present after the holding period. Conclusion:This is a substantial improvement over eel survival rates through conventional Kaplan and Francis turbines, which may range from 40% to 95%, and suggests that hydropower turbines designed for safe downstream fish passage could be implemented without major impacts to eels.

Deployment of small-scale hydropower, which generally ranges in capacity from 1-10 MW, may partly depend on its ability to mitigate environmental concerns while generating sufficient revenues. In this paper, we quantify net revenue and downstream flow impact trade-offs of a cascading series of 36 small-scale hydropower facilities under consideration for development in Northeast California. To do so, we develop a net-revenue-maximizing optimization model that determines hydropower operations while capturing key technical and river network constraints. We find that significantly constraining maximum discharges from each facility largely eliminates downstream flow impacts but negligibly changes the 36 facilities' combined operations and net revenues. Thus, we find a negligible trade-off between net revenues and downstream impacts in our study system, suggesting small-scale hydropower can contribute to decarbonization efforts while limiting local environmental impacts on downstream flows at little economic cost.

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