Dam Turbine Design Helps Fish Move Safely Downstream

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Kevin Bunch
american eel

A new turbine design for hydroelectric dams may help improve the survival of fish and other species moving downstream in river systems, according to research conducted by Natel Energy.

Along the transboundary region, there are numerous dams that impact fish passage, such as those on the St. Croix and St. Lawrence rivers. While some of these include fish ladders to allow fish to move upstream, in many cases species are faced with the prospect of trying to make it through spinning blades of hydroelectric turbines to move back downstream. Screens are typically required to filter out larger fish and direct them to other routes, but these aren’t always reliable or fine enough for smaller fish.

While this isn’t a major problem for fish such as the majority of Pacific salmon that only return to the river to spawn before dying, it can impact species such as alewives where spawning adults return downstream and can have a high mortality rate along the way. Others such as American eels grow to adulthood in river systems before heading out to the sea and therefore, as a population, are particularly vulnerable to turbine-related injuries.

IJC Fish Passage Projects

Atlantic salmon, alewives, American eel and shad are among migratory species of interest in the St. Croix watershed, as well as further north in the St. Lawrence River. Recognizing these issues, the IJC’s International St. Croix River Watershed Board has worked on several projects related to fish passage on the river.

In 2018, the board published a report studying the efficiency of fish ladders on the lower St. Croix River; another project developed a tool to model how alewives respond to changes in fish passage conditions.

Most recently, the board published a report in 2021 discussing fish passage improvements on the Grand Falls and Woodland dams and highlighting the most viable alternatives; partner organizations have been working to acquire funds to construct these new passageways. All of these studies were funded through the IJC’s International Watersheds Initiative and involved a range of partners on both sides of the river, from government agencies and local organizations to Indigenous Nations.

In 2019, the California-based hydropower company Natel Energy designed a new propeller-style hydro turbine, called the Restoration Hydro Turbine, to be safer for fish.

Sterling Watson, an engineer with the company, described at the Joint Aquatic Sciences Meeting in 2022 how the new model was based on existing research into survival rates of fish struck by turbine blades and friendlier turbine development, as well as original staff research.

Natel Energy began live fish testing in 2020 with rainbow trout (which are a good stand-in for salmon species more broadly, Watson added) at their hydro plant in Culver, Oregon. Natel followed that with passage tests of American eel at an in-house facility at company headquarters in Alameda, California, as well as another dam location test at Sandy Stream in Freedom, Maine, in 2021 to see how juvenile alewives handled the turbine design.

Watson said survival rates for all three of these target species were strong. The eels had a 100 percent survival rate after going through the turbine; those sent through a second time also had 100 percent survival rates. Watson said the company targeted a 99 percent survival rate for eel due to their specific life cycle.

“This is important because eels, or any fish moving through headwaters, may need to pass through multiple turbines, and that’s been hard to test in the past,” Watson said. “Survival rates through conventional turbines range from 60 percent up to 90 percent for an individual turbine, but again, with repeat eel passage tests, if they have to pass through multiple series of turbines, even 90 percent survival rate per turbine can compound into a larger number.”

Meanwhile, after a 48-hour observation period, the mortality rate of alewives that passed through the turbine was statistically identical to the control group that didn’t pass through, which Watson noted was impressive for a sensitive species. Rainbow trout had similar results.

Additionally, since the Sandy Stream test site was in the wild, several unexpected species made the trip through the turbine, including suckers, crawfish, freshwater mussels, dragonfly larvae, sunfish, black bass and a 40 cm (15.7 inch) eel that managed to squeeze past the screen. In all cases, the aquatic wildlife made it through without mortal injuries or general harm, according to Watson, though she noted this is anecdotal data.

Study results of a laboratory validation test for the novel turbine blade design were published in the Journal of Ecohydraulics, while the study on American eels was published in the scientific journal Transactions of the American Fisheries Society. The study results for alewives have been accepted by the North American Journal of Fisheries Management for publication in 2023.

Aside from the installation in Maine, Watson said the new model turbines have been or are being installed in Oregon, Virginia, Louisiana, Austria and the Democratic Republic of Congo. Discussions are ongoing with Fisheries and Oceans Canada about its usage in hydropower plants there, too. Watson said experts with the US Fish and Wildlife Service, US Geological Survey and the US National Marine Fisheries Service have all been instrumental in these experiments.

kevin bunch
Kevin Bunch

Kevin Bunch is a writer-communications specialist at the IJC’s US Section office in Washington, D.C.