The path to FishSafe™ hydraulic designs at 40 meters of head

July 10, 2023

We designed the first Restoration Hydro Turbine (RHT) blade in early 2019 based on the hypothesis that adding a forward tilt to relatively thick leading edges would allow fish to survive after being struck at much higher speeds than the same thicker blades without any forward tilt. 

We confirmed that hypothesis in blade strike tests at Alden Research Laboratory (also in 2019) and built and installed several reference turbines with RHT blade designs. Over the past four years we’ve used those turbines to conduct fish passage tests on multiple species including American eel,Rainbow trout, and juvenile alewife — all with perfect or near-perfect survival.

Natel FishSafe™️ RHT designs are validated in through-turbine fish passage studies that include high-speed video documentation.

Even as our fish passage studies highlighted the larger potential of RHT designs, we focused on creating a standardized family of fish-safe turbines (with capacities less than 3 MW and with runner diameter less than 2.5 m). These turbines were primarily intended for non-powered dam (NPD) retrofits in the small hydro market. Soon, however, it became clear that the demand for fish-safe turbines extended far beyond NPD retrofits and that our FishSafe™ designs could be applied much more broadly.

Since 2021 we’ve received increasingly-frequent requests to engineer fish-safe turbines to rehabilitate existing hydropower plants. In response we’ve created numerous custom designs ranging from horizontal turbines at only a few meters of head to vertical turbines at greater than 30 meters of head, with runner diameters exceeding 4 meters and power in excess of 40 MW. In delivering on these requests, we’ve honed our capabilities to rapidly generate new runner designs optimized for simultaneous satisfaction of multiple goals, including fish safety, hydraulic efficiency, cavitation resistance, low structural stress, and good manufacturability.

Meeting the market need on a timeline that matters

The speed at which we can install fish-safe turbines is important for the climate, for the fish, and for owners working to meet relicensing requirements. To ensure we can install fish-safe turbines on a timeline that matters and to maximize benefits to our customers, we've begun collaborating with other turbine manufacturers, allowing our industry-leading knowledge in fish-safe runner design to be implemented by familiar and trusted manufacturing organizations.

We’ve also formalized our engineering services for developers and owners. Natel’s industry-leading modeling capabilities are now available to inform decision-making about how best to maintain, retrofit, or upgrade assets. Additionally, we can combine our analysis and modeling tools with scale-model testing at our in-house hydraulic loop to provide a complete picture of hydraulic and environmental performance.

Our onsite hydraulic loop enables fish passage testing and performance testing of scale models.

Interested in working with Natel on fish-safe modeling or design? Please reach out to us at

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