PNNL

Abstract

Knowing the likelihood and severity of physical stress experienced by migrating fish through different types of hydropower turbines can help optimise technologies and drive better outcomes for fish passage. This paper assesses the hydraulic conditions experienced through three different low-head turbines, taken in situ using an autonomous sensor: a VLH turbine at high and low power, a screw turbine at high and low power, and a horizontal Kaplan turbine. A total of 127 Sensor Fish deployments were undertaken across all three turbines, from which 82 valid datasets were retrieved. Decompression was rare at the VLH and screw turbines and typically never fell more than 10 kPa below atmospheric pressure. In comparison, the horizontal Kaplan was capable of generating sub-atmospheric pressures as low as 55.5 kPa (approximately 45 kPa below atmospheric pressure), over shorter periods of time, at the turbine blades. Therefore, severer ratios of pressure changes (previously shown to cause injury) could be expected for both surface and depth acclimated fish at the horizontal Kaplan when compared to the VLH and screw turbines. Strike was another possible source of fish injury (detected in 69-100% of sensor deployments), and although strike severity was highest at the Kaplan, strike was more likely to be encountered at the screw and VLH than the Kaplan turbine. Shear appears less of a concern, only occurring near the blades of the horizontal Kaplan and not at severe levels. The results demonstrate that low-head hydropower facilities are not without their risks for downstream migrating fish. Potential ways of reducing fish passage risks are recommended for further investigated: such as reducing the likelihood of strike by minimising structures near the tailrace entry of screw turbines or operating the VLH turbine at higher powers with greater runner blade openings.