LAUSR

Abstract Siphon turbines are an attractive type of small-scale hydropower turbines because they can be retrofitted into existing structures where there is already a drop in water elevation. A siphon turbine conveys water from an upper reservoir to a lower reservoir through the use of a siphon structure that goes over the top of the dam. A small, neutrally buoyant autonomous sensor package known as a Sensor Fish was deployed through a siphon turbine at the Head of the U Hydroelectric Project in Idaho, USA. Comparisons were made between the siphon turbine in this study and other low-head turbines that have been studied using Sensor Fish. The Sensor Fish measurements indicate that this siphon turbine can generate nadir (i.e., minimum) pressures during runner passage of 22.4 kPaA, which is much lower than those of other low-head turbine types that have been studied using Sensor Fish and could be potentially harmful to fish species susceptible to barotrauma injury. Severe acceleration events occurred in the wicket gate and runner regions at rates of 12% and 47% respectively. These numbers are comparable or lower than other low-head turbines that have been studied with Sensor Fish. Due to the low nadir pressures measured, stakeholders should determine the presence of any fish species-of-concern in the area that are susceptible to barotrauma, and if so, methods to avoid or reduce fish entrainment such as screening technologies or diversions should be investigated.