Hydroturbine Pressure Change Scenarios Affecting Passage and Survival of Juvenile Salmonids at Lower Columbia and Snake River Dams

Barotrauma caused by rapid decompression during hydroturbine passage may occur as fish move from acclimated pressure depth prior to turbine passage through the low pressure region (nadir pressure) below the turbine runner. The US Army Corps of Engineers and Battelle released Sensor Fish into lower Columbia River hydroturbines to determine the magnitude and rate of pressure change fish might experience. Recorded pressures were simulated in laboratory studies to determine the affect of rapid decompression on tagged and untagged juvenile Chinook salmon. The natural log (ln) ratios of acclimation pressure and nadir pressure (LRP) have been reported at ≥2 as a worst-case scenario predicting ≥95% probability of mortal injury for study fish surgically implanted with acoustic tags. The predicted mortality of untagged cohorts was ~20% less.  However, sensor fish data indicated a lower average LRP (~0.22) for turbine passed fish (acclimation depth 15 ft) predicting mortality from barotrauma of ~≤5% for tagged and ~≤1% for untagged cohorts. The US Army Corps of Engineers continues to address barotrauma and the associated effects of tag burden by developing new hydroturbines designed with higher nadir pressure criteria and improving test methods to evaluate performance of both existing and newly designed hydroturbines.