Concurrent Sessions D: Fish Passage Around the World - Effect of Unsteady Flow on Downstream Behaviour and Passage of the European Eel and Iberian Barbell Over a Spillway

The behavioural response of downstream moving European eel and Iberian barbel to unsteady flow created by standard WES ogee spillways with upstream face inclinations of ? = 90º (standard) and ? =45º and 30º (modified geometry) were studied. Detailed velocity measurements made using particle image velocimetry (PIV) and acoustic Doppler velocimetry (ADV) at the upstream end and over the spillway in the stream wise-wall-normal plane were used to characterize flow and link fish behaviour with local hydrodynamic variables. A distinct recirculation pattern was found upstream of the 90º spillway, which was not observed in the other two spillways. This recirculation area seemed to have a strong impact on individuals of both species. Fish exhibited strong avoidance behaviour to turbulence as well as to rapid changes in flow velocity, in particular Iberian barbel. Interspecific variations on behaviour were evident. Eel moved downstream and passed the spillway headfirst. They were predominantly thigmotactic exhibiting a more structure–oriented behaviour and responded after physical contact with the spillway. Barbel moved downstream head?rstbut switched orientation at points of rapid velocity variation and passed over the spillway tail first without contacting the structure. Geometry-related differences were found for the eel, which exhibited the highest rates of passage success in experiments conducted with upstream inclinations of ? = 45º and 30º, and the greatest times of passage and resident times when tested under spillway designs of ? = 90º. Overall European eel had a higher passage success (80%) when compared to Iberian barbel (32%) which spent more time in the test section and took longer to pass the spillway. Results indicate that the design of spillways and associated hydrodynamics strongly impact downstream movements of these two species which have distinct biomechanical capabilities and behaviour. The observed reduction of delay time before passage and the highest passage success rates for the modified spillways suggest that these facilitate appropriate timing of migration and enhance passage survival. Results may have direct application for spillway design to improve survival rates for these and other fish species, as well as other aquatic biota. Future tests should expand this work across species, life stage and body morphology.
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