Fish passage design for Southern Hemisphere small-bodied fish: Hydrodynamic and behavioural assessment using spoiler baffles
This research aims to enhance our understanding of the behaviour of two Southern-Hemisphere small-bodied species, Galaxias maculatus and Galaxias brevipinnis, during their upstream passage through spoiler baffles. The comparative behavioural assessment, together with the measured hydrodynamic information, is used to assess three different arrangements of spoiler baffles. The primary objective is to identify the baffle arrangement that can potentially be used as fish passage solution for future remediation of culverts. To achieve this, at first, a framework has been established to measure and quantify fish behavioural information in a highly heterogenous turbulent flow. The required turbulent flow is generated using three different arrangements of spoiler baffle, known as a patch. A ventral view of fish movement while swimming upstream through these patches is then recorded using two synchronized cameras. A high-frequency flow measurement using an acoustic Doppler velocimeter (ADV) at grid spacing of 5 × 4 cm along the streamwise and lateral direction provided a small-scale hydrodynamic characteristic for each patch. Flow parameters such as velocities, turbulent kinetic energy, Reynolds stress and dimensionless hydraulic drag function are calculated. A novel workflow developed using a recently released machine learning-based tracking tool, and triangulation tool allowed automatic tracking and transformation of fish coordinates. Swimming and resting locations in all three patches were delineated and overlaid with hydrodynamic information to calculate the fish's likelihood to swim and rest at locations with different magnitudes of hydrodynamic variables. The observed behaviour indicates both the species prefer to swim at locations with velocity near to the G. maculatus sustained swimming speed and rest at a location with minimum streamwise velocity. Furthermore, analysis on behavioural rule indicated both the species prefer a pathway that follows the location with similar streamwise velocity. Further assessment of the baffle patch based on the extent of locations with preferred hydrodynamic ranges indicated the arrangement consisting of a smaller baffle and medium aerial density would provide the largest proportion of preferred low-velocity zones. This arrangement thus has the potential of being used as a possible alternative to existing solutions.
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