Fish Passage Hydrodynamics: Validation of an At-Scale Experimental Facility for Ethohydraulic Studies of Small-Bodied Fish in Culverts

This paper introduces a new experimental setup for ethohydraulic research at the University of Auckland, specifically studying the interaction between hydrodynamics and fish behavior. Many countries, particularly island nations, are home to diadromous fish species that migrate from marine into riverine ecosystems at an early life stage. On their journey upstream fish can encounter various man-made obstacles, of which culverts are one of the most prevalent. As the number of existing culverts is too high to afford reconstruction of all barriers in the short term, remediation presents itself as a more efficient alternative. However, reconciling remediation with the passage requirements for small-bodied fish is challenging. Current best practices focus on averaged parameters, such as fish swimming endurance or average water velocities in the culvert cross-section. This approach disregards the individual capabilities of fish to deal with turbulence. To understand the interplay of fish locomotion with small-scale flow features in a controlled and replicable manner, an experimental facility to simulate culverts with various design features and discharge rates is presented. We describe the experimental design, validation methods and measurement techniques to be applied. The at-scale design is aimed at complementing field studies, ensuring comparability to large-scale prototypes. Use of parallel setups of, for example, culvert designs within the same flume, is discussed with respect to entrance efficiency as an important aspect of fish passage. Results obtained will inform passage guidelines for small-bodied fish, giving consideration to turbulence effects that can benefit or destabilize fish swimming, and utilization of small-scale low-velocity zones.