Smart Baffles to Assist Upstream Culvert Passage of Small-Bodied Fish

Current culvert designs are very similar to ancient designs. Some recognition of the ecological impact of culverts on natural streams and rivers led to changes in culvert design guidelines, too often associated with un-economical design recommendations. A simple triangular baffle system, developed at the University of Queensland, may assist upstream passage of small body-mass fish in box culvert structures on very flat bed slope, while inducing little reduction in discharge capacity at design flow conditions and creating sizeable slow flow regions in less-than-design flow conditions. The system was tested systematically in a near-full-scale physical facility, 0.5 m wide and 12 m long. The present investigation delivered a detailed characterisation of the flow field in smooth and triangular baffle channels, at a scale comparable to a small standard box culvert barrel. Tests showed that small-bodied fish preferred to swim in slow-velocity regions, typically in the baffle corner. To be most effective, the corner baffle size had to be comparable with the fish dimensions, while strong flow reversal had to be avoided, since it might confuse fish attempting upstream passage. Finally, design guidelines of fish-friendly culverts must be rethought, with a focus on fish passage for less-than-design flows and maximum discharge capacity at design flow