Ventilated Corner Baffles to Assist Upstream Passage of Small-Bodied Fish in Box Culverts

Abstract

Standard box-culvert designs are similar to ancient designs. The acknowledgment of the ecological impact of culverts and road crossings on rivers has led to changes in culvert design guidelines. A small triangular corner baffle system was tested to assist upstream passage of small body-mass fish in box-culvert structures on a flat bed slope. The study was conducted in a near full–scale physical facility, which had a width of 0.5 m and a length of 12 m. The investigation presented a detailed characterization of the flow field. Tests showed that small-bodied fish preferred to swim in slow-velocity regions (i.e., in the baffles’ corner). The most effective baffles had heights comparable to fish length. A key outcome of the study is the adverse impact of strong flow reversal on small-bodied fish, because strong flow reversal may confuse small-bodied fish attempting upstream culvert passage. A remedial measure is the ventilation of baffles, tested successfully herein.