Baffle design to facilitate fish passage through culverts
A common obstruction to fish movements is high water velocity i.e., fast flowing water, through culverts.
When the speed of the water exceeds the speed that fish can swim, fish are unable to pass. One way to reduce water velocity in culverts and provide resting areas is to install baffles inside the culvert. Our work has shown that baffle design and layout is important for optimising the number of native fish that can pass through a culvert (Stevenson et al 2008; Feurich et al 2011; Feurich et al 2012). Based on our investigations so far, our recommendation is to use staggered rectangular spoiler baffles (Figure 3a), rather than weir type baffles (Figure 3b), to facilitate the passage of native fish species through culverts. Spoiler baffles based on this design have now been installed at a number of sites around New Zealand and in Australia (see case study below for one example).
Figure 1A: Examples of spoiler baffles with a continuous pathway along the base of the culvert. [Jacques Boubée]
Figure 1B: Example of weir baffles which can act like multiple mini barriers through a culvert. [Cindy Baker]