Ecohydraulics of Culvert Fish Passage

Fish passage through culverts has been addressed through various strategies, ranging from empirical approximations to ecohydraulic studies, which integrate ecological, biological and habitat needs, as well as fish abilities and behaviour with hydraulics, hydrology and morphodynamics.  Maximum scour, appropriate culvert invert placement or tailwater weirs or fishways may address outlet drops and low depths.  Optimum hydraulic conditions within the barrel or at the inlet, depend on how well-matched the swimming ability and behaviour of different species and sizes are with velocity and turbulence distributions within a culvert.  Mitigation strategies, which need to be compatible with river and stream morphodynamics, include: a) stream simulation, as it was pioneered in the late 1970s for Liard Highway crossings (i.e. maintaining average stream slope and width within a culvert) or more recent nature-like designs; b) using oversized culverts which are embedded with or without a natural; or c) installing several types of vanes, baffles or fishways.  Field and laboratory studies on hydraulics and swimming performance have contributed to improved understanding of fish passage effectiveness.  Proper interpretation of such study results and more focused ecohydraulic studies are key to advancing effective culvert fish passage mitigation measures.