Laboratory Study of Fish Passage and Discharge Capacity in Slip-Lined, Baffled Culverts

Culvert rehabilitation is a cost-effective alternative to culvert replacement for many applications where the culvert has reached the end of its useful life. When a profile-walled existing (host) culvert is relined with a smooth-walled pipe, the culvert flow velocities typically increase, the corresponding flow depths decrease, and the resulting flow conditions can create a potential barrier to fish passage. In an effort to provide some baseline data for fish passage through baffled culvert liners, fish passage behaviors of wild brown trout through prototype-scale 0.61-m-diameter, 18-m-long smooth-walled baffled and nonbaffled culverts were observed in the laboratory under a variety of culvert slopes and discharges. The baffles significantly increased the range of culvert slopes and discharges over which the fish could successfully pass. The baffled culvert hydraulic roughness coefficient (Manning’s n) increased 274% (approximately equivalent to corrugated metal pipe values) relative to the nonbaffled culvert.