A deteriorated concrete box culvert conveying a tributary of the Saugeen River under Highway 21 in Ontario had reached the end of its lifespan and was in need of replacement. The tributary supports a diverse range of coldwater fish species such as Rainbow Trout; however, fish passage, particularly upstream migration, has been cut off since the culvert and highway were constructed over seventy-five years ago. Specifically, fish passage has been hindered by shallow sheet flow along the sixty metre flat bottom, excessive velocities associated with the smooth, seven percent gradient, and a perched barrier at the downstream outlet. A key component of the culvert replacement was an effort to improve the overall condition of the tributary’s natural environment, including the promotion of fish passage and migration opportunities. The culvert replacement project undertaken by the Ontario Ministry of Transportation (MTO) and MMM Group, coupled resources with the Saugeen Ojibway Nation (SON) Environment office, Parsons biologists, and Aquafor geomorphologists. The most ecologically sensitive replacement methodology of an open bottom structure was not viable for this project as it would have required a full closure of the Highway for approximately four months. A circular steel pipe culvert installed through tunneling was designed to by-pass and replace the existing concrete box culvert. In an effort to mitigate the current barriers to fish with the new pipe culvert, a prefabricated corrugated steel slip liner with engineered baffle arrangement was integrated into the design. The baffle configuration and geometry was designed by Jason Duguay (Université de Sherbrooke) and Ken Hannaford (Gov. NFLD), and the slip liner construction by the Corrugated Steel Pipe Institute. Construction of the new culvert and slip liner was completed in December, 2015, and a two year monitoring program will be undertaken to assess the effectiveness of barrier mitigation and geomorphic stability of the tributary
