Restoring connectivity: A comparative analysis of culvert barrier remediation techniques in British Columbia

Objective Barrier culverts are one of the leading anthropogenic causes of stream fragmentation globally and a frequent target of restoration efforts. In British Columbia (B.C.), an estimated 92,000 culverts act as barriers to fish passage. Since 2008, two techniques (retrofits and replacements) have been used to remediate fish passage at approximately 200 barrier culverts in B.C. The retrofit technique involves leaving the culvert in place and installing baffles and/or weirs, whereas replacements involve removing the culvert and replacing it with an open-bottom structure. Rarely has the efficacy of these techniques or their compliance with best practices been evaluated. Methods We performed a posttreatment audit of culvert barrier remediations in B.C. through an examination of the current physical attributes at 15 retrofit and 15 replacement sites and scored the sites based on the B.C. culvert fish-passage assessment procedure and on best practice guidelines for stream crossings in B.C. Results We found that 80% of retrofits and 13% of replacements were classified as barriers based on the B.C. culvert fish-passage assessment. The sites that were classified as passable were shorter and did not constrict the stream relative to those classified as barriers. The retrofits did not meet the standards for best practices for remediating barrier culverts. The replacements aligned more with best practices, but improvements are needed to ensure that the structure span exceeds bank-full width and that natural stream morphology is maintained. Conclusions Although less expensive, the failure rates of retrofit remediations indicate that they should only be used as a stop gap or emergency technique until a replacement can be performed. Furthermore, our finding of continued noncompliance with best practices in B.C. highlights an issue that is likely affecting culvert remediations and new installations. This study demonstrates the need for rigorous compliance and effectiveness monitoring at future remediations to ensure their immediate and long-term success.