Trenched Crossing Techniques in Pipeline Construction: Case Studies of Watercourse Crossings That Demonstrate the Resilience of Natural Systems

Trenched crossing techniques are commonly employed for the installation of pipelines at waterbody crossings. These techniques can be invasive to waterbodies with instream activity lasting upwards of several weeks depending on the size of waterbody and the level of difficulty associated with the surrounding landscape. Success in conserving the long-term health of a waterbody at the crossing location and downstream hinges on proper mitigative and restorative procedures while insufficient restorative measures can lead to acute and chronic detrimental effects at the crossing location and further downstream.

To evaluate the long-term success of open-cut crossing techniques, case studies are provided describing the crossing of fish-bearing watercourses ranging in size from 1m³/s to greater than 100m³/s. Post-construction conditions at each watercourse crossing were identified in Environmental As-built reports. Restorative efforts were reviewed in annual post-construction monitoring reports for the five years after project completion. These monitoring efforts indicated that these systems recovered to pre-construction conditions within the five year monitoring period, demonstrating the resilience of natural systems when proper restorative and mitigative procedures have been implemented.