GEOHAZARD ASSESSMENT AND MAPPING OF A BEAVER DAM OUTBURST FLOOD AND PIPELINE EXPOSURE

Geohazard mapping and analyses along linear infrastructure is a vital to maintaining supply lines, protecting the environment and communities, and risk management. An exposed pipeline was discovered in 2020 on an unnamed creek northwest of Edson, Alberta. A depth of cover (DOC) survey and subsequent analysis of the residual hazards (if any) and high-level recommendations for the protection of the pipe were conducted. The unnamed creek drains an 11-ha lake into Lynx Creek, and ultimately into the Athabasca River. Lynx Creek is inhabited by brook trout, rainbow trout, mountain whitefish, long nose sucker, white sucker, burbot, long nose, dace, among other macro- and micro-invertebrates.

Reconnaissance mapping of the area identified multiple failed beaver dams upstream of the pipeline exposure. The beaver dams appeared to have failed in sequence producing a debris flood that deeply incised (caused considerable erosion to) the channel downstream, including the channel crossing above the pipeline. A pipeline inspection identified a significant dent as the pipeline had been within the mobile bed of the debris flood. In addition, a beaver dam was still holding back an estimated 330,000 m³ of water from a lake upstream of the pipeline. The beaver dam was beginning to erode and there was a high likelihood of another significant debris flood at this pipeline crossing. Several mitigation options were provided to the pipeline company based on experience and mapped conditions at the site. The geohazard assessment and mapping provide a clear understanding of the cause of the pipeline exposure and highlight the potential of an ongoing outburst flood hazard.