Modeling debris flows to mitigate hazards in mountainous terrain for pipeline construction

Debris Flow Hazard Mitigation for the Trans Mountain Expansion Project

Toward the end of construction of the 1,150-kilometre (715-mile) Trans Mountain Expansion Project pipeline, Trans Mountain had to decide whether to demobilize crews or keep them onsite to mitigate any potential debris flow hazards at newly constructed riser stations. On short notice and up against tight deadlines, they engaged our geohazard team to complete a debris flow hazard assessment and guide any necessary mitigation efforts.

We combined detailed debris flow models in DebrisFlow Predictor software with our novel area-based probability-intensity curves, which relate rainfall intensity to the likelihood of debris flow initiation. This allowed us to produce a high-resolution—5-metre (16-foot) spatial, 1-centimetre (0.4-inch) vertical scale—hazard map showing debris flow inundation footprints under a wide variety of rainfall scenarios that might occur over the structures’ 50-year design life. We also incorporated drone-captured imagery and climate change scenarios to support the results.

The assessment revealed that both design and construction of the riser pads made them self-mitigating during any potential hazard events. Trans Mountain