INNOVATION January-February 2022

F E A T U R E

L andslide activity during the storm predominantly took the form of debris slides, debris flows, and debris floods. Many landslide events impacted highways, railways, and pipelines. Surging river flows, channel realignments, and erosional avulsions further impacted highways and pipelines. Catastrophic flooding subsequently devastated numerous rural communities, as well as the town of Princeton, the city of Merritt, and the Sumas Prairie landform Debris flows are a particularly dangerous type of landslide that occur in steep gully systems and creek channels. Inputs to a debris flow risk assessment include the probability an event initiating, and the probability that it impacts a stakeholder point of interest on the hillslope or valley floor below. The size or volume of a debris flow tends to increase, often quite significantly, due to net entrainment of soil, rock, and organic material along its travel path. The onset of deposition is typically controlled by a change in slope gradient and loss of gully confinement. Where the infrastructure of multiple stakeholders is located in close proximity along a narrow corridor, each with associated modification to the original slope profile, the end of a debris flow travel path may finish with more than one depositional impact. While their channelized nature makes it possible to identify specific creeks where they may occur, debris flows can sometimes jump out of their channel and take new paths, presenting challenges for site-specific risk assessment and mitigation design in transportation and utility corridors. Significant experience was gained in BC with the design and construction of large debris flow protection structures in the 1980s following a series of damaging debris that is part of the Fraser Lowland. DANGEROUS DEBRIS FLOWS

flows along the Sea-to-Sky corridor. However, these types of structures are very expensive, so for them to be effective within a given jurisdiction or infrastructure network, prioritization of high-risk sites is necessary. Consideration of complementary or alternative mitigation options, including warning systems, is often warranted to make the best possible use of available funding. Research is underway around the world to help inform these types of decisions. Advances in field and remote mapping methods, including the use of drones and topographic change detection techniques, are improving the accuracy of debris flow volume estimates and helping to identify patterns in debris flow deposition. Physical and numerical models, along with field monitoring at well known debris flow sites, are improving the understanding of debris flow dynamics and the accuracy of flow velocity, depth and impact pressure estimates. In spite of these significant technical advances, several key challenges remain, including a lack of broadly applicable guidance for practitioners on tolerable levels of landslide safety in BC, and coordination between multiple stakeholders who occupy the same infrastructure corridor. PIPELINE IMPACTS There are a number of buried pipeline networks (e.g., oil, gas, water, etc.) that traverse the areas affected by the November 2021 floods. Some parts of the Trans Mountain oil pipeline were exposed due to soil scour and slope instability during the rainfall, and with further impacts from debris flows and flood waters. Based on the information available from Trans Mountain, the impacts were mainly in the way of coating damages and external dents with no pipeline failure leading to loss of pressure integrity. The pipeline service was initially subjected to a precautionary shutdown and, after engineering

methods, monitoring ground movements, and assessing pipeline performance. Another important aspect is emergency response—typically, the pipeline owners have comprehensive plans in this regard for communication controls, workforce coordination, etc., to conduct initial surveys and implementation of response actions. Mitigation against anticipated hazards is another important consideration in protecting pipelines, and typical mitigation principles include isolation from the hazard, design to tolerate the hazard, elimination of the hazard, and relocation from the hazard. FLOOD-GENERATION MECHANISMS Several factors conspired to contribute to the magnitude and impact of the floods. A very large input of atmospheric moisture flowing over the Coast Mountains landscape led to high intensity precipitation. The November atmospheric river event was not only large in magnitude, but remained focused on the southwestern region of BC for a relatively long duration of several days.

inspections followed by restoration of soil cover protection and pipeline repairs by the company, it was brought back to operation in the early part of December. The most prominent natural hazards to buried pipelines arise from soil forces due to permanent ground movements and loads imparted on exposed pipelines from rapid water flows and run-away debris. As past experience has indicated, these loadings could lead to undesirable coating damage, dents, excessive deformations/strain on pipelines leading to failure; damage to pipeline corrosion protection systems is another concern. The quantification of complex “demands” from natural hazards on pipelines is a key challenge, and guidelines of the Pipeline Research Council International have served well in assisting engineers to assess the performance and securing the integrity of pipelines subjected to these hazards; in particular, the guidelines provide pipeline integrity management strategies with respect to quantifying hazards, mitigation

Aerial view (looking southeast) of debris flows near Mount Cheam, near Chilliwack, BC, showing multiple impacts in the same corridor, including a railway, highway, hydroelectric transmission line and pipeline. P HoTo : J oSHUA N ICHolAS

KCB is pleased to announce the appointments of Ryan Douglas, P.Eng., P.E., as the firm’s new President and Simon Douglas, P.Eng., as Vice President of Power and Transportation.

Norton Rose Fulbright is grateful for the invaluable work of the Canadian Red Cross. Our firm has donated to the British Columbia Floods and Extreme Weather Appeal and remains committed to supporting ongoing recovery efforts. Our thoughts are with all those affected by the floods. Law around the world nortonrosefulbright.com

“Since joining KCB I have first and foremost been proud to represent this company, which has such a rich history and culture. I have approached all the opportunities I have been offered with my full commitment and energy, and this appointment will be no different.” Ryan Douglas, P.Eng., P.E. President

Simon Douglas, P.Eng. Vice President, Power and Transportation

“Being appointed to lead the Power and Transportation Business Unit at our illustrious company is a true honour and privilege, and something that I am both grateful and tremendously excited to be taking on. I look forward to working with our dynamic team and moving the group forward.”

Engineering, Geoscience and Environmental Services

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