INNOVATION January-February 2022

F E A T U R E

mechanisms of what we understood from historical records. Van der Eerden said that future extreme weather events are hard to predict because they’re not part of the historical data, “So applying statistical analysis to the historical record is becoming increasingly less valid,” he said. Van der Eerden and Kennedy are referring to a standard metric for extreme events—return periods. The water resources community is moving away from this term because of how the public often misinterprets the idea. For example, if this event was a 200-year flood, it isn’t true that it won’t recur for another 200 years—it means that there’s a 0.5 percent probability it will happen in any year—known as the annual exceedance probability (AEP). The AEP is also changing with a non-stationary climate. “We’ve often looked at annual exceedance probabilities on a singular basis—one event, one storm, one critical issue,” said van der Eerden. But what about when they compound?” For example, combining wet antecedent

vulnerability of our infrastructure, it also highlighted the resiliency of British Columbians. Many others joined the effort to protect the province from further damage: neighbours helped pull drowning livestock to safety, communities organized sandbagging efforts, and more than 150 volunteers worked tirelessly to save the Barrowtown Pump Station in Abbotsford. One of the most expensive disasters in Canadian history—a disaster that took six lives—leaves us with the lingering, uncomfortable knowledge that our infrastructure resilience and transportation redundancies proved to be no match for extreme weather events. What can we learn from this? HISTORICAL STATISTICS VERSUS MODELLING THE FUTURE Van der Eerden said atmospheric rivers are increasing in frequency and intensity, targeting the west coast of North America. Climate change—a leading suspect in the root cause of intensifying weather events—is altering the fundamental Associated Engineering offers specialized advisory services in emergency response and community resilience planning. In our approach, we collaborate with clients to create sustainable and resilient solutions that shape a better future for us all. We are hiring in our BC offices and across Canada. For more information, visit our website for details on our currently available career opportunities.

conditions with heavy precipitation and rapidly rising temperatures (contributing to snowmelt) can lead to extreme runoff. Kennedy agreed: we know with a high level of confidence that temperatures are going up at a given rate, but how that translates to rainfall, wind and snow, we know with less confidence. Compound events, like these events in BC, make this confidence decrease even further. Because of the cascading impacts of these compound events, “there is not a singular scenario that could result in this type of impact and the combination of events could be extensive,” Paré said. With a non-stationary climate, we can’t simply look at historical records to determine AEP. We must turn to climatological, hydrological and hydraulic modelling. Paré works with climate scientists “to determine what are representative climate indicators for typical design criteria and how we should apply the models that they run to get the indicators to help us inform design.” OVERWHELMED INFRASTRUCTURE The dikes and highways that failed were built to the standards of the day. “The Coquihalla Highway was built to a very good engineering standard, especially for the mid-1980s,” said Kennedy. But we can improve highway and bridge standards: railway companies often support their bridge abutments on piles so they don’t fail as easily from scour, hence rail lines were able to reopen quickly. Van der Eerden added that the overtopping dike breach in the Sumas Prairie was a result of the volume of water the system had to deal with. Neil Peters, P.Eng., of Northwest Hydraulic Consultants, agreed: the primary problem with the dike was that it was just overwhelmed. Older standards can be problematic given our new climate conditions. Peters said the Fraser River dikes were generally

Crews work to repair sites near the Othello Interchange on Highway 5. P HoTo : m INISTRy of T RANSPoRTATIoN AND I NfRASTRUCTURE ( flICkR . Com / PHoToS / TRANBC /)

Paré, who works across Canada, said that BC is off to a good start. “In their approach to looking at how to incorporate climate change into design, engineers and geoscientists in BC are

future preparedness: How do we prevent this from happening again? How do we mitigate risks to public safety in our professional practice? How do we design and build for a non-stationary climate?

built to design levels established in 1969, without the benefit of computer modelling or climate change projections. Monica Mannerström, P.Eng., also of Northwest Hydraulic Consultants, has extensive experience with flood modelling and mapping of the Fraser River. “We could view this Abbotsford flooding as a mini, confined Fraser River flood,” she said. “We saw a limited portion of the floodplain underwater, but in a Fraser event the entire floodplain, from Hope to the ocean, could be affected. We saw some supply chain problems during the Nooksack/Sumas flooding and I think those would be much worse in a Fraser event.” Peters estimates that a Fraser River flood could be ten times as severe as the event this fall, and Mannerström and Peters agree that more preparedness is needed to protect the floodplain from future disaster. BUILDING FOR FUTURE RESILIENCE Engineers and geoscientists are now helping to answer questions about

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