INNOVATION January-February 2022

F E A T U R E B C’s weather in 2021 was extreme. The “heat dome” in June smashed temperature records and was linked to hundreds of deaths. Forest fires destroyed Lytton, along with vegetation across hundreds of hectares of land, creating hydrophobic soil conditions. September and October 2021 brought antecedent moisture to 98 percent of BC soils, even saturating those affected by forest fires. Elise Paré, P.Eng., WSP’s National Practice Lead for Climate Risk and Resilience, drove through the Lower Mainland in November, noting that the ground was already filled with water. “Farmers’ fields were saturated or flooded already, so the runoff from any type of rain event in any kind of significant volume had no place to go,” she said. That was before the massive atmospheric river hit.

John van der Eerden, P.Eng. and Vice President of Water Resources for Associated Engineering. “[They’re] like the end of a fire hose that’s not being held; [they] can whip around and it is very challenging to predict exactly where the most intense precipitation will be concentrated.” BC has weathered intense atmospheric rivers before, but this one targeted southern BC and, on November 13, struck an area that hosted critical highways and bridges, along with substantial population centres. The storm smashed precipitation records in much of the province, flooding farms and triggering landslides that tore down mountainsides into valleys, taking down highways, bridges, and rail lines in their path. Highway 7 near Agassiz succumbed to two landslides, stranding travellers on the stretch of highway between them. Hundreds more people were stranded in Hope as the Coquihalla and Highway 1 became unpassable. The Sumas Prairie dike breached, and City of Abbotsford began issuing evacuation orders on November 14, followed by Merritt and Princeton on November 15. Another landslide on November 15

with assistance from the Canadian Armed Forces. This work, combined with emergency works undertaken by Abbotsford, provided additional protection against future breaches along the entire length of the Sumas Prairie dike. November 24 to 30 saw the next three atmospheric rivers unleash another barrage of precipitation on already flooded areas of the province, although these were faster moving and far less damaging than the first major event. Don Kennedy, P.Eng., Vice President, Transportation Structures for Associated Engineering, said, “Our engineered systems are vital to our continued function as a society in the coming decades. [The importance of] our transportation networks have been demonstrated from natural disasters over decades to the arteries of response and recovery […] We have quite a bit of redundancy of our transportation networks in the Lower Mainland and in British Columbia, a lot of numbered highways, but in this case, which highways were hit? Highways 1, 3, 5, 7, 8, 11, 97, 99 […] but still, it proved not to be enough for these events.” While the atmospheric events exposed the

blocked Highway 99, the last remaining route (by road or rail) between the Lower Mainland and the rest of Canada. Van der Eerden joined the PREOC (Provincial Regional Emergency Operations Centre) in Surrey after the first atmospheric river. While responding to the initial event, the team began planning for the next three forecasted atmospheric rivers. They evaluated weather and river forecasts from Hope to Pemberton and, using hydrologic and hydraulic models, determined areas of elevated risk. “We were in touch with Abbotsford almost continuously,” van der Eerden said. When Abbotsford received emergency approval to complete a temporary upgrade to the Sumas Prairie dike between the Barrowtown Dam and Highway 1 (including the section that breached), the team at PREOC identified Highway 1 in Abbotsford as the next most vulnerable spot. PREOC reached out to the BC Ministry of Transportation and Infrastructure (MoTI) to highlight this vulnerability and to provide support. In response, MoTI installed a Tiger Dam (water-filled tubes that act like sandbags) across Highway 1

Meteorologists sounded the alarm of a pending storm, but the unpredictable nature of an atmospheric river’s path made advance warnings challenging. “Atmospheric rivers can be quite narrow, not like traditional frontal systems,” said

A rail line falls victim to a landslide. P HoTo : m INISTRy of T RANSPoRTATIoN AND I NfRASTRUCTURE ( flICkR . Com / PHoToS / TRANBC /)

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