Innovation Fall 2024

Sector, which were jointly published by Engineers and Geoscientists BC and Forest Professionals BC. The guidelines provide a pertinent framework for the management of hydrologic and geomorphic risk in consideration of the changing climate. Carver says registrants can also reach beyond the guidelines and be up to date with peer-reviewed literature. It’s up to registrants to get it right, he says, as billions of dollars of infrastructure are located in flood plains. Addressing magnitude and frequency Dr. Younes Alila, P.Eng., a professor in UBC’s Department of Forest Resources Management, also champions the probabilistic method. Alila is trained in civil engineering — not forest science — so he analyzes pre- and post-logging data using a different experimental design than other professionals. “The causes of floods are multiple and randomly occurring over time,” he says. “(Determinism) tells you a story about how logging affects the magnitude, but it’s not the right story. Why? Because the only right story is the probabilistic framework that evaluates both the effect on the frequency and the effect on magnitude simultaneously. “The magnitude, or severity, of the flood event is affected not just by the size of the storm, but by the state of moisture or wetness of the watershed at the time of the arrival of the storm.” Disturbing the forest through logging, wildfire, beetle infestation, or other factors, increases the magnitude, and that automatically increases the frequency of floods over time, he says. Eliminating tree cover means snow melts faster due to sun exposure,

Dr. Younes Alila, P.Eng. Photo submitted.

so water has less time to seep into the earth. Climate change’s impact With climate change, Alila believes the effect of logging on the magnitude of floods has been underestimated. The same would apply to drought, landslides, wildfire, and all other weather extremes that are characterized by magnitude and frequency. Repeated flooding carries sediment downstream, often to populated lowlands where the risk is maximized. The silt that’s deposited when the water slows raises the channel bed and chokes the flow capacity of dikes. “Typically, engineers and geoscientists control flood risk in

downstream areas to protect the populated area by increasing the size of bridges, increasing the size of culverts, and raising dikes,” says Alila. “All such purely engineering solutions to managing floods in the lowlands have been giving us a false sense of security against flood risk because these structures will fail most of the time geomorphically and not hydrologically.” (Geomorphic failure is caused by more frequent, longer flood events that batter the infrastructure, destabilizing the structures downstream; hydrologic failure is caused by a flood event with a magnitude larger than the capacity.) Alila suggests designing for strength and not size. “Increasing the size is not going to save the day,” he

Innovation Fall 2024

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