By Steve Hubrecht
Last week Columbia Valley residents learned more about the dangers presented by debris flows, as well as about local officials’ efforts to mitigate the hazard.
The Fairmont Hot Springs area has been subjected to several major natural disasters in the past decade, including flooding along Dutch Creek, and two significant debris flow events in Cold Spring Creek and Fairmont Creek that caused considerable damage and generated plenty of headlines.
On Wednesday, Oct. 30, Regional District of East Kootenay (RDEK) planners, along with consultants and scientists, hosted an online meeting to provide more awareness about debris flows, and to get public feedback to help direct future policies on development and land use in the Fairmont Hot Springs area.
University of British Columbia (UBC) fluvial geomorphologist Brett Eaton explained the difference between flooding, debris floods, and debris flows. “Floods are bad, debris floods are worse, and debris flows are the other end of the spectrum,” he said.
A debris flow occurs when a landslide or avalanche hits a stream channel during a rainstorm. This “shocks the whole system,” said Eaton, and can generate a slurry that is similar to concrete that can literally liquefy the whole stream channel, including trees.
Debris flows have the most potential to cause damage and are more likely to occur on steep creeks, such as Cold Spring Creek and Fairmont Creek. They often end with the debris material fanning out where the creek becomes less steep, but this is also, unfortunately, where humans typically build infrastructure.
Geologic engineer Jack Park ran over the history of debris floods and debris flows on Fairmont Creek and Cold Spring Creek. These include the infamous debris flows in July 2012 and May 2020, as well as floods, debris floods or smaller debris flows in June 2013, August 2019, May 2021, July 2022, and May 2023.
Eaton tried to parlay the risk associated with such events into terms more easily understood. For instance, he noted that your odds of encountering a “moderate” 50-year debris flow (one that occurs at a level expected once every half century) are quite literally one in 50, so long as you live in the given area for just one year. But if you live in that place for a long time, your odds of encountering that 50-year debris flow increase, even though it remains a relatively rare event. If you live in that spot for 10 years, the odds of encountering a 50-year debris flow are one in 5.5. Live there for 25 years and it’s one in 2.5; for 50 years it’s one in 1.6; and for 100 years it’s one in 1.2.
The odds of encountering a 500-year debris flow (a catastrophically large natural disaster) are one in 500 if you live in that spot for one year. Live there 10 years and it’s one in 50; for 25 years it’s one in 20; for 50 years it’s one in 10; and for 100 years it’s one in six.
Odds of one in six are also, coincidentally, the same chance as dying from a heart attack, Eaton pointed out, adding that the risk of heart attack is taken seriously enough by humans that it often prompts wholesale lifestyle changes in middle aged and older adults.
At this point, the meeting organizers conducted an online poll, and 25 per cent of respondents indicated they were “extremely uncomfortable” with the risk of debris flows in Fairmont Hot Springs.
In response to a question, RDEK Fairmont debris flow mitigation project manager Kara Zandbergen explained that the RDEK closely monitors rainfall and snowpack, but can’t control the weather. So, it takes steps “to control what we can” by building physical infrastructure to help protect residents. She later noted that work on debris flow and flood mitigation structures on Cold Spring Creek is ongoing, that as much as possible will be done this fall, and that completion will come in spring 2025. Zandbergen also noted that debris flow mitigation efforts are a $10 million project that is “fairly complex” and that there have been “reasonable delays that have the project behind, which are not uncommon in a project of this size.”
RDEK communication manager Loree Duczek encouraged Fairmont residents to sign up for the RDEK’s evacuation notification system, which she pointed out is an important part of any emergency response. It’s something relatively few Fairmont residents have done so far, noted Duczek, adding the RDEK would like to see more people sign up.
When asked how many landslides or debris flows had occurred in the Columbia Valley, Eaton said he couldn’t specifically narrow statistics down to the valley or even to the East Kootenay. What he could say was that there have been 390 major landslides in British Columbia over the last century, 123 of them fatal; and that “the Coast, the Kootenay, the Columbia, and the Rockies are where those fatal landslides are concentrated.”
The Columbia Valley is part of the Kootenay region, and sits sandwiched by the Columbia Mountains (which include the Purcells) and the Rocky mountains.
Asked about wildfires, Eaton said “debris flows and wildfires are quite strongly linked.” That’s because wildfires, especially really intense wildfires, burn off vegetation, and these now-open and bare slopes are more prone to landslides than vegetated ones.
When trees are lost in wildfires, their roots typically take about 10 years to rot away, so even a decade after a wildfire, it can help increase the risk of a debris flow.
