Winter offers time to fine-tune an early warning system for monitoring the risk of a debris flow impacting a Sicamous neighbourhood.
Over the spring and early summer, four evacuation alerts were issued for all residences in the Sicamous Creek Mobile Home Park. The alerts were triggered when forecast rainfall increased the risk of a landslide in the Wiseman Creek watershed. In each instance, no slide or flooding occurred, and each alert was lifted as soon as it was determined the risk had subsided.
“The early warning system was fairly successful,” said Columbia Shuswap Regional District (CSRD) protective services team leader Derek Sutherland. “We have some dialing in to do to fine-tune it in order to get a more accurate sense of what’s going to trigger a debris flow or a debris flood and what’s not.”
Funded by the province, the early warning system came on line at the end of March. It was one of the recommendations made by BGC Engineering after conducting an assessment for the CSRD of the 2,500-hectare area in the Sicamous Creek and Wiseman Creek watersheds impacted by the 2021 Two Mile Road wildfire.
At a December 2021 public meeting hosted by the CSRD, representatives from BGC explained damage caused by the blaze had increased the likelihood of a debris flow over the next two years as vegetation regrows. The watersheds are above the mobile park.
For the warning system, Sutherland said the geotechnical engineers took a conservative approach when setting a threshold for triggering an alert.
“Now they’ve gone back into the watershed, they’ve had another look around to see if there was any debris flows,” said Sutherland. “They did find some very minor stuff but nothing to speak of. They’ll take that information back and they’ll readjust the threshold so hopefully we have a more accurate idea of at least what won’t cause a debris flow.”
Currently, Sutherland explained the snow acts as a sponge and “essentially makes the risk of debris flows zero.” “When the snow comes off, that’s a danger time, especially if there’s a rain-on-snow event,” said Sutherland. “But for the winter, we’re in kind of a reset mode where we just go back to the original tool, make our adjustments and get ready for the spring freshet.”
Sutherland acknowledged the four evacuation alerts were cause for anxiety for residents. He noted it was explained early on to residents that with the new warning system, they may be put on alert more than they would like.
“There was a bit of pushback from the community saying ‘If these big rain storms are happening and we didnt’t have an event, then why are we still on alert,’” said Sutherland. “And they’re not wrong. Those are the same questions we’re asking. But the process to try and reevaluate that and be cautious and careful and deliberate in our consideration of it takes a little bit longer than some would like.”
Subsequent to the start of the early warning system, both the CSRD and the District of Sicamous have voiced concern regarding plans by BC Timber Sales (BCTS) to salvage timber in the wildfire-affected watersheds. In response, BC Timber Sales has said it will be proceeding with the salvage operation as well as mitigation of conditions contributing to slope stability concerns including a legacy network of non-status roads and trails that were not deactivated.
Sutherland didn’t know if that work has begun, and doubted he’d receive any reports about it from BCTS unless there are safety concerns.
“I wouldn’t expect them to be open with us about what the hydrologist’s finding unless there’s something putting the community at immediate risk,” said Sutherland.
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