After a noticeable increase in rock slides down Mount Currie in 2015 and 2016, Pemberton Valley residents finally have a quantified answer to just how big a hazard the prominent landform poses.
The Mount Currie Landslide Risk Assessment, conducted by BGC Engineering Inc. determined potential risk to communities below the mountain’s north face remain very unlikely, but still possible, officials announced last week (Jan. 18). Led by a steering committee including representatives from the Squamish-Lillooet Regional District (SLRD), the Village of Pemberton, Lil’wat Nation, the Ministry of Forests Lands and Natural Resource Operations and Rural Development and Emergency Management BC (EMBC), the assessment was provincially funded through EMBC.
“That possibility of a large-scale event is still very remote, but it is possible. We just have an idea now of how possible it is, and we have a little bit of science to know, if that large-scale event did occur, what it would look like,” said Ryan Wainwright, SLRD emergency program manager.
The final assessment determined the presence of up to 19 potential rock avalanche source zones on the mountain, with four of those designated as having high-hazard potential. Two out of those four were identified as having the potential for large-scale events powerful enough to travel north of the Green and/or Lillooet Rivers — therefore capable of having a larger impact on the valley bottom, Wainwright explained, stressing that those scenarios remain very unlikely.
The study identifies 15 properties within the regional district, Pemberton and Lil’wat that would likely be immediately impacted in the event a major rockslide occurs, as well as approximately 160 buildings that could potentially be impacted by flooding associated with one of the rock avalanche scenarios.
In this case, geoscientists calculated that the current annual probability of a modeled rock avalanche in one of those high-hazard zones — dubbed Scenario 1 — is approximately a 0.02 per cent chance of occurrence in any given year, while the annual probability of the modeled rock avalanche in the other zone (Scenario 2) is a 0.009 per cent chance of occurrence in any given year.
But those calculations only apply to current conditions, weathering and erosion rates. As Wainwright explains, the study also provides information around climate change and its impact to landforms in the Sea to Sky. “(That’s) the most interesting information that we got out of this study,” he said. “With the assumption that a lot of what holds these landforms together has to do with the amount of permafrost that exists at their core, and as the climate changes, what we might see is that that permafrost doesn’t hold things together so well.”
To that end, the assessment recommends ongoing monitoring as the most economic and practical risk-management strategy. The three jurisdictions will continue to cooperate on advocacy efforts to secure any additional funding needed to monitor the mountain, though what form that monitoring will take is yet to be seen.
“These kinds of large-scale, but very rare events don’t happen without a significant changes beforehand,” Wainwright said. “The question now, based on the recommendations in the report, is how do we work together, as the governments in the Pemberton Valley and as the community there, with our federal and provincial counterparts to make sure that we are looking for those signs, so we can make important decisions if we do see those conditions change.”
“Given the results of the study, officials are fairly confident the mountain isn’t changing quickly,” Wainwright said. “There’s no indication of imminence. It would be very unusual for it to fall down tomorrow.”
For those hoping for more information about the assessment report, the public can bring their questions straight to the source during a pair of community information sessions scheduled for both Pemberton and Lil’wat Nation next week. The sessions will take place at the Pemberton & District Community Centre on Wednesday, (Jan. 24) from 6:30 to 8:30 p.m., and at the Ull’us Community Complex on Thursday (Jan. 25) beginning at the same time.
Each information session will include a presentation of the assessment findings by BGC engineers, who will then be available for questions. Community members are encouraged to submit their questions before the community information meetings to one of the following community representatives: Sylvia Dan (Sylvia.firstname.lastname@example.org), Sarah Morgan (email@example.com) or Jill Brooksbank (firstname.lastname@example.org).
For more information or to read the complete report, go to slrd.bc.ca.