Squamish-Lillooet warned about landslide risk two years ago

Photo by Bonny Makarewicz, Special to the Sun

August 17, 2010

by Jesse Ferreras, Vancouver Sun

METRO VANCOUVER – Lawmakers with the Squamish-Lillooet Regional District received a scientific report two years ago warning that a major landslide was coming and urging the installation of an emergency early warning system for area residents.

The regional district board, which governs areas adjacent to the Village of Pemberton’s boundaries, discussed the report at a confidential meeting in March 2008, but later rejected a proposal to submit it to peer review or study the feasibility of an early warning system. The board opted instead to publish an annual public notice about the slide hazard at Mount Meager.

In the report — titled Hazard and risk from large landslides from Mount Meager volcano, British Columbia, Canada, and published in the Feb. 22, 2008 issue of the scientific journal Georisk — geoscientists caution that a landslide presents a high risk of loss of life for residents of the Pemberton Valley.

“The calculated risk exceeds, by orders of magnitude, risk tolerance thresholds developed in Hong Kong, Australia, England, and in one jurisdiction in Canada,” the report reads.

“This finding poses a challenge for local governments responsible for public safety.”

On Aug. 6, the region was hit by the second-biggest landslide in Canadian history, when about 40 million cubic metres fell from the summit of Mount Meager, sweeping down into Capricorn Creek and creating a natural dam at Meager Creek that backed up a 10-kilometre-long lake behind it.

Officials with the SLRD worried the dam could flood residences along the Lillooet River, but a 25-40 metre incision later formed in the dam that allowed three million cubic metres of water to flow out naturally into the Lillooet River. No homes were flooded.

The report states that debris flows of 100 million cubic metres would have a low probability of impact on the Pemberton Meadows, the residential area closest to the Aug. 6 landslide, but that a one-billion-cubic-metre debris flow would reach Lillooet Lake, several kilometres away.

The geoscientists calculate the annual probability of loss of life for Pemberton residents at anywhere from 0.000005 to 0.0005 deaths per year due to landslides. That’s 5.4 times higher than acceptable probabilities in Australia, England and Hong Kong, and 54 times higher than the acceptable probability in the Netherlands, according to the report.

The geoscientists thus recommended that the SLRD adopt an early warning system to alert people about landslides as soon as they happen. They recommended a tripwire system that could trigger an air-raid siren, or else a gauging system to monitor sudden changes in river flow.

Pierre Friele, one of the report’s three co-authors, says an early warning system could have gone a long way to alert residents about the Aug. 6 landslide.

The landslide occurred about 3:25 a.m. and Friele was the first geoscientist on the scene at 1 p.m.

An avalanche fell from the summit of Mount Meager, flowed into Capricorn Creek and formed a natural dam at Meagre Creek.

Officials discovered a breach in the dam around 10 p.m. It was then, 19 hours after the slide, that the SLRD ordered Lillooet Valley residents to evacuate.

Friele acknowledged in an interview that the slide was smaller than he calculated in the report, but he nevertheless said an early warning system would have detected a drop in river level as soon as the slide happened. A drop in river level, he said, is one of the surest indications that a landslide has occurred.

“There would have been absolutely no delay in detecting the landslide and the problem,” he said. “At first light, you could have had a helicopter up there with appropriate people on board to assess the hazard.”

Pemberton Mayor Jordan Sturdy, who represents his community on the SLRD board, said the report was “unsolicited” and just got “plopped” on the regional district’s agenda. He added there wasn’t money to pay for an early warning system.

“There was some discussion of studying the feasibility and cost of installing and operating an early warning system but I don’t think it was clear what that would entail,” he said. “I think it was clear, that in an area as remote as that, with no access to hydro and telecommunications, it was going to be an expensive proposition.”

Sturdy went on to say that the SLRD was never provided with an estimate of how much the system would cost, but he personally estimated a less expensive system at around $50,000 for installation as well as continuing maintenance.

Susie Gimse, the SLRD representative for Area C, which includes the Pemberton Meadows, said in an e-mailed response that the regional district discussed an early warning system with the province.

Asked why an early warning system was never implemented, a spokesman with B.C.’s Ministry of Public Safety and Solicitor-General said in an e-mail that the province only had informal discussions with the SLRD about such a system. The SLRD, he said, has to determine what its needs are and then the province will consider requests for support.

The spokesman declined to disclose the cost, saying the design of a system would determine the cost and that it’s “premature” to estimate the costs for the system proposed for the SLRD. The City of North Vancouver was the only jurisdiction with a warning system.

Special to The Sun

© Copyright (c) The Vancouver Sun
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About jesseferreras

Sea to Sky-based journalist. Snowboarder, cyclist, cinephile, bon vivant.
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