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Pemberton still working on landslide warning system

Village, regional district, dyking district in discussions with the province



Pemberton is still working to put up an early warning system for landslide activity, a little over a year after the second biggest in Canada's history fell north of the valley.

That, at least, is the contention of Pemberton Mayor Jordan Sturdy. He said the Pemberton Valley Dyking District (PVDD) is working in conjunction with the Ministry of Environment to install a hydrometric station at the Lillooet River forestry bridge that may contain a notification instrument to alert community members about sudden increases or decreases in flow.

Beyond that, the Geological Survey of Canada and the Ministry of Environment are looking into the feasibility of installing other systems in and around the Meager area, but Sturdy said that could end up a very expensive proposition - about $1 million, according to numbers he's seen.

He added that Rick Guthrie, a senior scientist with Vancouver-based environmental consulting firm Hemmera, is currently putting together a report assessing how to approach the issues of assessment of hazard and community response within a "reasonable need."

"Some of the numbers that have been bandied about have been in the millions," Sturdy said. "Hopefully Rick will be able to give us a sense of proportion and scale in terms of events like that and I think we certainly have an obligation to help provide notice with regard to the relative risks associated with this dynamic environment."

All of Pemberton was placed on high alert on the weekend of August 7 to 8, 2010 when a gargantuan landslide fell from the summit of Mount Meager, about 60 kilometres north of the Pemberton Meadows.

The slide measured approximately 40 million cubic metres, second only in Canadian history to the 1965 Hope Slide, which was 46 million cubic metres.

The landslide flowed down Capricorn Creek, crossed Meager Creek and created a natural dam at the latter's confluence with the Lillooet River. There were worries that the dam, which backed up a massive volume of water behind it, would flood the Lillooet downstream but a 25 to 40 meter incision in the dam allowed water to flow through it, bringing the river to a height of 3.7 metres and avoiding any serious flooding.

Officials in Pemberton began work shortly after the slide in conjunction with the provincial government to set up an early warning system to alert valley residents about any landslide activity.

Since then the Pemberton Valley Dyking District has obtained money to do a baseline riverbed study to monitor silt flowing out of the landslide area, work that has seen the dyking district monitor siltation and aggregation activity in the Lillooet over the past ten years but that also forms a baseline for what could happen over the next ten years.

"The new information's going to overlay historical data from the '60s, '70s, '80s and 2000s," said Jeff Westlake, operations manager with the dyking district. "What that will do is form a cross-section comparison to see general trends in the Lillooet River.

"The heavier material is trapped within the Lillooet system so it's accumulating someplace, but it's hard to determine exactly whether the accumulations are happening based on survey information."

As far as next steps go, Guthrie's report is expected soon but it's uncertain precisely when it will come. Sturdy said he calls him every couple of weeks to check on its progress and Westlake said it was initially expected in the spring.

Once it comes, it will provide recommendations drawn from opinions from a range of the scientific community, such as volcanologists, climatologists and debris flow experts. The report is expected to tell Pemberton what the likelihood is of a similar event recurring near the valley.

"What's the likelihood of another 45 million cubic metres falling off in the next year or two, or five, or ten? That's a difficult hypothesis to assess," Sturdy said. "But I think it's fair to say that an oddsmaker, you know, a bookie would be saying, well, we had the second biggest rock avalanche in recorded history last year, what's the chances of another one happening?"




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