Whitehorse begins another season of watching the escarpment

It's that time of year again, when the snow is melting in Whitehorse and people in the city start to cast an occasional wary glance at the escarpment looming over Robert Service Way. 

And city officials say they're also keeping a close eye on the escarpment, for any signs of an imminent slide. The city this past week started another year of actively monitoring the slope, using radar scanners, groundwater data, and other tools.

"This is the new reality," said Mayor Kirk Cameron, at a news conference on Thursday where city officials detailed their slope monitoring efforts.

Three years ago, with no apparent warning, a major slide on the escarpment just south of the downtown core sent a torrent of mud, rocks and trees spilling across Robert Service Way and the Millennium Trail, into the Yukon River. 

Nobody was hurt in that slide but it forced the city to close Robert Service Way, one of the major traffic arteries into the downtown, for six weeks as the debris was cleaned up and a protective barrier was built at the base of the slope. 

The slide that year followed an unusually snowy winter and it's believed that the spring melt saturated the soil enough to make the slope unstable. More slides could be expected in the future, experts warned.

On Thursday, Cameron called that slide in 2022 "a wake-up call, and a clear sign of the impacts of climate change on our community and on our infrastructure."

More slides, all smaller and much less disruptive, would follow in the next few years at different spots along the escarpment that flanks the entire downtown. 

Adam Wallace of Tetra Tech, the engineering firm that's doing the slope monitoring for the city, said the program underway again this spring involves a slope scanner trained on the area where the big 2022 slide happened, looking for any warning signs of movement.    

"Basically, it shoots a radar from across the river at the Robert Service Way slope, and by shooting repeated images it's able to detect really, really precise or really, really small scales of movement — and it does that practically constantly," he said.

Engineers are also now doing weekly visual inspections of the slope, he said, also looking for anything worrisome.

"Which would be visual observations of water seeping out of the slope, cracks forming, you know, at the top or on the slope, or even visual observations of material actively falling down the slope," Wallace said.

The annual monitoring efforts have already proven valuable, he said. Last year, a slope scanner detected some movement that prompted the city to quickly install a barrier of concrete blocks at the base. That barrier managed to stop a "medium-sized" slide from spilling onto the road, he said.

"So that's a good example and a real success story, in terms of seeing a problem before it really happens, responding to it and making it safe….  The practical result was, we didn't have to close the road."

Wallace said it's still too soon to predict the risk of more slides this year, but he said that snow survey data so far suggests that this year is similar to last.

"So that's an encouraging sign that might lead to a quiet and hopefully very boring year of monitoring," he said.

The city has budgeted $300,000 for the work this year to monitor and manage the landslide risk.

The $60M solution

The mayor says digital signs and concrete blocks have been now placed at both ends of what's considered the "slide zone" along Robert Service Way, in case the road needs to be closed on short notice.

Officials said the slope monitoring will continue into next month and possibly into June. That's considered the period of greatest risk, when snow is melting and potentially making the slope less stable.

Cameron said the city's priority, beyond the coming weeks of monitoring, is finding a permanent solution for the vulnerable roadway. That will mean re-aligning the most vulnerable section, which is pinched between the base of the slope and the river. 

It's a project that's estimated to cost about $60 million, Cameron said, but could very easily be more. He said it will be the biggest infrastructure project ever undertaken by the city. 

"In the current climate, economic climate, around the world we're vulnerable to cost increases right? That steel we got, to be able to put into that retaining wall a couple of years ago, I suspect would cost an awful lot more today if we had to go to purchase that wall again," he said.

Last spring, the federal government announced it would provide $45-million for the project. Cameron said he's hopeful that the territorial government will also chip in to help the city out. 

"We are growing, we are facing these impacts and we have to work with that," Cameron said.