Logging, forest loss may have set ancient B.C. landslides back in motion, experts say

A series of ancient landslides have been "reawakened"in British Columbia's Cariboo region, according to the B.C. government, costing hundreds of millions in federal disaster assistance funds.

While the province links the reactivation of the slides to climate change, experts warnthe problem is connected to logging in the area.

Slides and flooding in the springs of 2020 and 2021 washed out roadways surrounding Quesnel, B.C., where geotechnical studies have also linked ongoing land movement beneath hundreds of homes with historic, slow-moving landslides.

The financial scale of the problem is revealed in a document obtained through a freedom of information request, showing the B.C. government estimated that damage caused by the landslides throughout the Cariboo would be eligible for federal disaster assistance of $995 million.

The briefing note was prepared for B.C. Public Safety Minister Mike Farnworth in December 2021.

In response to a question about the estimate, B.C.'s Ministry of Emergency Management said the province has so far received $405 million in advance payments from Ottawa to aid rebuilding.

A B.C. government web page attributes the "unprecedented slides and road washouts"in the Cariboo to wildfires and weather patterns linked to climate change, saying the old slides had been "reawakened"and "reactivated."

But University of B.C. forestry professor Younes Alila says forest loss due to extensivelogging, as well as mountain pine beetle infestation and wildfires, is playing a key role in the hydrological disruptions behind the slides.

Alila said he's concerned money being spent on rebuilding roads will be wasted if officials and engineers don't account for that.

"If the government recognizes and admits to the cause of the landslides, or the flooding, I think they could actually make much better decisions moving forward,"he said.

Although approval ofloggingthat some link to the landslides was a provincial responsibility, it is the federal government that bears the bulk of the disasters' costs. Under assistance rules cited in the briefing note, 90 per cent of the costs are borne by Ottawa if the price tag for a disaster in B.C. exceeds $85 million.

Others share Alila's concerns thatlogginghas contributed to widespread hydrological disturbance.

Mike Morris, the B.C. Liberal member of the legislature for Prince George-Mackenzie and a former public safety minister, said the provincial government should be treating hydrological changes due to forest loss as "one of the most high-risk situations in the province."

"And they're not, quite frankly."

'Slope stability 101'

Bob Simpson, the previous mayor of Quesnel, said "massive clearcuts"from salvagelogginghad changed the hydrology of the area.

"Anybody who thinks otherwise is living in La La Land,'' said the former New Democrat MLA.

Alila, whose research is focused on watersheds in the province's Interior, said without forests to regulate springtime snowmelt, soils become oversaturated more often, and the water table stays elevated longer.

"It's when the groundwater pressure exceeds a certain threshold more frequently and over a longer period of time that the soil starts caving in,'' said Alila, who is also a professional engineer.

"This is slope stability 101."

A statement from the Forests Ministry said, "the impact of proposed forestry operations regarding ground saturation and land stability is always part of the overall permitting approval process."

The loss of forest cover can contribute to hydrological changes in a watershed, it said, without referring to specific areas. The province said this can be the result of harvesting, but "any disturbance"reducing vegetation can contribute to an increased risk of flooding.

"One of the best ways to mitigate landslide concerns is the prompt reforestation of harvested areas and those areas damaged by wildfire and pests, as well as addressing the impacts of climate change,"the ministry said.

WATCH |Climate change makes landslides a growing danger for B.C. Interior, experts say:

Climate change makes landslides a growing danger for B.C. Interior, experts say

3 years ago

Duration 1:55

British Columbia's interior Cariboo region is dealing with more dangerous landslides with shifting ground blamed for washing out roads and threatening homes, something experts say is made worse by climate change.

Alila said climate change is being used as a "scapegoat"and it takes decades for replanted forests to recover hydrological function.

"The fact remains that both climate change and land use and land-cover changes exacerbate the magnitude, the frequency and the duration of these extremes,"he said, referring to landslides, flooding and drought in B.C. and beyond.

The Cariboo landslides are clearly a regional problem, he said, and loss of forest cover is the only potential regional-scale cause besides changes in precipitation.

But Alila rules out precipitation, saying the science shows B.C.'s Interior is receiving less snow as a result of climate change, while the groundwater table is less responsive to short bursts of heavy rain than to snowmelt over time.

The forests west of Quesnel have been "logged to death,"said Morris, who was born in the town and has spent much of his life hunting and fishing the region.

"It's a completely different landscape than it was 30 years ago,"he said.

"There is nothing holding back the spring freshet anymore because of the overharvesting that we've seen in the entire area."

A statement from CaribooRegional District said officials understand extensive wildfires have significantly increased flooding and landslide risks but could not comment on hydrogeological factors that mightbe affecting land movement.

The district continues to "seek to work with the province on developing land and resource management solutions"appropriate for its communities, it said.

Public Safety Canada declined to respond to a series of questions.

Years before the Cariboo slides, the Forests Ministry was aware of the potential for large-scale forest losses to affect watershed hydrology.

A report released by the ministry in 2017, focusing on snowy watersheds in southern B.C., said natural orlogging-related forest disturbances over a large enough area can affect "hydrogeomorphic processes at the watershed scale."

Watersheds where more than 25 per cent of the forests had been clearcut experienced significant shifts in the timing and magnitude of snowmelt-dominated streamflows and peak flow events, the report said.

'Awakened the dragon'

The impact of the region's changing hydrology isn't limited to the destruction of roads.

Alila said extensive forest loss west of the Fraser River has "awakened the dragon"of an ancient landslide beneath neighbourhoods on the west side of Quesnel.

The city has recorded more than 80 centimetres of cumulative land movement there since 1998 although the movement is not occurring evenly across the slide.

About 20 per cent of the town's population of 10,000 live in the ancient slide area. City officials have advised residents to minimize tree removal and lawn watering, while a system of pumps and drains removes water from the ground.

The municipality, the province and the federal government have together spent more than $17 million on the system, which started as a trial program in 2012.

Groundwater levels and land movement had been gradually declining but rose with significant rain and snowfall in recent years, a city web page says.

The pumps and drains removed nearly 200 million litres of water in 2020, yet that year saw 8.4 centimetres of land movement, the greatest annual shift since 2005.

Tanya Turner, the city's director of development services, said geotechnical assessments have linked land movement with groundwater pressure, and tree removal has been identified as a contributing factor.

But studies commissioned by the city have focused on the ancient landslide area within Quesnel's jurisdiction, not what's happening in the broader region.

"The geotechnical experts have told us forever this is a really tiny amount of information to be making any huge assumptions on,"Turner said.

"I don't think anyone's going to draw an A and B conclusion on any of this, because I think there's multiple factors,"she said of the land movement.

The mayor of Quesnel, Ron Paull, declined to comment on the issue.

Turner noted that Quesnel is not the only community experiencing land movement.

About 120 kilometres south, in Williams Lake, the city and the regional district released a slope stability study showing movement in 11 areas between 2019 and 2021.

Simpson, mayor of Quesnel from 2014 to 2022, said the town's landslide study area is small, and changing patterns of snowmelt and precipitation linked to climate change are likely factors.

He said the significant land movement recorded despite the pumps and drains prompts the question, "what is going on?"

The landscape surrounding Quesnel is outside municipal jurisdiction, and the city doesn't have the resources to investigate further on its own, he said.

The B.C. government is responsible for managing public lands and forests, and Simpson said the province, not the municipality, approved the first subdivision on the ancient landslide area.

"I do think the city is in a position where they need to have conversationswith the provincial and federal governments about a broader analysis,'' he said.

'Super-sensitive' flood regime

Despite studying the surrounding area for more than a decade, Alila said he only became aware of the land movement in west Quesnel a few months ago.

A post-doctoral researcher whose thesis Alila supervised, Joe Yu, was looking at homes for sale in Quesnel and noticed prices seemed to be lower on the west side.

That led the pair to learn about the land movement, and they immediately began connecting the dots to their research on forest hydrology.

Alila said watersheds west of the Upper Fraser River as it flows through Quesnel have lost between 40 and 60 per cent of their primary forests due to mountain pine beetle infestation followed by high rates of so-called salvageloggingand, in 2017, one of the largest wildfires in B.C.'s history.

Extensive forest loss means significantly more moisture seeps into the ground and stays there, Alila said. There is no tree canopy to slow the spring melt by intercepting precipitation and shading the snowpack. At the same time, there are far fewer trees to pump moisture out of the ground.

West of the Fraser River, he said, oversaturation is putting excessive pressure on soils year after year, surpassing their capacity to absorb the water.

It's that pressure that can cause soils to cave in and land to move, he said.

In 2007, Alila produced a report for B.C.'s. independent Forest Practices Board watchdog, to model the effects of beetle infestation and salvageloggingon stream flows in the Baker Creek watershed, abutting the west Quesnel landslide area.

That work, along with subsequent research by both Alila and Yu, revealed a flood regime that's "super-sensitive'' to salvagelogging, Alila said.

They found substantial increases in both magnitude and frequency of peak flows as forest loss increased, he said.

At the time, the board urged the province to consider hydrological impacts in plans to harvest forests affected by the beetle epidemic, saying the economic objectives needed to be balanced against "hazards created by higher stream flows."

Morris said he recalls hearing about land movement in Quesnel as early as the 1990s, but he agrees with Alila thatloggingis worsening the problem.

"It's exacerbated by the fact that we have harvested even more in the last 25 years and we're still doing it without regard to the damage that's been caused."

Morris said the province could be in a predicament because it has been responsible for signing off on harvesting plans, a fact that could pose liability issues.

There has been a reluctance to point fingers at the forest industry over recent flooding and landslides because it has been the lifeblood for many B.C. families and communities for a century, Morris said.

But it's the government's job to guard public safety and infrastructure, he said, adding it would take decades to mitigate the hydrological changes.

"This is an issue that I think government needs to take seriously."