British Columbia

Rain increases spring landslide risk in B.C., expert says

Multiple landslides have taken place in B.C.'s Interior after the soil has become saturated with spring rain and melting snow.

Landslides have been recorded in Sunnybrae, Canoe and Kaslo within the month

The mudslide above Zwicky Road in Kaslo, B.C., is pictured in photos taken from a helicopter. A spokesperson for the Regional District of Central Kootenay says the slide is about 350 metres above the road. (Bronwen Bird)

When the April rains arrive and the snow begins to melt, the chance of a landslide on B.C.'s steep slopes goes up.

In the last few weeks, two homes in the Sunnybrae area near Salmon Arm were destroyed in a landslide.

On April 17, Highway 1 was closed near Canoe when several vehicles were caught in a slide. Then, evacuation orders were issued for 47 homes near Kaslo in the Kootenay region after a mudslide on Monday night.

Six families are still out of their homes.

"It's the wet time of the year and we've got snow melt and rainfall. B.C. is blessed with lots of steep terrain so the combination creates the potential for a landslide," explained engineering professor Dwayne Tannant, who teaches soil and rock mechanics and terrain modelling at the University of British Columbia Okanagan.

When all that water saturates the soil, it can cause a landslide.

'Err on the side of caution'

B.C. has seen multiple dangerous landslides, including one in Johnson's Landing in July 2012, where four people perished after a slide destroyed several homes.

Tannant says that history explains the cautious response to the Kaslo landslide — where homes were evacuated as a precautionary measure although there was no damage. (For reference, Kaslo is across Kootenay Lake within the same region as Johnson's Landing.)

"Clearly, if you're the decision maker and you see evidence of movement and it's occurring above where people are living, you're a little bit sensitized," he said.

"What we've seen in the Kaslo circumstance, it's probably the best to err on the side of caution. Mother Nature is a little bit fickle and unpredictable and I want to think if I were in that position, I'd probably make the same call."

Better mapping techniques

The deadly Johnson's Landing landslide also became the impetus for the province to map the terrain to better predict landslide risk.

For example, Tannant says there are new mapping techniques using lasers that can penetrate dense forest cover.

Experts can read the maps to identify old landslide features or other details that could make an area more susceptible to landslides.

The problem, however, is the mapping is only partially done.

"The effort to map the whole province is really still in its infancy," Tannant said.

"We need a lot more work. A lot more experts need to be mapping the hillsides above areas that are critical to us — particularly areas where people are living."

Listen to the full interview with Professor Dwayne Tannant on CBC's Daybreak South: