‘Massive’ BC Landslide Clogging River Expected to Burst in Next 24 to 48 Hours

A landslide along a river in British Columbia's central Interior has prompted the Cariboo Regional District to issue evacuation orders due to "immediate danger to life and safety" caused by flooding triggered by the slide. (The Canadian Press/HO-Central Cariboo Search and Rescue)

A  30-metre-high landslide has formed a dam across the Chilcotin River in the central Interior of British Columbia, prompting the evacuation of multiple properties as emergency officials warn of potential flash flooding downstream.

The river is expected to breach the “massive” 600-metre-long dam formed by landslide debris, located south of the City of Williams Lake, potentially in “the next 24 to 48 hours,” Cariboo Regional District Chair Margo Wagner said in a media briefing.

“As the water continues to flow and builds up behind that landslide, the pressure increases, but we do not have a definitive time of when that will let go,” she said.

While officials remain uncertain about the potential impact once the dam is breached, one thing is certain, Wagner said—it will result in a “mass of water” barreling down the Chilcotin when it lets go.

B.C. officials who are monitoring the landslide with drones say the material blocking the river roughly 22 kilometres upstream from the Farwell Canyon Bridge is made up of sand, silt, and clay, all of which are susceptible to rapid erosion, according to a news release.

The water is currently backed up behind the dam approximately eight kilometres up the river. When it lets loose, “a large amount of debris” could flow down the Chilcotin River to the Fraser River confluence, then south to Hope before pouring into the ocean.

So far, the Cariboo Regional District has issued two evacuation orders affecting 60 properties, and 12 homes.

But the province says other area residents also need to be ready to leave at a moment’s notice.

“People are urged to avoid the Chilcotin River and the Fraser River from Hope to the Chilcotin River confluence,” the province said. “People living in areas where a flood warning, flood watches and high streamflow advisory have been issued are encouraged to pack a grab-and-go bag and have an evacuation plan ready in case they are required to evacuate.”

The Tsilhqot’in National Government declared a state of emergency Aug. 1 and is warning people in the six communities it oversees to avoid the river. The advisory also warned that flooding has the potential to threaten bridges to the communities of Xeni Gwet’in and Yuneŝit’in.

‘Creating a Lake’

B.C.’s River Forecast Centre has issued a flood warning for the Chilcotin north of the slide, saying the debris is “creating a lake” that extends several kilometres upstream.

“The eventual overtopping of the landslide material may lead to sudden erosion of the debris and catastrophic failure of the landslide dam,” the forecast centre said, adding that this could cause an “outburst flood” with a surge of water rapidly flowing downstream.

Minister of Emergency Management Bowinn Ma is warning people and boaters to “stay off of and away from the banks of the Chilcotin River, as well as the Fraser River between the Chilcotin River and Hope.”

“Pulses of water and material being released” could pose a significant risk to people and infrastructure downstream, she said in a Facebook post.

She offered similar words of caution during an Aug. 1 press conference.

“Let me be clear, the risk to people and communities along the river is unknown at this time, but it has the potential to be significant,” Ma said.

A sudden release of debris has the potential to trigger more erosion as it flows downstream, raising concerns about the impact of the blocked water on salmon, Ma said.

“There are also concerns that persistent low water levels might impact navigation channels for fish like the ongoing chinook run and the sockeye run coming up,” she said.

“Those can have significant impacts on the ecology of the river system.”

The Canadian Press contributed to this report.