Evacuation orders, flood warnings issued after landslide blocks B.C.'s Chilcotin River

A landslide in B.C.'s Central Interior blocked a major tributary of the Fraser River overnight Tuesday, prompting evacuation orders, flood warnings and an emergency alert on Wednesday.

The landslide occurred near Farwell Canyon, 18 kilometres southeast of Hanceville, and blocked the flow of the Chilcotin River, according to the flood warning issued by the B.C. River Forecast Centre Wednesday afternoon. 

"This landslide has dammed the river and is creating a lake currently extending several kilometers upstream," the warning reads. "Higher water levels are expected along the Chilcotin River upstream of the dam."

The flood warning – which means "river levels have exceeded bankfull or will exceed bankfull imminently" and flooding "will result" – is in effect upstream of the landslide, but officials are warning there could be major consequences downstream, as well.

"The eventual overtopping of the landslide material may lead to sudden erosion of the debris and catastrophic failure of the landslide dam," the river forecast centre's warning reads.

"This could potentially cause an outburst flood downstream of the landslide. In this scenario, a surge of water would rapidly move down the Chilcotin River and into the Fraser River. Water levels could increase extremely quickly along the Chilcotin River as well as in the Fraser River immediately below the confluence. In the event of catastrophic failure, the flood surge could reach the Fraser River within hours, potentially traveling from the Chilcotin River to Hope within a day."

A flood watch – which means that "river levels are rising and will approach or may exceed bankfull" – is in effect downstream from the landslide and into the Fraser River as far as Hope.

Farther downstream, a high streamflow advisory – which means "river levels are rising or expected to rise rapidly, but that no major flooding is expected" – is in effect.

The river forecast centre says the Lower Mainland would see "less severe" effects from a catastrophic failure of the landslide dam, but may still experience "substantial increases in flow" on the Fraser River.

Emergency alert, evacuation orders

The provincial government issued an emergency alert Wednesday afternoon, advising all people and boaters anywhere along the banks of the Chilcotin and Fraser rivers from Hanceville to Hope to leave the area "immediately."

Earlier in the day, the Cariboo Regional District issued evacuation orders covering a total of 60 parcels with a combined area of 10,750 hectares – or more than 107 square kilometres – along the river. 

The Tsilhqot'in National Government activated its emergency operations centre at "Level 1" and is "looking into the situation," according to a statement on the nation's website. 

"Please avoid the Chilcotin River area due to danger of unpredictable water flow," the nation's statement reads.

The regional district issued its first evacuation order related to the incident shortly after noon. That order covered 34 parcels and more than 7,000 hectares, stretching from a few kilometres west of the Big Creek Ecological Reserve southeast to where the Chilcotin River joins the Fraser River.

The CRD issued a second evacuation order less than 90 minutes later. This one covered an additional 26 parcels and nearly 3,500 hectares, extending the evacuation zone west along the Chilcotin River to the Hanceville Bridge, just south of Highway 20 near Lee's Corner, B.C.

The regional district advised those in the evacuation zone to travel north to Highway 20 and east to Williams Lake.

"Due to immediate danger to life safety due to flooding caused by landslide, members of the RCMP or other groups will be expediting this action," the evacuation order reads. 

"You must leave the area IMMEDIATELY. Persons who disregard this evacuation order and remain in the evacuation order area do so at their own risk."

Dog missing

Central Cariboo Search and Rescue said in a social media post that it was responding to "an injured individual and landslide west of Williams Lake" Wednesday morning. 

In an update posted around 1 p.m., the SAR team said the injured man was in stable condition and had been transferred to the care of BC Emergency Health Services.

"The story that we got from the male was that he was rafting down the river – which is very common – and he had set up camp for the night, himself and his dog," explained Debra Bortolussi, CCSAR's public relations co-ordinator.

Around midnight, Bortolussi said, the man heard a rumbling and found himself running away from the landslide. He sustained his injuries while fleeing.

The man's raft got caught up in the debris and was visible from the SAR helicopter, according to Bortolussi.

She said the man's dog remains unaccounted for, but crews are "really hopeful" that the animal will be found.

What happens next?

Davide Elmo, a professor of rock engineering at UBC's Norman B. Keevil Institute of Mining Engineering, told CTV News the type of slide seen Wednesday is not unprecedented.

He said he found records of previous slides on the Chilcotin River that occurred in 1964 and 2004, with debris from the 1964 event eventually being recovered as far downstream as New Westminster.

The first step in remediating the damage caused by the slide will be to determine how stable the dam it created is, Elmo said. Is it solid enough for a person to stand on it? If so, what kind of machinery can be brought onto it?

The answers to those questions will determine the next steps that can be taken, the professor said, noting that safely creating an outlet to drain the lake forming behind the dam is a priority, if it's possible to do.

"You cannot simply just make any action until you know what kind of access you have to the body of the dam," Elmo said. "Based on that, they may actually decide, 'OK, let's build, basically, a canal to help as the water comes out of the reservoir that's being formed.'"

Such a canal would function similarly to a spillway on an artificial dam, allowing a more controlled and gradual release of water bypassing the dam structure itself.

With that kind of structure in place to manage the flow of water and bypass the dam, crews could actually go in and remove debris from the landslide safely, Elmo said.

If such an approach is not possible, or can't be achieved before the water in the newly formed lake overtops the dam, then the catastrophic failure scenario outlined in the river forecast centre's warning becomes more likely.

Elmo warned that a crack or hole in the dam itself could quickly erode as the water pushes through it.

"It's not, basically, 'Let's open up a hole and let the water drain,'" he said. "It's not that simple."

A photo shared by Central Cariboo Search and Rescue shows the scale of the landslide that blocked the Chilcotin River on Wednesday, July 31, 2024. (Facebook / Central Cariboo Search and Rescue)