B.C. preparing for 'worst-case scenario' if landslide-caused dam in Chilcotin River gives way

The risk to communities along the Fraser and Chilcotin rivers if a dam created by a massive landslide is breached is uncertain but has the potential to be "significant," according to officials.

The landslide prompted evacuation orders and flood warnings, and at a Thursday news conference the situation was repeatedly described by provincial ministers as both dynamic and concerning. The dam created by the slide is between 600 and 800 metres wide and 30 metres deep

"In the event of the dam collapsing, an outburst of water would flow down the Chilcotin River and into the Fraser River, bringing with it a significant amount of debris. Water levels could increase extremely quickly along the Chilcotin River, as well as in the Fraser River immediately below the confluence to Hope," Emergency Management Minister Bowinn Ma said.

"This is a dynamic situation, and we must be prepared for the worst-case scenario right now."

Assessing the downstream risks in the event the dam is breached is a priority, but pending those assessments, Ma said predicting if and when the dam will break and how far-reaching the impacts will be is impossible.

"I am urging all British Columbians that live or work near the Chilcotin River and the Fraser River between the Chilcotin confluence and Hope to remain extremely vigilant. If this dam were to break, it is possible that dozens of evacuation orders and alerts will be issued along both rivers and people need to be prepared," Ma said.

Local ranchers on edge

The landslide was first discovered by Ken Ilnicki, a Riske Creek resident whose family ranch is one kilometre away. His wife Deb says if and when the dam breaks, she hopes it's during waking hours.

“Hopefully, it lets go during the day when people can watch and prepare and know what’s coming at you,” she said Thursday.

So far, no homes have been damaged, but those living nearby are on edge, and Deb notes the property closest to the dam – another ranch -- is located close to the river’s edge.

“If this breaks and goes quickly, it’s going to be pretty much catastrophic for their place,” she said

Deb's husband not only called in news of the landslide when he discovered it, he also called for help after spotting a camper who had broken his leg while trying to escape.

“They could then hear a noise and realized it was someone calling for help from across the river,” she recounted. “He’s extremely lucky, he’s really lucky.”

Search and rescue crews found the man, who had been rafting down the river, and got him to safety. But the man's dog is still missing.

More emergency alerts possible

In the event the dam does suddenly break, officials say they estimate it would take between 12 and 24 hours for the water to reach Hope. 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.

Nathan Cullen, minister for water, land and resource stewardship, says a sudden break sending a surge of water downstream is the worst-case scenario. Work is, however, underway to "understand if a slower release of water is imminent or possible, in a natural way or through other interventions."

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.

"Sudden potential flooding and debris flow in and around the Chilcotin and Fraser rivers poses a threat to human life," the alert said.

Ma said further alerts are possible as the situation evolves. She also said that the evacuation orders in place – which cover an area of more than 107 square kilometres – don't include any primary residences. A reception centre has been set up in Williams Lake as what Ma describes as a "precautionary measure."

Threats to human life and property aren’t the only concern, Cullen said during the news conference.

"We also know that the Chilcotin is a critical spawning habitat for salmon and other fish. Very critically, the sockeye moving up the system right now are meant to arrive in a couple of weeks," he said.

"So we are initiating early plans as to what we can do to make sure that those stocks remain intact." 

With files from CTV News Vancouver's Ian Holliday.