Chilcotin River could breach landslide dam within 24-48 hours: CRD

A dam created by a massive landslide along the Chilcotin River west of Williams Lake on Wednesday is expected to be breached within the next 24 to 48 hours, creating a serious safety risk to those downstream, the Cariboo Regional District said.

In an update Thursday morning, CRD Chair Margo Wagner shared that there is an “imminent risk to public safety” due to the possibility of a breach.

“The Chilcotin River was completely blocked by a large landslide approximately 20 kilometres upstream from the Farwell Canyon Bridge,” Wagner said. “We are really stressing how important it is to stay away from the Chilcotin River and Valley.”

“Flooding is building up above the dam created by the landslide,” she explained. “It’s like a lake, and there is a risk of a flash flood downstream if the river breaches that landslide, which it is expected to do eventually.”

Wagner explained that while it’s difficult to accurately assess when the dam will break, the “current estimate is within the next 24 to 48 hours.”

“It will be one of two ways — the water will either rise enough that it will end up going over the top of the landslide, which, remember, is 30 metres deep, or there will be a small fissure develop in some soil and water will start oozing through,” she explained.

Wagner says the situation can be dangerous for those in the surrounding area.

“Because it’s sand-based, and water and sand don’t do well together, it’ll just disappear and that will end up giving way.

“Evacuation orders are in place around the slide site and down river to the Fraser River, where further actions have been taken to protect public safety, including high streamflow advisories and stopping ferry services at Lytton and Big Bar,” she added.

“We don’t have a certain timeline of when that could breach, [but] the risk is imminent, and that is why the evacuation order has been put in place downstream of the dam. There is an imminent risk to public safety.”

Approximately 13 residents are currently covered by an evacuation order within the CRD, Wagner said, and have been ordered out of their properties.

Due to the instability of the area, a geotechnical analysis has not been able to be completed, Wagner shared.

“However, we do know that this slide occurred on a burned-out area on the Chilcotin River banks from the 2017 fires,” she said. “Unfortunately there is a lot of area where the trees are dead.”

“The trees are still standing, but their root system is totally dead, and they are not absorbing water, which is an issue, because then you have nothing to absorb any water that is in the ground.

“It’s all a sand-based area, so then the ground becomes unstable.”

Wagner shared that while speaking to Emergency Management and Climate Preparedness Minister Bowinn Ma on Wednesday night, she was informed that some engineers have flown to the landslide site, and the province was expected to send in geotechnical engineers Thursday.

“The landslide remains high risk. It’s not safe for first responders or equipment to be on or near the slide, let alone downstream of the slide area,” Wagner explained, adding that the Ministry of Water, Lands, and Resource Stewardship is coordinating the information gathering about the landslide.

Wagner confirmed that one man was injured during the incident on Wednesday, breaking his leg while trying to escape the landslide. “He is doing well, he was in stable condition when he was admitted to Williams Lake Memorial Hospital,” she said, adding that the man’s dog is still missing.

Stay away from Chilcotin and Fraser rivers, emergency minister says

The province is urging all British Columbians to stay away from the Chilcotin and Fraser rivers as the risk to people along the rivers “has the potential to be significant,” Minister Ma said in an update Thursday afternoon.

“Our primary concern right now is the potential impacts to people and communities if this dam were to experience a sudden collapse,” Ma said.

“In the event, the water would flow from the Chilcotin River into the Fraser River, bringing with it a significant amount of debris. The river could increase extremely quickly along the Chilcotin River as well as in the Fraser River immediately below the confluence to Hope.

“This is a dynamic situation, and we must be prepared for the worst scenario right now.”

“I’m asking everyone to avoid the Fraser River from the Chilcotin confluence to Hope until the province can have a better understanding of the potential impacts if this dam were to fail,” Ma urged.

If the dam were to fail, all boaters and people along the rivers would need to leave the area immediately. Ma explained that in the event of the breach, officials anticipate the water from the blockage in the Chilcotin to take about 12 to 24 hours to reach Hope via the Fraser River.

“If you were planning to boat on the Fraser this weekend, I am urging you to change your plans and avoid the Fraser, particularly between Hope and the Chilcotin confluence.”

“This includes avoiding the shoreline of the rivers, the banks can become unstable if there’s a sudden rush of water,” Ma added.

Ma said the landslide is creating a “number of concerns” for officials.

“There is the potential for sudden release of the blockage that would send not only water, but heavy amounts of debris downstream — this could be exacerbated further by erosion along the way. 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, and those can have significant impacts on the ecology of the river system. So, those kinds of impacts can be more widespread than the immediate concern for life safety,” she explained.

“Our most immediate concern is for life and safety.”

Flood warnings, watches, and high stream advisories are in place for rivers and tributaries of the Chilcotin and Fraser rivers, Ma said.

“The Fraser River Forecast Centre has issued a flood warning for the Chilcotin River upstream of the landslide in the vicinity of Farwell Canyon. They have also issued a flood watch for the Chilcotin River downstream to Hope,” she explained. “There is also a high stream flow advisory for the Fraser River down out into the mouth of the Fraser.”

Engineers, geologists, hydrologists, biologists, and other technical experts are currently on site assessing the situation, and mapping is currently underway, Ma said.

“There is evidence that there is water seepage through the dam. And so while it was anticipated, or it appeared, to be a total and complete blockage yesterday, our on-site monitors are reporting that there is some water seepage at the blockage site,” Ma added. “Of course, the Chilcotin is also fed by many other tributaries, it is possible that the water is finding its way elsewhere. But again, these assessments are dynamic and happening, as we speak.”

Officials bracing for breach

Officials say they’re bracing for what will happen when the debris — which is about 600 metres wide and 30 metres deep — gives way.

“In the event of the dam collapsing, an outburst of water could flow down the Chilcotin River and into the Fraser River, bringing with it, a significant amount of debris,” said B.C. Minister of Emergency Management and Climate Readiness Bowinn Ma.

“So 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.”

The slide prompted evacuation orders for 60 properties, including 12 homes.

With files from Monika Gul.

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