Water likely to overtop Chilcotin landslide Sunday or Monday; threat to communities remains less than originally feared, says B.C. government

In an update Sunday afternoon, the provincial government said the water collecting behind the Chilcotin landslide is likely to overtop the dam soon.

“Based on current modelling, it’s expected that water will start to move over (overtop) the blockage late on Sunday, Aug. 4, 2024, or early on Monday, Aug. 5, 2024, and enter the riverbed below the slide site,” the news release said.

On Saturday, the government said that even in a worst-case scenario, risk to communities along the Chilcotin River due to a landslide earlier this week is likely to be lower than previously thought, the provincial government said in an update Saturday afternoon.

This is based on the latest modelling and monitoring conducted by the Water Management Branch.

“The news today is that we’re more confident that the river will naturally overtop the dam, that the risk to public and communities downstream is likely lower than what we all feared just a few days ago, but we also know that these are models, not guarantees,” said Minister of Natural Resources Nathan Cullen.

“The modeling now suggests that even those worst-case scenarios of a significant breach happening quite quickly, levels, particularly in the Fraser River, might only be slightly higher than what we would expect in spring snowmelt season, although flows on the Chilcotin River are expected to be above normal freshet flows by a significant margin, which brings real risk for that ecosystem and the banks along that river.”

Minister of Emergency Management Bowinn Ma says this latest update is encouraging for downstream communities, but we aren’t out of the woods yet.

“We nevertheless continue to coordinate closely with communities along the rivers to ensure that we’re prepared to protect people from potential flooding,” Ma said.

“We are taking the necessary precautions to protect people, livestock, and infrastructure.”

For example, Ma says, Interior health is relocating patients from Lillooet to an alternative location. As well, 2,500 cattle have been evacuated from the landslide area.

She says she wants to remind the public that an evacuation order along the entire Chilcotin River between Hanceville and the Fraser River has been in place since July 31.

Connie Chapman, executive director of the Water Management Branch, says the landslide is around 1,000 metres long, 100 metres wide, and 30 metres high. She says the lake behind the dam has been increasing at a rate of about 22 centimetres per hour.

“This is a little bit of a decrease from what we’ve seen in the first couple days, but to be expected, as the water has more area to spread out once it’s reached past the banks of the the channelized structure,” Chapman said. “You’re still seeing no seepage at the toe of the dam, which is a good thing.”

On Thursday, the Cariboo Regional District said a dam created by a massive landslide on the Chilcotin River west of Williams Lake on Wednesday was expected to be breached within the next 24 to 48 hours, which they felt at the time posed a serious safety risk to those downstream.

Officials said earlier this week that they were bracing for what will happen when the debris gives way.

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

Even in light of the latest news, Cullen says it is important to be prepared for any eventuality.

“We are not letting our guard down even for a second,” he said.

With files from Charlie Carey, Joe Sadowski, and Monika Gul.