Dam overflow seems more likely than sudden dam break on Chilcotin River, provincial government says

While a dam created by a massive landslide along the Chilcotin River west of Williams Lake remains a serious safety risk for those living downstream, current modeling shows an overtopping of the dam appears more likely than a sudden release or dam break, the provincial government said in a news conference Friday afternoon.

B.C. Minister of Emergency Management and Climate Readiness Bowinn Ma says depending on the distribution and nature of the overtopping flow, the impacts could still be significant.

So far, the modeling doesn’t indicated the likely need for mass evacuations, Ma said.

“However, this is based on information that is actively being developed and underway, and we do need people to be prepared for the first scenario, which is why we are asking everyone who lives by the Chilcotin River and the Fraser River between the Chilcotin River and Hope to be prepared with emergency grab-and-go bags just in case,” she said.

“Please, keep in mind this is not a confirmation of what will occur. Rather, it is not the only scenario that we are planning for, but it is one that we are planning for.”

Minister of Municipal of State for Lands and Natural Resource Operations Nathan Cullen says the government now has a greater understanding as to the nature of the slide and its potential impacts due to monitoring equipment and time lapse cameras.

“The Water Survey of Canada is also in stage to gage on the lake behind the dam to monitor the water level and its rate of change, because this monitoring is in effect 24 hours, seven days a week, we can ensure we have the best information available so we can understand the dynamic situation,” Cullen said.

Ma says the province will issue emergency alerts to cell phones, radio, and TV if evacuation is necessary.

“If you receive [an emergency alert], please take it seriously,” she said. It remains imperative for people, especially those living along the Chilcotin downstream of the landslide, to be prepared to leave on a moment’s notice if necessary, please make sure that you have your grab and go bags. Make sure you have an emergency plan that considers all family members and pets.”

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, creating a serious safety risk to those downstream.

Officials said 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.

According to Connie Chapman, executive director of B.C.’s water management, the material that makes up the dam is highly susceptible to erosion and landslides in this location.

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