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.
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.”
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.”
With files from CTV News Vancouver’s Ian Holliday.