Dam in Chilcotin River will be overtaken by water within hours: B.C. officials

A landslide along the Chilcotin River near Williams Lake, B.C. is shown in this Thursday, Aug. 1, 2024 handout photo. (THE CANADIAN PRESS/Chief Willie Sellars)

Water is expected to start flowing over a landslide-created dam in the Chilcotin River Sunday night or early Monday morning, according to an update from officials.

The Ministry of Emergency Management issued an information bulletin with the updated timeline, while repeating its plea for people to avoid the river between Hanceville and the confluence of the Fraser River.

“People are also advised to stay away from the banks of the Fraser River. Planning continues to address potential impacts of debris as it relates to public safety,” the statement says.

“Risks to public safety include the potential for further landslides upstream of the natural dam and downstream of the dam once water begins to flow past it.”

Since July 30, minimal water has seeped through the massive obstruction – which is estimated at 30 metres deep, 1,000 metres long and 600 metres wide – and water levels behind the dam have been steadily rising by about 18 centimetres per hour.

However, modelling shows that the water is not likely to suddenly burst through the dam, which provincial officials have said would have been the worst-case scenario.

Officials say the best—and most likely—scenario is that it will take 12 to 24 hours for the water to move past the blockage. That would result in water levels below typical spring flooding on the Fraser River, but flows would still exceed freshet peaks on the Chilcotin.

"Ultimately, this is an encouraging development for communities downstream,” Emergency Management Minister Bowinn Ma said at a news conference Saturday.

“Though similar to elevation of heights during freshet flows, the water will react differently, with greater momentum and force, than a gradual increase in water levels,” Sunday’s bulletin reads.

Updated modelling now shows that in the case the lake behind the dam drains rapidly, within an hour, flows would be higher than what was predicted Saturday. The latest bulletin says water levels would be “significantly higher” on the Chilcotin River and at or below spring snowmelt flows on the Fraser.

“In this scenario, the water in the Chilcotin River could potentially rise to 21 metres at the Farwell Canyon bridge and 12 metres where the Chilcotin River meets the Fraser River,” the statement reads.

An evacuation order for 60 parcels of land along the northernmost part of the Chilcotin remains in effect, and officials asked people to stay away from the banks of the Fraser.

Members of the public have also been urged not to fly drones in the landslide area. The BC Wildfire Service issued an NOTAM (Notice to Airmen) on Friday, which makes using any aircraft in the area not part of landslide response illegal.

"For the safety of the air crew and of the public we are asking everyone to stay clear of the area both on the ground and in the airspace. This is extremely dangerous, and poses a threat to both the people that re-enter the area and experts who are assessing the situation on the ground,” Ma said Saturday.

Officials reiterated Sunday that the landslide could impact spawning salmon in the area, and said they are planning mitigation efforts. 

The province has also created a new, online portal dedicated to sharing information about the landslide and the response by provincial and local officials.