Rivers can be a fun place to beat the summer heat.
This August long weekend, though, B.C. officials are warning residents and visitors to stay away from the Chilcotin and Fraser rivers because of a potential rush of water from a landslide in the Central Interior.
As of Saturday morning, emergency alerts are still in place because of the remote but massive landslide that’s blocking the Chilcotin River.
Located around 100 km southwest of Williams Lake, the landslide came down Wednesday, damming the river and creating a temporary lake about 11 km long.
The landslide is 22 km upstream of the Farwell Canyon Bridge, which is around 82 km from Williams Lake. The Chilcotin River eventually feeds into the Fraser River.
The fear is if the dam suddenly breaks, the downstream rush of water could be disastrous.
“We cannot emphasize enough how important it is for people living in the area and downstream of the slide to remain vigilant and stay away from the river for their own safety,” said Nathan Cullen, the province’s water and land resources minister.
B.C.’s Emergency Management Minister, Bowinn Ma, says the best-case scenario is a gentle clearing (water flowing over the dam’s top) that doesn’t take flood debris down the river.
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However, both Ma and the B.C. River Forecast Centre say they’re planning for the worst-case scenario:A burst dam with water rushing down the Chilcotin and into the Fraser River.
The province issued an emergency alert late Friday, warning people anywhere on the Chilcotin River or along its banks between the Hanceville Bridge and the Fraser River to evacuate immediately.
A geotechnical engineering professor at UBC Okanagan, Dwayne Tannant, says the water “will erode and cut through that dam, probably releasing a substantial pulse of water.”
“It’s really all up to Mother Nature,” added Margo Wagner, chairperson of the Cariboo Regional District. “We can’t stress enough how important it is for people to stay away from the banks of the Chilcotin River.”
Wagner says the banks around the Chilcotin River are sandy and limestone and have been affected by wildfires.
“So the soil is pretty porous and the concern is that the rush of water – whether the dam breaks or the water goes over the top — could cause other land slippage,” said Wagner.
“We’ve been talking with the agricultural ranchers along the Chilcotin to remove their cattle from the banks, and make sure that everybody is as safe as possible.”
The River Forecast Centre says its modelling shows that if that occurs, the level in the Chilcotin River would be well above peak spring runoff until it gets to the Fraser River, while the estimated flows in the Fraser would be below typical spring peak water levels.
Ma says they are sending flood preparation equipment and sandbags to some communities along the Fraser River and are planning in case there’s a need to evacuate some communities, although that is unlikely.
The federal fisheries department is also monitoring the situation. It says adult chinook and sockeye salmon are currently present in the river and likely to be affected by the blockage.
Wagner added this reminder: “It’s best to stay off the Fraser and certainly off the Chilcotin because that will be the river that will be first impacted.”
— with files from the Canadian Press
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