Water rise from Chilcotin River landslide may not be as high as feared: B.C. officials

globalnews.ca:

A remote landslide in B.C.’s Central Interior that’s blocking a river is still being closely monitored.

On Saturday afternoon, the province issued an update, saying the Chilcotin River landslide is still seeing activity as some debris continues to tumble down.

The government said this is expected, considering Wednesday’s landslide is still relatively new.

Located around 100 km southwest of Williams Lake, the dam is estimated to be 1,000 metres in length, 100 metres high and 30 metres in depth.

It also said the sudden lake from pooling water behind the dam is continuing to grow at a rate of 22 cm per hour.

Officials also discussed worst- and best-case scenarios.

In the worst-case scenario, water breaches the top of the dam, with the dam then failing one hour later.

The rush of water would be instant and stunning, with the Chilcotin River rising around 10 metres.

A typical freshet flow during spring runoff in the Chilcotin River is around 300 cubic metres per second. In this case, that would incredulously spike to 6,500 cubic metres per second.

Officials say it would take that water three hours to rush down the Chilcotin River and into the Fraser River, where it empties.

At that confluence, this scenario would see water rush into the Fraser at around 5,500 cubic metres per second. That equates to peak height being around four metres higher above their current elevation.

Downstream at Lillooet, which would take 15 hours to reach, the peak height would be around 1.8 metres above water levels now. The flow there would be around 2,650 cubic metres per second.

“The good news is that once we hit the Fraser River, this water and material has a significant amount of room to spread out and disperse,” said Connie Chapman, who is