B.C. flood: American waterway at the root of Sumas Prairie disaster

Vancouver -

In the hours before the Sumas Prairie flooded, the rain was coming down hard and fast in the Fraser Valley. However, experts say, the rain is not what put the prairie underwater.

“A lot of that water is coming from spillover from the Nooksack (River),” said Dave Campbell, head of the B.C. River Forecast Centre.

The Nooksack River flows north of Bellingham in Washington State. When it overflows, Campbell says, floodwater can end up in the Sumas River. From there, the water flows northeast, crossing the border into Abbotsford.

Usually, the Barrowtown Pump Station keeps the Sumas Prairie from pooling, but this time, the Sumas river breached a dike, causing disaster.

“It’s signalling a significant shift in how floods are caused,” said Campbell.

Floodwater from the U.S. has been a concern for Abbotsford. In 2019, the city commissioned engineering firm Kerr Wood Leidal to create the Nooksack River Overflow Flood Mitigation Plan. The report, completed in 2020, offers several options to prevent Nooksack River floodwater from entering Abbostford, including rerouting waterways or constructing a physical barrier along the Nooksack to block it from overflowing.

Once water levels recede and officials investigate, Campbell says the city’s mitigation plan will be a valuable resource.

“To look at what some of those (prevention) options are,” he said. “Obviously, interaction with our U.S. counterparts is key to that, but also looking at what we can do on the Canadian side.”

The Nooksack River breached its bank because of the same atmospheric river that brought heavy rain and warm temperatures to B.C. Parts of the Fraser Valley saw one month’s worth of rainfall in just two days.

In Merritt and Princeton, snowmelt made the storm even worse. So did the many hectares of scorched land in B.C.'s Interior after a devastating wildfire season.

“The ground essentially becomes hydrophobic,” explained Bobby Sekhon, a meteorologist for Environment and Climate Change Canada.

“It doesn’t have trees or root structures to hold the moisture in place, and oftentimes, water will just run right over that soil.”

While large-scale flooding like what’s happening in Sumas Prairie is a rare phenomenon in the province, experts say it could become a routine occurrence because of climate change.

“We know we are warming and can expect more extreme weather in the future. That could be more intense atmospheric rivers,” said Sekhon.​