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The overflowing Nooksack River played a big part in Abbotsford’s devastating floods, but communities and researchers are still debating whether the river is more flood-prone than it used to be – and if so, why

An acoustic Doppler current profiler scans the bottom of the Nooksack River near Everson, Wash., on Dec. 1, as workers with the U.S. Geological Survey take measurements from a nearby bridge.Nathan VanderKlippe / The Globe and Mail

Dexter Cunningham is no hydrologist. He has no credentials in river studies.

What he does possess is a house located at almost the exact spot where Nooksack River waters occasionally spill over Main Street in Everson, Wash. So for 18 years he has carefully monitored the gauges that measure the river’s height. His read of the river is so keen that local officials have told him they calibrate their flood-response preparations in part by watching how many sandbags he has stacked around his property.

What he sees is important to Canada, too, since the flood waters that pass his house flow toward the Abbotsford area of British Columbia. Nooksack water was a powerful contributor to the floods that destroyed property and killed hundreds of thousands of farm animals in the province last month.

If changes in the river make it more prone to overflow, that has direct consequences for the severity of floods in Canada.

And Mr. Cunningham is convinced the river is changing. In the early 2000s, the water from record Nooksack heights, as measured at a gauge nine kilometres away, rose only to 15 centimetres below the main floor of his house. In mid-November, the river set a new record, roughly 30 centimetres higher as measured at Cedarville, a nearby spot where the U.S. Geological Survey maintains a gauge. But the flood waters in Everson rose more than a metre higher, sending water coursing through the Cunningham home.

In a subsequent flood that began Nov. 28, the river gauge showed waters well below the previous record. That water “shouldn’t even have crossed the road,” Mr. Cunningham said. Instead, it once again flooded his house, carrying a children’s playset into berry fields behind his property.

“The concerning thing is now we don’t know what to expect,” he said. “Lower height water is causing more damage than in the past.”

Something, he thinks, has changed in the Nooksack. Decades ago, he pointed out, local contractors harvested gravel from the river. But concerns about the destruction of salmon habitat largely put a halt to that practice almost 30 years ago.

Over the years, Mr. Cunningham believes, sediment has built up in the river, making it more likely to burst its banks. He likens the river to a five-gallon pail full of water: The water will spill out if the pail is filled halfway with sand.

“As far as the river is concerned, a lot of people are screaming, ‘Dredge the river! Dredge the river!’ ” he said.

A Canada-U.S. border marker is surrounded by floodwaters in Abbotsford on Dec. 1.Darryl Dyck/The Canadian Press

Mr. Cunningham isn’t alone in wondering whether what the Nooksack left behind near his home is part of the reason the November floods were so devastating.

“It has been observed that the Nooksack River has been aggrading in certain locations including near Everson at the overflow location,” engineers wrote in a flood-mitigation plan completed for the city of Abbotsford in November, 2020. “Aggrading” is a technical term meaning “filling with sediment.”

As a result, “it appears that the overflows are occurring at lower Nooksack River flow rates as evidenced by the recent February 2020 overflow event,” the report found, saying it would be “prudent” to make changes to computerized flood models “as the overflows may become larger than previously modelled for the same return period flood.”

Restoring the river to its 1971 throughput was among the first recommendations from an international task force created in 1991.

But the Nooksack drains into the Salish Sea, and its waters sustain chinook salmon in the river and, in the waters beyond, resident orcas for whom those fish are a preferred food source. Chinooks are listed as a threatened species. The resident orcas are considered critically endangered. Restoration of the river’s salmon has been a key priority for the Lummi Nation, a Coast Salish group that lives at the mouth of the Nooksack.

Some scholars, too, dispute the notion that a changing river bottom could affect the river’s likelihood of spilling over.

“I am not aware of evidence that supports the claim that increasing sediment in the Nooksack stream channel is causing the flooding,” said Robert Mitchell, a geologist at Western Washington University. And the record rainfalls in mid-November meant some flooding was inevitable.

But there is no question that the Nooksack, a wild river without dams, is being constantly remade in ways that make its behaviour difficult to predict – a factor that may have contributed to the degree of the recent flooding.

The U.S. Army Corps of Engineers attempt to build dikes to prevent additional flooding on the Sumas Prairie in Nooksack, Wash.Nathan VanderKlippe/The Globe and Mail

It descends from glaciated peaks and in heavy rains its current can reach 16 kilometres an hour at Cedarville, turning its waters into a powerful force that sculpts the land. Every year, the Nooksack carries an estimated 1.4 million tons of sediment along its route.

It’s possible a slug of sediment has settled near the spot where it floods toward Canada, scientists say.

“It is reasonable to believe that sedimentation has settled in there along the Everson area,” said Brent Bower, a senior service hydrologist for the National Weather Service Seattle. That could mean the Nooksack was “sitting higher in the stream and overflowed north.”

What to do in response is a question of considerable debate.

Political leaders in B.C. and local authorities in northern Washington have for many years called for the river to be dredged. But salmon lay their eggs on the river bottom.

“Looking at the environmental concerns, it has been difficult to remove a lot of gravel” while maintaining “a viable fishery there,” said Dave Radabaugh, Washington’s National Flood Insurance Program Co-ordinator. Better, he said, to build resilience outside the river. He has recently been speaking to people “about where buildings need to be elevated.”

Watch the U.S. Geological Survey at work as it studies the behaviour of the Nooksack River.

The Globe and Mail

Over the past month, workers with the U.S. Geological Survey have come out to make additional measurements each time the Nooksack has risen toward flood levels.

They were here in the worst floods of mid-November, when the raging torrent created standing waves and swept away Douglas fir trees, which can reach 75 metres in height. They returned again repeatedly as the waters rose, in early December, when they stood on a bridge near the Cedarville gauge. Here, they lowered into the water an acoustic Doppler current profiler, a device that looks like a miniature boat and uses sound waves to scan the river bottom and detect particles in the water, to determine the speed and direction of those particles.

The scans provide a detailed profile of the river bottom and have shown that, in the past month, the waters dug out a further two metres from the deepest part of the river. Elsewhere, more sediment has been deposited.

“We did see some pretty significant stream bed change,” said John Greene, chief of the northwest Washington field office of the U.S. Geological Survey.

Those measurements, however, only show a single cross-section of the river. What has happened elsewhere remains a mystery.

Whatever that is, Mr. Cunningham’s family no longer feels safe.

“My wife refuses to move back in here,” he said. And “I can’t as a good human pass this problem on to somebody else.”

That leaves him in a bind: Keep the house until it is paid off? Or find some other solution?

“There’s a few houses along here that shouldn’t be here, in my opinion,” he said. “Because of danger to life and property.”

B.C. floods: More from The Globe and Mail

The Decibel

Reporters Andrea Woo and Ann Hui spoke on The Globe and Mail’s news podcast about the post-flood situation in Abbotsford, part of B.C.’s agricultural heartland, and what impact it will have on the food supply. Subscribe for more episodes.

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