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United States 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

Months after floodwaters from a Washington State river destroyed property in British Columbia, U.S. authorities are proposing measures that would protect their urban areas from future disasters but could send additional water north to Canada.

In Washington’s Whatcom County, officials are discussing plans to clear houses from a floodway that carries water to Canada and build a ring dike around Everson, the community on a bend in the Nooksack River where it has repeatedly breached its banks. Water that spills there flows downhill toward a drained lake in B.C., known as Sumas Prairie, that forms some of the most prime agricultural land in the province.

Such a dike would keep Everson dry, but would mean those diverted floodwaters “would be added to the overflow” heading toward the border, Paula Harris, the river and flood manager for Whatcom County, said in an interview.

It’s a proposal that has renewed attention to long-standing failures by Canada and the U.S. to co-operate on management of a flood-prone waterway.

Discussion of such a dike remains preliminary, and any additional water would be modest relative to the torrential overflows that caused an estimated $1-billion in damages to the Abbotsford area in November, 2021. Modelling work would need to be done to determine the exact effect of an Everson ring dike on Nooksack flooding.

But “I doubt it’s going to be significant in increasing any flows north,” said Ms. Harris, an expert in hydraulic modelling who has worked at the county for nearly a quarter-century, and is an authority on the Nooksack.

Flooded farms in Sumas Prairie, Abbotsford, B.C., on Nov. 22, 2021.DARRYL DYCK/The Canadian Press

The existing flood path has proven dangerous to property north of the Nooksack, and the focus on protecting some urban areas rather than holding back the river has raised anxieties on both sides of the border.

“If we don’t plug it up, the water keeps coming this way,” said Bruce Bosch, the mayor of Sumas, the Washington border town that receives Nooksack floodwaters before they enter the Abbotsford area. “We’re concerned about it, too.”

The contribution of Nooksack floodwaters to destruction around Abbotsford has prompted cross-border finger-pointing, and even raised questions of whether Canada could sue the U.S. for damages.

A recent engineering study for the city of Abbotsford suggested that a $29-million Nooksack levee at Everson could prevent hundreds of millions of dollars in damage around Abbotsford. Modelling by officials in Washington State, however, shows that such a project would cause greater downstream damage in the state, including more flooding of I-5, a key highway.

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Now, the prospect of U.S. officials taking flood action that could keep water flowing toward Canada has raised alarm that the two countries are reprising a history of ineffective co-operation on managing the Nooksack.

A Nooksack River International Task Force, struck three decades ago, has not met since 2019 – and no dates have been set for new meetings, although talks have begun toward reinvigorating that body. The B.C. government has also not encouraged the referral of a case to the International Joint Commission, a joint U.S.-Canada body dedicated to resolving cross-border issues.

“The Americans are doing what you would expect the Americans to do, which is begin to explore options to minimize damage from this catastrophic flooding,” said B.C. Abbotsford-West MLA Mike de Jong, who sits in the provincial opposition. “If the Americans begin to make decisions in the absence of submissions from Canada, we may find that this train leaves the station, and those concerns are ultimately ignored.”

Other plans under discussion in Washington State could address some of those worries. Local and county officials have begun examining ways to buy out houses in the Nooksack floodway between Everson and the Abbotsford area. In Everson, that could involve the purchase of roughly a dozen properties, which would then be demolished. Those buyouts alone could cost US$6-million, and work is already under way to seek grant money to make the purchases.

Clearing away those houses would not alter floodwater volumes, but it could make it easier to make changes that would slow their flow, such as raising roadways. Intervening to increase water levels in the floodway is more difficult when it stands to damage property.

“Our current proposal is to try to get people out of harm’s way and create some landscapes that could provide an opportunity to do something like store more water,” Ms. Harris said. She pledged a cautious approach. “We just don’t go directing water to other places without fully trying to mitigate the impacts there,” she said.

The B.C. government said last week it is “in very active discussions with Washington State on the Nooksack River,” including direct conversation between Premier John Horgan and Washington State Governor Jay Inslee.

Provincial and state officials have connected weekly since the floods, and both sides “agree that solutions must protect people and communities on both sides of the border, including Abbotsford,” Mr. Horgan’s office said in a statement. “Intentional flooding over the border is out of the question for both B.C. and Washington State.”

Local leaders have also made contact, including phone calls between Abbotsford Mayor Henry Braun and his Everson counterpart, John Perry. Several weeks ago, Everson created a 60-centimetre-tall sandbag levee near the sections of the Nooksack that is prone to breaching its banks. It’s a temporary solution, but in a 20-year flood event that could lower the level of northbound floodwaters by some 30 centimetres, “which would in turn help Sumas and Abbotsford,” Mr. Perry said.

Long-term, likewise, “the idea is that we could create more capacity in those areas to hold more water,” he said. “Not necessarily to send more north.”

Such efforts have been complicated by changes to the Nooksack itself. Accumulations of sediment and vegetation near Everson have diminished the river’s carrying capacity, making it considerably more prone to flood. Salmon concerns have barred some solutions, such as dredging the river.

One potential alternative involves creating side channels that could absorb floodwaters while adding areas for salmon habitat, Mr. Perry said.

But any change to managing the river carries costs as well as benefits, he said.

“If you take water away from one area, then it’s going to go somewhere else,” he said. “You push on the river and it tends to push back.”

With a report from Justine Hunter

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