A 100-year flood event combined with a breaching of the Nooksack River’s banks would inundate much of Sumas Prairie, and leave much of the area south of the Interceptor Dike under more than one-metre of water. An overtopping of the Nooksack (top left) would be slightly less devastating, while a flood that didn’t include a Nooksack breach (bottom right) would be less serious, according to new modelling.

A 100-year flood event combined with a breaching of the Nooksack River’s banks would inundate much of Sumas Prairie, and leave much of the area south of the Interceptor Dike under more than one-metre of water. An overtopping of the Nooksack (top left) would be slightly less devastating, while a flood that didn’t include a Nooksack breach (bottom right) would be less serious, according to new modelling.

Nooksack River flood risk study gets go-ahead after years of task force inaction

Modelling shows dangers of Nooksack to Sumas Prairie, but cross-border group hasn’t met since 2012

After years of dormancy, a cross-border group formed to try to reduce the damage of another Sumas Prairie flood is set to meet again over the coming months.

The federal government has also told the city it will get $250,000 it has asked for to prepare for such a disaster and collect information that can be used in upcoming meetings between stakeholders on both sides of the Canada/U.S. border.

The Nooksack flows through northern Washington from the slopes and valleys of Mount Baker west through Everson and Lynden, just south of Highway 1, and empties into Puget Sound near Bellingham.

When the Nooksack topped its banks in 1990, its waters inundated parts of Sumas Prairie and closed Highway 1 to traffic for 26 hours.

That flood led to the creation of an international task force to try to prevent a future event from occurring.

But after some initial work, the task force has sat dormant since 2011. (Technical meetings took place in 2012 and again this year.)

The issue, though, is back on the radar of local and provincial officials, and the city says a new task force meeting will be convened by the province by the end of next spring.

By that time, the city also hopes to have completed a study that will look at past data and develop a new plan to mitigate possible flooding. The goal, according to staff, is to give the province information that can contribute to discussions with Washington State on how to manage the Nooksack.

The task force convened more than two decades ago, with several goals, including to improve floodplain management, better the emergency responses to floods, and restore the capacity of the early 1970s Nooksack.

Most recent work, though, has been on developing a “comprehensive flood damage reduction plan.”

The 1990 flood was previously pegged as a one-in-35-year event.

Included in this week’s staff report on the issue are maps illustrating the extent of possible flooding were the Nooksack to breach its banks in a 100-year flood scenario.

Those maps show almost that all of Sumas Prairie south of the Interceptor Dike would fill with metres of water. The old Sumas Lake bed would also see water accumulation.

The report does not mention any investigation into a possible “avulsion” event, which would potentially see the Nooksack River change course and begin to flow north into Canada and toward the Fraser River.

A previous study suggested that such an event would “cause catastrophic damage to Sumas and West Sumas Prairie.”

RELATED: The Fraser River doesn’t pose the only flood threat to Abbotsford

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