Some of the most fertile land in southern B.C.’s Fraser Valley is the former lake-bed of Semá:th Xhotsa (Sumas Lake), where water has been held back for a century. The region, which once supported an ancient Indigenous food system, has been home to farms and ranches since it was drained in 1924. But during the disastrous 2021 B.C. floods, part of the lake reflooded again, causing millions in damages.

A team of researchers, led by the University of British Columbia along with members of the Sumas Nation, analyzed four flood response scenarios proposed by the City of Abbotsford. They concluded it could be cheaper to buy back some private land and reflood part of the former lake-bed — now known as Sumas Prairie — rather than build up the concrete infrastructure necessary to try to keep Semá:th Xhotsa dry forever. “We find that the cost of buying out properties in the lake-bed and allowing the lake to return is close to half the cost ($1 billion) of maintaining the status quo ($2.4 billion),” the authors conclude in the newly-published paper.

The Semá:th People relied on the lake before it was drained and the Sumas Nation supports further research into flooding part of the lake to support the restoration of the ecosystem and mitigate disasters. But the city made it clear that managed retreat is not an option it’s planning to consider.