Time and tide wait for no man. Neither does sea level rise.
The Chignecto Isthmus—the low marshy strip connecting New Brunswick and Nova Scotia—may be one of the most vulnerable places in Canada to sea level rise. At just 21 kilometers wide, the interprovincial land bridge is battered on its southwestern flank by the famously extreme tides in the Bay of Fundy. Protected by a network of earthen dikes first constructed in the 1600s, “the tops of the dikes are only a little higher than the spring high tides,” says Jeff Ollerhead, a coastal geomorphologist at Mount Allison University, located in Sackville, New Brunswick, at the western end of the isthmus. “If we have a big storm,” he says, “water will go over the dikes.”
When scientists and the public fret about sea level rise, they mostly focus on when and where communities will be permanently flooded. But there’s another consequence of rising seas that will affect many more people much sooner: getting cut off from roads and other critical infrastructure. It’s a threat that society has not paid nearly enough attention to, says Allison Reilly, a civil engineer at the University of Maryland.
The flood-prone Chignecto Isthmus shows what’s at stake. Hidden behind the barely sufficient dikes are reams of vital infrastructure: the Trans-Canada Highway, a Canadian National Railway line, multiple electrical transmission lines and fiber-optic cables, a wind farm, and agricultural land.
Though it’s unlikely the Chignecto Isthmus will be fully flooded any time soon—a disastrous outcome that would sever the link between New Brunswick and Nova Scotia—disruptions from storm-related flooding are becoming more common. That’s bad news for people like Ollerhead, who frequently cross the isthmus to get to medical appointments, access the international airport in Halifax, Nova Scotia, or even take shopping trips to Ikea. At a broader scale, temporary flooding of the highway or rail line could disrupt activity in the Port of Halifax, a major economic driver for the region.
In a new paper, Reilly and her colleagues show the breadth and pace of the isolation threat. Inspired by her work on the eastern shore of Maryland, where people already need to adjust their travel and work schedules to account for tides that frequently swamp roads, Reilly and her colleagues calculated that, with one meter of sea level rise, twice as many people across the coastal United States will be isolated than will be inundated. “People who live [three meters] above sea level, their house might be okay,” she says. “But that doesn’t mean they will be reliably able to get to the grocery store…”