Study warns efforts to protect Highway 12 could be making flooding worse

Waves from Hurricane Erin surged over N.C. Highway 12, Wednesday, pushing seawater and sand across the asphalt and breaching dunes along the fragile barrier islands of the Outer Banks.

For longtime residents, scenes like this are no longer rare. And a new collaborative study suggests that these disruptions are only the beginning.

“Storms and even high tides, as we’ve been seeing in recent years, cause flooding and overwash of sand onto oceanfront roads,” said Laura Moore, a UNC-Chapel Hill professor and one of the study’s lead authors. “That’s problematic for transportation, but the washing up of sand is actually vital to maintaining island elevation and width.”

For decades, the state has tried to protect Highway 12 — the only road connecting Ocracoke Island to Hatteras and the mainland — by building dunes, placing sandbags, and repairing washed-out stretches after every major storm. But Moore and her colleagues warn that these strategies may be making the problem worse.

“When we protect roadways by building dunes and placing sandbags, we’re preventing sand from washing onto the islands like it naturally would,” Moore said. “That means the islands become lower and narrower over time. And when sea levels are rising as quickly as they are now, that narrowing and lowering happen even faster, which means roads and property become more and more vulnerable.”

The paradox, researchers say, is that the very storms that threaten homes and infrastructure are also essential to the islands’ survival.

“The storm events we need to protect roads and buildings from are actually the same events that would otherwise be building island elevation and allowing islands to grow wider,” Moore said. “The more successful we are in preventing storm impacts, the more quickly we’re essentially managing the barrier islands out from underneath us.”

The team used advanced computer models to simulate different management scenarios: continuing current practices, adding beach nourishment, or allowing natural overwash to resume while exploring alternative transportation options such as elevated bridges or rerouted ferries.

The results were sobering. In scenarios where Highway 12 continues to be defended in its current location, the models suggest the road will require increasingly frequent repairs while the island itself loses elevation and width.

“If we invest in the roadway, it will be a short-term investment, not a long-term one,” Moore said.

The report comes as Erin offers a stark illustration of those findings. The Category 1 hurricane isn’t even expected to make landfall, yet its offshore winds and storm surge are already swamping the highway and flooding low-lying streets.

“It doesn’t take a storm making landfall for these roads to be affected,” Dr. Moore said. “People’s lives and livelihoods are hugely impacted when that road closes, sometimes for weeks at a time. But if we continue managing barrier islands the way we are, the ability to live on them at all may eventually be at stake.”

The study underscores a painful dilemma for Ocracoke and other coastal communities up and down the Eastern Seaboard. Protecting the road and nearby development can keep residents connected in the short term. But doing so may be accelerating the very processes — island narrowing, lowering, and erosion — that threaten the long-term habitability of the islands themselves.

“It’s the overwash of sand that built these islands in the first place and allows them to persist,” Moore said. “By blocking that process to defend roadways and buildings, we’re starving these islands of the lifeline they need to exist.”

For now, crews with the North Carolina Department of Transportation are working to keep Highway 12 open as Erin’s waves continue to pound the shoreline.