Study: A bulkhead doesn’t mean property along North Carolina’s estuaries is safe
Property owners with bulkheads along North Carolina’s sounds and Intracoastal Waterway tend to build their homes closer to water and suffered more damage during 2016’s Hurricane Matthew, according to a new study from the University of North Carolina at Chapel Hill and Northeastern University.
“Homes with bulkheads were much closer to the water and were damaged more frequently than homes with natural shorelines, suggesting that shoreline hardening may not be a consistently effective storm damage mitigation strategy,” Carter Smith, then of UNC’s Institute for Marine Sciences, and co-author Steven Scyphers wrote in the conclusion of their study, which was recently published in the journal Environmental Science and Policy.
The study is based on a survey of 295 homeowners with property on sounds in Carteret and Dare counties, as well as the Intracoastal Waterway in Brunswick. Researchers used satellite imagery to measure the distance from homes to the shore, finding that bulkheads were the most frequent kind of shoreline when homes were less than 35.7 meters away from the water, while natural shorelines were the most common option for homes more than 68.6 meters from the water.
About 24% of 145 homeowners with bulkheads reported damage from Hurricane Matthew, compared to 12% of 100 homeowners with natural shorelines and about 5% of those with riprap, according to the study.
“Maybe bulkheads aren’t necessarily the dream damage mitigation strategy,” Smith said in an interview, “because they’re clearly not eliminating damage to homes.”
Further, the research found the most likely indicator of whether the shoreline in front of a property would be damaged during the 2016 storm was whether it had been before.
Smith, who is now a postdoctoral researcher at Duke University, said the survey results “suggest there are certain properties that are experiencing repeated damages, which suggests that we’re either not taking appropriate adaptive action after previous hurricane events or that the strategies we think are going to work are not working as well as we think they’re going to.”
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What preparations changed this year?
Earlier this year, the N.C. Division of Coastal Management announced the approval of a long-awaited general permit allowing homeowners to build marsh sills as easily as they had historically been able to build bulkheads or riprap. The division worked with the U.S. Army Corps of Engineers to secure a regional general permit for the sills, allowing the state agency to then issue its own general permit, significantly expediting the living shorelines’ review time.
Braxton Davis, director of the Division of Coastal Management, said of the permits, “Now we can issue them in a matter of days for small-scale living shoreline projects, and I think that will definitely reduce the regulatory burden and provide yet another incentive for property owners to consider (marsh sills).”
Tracy Skrabal, manager of the N.C. Coastal Federation’s Wrightsville Beach office, has advocated for the permit for about two decades.
Where waves crashing into the coast scour out bulkheads or cause erosion on adjacent shorelines, Skrabal said, marsh sills are built about 20 to 30 feet away from the shore, with marsh plants behind them.
“It’s kind of a speed bump to energy, and that’s exactly how they’re designed -- that trapazoidal shape,” Skrabal said.
When waves roll over the sills, they often drop sediment that becomes trapped behind the structure, a feature supporters say helps the structure fend off sea-level rise.
While exact numbers were not available, Davis said the division has typically approved about five marsh sill permits annually, which may be up to a dozen. By comparison, about 400 bulkheads are approved annually, including construction and repair permits.
Davis said he expects the number of marsh sill permits to increase.
As part of its release announcing the general permit, the Division of Coastal Management noted that natural shorelines and marsh sills often held up better during Hurricane Florence than nearby bulkheads.
“They basically maintained structural integrity,” Davis said, “and they maintained most all of the salt marsh behind them, so you didn’t lose much habitat.”
This story was produced with financial support from Report for America/GroundTruth Project, the North Carolina Community Foundation and the North Carolina Local News Lab Fund. The N&O maintains full editorial control.
