Multi-decadal Barrier Island Fate Varies as a Function of Management Strategy

Benton Willis Franklin, Laura J Moore , Katherine Anarde, Brad Murray, K.C. Busch, D. Reide Corbett, Michael Flynn, Meaghan Johnson, David Hallac, Roya Sahraei

Barrier islands are highly dynamic components of sandy coastlines, making up 10% of coastlines globally. Barriers provide recreational opportunities, protect mainland communities from storms, support tourism, and provide ecologically important habitat. Using a spatially explicit barrier island model, CASCADE, calibrated to represent the historical dynamics of Ocracoke, a barrier island in the Cape Hatteras National Seashore in the North Carolina Outer Banks facing severe transportation challenges and divergent stakeholder missions and goals, we investigated how different strategies for maintaining a transportation corridor can affect future barrier island morphology and evolution. Compared to natural conditions, model runs in which roadways are maintained on land using artificial dune construction, sandbag emplacement, washover removal, and beach nourishment result in decreased washover deposition in the island interior leading to increased risk of island drowning along some portions of the barrier, potentially within 50 – 100 model years. The effects of decreases in washover deposition become increasingly severe under higher rates of relative sea-level rise, leading to more rapid island drowning from backbarrier inundation, precluding maintenance of a land-based transportation corridor. Model results also indicate that preemptively halting land-based roadway maintenance allows natural processes to resume, leading to rollover and longer-term island persistence. Consistent with observations and modeling from previous studies, our results demonstrate quantifiable differences in island morphology and evolution based on different management practices undertaken to protect transportation corridors on barrier islands. These outcomes highlight the challenges and tradeoffs associated with addressing competing priorities on barrier islands managed for divergent interests.