Constructed Dunes and Roads Reduce Decadal Washover Flux on Transgressing Barrier Islands

Abstract

On developed barrier islands, washover deposition is regarded as a hazard, despite its essential role in natural island transgression. Measures taken to prevent erosion and halt overwash such as dune stabilization can exacerbate disequilibrium and accelerate island drowning. Although such management practices have been implemented on some U.S. barrier islands for over a century, decadal-scale remote sensing data have only recently become available to evaluate their long-term impacts on island morphology. We analyzed a 30-km stretch of northern Hatteras Island, North Carolina, divided into seven zones with similar geomorphology and management history. This region includes the Pea Island National Wildlife Refuge, with minimal development beyond a shore-parallel road (NC 12), and three towns. Using 11 lidar data sets (2005–2019) and 2013 satellite imagery, we quantified washover flux, geomorphology, and human development metrics along 20 m spaced transects. Zone-averaged washover flux ranged from 0.99 to 5.19 m³/m/yr, aligning with sediment core-based metrics but lower than values reported in single-storm studies and the equilibrium flux (6.48 m³/m/yr) required for mass conservation during island retreat. Decadal washover flux was not significantly correlated with dune heights, shoreline change, or development density but was linked to development setback, dune height change, and barrier island volume deficit. Flux variability was high even within similarly developed zones, with dune and road maintenance alone reducing washover flux and extent by ∼50%. This suggests that management practices, rather than development density or traditional predictors like dune height, play a dominant role in controlling washover susceptibility, significantly restricting natural barrier island rollover processes.