Sound-Side Inundation and Seaward Erosion of a Barrier Island During Hurricane Landfall

Barrier islands are especially vulnerable to hurricanes and other large storms, owing to their mobile composition, low elevations, and detachment from the mainland. Conceptual models of barrier-island evolution emphasize ocean-side processes that drive landward migration through overwash, inlet migration, and aeolian transport. In contrast, we found that the impact of Hurricane Dorian (2019) on North Core Banks, a 36-km barrier island on the Outer Banks of North Carolina, was primarily driven by inundation of the island from Pamlico Sound, as evidenced by storm-surge model results and observations of high-water marks and wrack lines. Analysis of photogrammetry products from aerial imagery collected before and after the storm indicate the loss of about 18% of the subaerial volume of the island through the formation of over 80 erosional washout channels extending from the marsh and washover platform, through gaps in the foredunes, to the shoreline. The washout channels were largely co-located with washover fans deposited by earlier events. Net seaward export of sediment resulted in the formation of deltaic bars offshore of the channels, which became part of the post-storm berm recovery by onshore bar migration and partial filling of the washouts with washover deposits within 2 months. This event represents a volumetric setback in the overwash/rollover behavior required for barrier transgression, but the new ponds and lowland habitats may provide beneficial habit for endangered species and will likely persist for years. Plain Language Summary As sea level rises, barrier islands tend to migrate toward land, helped by storms that move sand from the ocean to the back side. In rarer events, such as Hurricane Dorian (2019), storms can transport sand from the back side to the ocean. Using overlapping photos collected from a plane, we created 3-D elevation maps and stitched-together photo mosaics of North Core Banks, North Carolina, immediately before and after Hurricane Dorian, and then once a month for 3 months afterward, to document the erosion and recovery of the beach and barrier island. We found major changes. During the storm, abnormally high water levels in Pamlico and Core Sounds flooded the island and created distinct channels as water drained from the sound side into the Atlantic Ocean. This process, called outwash, moved 18% of the island sand into the ocean over the course of a few hours. The maps also showed the initial stages of a recovery process, as beach sand was moved by ocean waves and plugged the channels, creating new, and semi-permanent, habitats within the barrier island. Events such as Hurricane Dorian may slow the typical migration process of barrier islands and change the landscape for years to come.