SOUND-SIDE INUNDATION AND DISSECTION OF A BARRIER ISLAND DURING HURRICANE DORIAN

Conceptual models of barrier-island morphodynamics emphasize landward migration with time due to both overwash processes and inlet migration. The landfall of Hurricane Dorian in 2019 at Cape Hatteras, North Carolina resulted in sound-side inundation and seaward-directed erosion of North Core Banks, a 36-km long barrier island. More than 20% of the subaerial volume of the island was lost through the formation of over 90 dendritic erosional channels extending from the back-dune washover terrace through the primary dune line to the ocean. Sediment that was transported seaward was deposited in deltaic bars offshore of the newly formed channels. Erosion was caused by overtopping of the island from Pamlico Sound, as evidenced by storm-surge models, water-level observations, and high-water wrack lines. Wrack was stranded at an elevation of 2 m above mean higher-high water on the sound side of the primary dune line. Peat was exposed in the thalwegs of the eroded channels. The mean elevation of the island decreased from 1.47 m to 1.23 m. Post-storm recovery by onshore bar migration and partial filling of the channels with beach sand was observed but, because much of that sand originated from the foredunes and upper beach profile, island volume had increased only 4% after four months. The partially filled channels created a new habitat of ponds and lowlands that we predict will persist for years. The morphodynamic response of North Core Banks to Hurricane Dorian suggests that sound-side hurricane erosion events add richness and complexity to the classic rollover model and may play an important role in modulating the landward migration of some barrier islands.