Sound-side inundation and erosion of North Core Banks during Hurricane Dorian (2019)

Abstract:

Along the east coast of the United States, understanding of barrier island response to hurricanes and the long-term evolution of barrier islands has focused on inlet breaching and overwash from ocean-side elevated water levels and wave overtopping, and sediment transport towards the back barrier. Relatively rare inundation events from the sound side provide opportunities to improve our ability to quantify the hydro- and morphodynamics of sound-side inundation and its contribution to long-term barrier island stability. During Hurricane Dorian, extensive flooding occurred along North Core Banks, NC, a <1 km wide barrier island that separates Pamlico Sound from the mid-Atlantic Ocean. As the hurricane transited along the coast, water in the Sound was initially driven towards the mainland, but as the wind shifted, was driven back across the sound, inundating the barrier island and forming nearly 100 erosional channels. Structure-from-motion from aerial imagery allowed quantification of individual channels, high water marks along the backside of the barrier island, and sediment volume changes (Sherwood et al., 2020).

We use the Coupled Ocean-Atmosphere-Wave-Sediment Transport modeling system to explore the hydro- and morphodynamics of this event through a series of nested grids increasing in resolution to the O(2 m) scale. Using different grid configurations, we resolve highly localized spatial variations in water-level maxima across Pamlico Sound, which we compare with high-water marks derived from the imagery and with water level observations from rapid deployments of pressure gages in advance of the storm. At the highest resolution, we hindcast the development of two large (~50 m across) erosional channels. Preliminary results suggest maximum water levels of ~2.5 m along the backside of the barrier island, and current velocities of nearly 3 m/s and bed shear stresses exceeding 50 Pa in the new channels. Within the model framework, we further explore the mechanisms of this event and their effect on the barrier island and nearshore morphology.

Sherwood, C.R., J.A. Brown, C. Kranenburg, A. Ritchie, J.A. Warrick, C.W. Wright, and S.L. Ziegler, 2020. Morphologic changes from sound-side inundation of North Core Banks, Cape Lookout National Seashore, North Carolina, USA during Hurricane Dorian. AGU Ocean Sciences.