Understanding Spatial Variations in the Storm Driven Evolution of Masonboro Island, North Carolina

Abstract:

Over short timescales, extreme storm events significantly alter the morphology of coastal areas by reducing beach widths and eroding dune systems. Erosion caused by these brief yet powerful events increases the vulnerability of coastal areas to future storm-driven morphological changes and often offsets coastal management actions intended to promote resiliency of coastal environments (e.g., erosion of sand placements). The primary objective of this research is to better understand the spatially varying morphological response of barrier islands to extreme storm events caused, in part, by variations in total water levels (primarily setup and swash) and dune elevations by using a combination of in situ sensors, remote sensing, and a 2D XBeach model developed for Hurricane Florence. The study area encompassed Masonboro Island, a 13.5-kilometer-long undeveloped barrier island off the coast of Wilmington, North Carolina, and located just south of where Hurricane Florence made landfall in 2018. Beachface and dune water levels were obtained from two cross-shore arrays of pressure sensors on the northern and southern sections of the island that are characterized by dunes with high and low elevations, respectively. Aerial drone imagery was also collected to derive pre- and post-storm elevation data to quantify spatially varying erosion and overwash. These data were used to validate the model which was then used to evaluate dominant drivers of the spatially varying morphological response including beach slope, the occurrence of small erosive events early in a storm, and spatially varying sediment characteristics. The model setup was then used to determine the efficacy of different sand placement scenarios at different locations under existing conditions and realistic future sea-level rise scenarios.