Application of a Coupled Ocean Wave Sediment Transport Modeling System to Investigate Morphological Changes during Hurricane Sandy.

Barrier islands provide a means of defense against large storm impacts. While a vast majority of studies focus on the subaeial areas of barrier islands, a significant component of barrier island geologic framework is submerged. Understanding how barrier islands respond to storms requires a thorough investigation of the complete inner-shelf to surf-zone region.

Hurricane Sandy impacted the US east coast in 2012 and was one of the most destructive storms in US history with impacts including flooding, coastal erosion, dune overtopping, breaching. Here we evaluate the oceanographic processes and morphological changes during Hurricane Sandy on Fire Island, NY and the adjacent inner continental shelf using geophysical observations and numerical modeling. Geologic investigations of the seafloor in 2011 and 2014 demonstrate changes of seafloor morphology and modern sediment thickness revealing up to 450 m of lateral movement of sedimentary features and deposition at depths up to 30 m.

Physical processes responsible for these morphological changes were investigated using a coupled ocean-wave-sediment modeling system (COAWST) with grid refinement to simulate oceanographic conditions on a regional 5-km grid along the entire US east coast, with increased resolution of 700 m in the NY bight, 100 m along Fire Island, and 5 m at the breach formed due to Hurricane Sandy. Model results identify maximum surge of up to 3 m, surface currents up to 2 m/s, and wave heights up to 8 m. Sediment redistribution along Fire Island showed erosional patterns consistent with geologic observations.

Modeling advancements using an infragravity wave component (InWave) identify key aspects of barrier island response during the storm. Total storm water levels along Fire Island are shown to be a combination of surge, tidal, and infragravity signal. During the peak of the storm total water level and wave action was able to create a breach. Models results are compared to field observations.