Nearshore circulation and sediment transport at a barrier island breach during Hurricane Matthew (2016)

Elevated water levels and extreme waves during hurricanes cause widespread changes to coastlines and introduce vulnerabilities to low-lying coastal communities. Along the east coast of the United States, barrier island breaching during hurricanes in particular poses a significant threat to communities both on the barrier island itself and along back-barrier estuarine coasts. Breaching is controlled by wave dynamics, nonlinear tide and surge dynamics, wind-driven circulation over the shelf and back-barrier estuary, and geomorphic features of the dune system, including elevation, slope, and land cover. To mitigate hazards associated with extreme events, prediction of hydrodynamics and sediment transport across ocean (O [1,000 km]) to breach (O [m]) scales is necessary.

During Hurricane Matthew (2016), extensive breaching occurred along a barrier island south of stable Matanzas Inlet, FL. Using the hydrodynamic, surface gravity wave, infragravity wave, and sediment transport components of the Coupled Ocean-Atmosphere-Wave-Sediment Transport (COAWST) modeling system, we simulated barrier island breaching during Hurricane Matthew. Morphological results were compared with observed pre- and post-storm topography and bathymetry. At the peak of the hurricane, significant wave heights in 20 m water depth were 7 m, and water levels at Matanzas Inlet were 2.5 m. Overwash and dune erosion occurred initially from infragravity wave runup, although the breach developed from ocean-directed flow due to a barotropic pressure gradient between the back-barrier Intracoastal Waterway and the ocean. The development of the breach is sensitive to transport and deposition of sediment in alongshore bars and in the back-barrier estuary. We will further explore the vertical structure of the nearshore circulation and sediment transport to elucidate interactions between hydrodynamics and morphodynamics during this breaching event.