Bay- and inlet-scale hydrodynamics in a back-barrier system during storms

Hydrodynamics in shallow, large, back-barrier bays are spatiotemporally variable owing to bay geometry, presence of inlets, and storm forcing conditions. We investigate the relative contributions of winds and ocean waves to hydrodynamics in the Albemarle-Pamlico Sound, rimmed by the Outer Banks of North Carolina, USA, during storm events. These events include Hurricane Isaias (August 2020) and a Nor’easter combined with the remnants of Hurricane Teddy (September 2020). The hydrodynamics on a bay scale O(100,000 m) across the Sound and on an inlet scale O(100 m) at Oregon Inlet are investigated using field observations and numerical simulations. Winds create a water level gradient across the north-south axis of the bay, contributing to local water level gradients in both the along- and cross-inlet directions at the inlet. The strength of wind impacts depends on wind speed, direction, and barrier island geometry. Ocean waves have bay-scale impacts of driving a nearly-uniform increase in water levels throughout the Sound that depends on wave height, direction, and storm duration. Local to the inlet, wave impacts vary spatiotemporally with tidal phase and bathymetry. Currents through the inlet are typically wind-dominated, with wave impacts becoming important only over longer storm durations. The novel combination of field observations with numerical models at different scales reveals the detailed storm-driven response of a major inlet that connects a large estuary to the ocean, with implications for understanding the hydrodynamic responses of other large back-barrier bay-inlet systems.