Large estuaries are influenced by winds over adjacent coastal ocean and land areas causing significant spatial variations in water levels, currents and surface waves. In this study we apply a numerical model to simulate hydrodynamics and waves in the Albemarle-Pamlico Estuarine System, a large and shallow back-barrier basin in eastern North Carolina, over a one-month study period (September, 2008) with observations from several storm wind events of differing time scales and directions. Model performance is evaluated for a spatially varying wind field from the North American Regional Reanalysis (NARR) dataset in comparison to spatially uniform forcing from wind observations at offshore, coastal and land-based sites across the region. A spatially uniform wind field from offshore winds observations results in statistically better hydrodynamic simulations of water levels (R=0.88) in the estuaries than NARR (R=0.48) after comparison with measurements and indicates the importance of strong marine winds over most of the estuary surface area.The influence of a prominent bathymetric feature on hydrodynamics in Pamlico Sound is also investigated by numerically removing a 30 km long and 2-3 m deep shoal from the model grid and replacing it with an idealized depth of 6 m. The removal of the shoal increases water level setup by 14% at the estuarine shoreline, decreases current magnitudes by up to 40% in the shoal region and increases significant wave heights locally by up to 25% in the sound, indicating the importance of this relict geomorphic feature as a major control on the hydrodynamic response of the system during wind events.The results suggest that increasing the water depth over the shoal can lead to higher storm surges and wave heights with the possibility of increased inundation and erosion of the back-barrier and mainland coastal regions. The complex bathymetry and marine wind influence are critical input conditions for modelling large and shallow lagoonal estuaries like the Albemarle-Pamlico Estuarine System.

Pamlico Sound, a large back-barrier estuary in North Carolina, is under threat of climate change due to increased storm activity and sea level rise. The response of this system is investigated by considering what has already happened during changes in sea level over the late Holocene epoch. The hydrodynamic changes that occurred in response to geomorphic evolution are simulated using a 3-D numerical model for four distinct "time-slice" scenarios. To accomplish this, the present-day bathymetry was obtained from a high-resolution digital elevation model, and paleobathymetric grids were developed from sediment cores and seismic observations. Using the same hydrodynamic forcing for each geomorphic scenario, the models are compared to assess the combined response to: different inlets connecting the back-barrier estuary to the ocean, changes in basin geomorphology due to sedimentation, and sea level rise.The results indicate that these factors have a considerable effect on hydrodynamics, waves, and salinity in the estuary. The time-averaged tidal ranges were up to 3 times as high for the past environments in comparison with present-day water level elevations, and maximum current velocities were over 3 times higher in regions close to paleo-inlets. The simulations for each time slice suggest that the salinity distribution in Pamlico Sound is strongly influenced by the hydraulic connectivity with other estuaries and the number and size of tidal inlets through the barrier island system. The results indicate that changes to barrier systems induce strong, nonuniform, and complex responses in back-barrier estuaries with regime shifts in hydrodynamic energy and water mass properties. Key Points: • A modeling approach is developed for simulating the response of an estuary to different geomorphological conditions over a long time scale • Geological observations were used to define inlet locations, basin morphology, and sea levels in the hydrodynamic model • The results indicate controls on the water levels, current velocities, and salinity distributions in paleo-estuarine environments

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