Modelling flooding in a coastal estuary from combined storm surge and rainfall during hurricanes

During extreme storms, intense precipitation and wind-driven water levels can both contribute to flooding. Particularly on low-lying coastal plains, storm-driven flooding can cover large areas and overland flow can cause major damage. To investigate the roles of both rainfall and storm surge on coastal flooding, a coupled flow-wave model that includes precipitation is used to simulate two major storm events. The Delft3D-SWAN modelling system is applied over a domain covering coastal North Carolina, USA, including the large Albemarle-Pamlico estuarine system. Within this area, a long and narrow back-barrier estuary (Currituck Sound) that experiences major water level variations is investigated in detail. A high-resolution (50 m) grid with 8 vertical layers is used to simulate the conditions during Hurricane Matthew and Tropical Storm Hermine in 2016. Five different hindcasts (winds, pressure, and precipitation) from different atmospheric models are used as model input conditions, and the results are compared with detailed observations of surface waves, currents, water levels, and turbidity from sensors mounted on five monitoring platforms in Currituck Sound. The impacts of precipitation, wind-driven surge, waves, and tides are examined separately to better understand the contribution from each process to coastal flooding. These results help to understand the important contributions of each physical process and provide guidance on the impact of atmospheric forcing conditions on back-barrier environments during hurricanes.