Investigating Hurricane-Induced Salt Variation Across the Land-Estuary-Ocean Continuum Using a Dynamically Coupled Hydrological-Ocean Model

Abstract

Salinity variations across the Land-Estuary-Ocean (LEO) continuum are critical for coastal ecosystems and impact the socioeconomic benefits to local communities. However, evaluating these variations is challenging due to the complex interactions of terrestrial and oceanic processes, including river discharge, winds, tides, sea level rise, and storms. This study incorporates a salinity module into a newly developed dynamically coupled hydrological-ocean model on the COAWST platform, which is, to the best of our knowledge, the first process-based modeling that achieves seamless two-way land-ocean water and salt exchanges across the LEO continuum, facilitating simulations of landward salt input and transport. Using Hurricane Florence (2018) as a case study, we examined how various physical processes influence salinity dynamics and freshwater plume development in the Cape Fear River Estuary, North Carolina. The model simulated saltwater intrusion into freshwater wetlands upstream of the estuary and demonstrated that salinity in the estuary was initially regulated by wind-driven water level gradients, followed by a dominant influence from significant river runoff. In the coastal ocean, runoff created a large freshwater plume that moved westward, driven by the interplay between runoff, winds, and the estuary's geomorphology. The excellent performance of the coupling approach for salinity simulation underscores the importance of the seamless transport of water and salt at the land-ocean interface. This study demonstrates that the coupled model is a valuable tool for representing saltwater intrusion, tracking coastal pollutants, and understanding water and material exchange across the LEO continuum.