Numerical Modeling of Tidal Flat Morphodynamics in a Semi-Enclosed Macrotidal Bay: A Case Study of Garolim Bay, Korea

Understanding the morphodynamic behavior of tidal flats is essential for predicting their stability and ecological function under changing coastal conditions. This study focuses on Garolim Bay, a semi-enclosed macrotidal bay located on the west coast of South Korea, characterized by a wide tidal basin with a narrow entrance, forming a pot-shaped coastal geometry with minimal riverine input. The absence of significant terrestrial sediment sources provides an opportunity to isolate marine process-driven morphological evolution.

A fully coupled three-dimensional numerical model was employed to simulate tidal current, wave action, sediment transport, and morphological changes. For model forcing, a combination of global model outputs and local observational data (tidal, currents, wave, and in-situ suspended sediment concentration) was used. Observational datasets were also employed for validation to ensure model reliability. To construct the model topography, a hybrid approach was adopted. Bathymetric survey data were used to define the main tidal channels in both the inner and outer bay. For the extensive tidal flat areas, satellite imagery was employed to extract and integrate isobath lines, enabling the reconstruction of a high-resolution digital elevation model. This approach addressed the limitations of drone-based surveys, which were impractical due to the wide spatial extent of the tidal flats and the large tidal range (~8 m).

The simulation focused on the summer flood season, during which external forcings such as typhoons frequently affect hydrodynamic regimes. Results show that tidal currents dominate the sediment transport regime, while wave-induced shear stress plays a secondary. Morphological changes are spatially heterogeneous due to current convergence zones and limited sediment resupply. These findings suggest that Garolim Bay exhibits dynamic but internally constrained sediment redistribution patterns. These findings contribute to long-term modeling of intertidal evolution and offer valuable insights for assessing the preservation potential of tidal flats, their role as prospective blue carbon resources, and their morphodynamic response to future environmental changes such as sea-level rise.