Recent human-induced alterations to coastal systems have affected the geomorphological and hydrodynamic characteristics. Gyeonggi Bay, located on the west coast of Korea, has undergone reclamation and major construction, resulting in severe sedimentation in the southern part of Ganghwa Island. To elucidate how these recent geomorphological changes influence the hydrodynamic and benthic sedimentary environments, comprehensive field observations were conducted during July and August 2025. The current velocity and suspended sediment concentration (SSC) were observed using an acoustic Doppler current profiler. The particle size distribution and hologram images of suspended sediment were acquired using LISST-Holo. The along-channel current velocity and SSC reached up to about 2 m s^-1 and 500 mg L^-1 during the tidal cycles, with an intermittent increase in SSC at a specific depth (about 12 m) during the flood tide. The northward across-channel current velocity, especially at the bottom layer, temporarily increased, indicating the residual current-induced sediment resuspension. During two major meteorological events characterized by strong winds and precipitation, a strong seaward residual current developed. The results indicate that not only does the tidal energy mainly drive sediment transport in the study area, but also extreme meteorological events directly affect the seaward sediment transport. After the major alteration of Gyeonggi Bay, the study area has functioned as a major waterway between the Yellow Sea and the Han River. In addition, the physical characteristics (e.g., fractal dimension and settling velocity) of suspended sediments were different between the high and the low slack waters, indicating that the comparatively coarser sediment was washed off from the tidal sand ridge during the ebb tide. The tidal sand ridges were formed after the severe sedimentation in the southern part of Ganghwa Island. The cross-sectional hydrodynamic structure and the tidal-regime characteristics of Gyeonggi Bay will be discussed in the presentation.

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