Long-term geomorphodynamic responses of macrotidal flats to human modification (1975-2025)

Macrotidal flats in coastal environments experience complex interactions among hydrodynamic and sedimentary processes and their morphodynamics have been increasingly modified by human activities over recent decades. Because human-driven disturbances in geomorphic evolution are reflected across a range of spatial and temporal scales, identifying the dominant controlling factors driving geomorphic changes is therefore essential for interpreting coastal morphodynamics and predicting future coastal evolution. However, these aspects remain poorly understood in macrotidal environments.

Two macrotidal flats on the west coast of Korea, the Donggeom and the Shinsi tidal flats, which have been heavily impacted by embankment construction and tidal-flat reclamation, were examined to identify the dominant controls on long-term morphodynamic responses to coastal development. Multi-source remote sensing data, including satellite and drone imagery, were used to quantify changes in tidal channel morphology, channel geometry, and surface bedform migration across seasonal to multi-decadal timescales (1975–2025). Seasonal to annual variations in grain-size distributions were analyzed using surface sediment samples to characterize sedimentary processes and surface sediment dynamics.  

The Donggeom tidal flat, developed within a deltaic setting with sustained fluvial sediment supply, exhibited increasing channel sinuosity and a transition toward a dendritic and narrower channel network, indicating progressive tidal-flat aggradation. In contrast, the Shinsi tidal flat, which lacks a direct fluvial sediment source, experienced tidal-channel development accompanied by seaward sediment export. Annual grain-size variations indicate that embankment construction enhanced wave exposure and promoted coarser sediment deposition, suggesting intensified sediment reworking and erosion. The contrasting geomorphic responses to coastal development are primarily attributed to differences in sediment availability and local hydrodynamic conditions. These results highlight sediment supply and geomorphic configuration as key controls on the spatial variability of macrotidal flat evolution subjected to long-term human modification.