Long-term Changes in Sediment Grain Size Characteristics of Tidal Flats along the Western and Southwestern Coast of Korea

This study investigated the long-term changes in sediment grain size characteristics of tidal flats along the southwestern coast of Korea using datasets collected through the National Marine Ecosystem Survey from 2015 to 2025. The study area consisted of 129 survey lines and 387 monitoring stations distributed across the western and southwestern coastal regions of Korea, including the Gyeonggi-do, Incheon, Chungcheong, Jeonbuk-do, and Jeollanam-do regions. Spatial distributions and temporal variations of mean grain size were analyzed to identify regional sedimentary characteristics and long-term trends. The results showed that relatively coarse sediments were dominant in the Gyeonggi-do, Incheon, and Chungcheong regions, whereas finer sediments were generally distributed in the Jeonbuk-do and Jeollanam-do regions. These spatial differences were interpreted as the combined effects of tidal and wave energy, exposure to the open sea, terrestrial sediment supply, and geomorphological enclosure. Long-term time-series analysis revealed that although sediment grain size variations were observed in some regions and years, no clear nationwide trend of overall coarsening or fining was identified during the study period. In addition, grain-size class analysis indicated that coarse sediments showed relatively large interannual variability, whereas fine sediments exhibited comparatively stable distribution patterns. These findings suggest that tidal flats along the southwestern coast of Korea are characterized not by a simple one-way erosion system, but rather by a dynamic equilibrium environment where resuspension and redeposition continuously occur under tidal and wave influences. This study is meaningful in that it quantitatively evaluated long-term sedimentary environmental changes in Korean tidal flats based on a national-scale monitoring dataset, and the results are expected to provide fundamental information for future tidal flat conservation and coastal management policies.