Engineering Assessment of Long-Term Coastal Siltation in the Northern Sector of Taichung Port, Taiwan, Using Tide-Normalized SAR Time Series

Persistent coastal siltation at port entrances increases dredging demand and threatens navigation safety, while bathymetric surveys remain costly for decadal assessment. This study presents a tide-aware Synthetic Aperture Radar (SAR) framework for quantifying siltation evolution in the northern sector of Taichung Port, Taiwan, using 276 Sentinel-1 ascending-track VV images acquired from 2015 to 2024. The ascending VV configuration was selected based on sample-area ocean–siltation separability, and all images were processed using a standardized radiometric and geometric workflow. Siltation boundaries were delineated using an Active Contour Model to extract continuous water–siltation interfaces under speckled, diffuse-backscatter conditions without training data. Among the archive, 82 convergent images were retained and grouped into six tide-gauge–based tidal-height classes. Tide-normalized results show persistent expansion across all tidal groups, with regression-based annual increases of 0.051–0.074 km2/yr. Endpoint-based rates of 0.047–0.075 km2/yr were consistent with the fitted slopes. Under comparable low-tide conditions, the mapped area increased from 1.722 km2 in 2016 to 2.215 km2 in 2024, yielding a net expansion of 0.493 km2. Independent optical aerial photos showed consistent directional expansion, with paired optical/SAR areas of 1.063/1.197, 1.533/1.503, and 2.231/2.147 km2 in 2016, 2023, and 2024, respectively. These results support quantitative siltation assessment and port maintenance planning.