Evolution of sand wave migration and morphodynamic changes in the Taiwan Strait

High-resolution bathymetric and seismic reflection data reveal distinct sand wave characteristics within offshore wind farm areas in the central Taiwan Strait. Based on five consecutive surveys conducted near the Zhuoshui River, the largest river in Taiwan, we quantified the morphodynamic changes of these bedforms. The results present pronounced seabed variability, with a maximum elevation change of 6.7 m and a migration distance of 89.4 m, indicating meter-scale fluctuations within days. Two primary migration regimes are identified: (1) topography-driven bidirectional migration within the sand bank zone, and (2) current-driven, non-uniform oscillatory migration over timescales of 12 days to 27 months. To better resolve subsurface sand wave structures and support improved seismic data processing and integration, a representative time-depth sound velocity function was derived for this offshore region. By integrating sequence stratigraphy with seismic profiles, this study demonstrates that sand waves migrate above a basal surface located approximately 5 to 15 m beneath the seabed. To further advance understanding and enhance the predictability of sand wave dynamics, we propose a four-stage stratigraphic evolution model describing their development since the Last Glacial Maximum. This framework provides new insights into sand wave evolution, bedform stability, and basal fluctuations, and offers a practical reference for predicting seabed level changes relevant to subsea infrastructure and engineering in continental shelf environments.