Impact mechanisms of shoreline change on material transport in semi-enclosed bays: A case study of Laizhou Bay

Laizhou Bay, a semi-enclosed bay located in the southern Bohai Sea, China. This study focuses on long-term shoreline evolution (1990–2023). Remote sensing data and the Digital Shoreline Analysis System (DSAS) were integrated to quantify shoreline change rates, and the Delft3D model was used to conduct multi-period hydrodynamic and particle-tracking simulations. The research reveals the cascading mechanism by which shoreline morphology modulates tidal systems and residual current structures, thereby influencing material transport pathways. The shoreline of Laizhou Bay advanced seaward overall, with the most pronounced changes occurring in the human-dominated southwestern region, where average annual rates reached 125.19 m/a (End Point Rate, EPR) and 139.70 m/a (Linear Regression Rate, LRR). Shoreline changes shifted the amphidromic points of the M 2 and K 1 tidal constituents in the Bohai Sea, increased tidal amplitudes, and reorganized the tidal system. Their impact on Eulerian residual currents was localized: in areas of intense modification, such as port zones, the residual current structure and intensity were significantly reshaped, leading to deflections in particle transport paths. Overall material transport in the bay followed a counterclockwise trend. This study clarifies the complete dynamic chain of "shoreline change → tidal adjustment → residual current reorganization → transport path shift," providing valuable regional insights and mechanistic support for hydrological modeling and coastal management in semi-enclosed bays. • Quantified 30-year shoreline changes in Laizhou Bay, most severe in southwest. • Analyzed major tidal constituents and residual current variations in the bay. • Simulated particle trajectories: western part showed larger movement range. • Shoreline change intensity correlates with particle movement magnitude. • Compared to bathymetry, the shoreline dominates the driving forces of hydrodynamics.