Assessment of asymmetric scour and deposition patterns at cross-estuarine infrastructure based on vortex dynamics

Cross-estuarine infrastructures suffer from severe scour and deposition due to their exposure to river runoff and tide cycles. Understanding the flow structures and resulting intricate patterns of scour and deposition around such large-scale structures is critical for ensuring their long-term safety, minimizing environmental impacts, and informing sustainable estuarine engineering practices. The recent cross-estuarine infrastructure, Shenzhen–Zhongshan Link (SZL), is one of the best examples for studying these patterns, which includes long span bridges, artificial islands, and an immersed tunnel in the Pearl River Estuary. This study employs a high-resolution 3D hydro-sediment model to quantify the asymmetric hydro-morphodynamic evolution around variable-scale structures. The results reveal that runoff-tide coupling acts as the primary driver for asymmetric vortex propagation, extending the advective range of ebb-tide coherent structures significantly further than their flood-tide counterparts. This hydrodynamic forcing translates into a bipolar morphological pattern characterized by intense ”flank-scour” (with annual depths exceeding 0.5 m) and extensive ”wake-deposition” (accumulation of approximately 0.3 m). Beyond specific case metrics, this study identifies a generalized geometric scaling law: despite the vast size disparity between the artificial island ( D ≈ 1000 m ) and bridge anchorages ( D ≈ 150 m ), the normalized downstream deposition length ( L d e p / D ) converges to a constant range of 4.0–5.0 for both structure types. This finding implies that wake-induced sedimentation is governed by intrinsic shallow-water stability limits rather than site-specific conditions, offering a generalized predictive metric for assessing the environmental impact of future estuarine projects. • High-resolution SCHISM modeling simulated asymmetric bridge scour and deposition. • Okubo–Weiss analysis revealed von Kármán vortex shedding around bridge structures. • Vortex propagation distances scaled with deposition lengths in the lee of structures. • Seasonal asymmetry driven by runoff-tide coupling intensified ebb sediment transport. • The maximum erosion near the artificial island exceeded 0.5 m if without protection.