The morphological-hydrodynamic resilience mechanisms against the highest storm tide level in a Bay-Inlet-Channel system

Extreme storm tide levels, arising from nonlinear cross−scale interactions among surge, astronomical tide, and fluvial flood, threaten estuarine stability and cause major economic losses. The Bay-Inlet-Channel (BIC) system, pivotal to the Greater Bay Area, was severely impacted by Typhoon Hato, which produced record−breaking winds and severe inundation. To quantify the morphological-hydrodynamic resilience of the BIC system against the highest storm tide level (HSTL), the Delft3D model was employed to reproduce characteristics of Hato. Simulation results indicate that HSTL exhibited a sharp gradient along the Bay, with a relative increase of 63.84%, and a more moderate one in the Channel (37.00%), associated with the Channel’s higher resilience (RG = 0.87). Under a hypothetical “Triple Coincidence” scenario involving a stronger flood discharge, the robustness of the BIC system decreased, with a more pronounced decline for the Channel (ΔRG = −0.23) than for the Bay. Contribution analysis identified surge as the dominant driver of HSTL during Hato (52–75%), followed by astronomical tide (25–51%), nonlinear interactions (−7–6%), and flood (<2%). Surge dominance diminished under “Triple Coincidence” as nonlinear interactions intensified. Momentum and energy analyses showed that lateral HSTL differences were primarily governed by direct wind stress, while longitudinal variations were modulated by morphological heterogeneity. Stronger floods amplified HSTL unevenly, mainly through enhanced nonlinear convection. These discoveries advanced the understanding of the morphological-hydrodynamic resilience and its mechanism regulating HSTL in estuarine systems, providing insights for storm tide risk management.