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Aiming at the problems of siltation promotion and siltation return in the beach area of Hangzhou Bay, a numerical calculation model of hydrodynamic and scour and siltation in the south bank of Ningbo Bay was constructed, and the reliability of the short-term scour and siltation numerical calculation model was verified by combining with the field measured scour and siltation data, so as to obtain the natural siltation situation in this area under a longer time scale in the future. Meanwhile, the siltation promotion scheme was selected by comparing with artificial embankment construction. The research results show that the restoration effect of natural silt beach under the action of excavation diversion is remarkable, and the construction of barrier has a significant effect on the retention and sedimentation of sediment in the trench. After the construction of the barrier with a height of -2.22m, the average thickness of sediment promotion in the low-lying area reaches 0.22m, and the elevation of seabed in the low-lying area can reach about 2.5m. Therefore, it is particularly effective for the sediment deposition in low-lying areas in the high sediment content sea area to adopt the method of natural diversion and separation embankment.

The Western Pacific region is highly vulnerable to typhoon storm surge disasters, with localized erosion posing a particularly prominent issue for coastal marine structures. The prevalence of extreme typhoon storm surges poses a significant threat to the safety of engineering projects in these areas. In this study, a parameterized wind field model with precise calculation of wind speed was employed to establish a numerical model for typhoon storm tides. Based on the Western Pacific typhoon data from 1949 to 2023, hydraulic simulations were conducted for Hangzhou Bay, Xiangshan Port, and Yueqing Bay, revealing maximum flow velocities of 4.5 m/s, 1.95 m/s, and 2.09 m/s, respectively. These velocities exceeded the maximum possible tidal flow by 0.47–1.17 m/s. Additionally, using Sun's velocity formula, the initiation flow velocities were calculated to be 1.85 m/s, 1.81 m/s, and 2.06 m/s for the aforementioned locations. Through localized erosion tests conducted around typical bridge piers and the subsequent application of similarity criteria, the maximum depth of localized erosion in the study area was determined to range from 2.16 m to 16.1 m, which corresponds to 1.1–2.3 times the scour caused by the maximum tidal flow scenario. A comparison of the erosion test results with calculations based on several formulas demonstrated that the scour prediction formula proposed by Sun exhibited the highest accuracy. This study supplements the understanding of the impact of typhoon storm surges on bridge pier erosion and provides a scientific basis for the design of bridge foundations. [ABSTRACT FROM AUTHOR]