Impacts of jetty construction on hydrodynamics, seabed morphology and marine ecology: a case study of Tongzhou Bay, Nantong, China

Coastal port engineering is a crucial strategic measure for promoting regional economic development and optimizing the national marish logistics system, yet the disturbances of large-scale coastal development to the nearshore hydrodynamic environment, seabed topography and coastal ecosystems cannot be ignored. Taking the jetty project in the Third Harbor Basin of Tongzhou Bay Port Area, Nantong Port as the research object, this study systematically explored the coupled impacts of the jetty project on hydrodynamics, beach-trough erosion and deposition, and marine ecology in the adjacent sea areas by combining in-situ measurements and the Delft3D-FM numerical simulation. The model was calibrated and validated with the measured data of tidal level, tidal current, suspended sediment and ecology from 2019 to 2024. We simulated and analyzed the flow velocity response and beach-trough erosion-deposition evolution under three conditions (no jetty, Jetty 1, Jetty 2), and evaluated the project’s ecological disturbance on aquaculture areas and benthic habitats. The results show that the jetty project significantly reshaped the erosion and deposition pattern of the adjacent sea areas by changing tidal current convergence and flow direction, showing a spatial feature of strong near-field response and weak far-field impact. Jetty 1 had an influence range of about 2 km, with a maximum cumulative scouring of 0.88 m at its corner in two years. Jetty 2 extended the influence range to 5 km, with a maximum cumulative scouring of 2.21 m at its top in two years, and its disturbance to hydrodynamics and erosion-deposition was significantly greater than that of Jetty 1. Severe erosion-deposition and flow velocity changes caused by the project were mainly concentrated in non-aquaculture areas, so the overall impact on aquaculture areas was controllable; only Jetty 2 caused slight additional scouring at the edge of the northern aquaculture area, leading to minor disturbance to local benthic habitats. The research results provide a scientific basis for the layout optimization of port engineering, the prevention and control of coastal engineering impacts, and marine ecological protection in the Tongzhou Bay Port Area.