Abstract: Tidal inlet, which connects water inside and outside a bay, and maintains water exchange and channel’s navigation, is the core and foundation of an inlet system. Based on observational data, sea charts and topographic maps, the hydrodynamic and sediment transport processes affected by natural and human activities in Zhelin Bay were studied with SELFE (semi-implicit Eulerian-Lagrangian finite-element) model, and the evolutions of the tidal inlets were revealed. It was confirmed that tidal areas of Zhelin Bay with 125 km² before the reclamation were independent and large for each inlet, whose stability was maintained. After the 1970s, the reclamation made the tidal water areas dropped to 50%, the hydrodynamic structure of tidal inlets changed accordingly, and the suspended sediments from the outside of the bay transported into Zhelin Lagoon and deposited into the Sanbaimen Channel. The tidal area of Xiaojinmen Inlet changed little, so the hydrodynamic and sediment transport of inlet was still ebb-tidal dominant. The circulation of Xiaojinmen Inlet was enhanced, which resulted in the adjustment of erosion and deposition. The tidal area induced by Dajinmen Inlet dropped 1/3 to 40 km², which weakened the asymmetry of flow velocity. The circulation of Dajinmen Inlet promoted the deposition in the west and the erosion in the east of the inlet section. The tidal area of Xiaomen Inlet collapsed by more than half, which resulted in narrowed inlet width, extended length and shallower water depth; and the circulation between Dajinmen Inlet and Xiaomen Inlet intensified the deposition and instability of Xiaomen Inlet.

Key words: tidal inlet, Zhelin Bay, area of tidal water, stability, reclamation, circulation between inlets