The Three-dimensional Numerical Model Of Storm Surge Of Bohai Bay Incorporating Wave-current Coupling

Bohai Bay is one of sea regions where storm surges take place most frequently in the world. In the past, the research on storm surge is mainly about the simulation of the change of water level and the spatial-temporal variation of the flow field due to the storm surges. However, the wave set-up and wave-induced currents hardly be taken into account in the simulation of storm surge.In this paper, a three-dimensional numerical model based on coupling of ROMS and SWAN, with incorporation of the three-dimesional radiation-stress terms, is establishded to simulate the storm surge of Bohai Bay. By this model, the nonlinear interaction between astronomical tide and storm surge can be simulated, moreover, the influence of wave set-up and wave-induced current on the storm surge can be considered.The main contents and results are as follows:1. The numerical models including ROMS and SWAN are verified and calibrated with measured data, and the reasonable parameters of model are determined. And then, the wave set-up and wave-induced current over an idealized bathymetry are simulated and compared with the theoretical results. It is indicated that the wave set-up is directly proportional to the wave height in deep water and the slope of beach;The wave-induced currents are greater near the break point than those near the nearshore and offshore.2. The model is applied to simulate the storm surge of No.9216 and No.0310 occurred in Bohai Bay. Three situations, only astronomical tide, surge storm without wave effect and surge storm with wave effect, were carried out to explore the characters of water level processes and spatial-temporal variation of the flow fields. It can be shown that the rising of water level on the windward coast is larger than other locations and the velocities along nearshore increase greatly, the local reversing tidal current is changed to unidirectional flow. In vertical direction, the velocity gradient increases obviously and the current direction varies among every layer.3. By analyzing the influence of wave on water level and flow field, it is concluded that the maximum value of wave set-up is 0.3～0.4m, 6%～8% of incident wave height in Bohai Bay, which can not be neglected in prediction of storm surge. The influence of the the wave-induced current on velocity is significant. If the direction of wave-induced current is the same as tidal current, the velocity increase, and vice versa.