Study On Nonlinear And Resonance Effects And Risk Assessment Of Storm Surge In Typical Bay

The storm surge causes great damage to Southeast and South China every year.Especially,many reclamation projects have been initiated and resulted in coastline change and hydrodynamic conditions change.The loss would be severe once marine disasters occur.Therefore,it is critical to study the mechanism and risk assessment of storm surge in typical bays to improve storm surge disaster prevention.Tieshan Bay in Guangxi and Sanmen Bay in Zhejiang are selected as research objects in this paper.The main research contents and conclusions are as follows:Firstly,a two-dimensional ADCIRC model has been presented in which the storm surge in Tieshan Bay induced by Typhoon Rammasun of July 2014 to investigate tide-surge interaction.The result shows that nonlinear effect is strong in Tieshan Bay and leads to large error in storm surge simulation when only meteorological force considered.Nonlinear levels due to tide-surge interaction increase from outside the bay to inside.Through the derivation of theoretical formula,a direct relationship between the nonlinear residual levels and the dynamic influencing factors is established.It is demonstrated that the combination of wind stress and bottom friction terms and advection terms play leading roles in the derivations.The combination of wind stress and bottom friction terms and advection terms show complex spatial and temporal variation.Numerical experiments are conducted to study the surge peak superimposed with different phase of tidal levels.The nonlinear level reaches maximum negative value at high tide and maximum positive value at falling tide.Moreover,the lag time of maximum total level relative to the high tide gets longer where the nonlinear effect is stronger.Secondly,Empirical Mode Decomposition method(EMD)is applied to decompose storm surge data in Sanmen Bay and presence of resonance is found.Then the resonance phenomenon is studied by theoretical formula derivation and numerical simulation.The numerical model results show that there are less than five resonant period modes in the Sanmen Bay and resonance characteristics of the waterways in Sanmen bay are different.The amplitude of first mode of the resonant period is largest and decreases in sequence.The resonant amplitude gain gradually increases from outside of the bay to inside,especially significant at the top of bay.Reclamation projects in Sanmen Bay have changed the natural shoreline and topography.A two-dimensional numerical model is applied to evaluate the impacts of reclamation projects on tidal and storm surge levels in Sanmen Bay.The model result shows that the tidal level decreases due to reclamation projects and bathymetry change has a more significant impact on tidal amplitude than shoreline change effect.The variation of surge level in different types of typhoon paths is complex.Similarly,the rise of peak surge levels due to the change of topography is also significant.The maximum surge level rise occurs in the path of northwest landing typhoons and exceeds 0.4m at the top of the bay.At last,a storm surge model for Sanmen Bay is established and a number of hypothetical typhoon paths using possible maximum tropical cyclone parameters are applied to calculate the possible maximum storm surge at Sanmen Bay.The model results show that the north-west landfalling path to the left of bay by maximum wind radius causes the maximum storm surge in Sanmen Bay.Strom surge inundation happens when the PMSS superposed with high tidal level and the land height data is then generalized in model to calculate flooding areas.The maximum inundation area reaches 120 km~2 and the total water level near sanmen nuclear power plant gets lower by 0.5m than that without inundation.The conclusion could provide scientific basis for the protection of the sanmen nuclear power plant and reclamation projects.