Numerical Simulation Of Sandy Beach Profile Response To Storm Surge In Xiamen Island

The strength of typhoon-induced disasters increases under the influence of globe climate change.Strong typhoons can cause a wide range of storm surge disasters,which could result in beach and dune erosion,overflowing,flood and even temporary failure of coastal system.Typhoons play a significant role in beach evolution.Typhoon-induced storm surge and wave runup can result in beach morphology changing significantly in a short period.The beach profile evolution mechanism and beach profile shapes response to strong typhoons have the obvious difference with the situation under normal dynamic conditons.Thus it is difficult to apply the traditional profile morphology theories to explain these phenomena.Meanwhile there is no enough domestic research concerning characteristics of beach sediment and hydrodynamic condition in China's coastal areas.Thus researches concerning mechanism of beach profile evolution response to storm surge have important practical significance and theoretical value.In this paper the coupled Delft3D and XBeach model was established and had been applied to simulate the sandy beach profile in Xiamen Island response to No.9914 Typhoon.And the process of the sandy beach profile evolution and sediment erosion and deposition alongshore was anlyzed.The main contents and results are as follows:(1)The established coupled Delft3D-FLOW and Delft3D-WAVE model is validated comparing the modelled and observed storm surge and siginificant wave height timeseries.Then the Delft3D model and XBeach model are coupled,and the coupled Delft3D and XBeach model is used to simulate the process of sandy beach profile response to No.9914 Typhoon.The modelled location and volume of sediment erosion and deposition induced by this typhoon accords with the observed result.Thus the coupled Delft3D and XBeach model is well validated and this coupled model can be apllied in modelling similar sandy beach profiles response to storm surge along China's coastline.(2)The sensitivity analysis of XBeach paramaters,including facua,bottom roughness and critical slopes for avalanching has been finished.The facua has a negatively relationship with both sediment erosion volume in upper sandy beach profile and sediment deposition volume in lower sandy beach profile.In other words the sediment erosion volume in upper sandy beach profile and sediment deposition volume in lower sandy beach profile decrease with the increasing of facua' value.And with the increasing of manning,the sandy beach profile change induced by the typhoon is less.The upper sandy beach profile change caused by manning's change is more obvious.Critical slopes include the dryslp and wetslp.The dryslp can hardly influence sandy beach profile change while wetslp is the opposite.With the wetslp's value decerasing,the avalanching is occurred more easily for sandy beach under sea water level,which will result in a larger sediment erosion.(3)Tthere are three main regimes of sandy beach profile response to storm surge induced by No.9914 Typhoon,including collision regime,overewash regime and inundation regime.There is no sediment landward transport occured in collision regime,in which sediment erosion and deposition occur in middle and high tide zone,while the sediment erosion speed is lower than overwash regime and inundation regime.Howerver,a great sediment erosion occurred in midlle and high tide zone in overwash and inundation regime in a short period,and the erode sediment is mainly transported landward and deposited in upper high tide zone and backward land.The sediment erosion volume in overwash and inundation regime is 40%to 60%of the total erosion volume in the whole process.Thus these two regime are siginificant stages in sandy beach profile response to storm induced by No.9914 Typhoon.