| Storm surge disasters occur frequently in coastal areas of China,they can directly affect the safety of life and property in coastal cities.The China Ocean Bulletin showed that in the past 20 years,the direct economic losses caused by storm surge disasters had always ranked first among marine disasters in China.The Bohai Sea was the highest latitude inland sea in China,due to its special geographical location,the Bohai Sea was not only affected by cold wave storm surge,but also often affected by the northward typhoon storm surge.With the progress of computers and the development of numerical models,numerical simulation was a convenient way to conduct study about storm surge disaster,which could significantly reduce the cost and improve the accuracy of simulation results.At present,the current study mainly focused on the simulation for storm surges in two-dimensional models,limited studies were carried out in three-dimensional simulations.There were more studies in one-way coupling between hydrodynamics and winds,and less two-way coupling was introduced.Moreover,there were much studies in pure storm surges and less studies for disaster prevention measures.The Liao River Estuary was located in the northernmost part of the Bohai Sea with large tidal flats and slat marsh wetlands,and there were a variety of salt marsh plants in the tidal flats.The salt marsh plants played an important role in protecting the mudflats from erosion and mitigating the extreme storm surge hazards.Therefore,we constructed a numerical model to investigate the effects of wetland vegetation in storm surge disasters in the northern sea of China during typhoons' transit,there was of great significance for both physical oceanography and marine disaster prevention and mitigation.In this paper,firstly,a storm surge model in the North Huanghai Sea and Bohai Sea was established based on the coupled model of FVCOM and FVCOM-SWAVE,a synthetic wind field superimposed by the Jelesnianski parametric wind field and the ECMWF reanalysis wind field data was adopted as the external driving force.The model was applied to simulate tide levels,currents and wave heights caused by Typhoons 8509 Mimie,9711 Winnie,0509 Matsa and 1818 Rumbia.The growth and abatement processes of storm surge and waves caused by Typhoons were analyzed in the North Huanghai Sea and Bohai Sea.The simulated results of the FVCOM model were compared with the observed data,and the results showed that the maximum wind speed and the occurrence time of the synthetic wind field were in good agreement with the measured data,and the results of the synthetic wind field were reasonable,which can provide accurate wind conditions for the simulation of the hydrodynamic changes in the study area under the conditions of wave-current interaction.The simulated results of the storm surge at several stations were in good agreement with the measured data,it revealed that the coupling system of FVCOM and FVCOM-SWAVE can reasonably reproduce the storm surge and wave processes caused by the typhoon in the North Huanghai Sea and Bohai Sea.In addition,the calculated results of Typhoon Rumbia showed that the maximum effective wave height in the Huanghai Sea and Bohai Sea was distributed around the center of the typhoon and was located in the forward direction,and the maximum significant wave height was related to the typhoon intensity.During the typhoon transit,waves had a certain influence on the vertical distribution of the flow velocity in the near-shore area,thus the wave-flow coupling model coud effectively improve the numerical simulation accuracy of typhoon storm surge.Secondly,the resistance caused by salt marsh plants was added to the N-S and the turbulence equations.The model was adopted to simulate the hydrodynamic process of an ideal experiment,and the results showed that the simulated results of the FVCOM model matched with the literature data.The results indicated that it was reasonable and reliable to add the vegetation term into the FVCOM model to simulate the resistance of vegetation on water flow,and the model could be used to study the interaction mechanism between vegetation and hydrodynamics in the wetlands of Liao River Estuary during the storm surge.The typical salt marsh vegetation in the tidal wetlands of Liao River Estuary were Phragmites australis and Suaeda heteroptera.Based on satellite remote sensing images,a decision tree classification method was used to obtain the spatical distribution of salt marsh vegetation in the Liao River Estuary.The vegetation locations were reflected onto an unstructured grid within the study area and the vegetation parameters,including vegetation height,vegetation width,and vegetation density,were determined from the field survey.Numerical simulations were conducted using the FVCOM model,and the simulation results showed that both Suaeda heteroptera and Phragmites australis in the wetlands of Liao River Estuary could reduce the flow velocity in the vegetation zone,the maximum attenuation rate of flow velocity in the vegetation areas of Suaeda heteroptera and Phragmites australis were 61.46% and 82.56%,respectively,and Phragmites australis had a greater attenuation effect on the flow velocity.Thus,the above two types of salt marsh vegetation in Liao River Estuary can effectively attenuate the potential threat of storm surge.In addition,the salt marsh plants growing in the intertidal patch of the Liao River Estuary obviously changed the distribution of high and low tide velocities,and they would further affect the sediment erosion and deposition in the coastal area.Furthermore,the presence of typhoons also caused a change in tidal level,which also changed the flow field,the inundation time and inundation depth of wetland vegetation areas,thus indirectly changing the growth environment of tidal wetland vegetation.The above findings contributed to further understanding of the combined effects of wetland vegetation on hydrodymatics generated by tropical cyclones in the Bohai Sea. |
PDF Full Text Request