Study On Characteristics And Forecasting Model Of Storm Surges In Tianjin Coastal Area

Located in the west top of the Bohai Bay,Tianjin is attached by storm surges very frequently.As the most important harbor city of the Bohai Economic Circle,the economic of Tianjin develops rapidly.Therefore,the demand of disaster prevention and mitigation is increasing.In order to protect the life and property,it is necessary to increase the understand of the characteristics of storm surges in Tianjin coastal area,and to improve the storm surge forecasting and warning tecnique.The characteristics of storm surges in Tianjin coastal area were statistically analyzed based on the measured data of 113 cases that have significant impact on Tianjin coastal area in the past 65 years.It is found that storm surges are likely to occur throughout the year,and August,October and November are the peak periods.The storm surges were divided into two categories,i.e.extratropical storm and tropical storms,and the characteristics of both were analyzed.The relationship between the frequencies of strong wind and the set-up was analyzed.The maximum water levels with different return periods were calculated using the Gumbel distribution to obtain the tide level of different return periods.The influence of the extraordinary value was taken into account in the calculations and the reference return period was determined to be 400 years.The results show that the accuracy of the maximum tide level is improved by considering of the extraordinary value and reference return period.Details of the settlement of ground and the sea level rise were discussed.After correcting the land subsidence,the calculated tide levels for different return periods increased significantly.In order to forecast set-up of different categary storm surges,three kinds of multiple regression equations were established by using the collected measured data of set-up and the wind and pressure field offered by NCEP.Ultimately,the best regression equation was determined.A storm surge model coupling Hydrodynamic model and SWAN wave model was established.By using the coupling model,some typical storm surge cases were simulated,and satisfied results were obtained.Then the characteristics of the flow field and set-up in the Bohai Bay were analyzed.