A numerical study on the impact of tidal waves on the storm surge in the north of Liaodong Bay

Abstract

A storm surge is an abnormal sharp rise or fall in the seawater level produced by the strong wind and low pressure field of an approaching storm system. A storm tide is a water level rise or fall caused by the combined effect of the storm surge and an astronomical tide. The storm surge depends on many factors, such as the tracks of typhoon movement, the intensity of typhoon, the topography of sea area, the amplitude of tidal wave, the period during which the storm surge couples with the tidal wave. When coupling with different parts of a tidal wave, the storm surges caused by a typhoon vary widely. The variation of the storm surges is studied. An once-in-a-century storm surge was caused by Typhoon 7203 at Huludao Port in the north of the Liaodong Bay from July 26th to 27th, 1972. The maximum storm surge is about 1.90 m. The wind field and pressure field used in numerical simulations in the research were derived from the historical data of the Typhoon 7203 from July 23rd to 28th, 1972. DHI Mike21 is used as the software tools. The whole Bohai Sea is defined as the computational domain. The numerical simulation models are forced with sea levels at water boundaries, that is the tide along the Bohai Straits from July 18th to 29th (2012). The tide wave and the storm tides caused by the wind field and pressure field mentioned above are calculated in the numerical simulations. The coupling processes of storm surges and tidal waves are simulated in the following way. The first simulation start date and time are 00:00 July 18th, 2012; the second simulation start date and time are 03:00 July 18th, 2012. There is a three-hour lag between the start date and time of the simulation and that of the former one, the last simulation start date and time are 00:00 July 25th, 2012. All the simulations have a same duration of 5 days, which is same as the time length of typhoon data. With the first day and the second day simulation output, which is affected by the initial field, being ignored, only the 3rd to 5th day simulation results are used to study the rules of the storm surges in the north of the Liaodong Bay. In total, 57 cases are calculated and analyzed, including the coupling effects between the storm surge and a tidal wave during different tidal durations and on different tidal levels. Based on the results of the 57 numerical examples, the following conclusions are obtained: For the same location, the maximum storm surges are determined by the primary vibration (the storm tide keeps rising quickly) duration and tidal duration. If the primary vibration duration is a part of the flood tidal duration, the maximum storm surge is lower (1.01, 1.05 and 1.37m at the Huludao Port, the Daling Estuary and the Liaohe Estuary respectively). If the primary vibration duration is a part of the ebb tidal duration, the maximum storm surge is higher (1.92, 2.05 and 2.80 m at the Huludao Port, the Daling Estuary and the Liaohe Estuary respectively). In the mean time, the sea level restrains the growth of storm surges. The hour of the highest storm tide has a margin of error of plus or minus 80 min, comparing the high water hour of the astronomical tide, in the north of the Liaodong Bay.