3-D Numerical Simulation Of Storm Surges In The Changjiang Estuary And The Hangzhou Bay

The Changjiang estuary and the Hangzhou Bay are situated in the middle of the coastline of our country, facing the West Pacific on the east, where are attacked by tropical cyclones almost every year. The induced disaster of storm surges brings great loss to the coastal areas. Therefore, the study of storm surge in the region of the Changjiang estuary is of opration significance. The study in the paper is based on a 3-D estuarine, coastal and ocean model ECOM-si, which is widely used in the world. By use of this model, three storm surges are numerically simulated.In the paper, three tropical cyclones are adopted, which ever influenced the sea area of the Changjiang estuary and the Hangzhou Bay.Thery are TC9711 (named Winnie), TC0012(named Prapiroon) and TC0014(named Saomai).Two famous formulae are adopted in the paper, which are widely used in the study of storm surge in the world. They are Fujita formula(named Formula I for short) and Fujita-Takahashi(named Formula â…¡ for short). The pressure fields computed by these two formulae are compared and analyzed. The main difference is the attenuation velocity of the pressure field computed by Formula I is slower than that by Formula â…¡.The gradient wind formula is utilized in solving the wind field.Thus, two gradient wind fields are generated from Formula I and Formula â…¡.The translation wind field is computed by use of Ueno.Thus, two different wind fields are obtained. By comparison, the wind velocities at the exterior region of the maximum wind radius circle, computed by Formula â… , is a little bigger than those by Formula â…¡. The observed wind data at Gaoqiao station during TC0012 is used for validation of the computed wind vectors. Through the validation, it is found obviously that the simulated outcome by Formula â…  is better than that by Formula â…¡, especially for the simulation of maximum wind speed.Three main factors in process of storm surge, that is, runoff, astronomical tide and storm surge, are concerned separately in this paper. The water level course and the flow field under the effect of each factor are numerically simulated. The effect of runoff can raise an elevation about 0.05m in regions nearby the mouth of the Changjiang estuary during summer. The effect of runoff is very strong at the mouth of Changjiang estuary and the speed of current can reach about 0.4m/s under the single effect of runoff. But the influence of the runoff is very small out of the mouth of the Changjiang estuary. Astronomical tide is a significant factor. Under single effect of it, the maximum tidal range is about 3.5m to 4m during three typhoons, while the flow velocity is about 1.5m/s for the maximum. As far as the effect of single factor of storm surge is concerned, the air pressure drop arise the set-up on one hand, and the wind stress drags to make the water body near the center of the typhoon flow in the character of cyclone on the other hand. The single effect of storm surge can make a set-up of lm to 1.5m at Gaoqiao station and a maximum velocity of wind-induced current is nearly about 2m/s.In addition, the water level courses and the flow fields under the coupled action of three factors are numerically simulated. In the simulation process, the pressure fields...