Numerical Simulation For The Current And Suspended Sediment In The Key Bays Of Guangxi Offshore Area

Based on the improved ECOM, a three-dimensional hydrodynamic and suspend sediment model is developed in the key bays of Guangxi offshore area, they are Qinzhou Bay, Fangcheng harbor, Zhenzhu harbor and Tieshan harbor. The model considered various dynamical factors synthetically, simulate and analyze the current fields, the change of the residual unit width water mass flux (RUWF) in both summer and winter, and also the distribution of suspend sediment in winter. The relationship between the tidal prism and speed of throat was also discussed. The main parts of this paper are as follows.(1) A three-dimensional hydrodynamic model is developed in the Beibu Bay, the calculate area of model include the entire Leizhou peninsula and the east bank of Viet Nam. Supplying boundary condition by the calculated results of the big area model, two three-dimensional, high resolution, hydrodynamic models are also developed in Qinzhou Bay, Fangcheng harbor, Zhenzhu harbor and Tieshan harbor. the filed-measured current in Qinzhou Bay in Jan.2007 and the elevation in tide table in Jan.2008 are used to validate this model, and the result is reasonable.(2) The small area model in four bays are used to simulate the current fields and the change of RUWF. The results show that:in the bays of Guangxi offshore area, the neap tide belongs to semidiurnal tide and the spring tide belongs to diurnal tide, The tidal current velocities at edd tide are higher than the current speed at flood tide, the ebb tidal duration is shorter than the flood tidal one, the current velocities in summer are bigger than the ones in winter. The RUWF are in the trend of inverse clockwise in Qinzhou Bay around in both summer and winter, and it is stronger in summer than in winter. The RUWF are smaller and in the trend of inverse clockwise outer Tieshan Bay in winter. The trend of inverse clockwise will be weaken by the monsoon in summer.(3) The output points and sections are designed in the throat of Qinzhou Bay to research the relationship between the tidal prism in Maowei sea and the speed of the sections. The results show that:the tidal prism change wildly with the increase of tidal hydrodynamic in Maowei Sea. The maximum tidal prism in neap tide is only over 2 hundred million cubic meters, and it can over 6 hundred million cubic meters in spring tide. The reason is that more than half area of Maowei Sea are tidal flat area. The relationship between the increase of the sections speed and accumulation flux and instantaneous flux are positive proportional.(4) A three-dimensional suspended sediment module is applied to the model according to the observed medium diameter in four bays, and the distribution of the suspended sediment in the key harbors of Guangxi offshore area in winter are computed. The results show that:at the time of spring tide, ebb tide, the range of the suspended sediment are more widely, and the concentration is higher, current velocity is the main factor to affect the Resuspension of suspended sediment. The maximum concentration of the suspended sediment is about 0.05 kg/m3, and it accords well with the observed data in feb. and mar.2009.