Three-dimensional mathematical modeling of pollutant transport in stratified estuaries

This study, in the flow computation, uses a three-dimensional shallow water BEM(Boundary Element Method) model. However, to investigate the temperature distribution, we adopt a three-dimensional advection-diffusion ELBEM(Eulerian-Lagrangian Boundary Element Method) model. The advection part of ELBEM model is treated by the concept of Eulerian- Lagrangian scheme, which overcomes the limitation of traditional BEM scheme which is incapable to deal with the arbitrary velocity field. The linkage of three-dimensional shallow water BEM model and advection-diffusion ELBEM model enables us to deal with the fluctuation of free surface and density stratification in a stratified estuary.The simulation results are satisfactory through the comparison with analytical solutions and the results from other numerical schemes. Furthermore, this model is applied to simulate conditions which flow field is effected under different boundary conditions such as surface wind shear or heat flux. The simulation results, as comparing with those of homogeneous flow field, show the phenomenon of overturn under the condition of unstable density stratification. As far as stably stratified flow fields are concerned, the phenomena of multiple circulating gyres and the thermocline are also captured.