| After consulting plenty of literatures about 3D numerical simulation, Princeton Ocean Model (POM) including σ coordinate system is selected as tool of studying offshore current. In this thesis, one of the improvements of POM is adding a suitable moving boundary technic in the model. Checks are applied to decide the 'wet or dry' fate of each cell by comparing cell's total water depth with critical water depth and forward water depth. This techinc has the advantages of conservation and no negative water depth. The application result of improved POM in Nantong sea aera shows that the model is capable of simulating alternate appearance of shoal going with ebb-tide and spring tide.Another improvement applied to POM is water quality model incorporated, which can simulate eight water quality indexs simultaneously, including phytoplankton, dissolved oxygen, chemical oxygen demand, organic nitrogen, ammonia, nitrate nitrogen, organic phosphorus and inorganic phosphorus. In order to validate the water quality model, central difference and one-order Smolarkiewicz upwind difference schemes were applied to simulate the concentration distribution in a rectangular flume with a continuous pollutant discharge. Error statistical analysis indicates that simulated values agree well with precise values. The simulated values of central difference are more precise than those of upwind difference, but the latter is better for water quality simulation in natural water body.3D offshore water quality model is applied to predict transport and circulation of pollutant in Nantong sea area, and the visualization of simulated results made by Matlab indicates that the model is competent in offshore water quality simulation.The improved POM has been successfully applied in water environmental impact assessment of Nantong sewage marine disposal engineering. This research extends scope and field of POM application, and provides technical support for utilizing environmental capability of ocean reasonably as well.
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