Application and improvement of the EFDC in numerical simulating of Yangtze River Estuary and adjacent sea

Based on the EFDC (Environmental Fluid Dynamics Computer Code),a three dimensional baroclinic model for lower reaches of Yangtze,Yangtze Estuary ,Hangzhou Bay and the adjacent sea areas was established with the sigma-coordinate in the vertical direction and orthogonal curvilinear coordinate in the horizontal directions. The orthogonal curvilinear coordinate grids of the studied water areas were setup by the attached program of Delft3d software. Grid lines of a model fit coastlines well in order to improve local spatial resolution. The dry-wet method was also used to deal with the moving boundary. The minimum water depth limit condition was introduced into the mode for numerical simulation stability and avoiding producing negative depths in the shallow water areas. The improved model was used in the reaches of Yangtze,Yangtze Estuary,Hangzhou Bay and the adjacent sea area.The simulated results are fairly consistent with observations. The errors of the calculated water level and current velocity are less than 10 % compared with the observation data from 10 tidal gauging stations and 9 current gauging sites. The simulation of the current in the Yangtze estuary in September 2002 shows that the current has asymmetry due to the runoff effect,the velocity of the ebb current is larger than the flood and the ebb tide duration is obviously longer than the flood in the South Branch due to the runoff effect. The EFDC model was improved efficiently and can be used more successfully in the coastal areas for investigating Hydrodynamic-Ecological environment numeric study.