中文摘要：

本文利用ECOM模式建立了一个长江口水动力盐度三维数值模型。当水底地形变化比较剧烈时，原ECOM模式中水平扩散项的计算就可能产生虚假的流场和物质输运，所以文中首先对ECOM模式物质输运方程的水平扩散项计算方法进行改进，采用返回z坐标系计算，离散变量利用σ层二次Lagrange插值得到。对于改进方法，文中采用Huang＆spaulding提出的数值试验进行验证，证明此方法大大地提高了水平扩散项的计算精度。改进模型采用长江口实测水文资料进行率定验证，计算和分析了南北槽垂向盐度分布和盐水通量过程，结果表明，模型能较好反映测点盐度变化过程，也能较好地模拟出垂向表底层的盐度差异。

英文摘要：

A three-dimensional hydrodynamic model of Ocean Model （ECOM） within the framework of a single grid Yangtze Estuary was established using the Estuarine, Coastal and system. When a steep bottom slop exits, the method presented in ECOM for calculating horizontal diffusion is tend to generate spurious velocity and transport. Hence, the present paper firstly modified the calculation approach to improve the accuracy, The horizontal diffusion was computed in z coordinate system. Through the verification of numerical test presented by Huang and Spaulding, it is proved that the computation accuracy was greatly enhanced. Meanwhile, in order to investigate the influence of deep-draft waterway construction to saltwater intrusion, the improved model was calibrated and verified by the in-sltu hydrologic data of Yangtze Estuarine, the result showed that the modeled data had a good agreement with the measured. The time-dependent salinity of each site was competitively modeled. The model was also used to calculate vertical salinity distribution and the results showed that the difference between the upper layer and the bottom layer was apparent. The model could well reflect the saltwater intrusion structure.