伶仃洋为一典型的复合型潮汐河口湾，以潮流动力作用为主. 伶仃洋枯季盐淡水混合具有很大的时空变化特点，不能认为是单一的缓混合型; 另外，航道加深会影响动力及物质输运. 文中在动力地貌学的基础上，采用机制分解法和三维数学模式研究了航道三期工程前后航道的动力变化和盐淡水混合特征. 结果表明: 伶仃航道上、中、下3 个
区段的动力特点以及盐淡水混合机制不同; 工程后陆架水从底层入侵河口比较明显; 涨、落潮流速增大，航道的垂向环流明显增强; 表层的流速增大幅度较底层大; 工程后分层系数和环流系数都有所加大，盐淡水混合作用加强.

Lindingyang bay is a typical complex tide-dominated estuary.In dry season,fresh salt-water mixing presents obvious temporal and spatial variations and cannot be regarded as a single partial mixing type.In addition,the dredged channel may affect hydrodynamics and material transportation.In order to reveal the dynamic change and fresh-salt-water mixing characteristics of Linding navigation channel before and after the third-stage engineering,a dynamical geomorphology analysis is conducted,and the mechanism decomposition method as well as the three-dimension mathematical model is adopted.The results shows that ( 1) Lingding channel can be divided into three parts,namely upper,middle and lower sectors,and the dynamic characteristics as well as the fresh salt-water mixing mechanism varies in different sectors; ( 2) after engineering,the shelf water intrusion from the bottom into Lingdingyang bay becomes obvious; ( 3) with the increase of the velocity caused by flood tide and ebb tide,the vertical circulation of the channel becomes strong.The surface velocity increases more significantly than that of the bottom; and ( 4) after engineering,the stratification and circulation coefficients both increase,and the fresh saltwater mixing effect is enhanced.