潮汐强度与咸潮上溯距离试验

Experimental study on the relationship between tide strength and salt intrusion length

采用物理模型实验方法对不同潮差驱动下咸水入侵距离进行实验研究,结果表明存在潮差临界值使得咸水入侵距离最短,当潮差小于该临界值,咸水入侵距离随潮差增大呈快速减小趋势,而大于该临界值则呈缓慢增大趋势。基于实验数据对盐淡水混合进行理论分析,揭示了实验现象的产生机制:①潮差增大过程中盐淡水混合由高度分层变为均匀混合,导致驱动咸潮入侵的动力发生了改变;②当盐淡水为弱混合类型,盐淡水高度分层,重力环流输运是盐进入河口的主要方式,潮汐强度增大减小了盐淡水分层,减弱了重力环流的输运作用,因此入侵距离变小;③当盐淡水为强混合类型,盐淡水混合均匀,重力环流输运作用大大减弱,潮汐扩散成为主要的输运方式,潮汐增强使得扩散能力增大,因此潮汐强度越大,咸潮入侵距离越大。

A series of channel experiments were carried out to investigate salt intrusion lengths with different tide ran- ges. The experiments show that there is a critical tide range value, with which the salt intrusion length reaches its minimum. Tide range increasing results in rapidly decreasing salt intrusion length if tide range is smaller than the crit- ical value, while salt intrusion length slowly increases with increasing tide range if tide range is higher than critical value. Analyses of fresh and salt water mixing based on the experiments data uncovered the essence of the phenome- na： （1） The stratification is broken during the tide range changing, which changes the forces resulting in salt intrusion; （2） Gain of salt is mainly due to the exchange flow if fresh water and salt water is stratified, stronger tide strength could damp the stratification and reduce the exchange flow salt flux, causes smaller salt intrusion length; （3） While if fresh water and salt water is mixing well, gain of salt is mainly due to diffusion, stronger tide strength could provide stronger diffusion, causes longer salt intrusion length.