珠江河口咸潮问题之我见

咸潮只是河口偏于向陆一侧盐度较低（0.5~10）的那一部分盐淡混合或冲淡水体，不宜将河口“咸水”和海洋“盐水”等同或混为一谈；视“咸潮上溯”为“盐水入侵”欠当。咸潮上溯为河口自身物质的随潮运动，基本上是一种被动的行为。咸潮上溯之动力机理，与河口水、盐物质于一年、一月和一天中随潮在河口的进出、“排”“蓄”循环运动过程有关。小潮向中潮变化时期（一月中）及其初落时段（一天中），河口正处于由“蓄”（进）转“排”（出）阶段，其时表“排”（淡水）、底“蓄”（咸水），水体高度呈层，受异重流的影响，底部咸潮进一步上溯“冲刺”达盐度最大值。大潮向中潮变化时的压咸效果最佳。

My Opinion on Salt Tide in the Pearl River Estuary

Salt tide is designated as the low salinity (0.5-10) water body mixing salty and fresh water on landward side of the estuary. The estuary “salt water” and oceans “brine” should not be equivalent or confused. It is inappropriate to take “salt tide tracing” as “saltwater intrusion”. The salt tide tracing upstream is that the estuarine material moves with the tide movement, that is essentially a passive act. The dynamic mechanism of salt tide tracing is relevant to the circular motion process that estuarine water and salt substance move in and out with the tide, or drain and retain in a month or a day. During the period from neap tide to moderate tide (in a month ) and that at the beginning of tide ebb (in a day), estuary is in the phase from retaining (moving in) to draining (moving out). Freshwater drains at surface layer, while salt water at bottom layer, forming an obvious stratification structure. Affected by the density current, salt tide at the bottom further traces upstream rapidly, and its salinity reaches the maximum. Best result can be achieved for lowering the salinity when spring tide is transforming into moderate.