径流-潮汐相互作用与咸潮上溯距离试验研究

Experimental study on the interaction of runoff-tide and salt water intrusion length

河口动力机制复杂,生态环境敏感脆弱,珠江三角洲咸潮上溯距离逐年上移,对生态环境造成了巨大的影响。咸潮上溯距离受径流和潮汐影响显著。该文采用物理模型试验方法,对径流和潮汐共同作用下的咸潮上溯距离进行分析,结果表明:1)增加上游径流量,引起河道水力坡度变陡使得咸界整体往下移动;2)存在临界潮差,使咸潮涨憩时上溯距离最小;3)上游同样增加相同径流量时,潮差小时咸界下移距离大于潮差大时的咸界下移。最后利用Fischer的分层-环流图阐述了产生其偏差的机理:一方面当潮差小时,引起的分层系数变化和/s fu u变化幅值更大;另一方面,增加径流量时改变了密度环流输运作用,而潮差较小时密度环流输运是主导因素,此时增大的径流量,改变了主导因素的输运比例,引起了较大的作用效果,反之,潮差大时作用效果则较小。

Estuarine complex dynamic mechanism, eco-environmental fragility and the increasing of Pearl River Delta salt intrusion length year by year have caused tremendous impacts on the ecological environment. Salt intrusion length significantly is affected by runoff and tidal. This paper uses physical model test to analyze salt intrusion length under interaction between runoff and tidal. The results show that： 1） Increasing upstream runoff can increase hydraulic gradient to make hydraulic gradient down. 2） There is a critical tidal range, the salt intrusion length is shortest when the flood slack. 3） When the upstream increasesthe same runoff, the smaller tidal range the lower fresh-salt water interface. Finally, Fischer＇s layered-circulation figure illustrates the mechanism of the deviation generating. On the one hand when closing the small tidal range, it causes coefficient of layering change and us/uf variation amplitude greater, on the other hand, increasing runoff increases the density circulation transport proportion and reduces the turbulent diffusion transport proportion. When the tide range is small, the density circulation is the dominant factor. Increasing the transport proportion of the dominant factor causes the positive effect of superposition, on the contrary, large tidal range reduces this effect.