三峡流量调节对长江口潮汐不对称的影响

Influence of discharge regulation by Three Gorges Dam on tidal asymmetry in Yangtze Estuary

利用非平稳调和分析方法(NS_TIDE)对长江口内6个水文测站的长周期水位资料进行调和分析,同时引入偏度指标刻画不同分潮组合产生的潮汐不对称时空演变规律。结果表明:随着潮波向河口内传播,潮汐不对称呈现先增大、后减小的趋势;流量的季节性变化使得潮汐不对称特征存在显著的季节性差异;通过敏感性分析探讨潮汐不对称对径流变化的响应,具体表现为流量增大会导致上游潮汐不对称性减弱,而下游的潮汐不对称性会随着流量的增大而增强;三峡大坝在洪季时的蓄水使大通站洪季流量显著减小,从而导致长江口上游地区的潮汐不对称现象更加显著,而下游地区则表现出相反的趋势。

This study applied a nonstationary harmonic analysis(NS_TIDE)method to analyze the long-term monitoring data of 6 stations in the Yangtze Estuary,and the spatial and temporal variations of multiple sources of tidal asymmetry were quantified by a skewness metric.The results indicated that the tidal skewness shows an initial increase followed by a slight decrease as it propagates landward.The detailed amplitude variations of tidal asymmetry due to changes in the seasonal discharge were investigated.The sensitivity analysis reveals the response of tidal asymmetry to the varying discharge,which is the tidal asymmetry of upstream decreases with the increase of discharge and the tidal asymmetry of downstream shows a opposite trend.The results spanning the periods before and after the operation of the Three Gorges Dam were compared to investigate the impacts of the Three Gorges Dam.Because of the decrease in river discharge during the flood season,tides became more asymmetric at the upstream region,but a contrary trend appears at the downstream region.