近20a人类活动对珠江河网径潮动力影响的洪枯季节差异

Seasonal differences in the impacts of human activities on river-tidal dynamics in the Pearl River Networks in recent two decades

受高强度人类活动干扰,珠江三角洲的动力特征发生了与自然过程截然不同的变化。为探明珠江河网径潮动力特征演变的季节差异,基于“997”与“177” 2场洪水和“012”与“1612” 2场枯水的同步水文资料,采用傅里叶变换方法获取余水位和潮汐成分进行对比分析。结果表明:珠江三角洲洪季余水位显著降低,且愈往上游余水位降幅愈大,而枯季余水位则因水库运行导致的上游来流增加而有所升高;同时洪枯两季珠江三角洲的潮差均显著增加。长期以来珠江流域水库建设引起水沙异变所造成的河网地形下切是导致近20 a余水位下降的重要因素;地形下切引起的余水位比降大幅削减揭示出珠江河网潮波传播阻力减小,潮波振幅衰减效应的减弱是河网潮差增大的主要原因。

The dynamic characteristics in the Pearl River Delta(PRD) were disturbed by dramatic human activities and changed differently from the natural evolution.To explore the seasonal differences in the evolution of river-tide dynamic characteristics in the river networks of the PRD,based on the synchronous hydrological data of "997" and "177" during flood seasons and "012" and "1612" in dry seasons,the Fourier transform method was adopted to obtain the residual water level(RWL) and tidal components in the PRD for comparative analysis.The results showed that the RWL in the PRD decreased significantly in flood seasons and the decrease of the RWL was greater in the upper reaches;while the RWL increased slightly in dry seasons due to the increase of upstream inflow caused by reservoirs operation.At the same time,the tidal range of the PRD increased significantly in both flood and dry seasons.For a long time,the riverbed down-cutting caused by the changes of water and sediment discharges resulted from dam constructions in the Pearl River Basin was the leading factor for the decrease of RWL in the past 20 years.Moreover,the significant reduction of RWL slope caused by riverbed down-cutting revealed that the decrease of the resistance of tidal wave propagation in the river networks and attenuation of the decay effect of tidal wave amplitude were the main reasons for the increase of tidal range in the PRD channel networks.