珠江磨刀门河口日均水位变化及影响因子辨识

Quantifying the impacts of external forcing on daily averaged water levels in the Modaomen estuary of the Pearl River

珠江磨刀门河口日均水位变动的态势受自然过程与强人类活动的驱动,呈现出明显的阶段性演变与季节性异变。辨识日均水位的影响因子,是河口动力学研究的重要内容,对河口治理和水资源高效开发利用具有重要指导意义。本文通过流量驱动的数据驱动模型,对磨刀门河口沿程主要站点长时间日均水位序列(1959—2016年)进行分解,分解出由地形和海平面边界共同驱动以及仅由上游马口站流量边界驱动引起的日均水位变化。地形和海平面边界共同驱动的结果表明:甘竹-灯笼山河段春夏两季日均水位变化主要由河道挖沙引起,日均水位下降(平均下降0.26 m);秋冬两季则由口门围垦与海平面边界控制,日均水位抬升(平均抬升0.07 m)。仅由上游马口站流量边界驱动的结果表明:春夏秋三季日均水位变化主要由水库蓄水主导,日均水位下降(平均下降0.13 m);冬季日均水位变化受水库调枯影响,日均水位抬升(平均抬升0.03 m);从量值上看,地形和海平面边界对磨刀门河口日均水位变动的影响大于上游水库调蓄作用。

The daily averaged water levels in the Modaomen estuary of the Pearl River are mainly driven by the natural processes and significant human interventions.Thus,the water level dynamics are featured by apparent stepwise evolution and seasonal variation.Understanding the evolution of water level dynamics and identifying the driving factors are essential with regard to sustainable water resources managements in estuaries.In this study,a data-driven model where the calibrated parameters were derived from river dis⁃charge was used to quantify the alterations in daily averaged water levels induced by the river flow ob⁃served at Makou station,and by the combined effects due to geometric change and mean sea level based on collected hydrological data from 5 stations along the Modaomen estuary over the period 1959-2016.The results show that the alterations in daily averaged water level driven by the combined effects of the geomet⁃ric change and mean sea level in spring and summer are mainly controlled by sand excavation,leading to a reduction in the daily averaged water levels(decline by 0.26m on average)over the Denglongshan-Gan⁃zhu reach;On the other hand,the alterations in autumn and winter are mainly controlled by land reclama⁃tion and mean sea level,leading to an increase in the daily averaged water levels(increase by 0.07m on average).The alterations in daily averaged water level driven by the river discharge is mainly due to the freshwater regulation by dams in the upstream catchment,which is negative in spring,summer and au⁃tumn,indicating a reduction in the daily averaged water levels(decrease by 0.13m on average),whereas it is positive in winter indicating an increase in the daily averaged water levels(increase by 0.03m on aver⁃age).Overall,the combined influence of geometric change and mean sea level is stronger than that of freshwater regulation due to dam constructions.