复杂地形河口盐通量的驱动过程及其对径潮动力的响应

With multi-variable dynamic conditions, rapid geomorphological changes, complicated sedimentation processes, estuary is one of the most vulnerable zones under the influence of global warming and frequent human activities. Better understanding of the hydrodynamic mechanisms and temporal and spatial variations of salt flux is of great importance to the study of sediment transport, pollutant diffusion, proper utilization of natural resources and prevention of disasters in the estuarine areas..The Pearl River Estuary (PRE) on the east coast of Guangdong Province in South China is one of the most complicated hydrodynamic systems. The West and North River enter the river network of the Pearl River Delta (PRD) at Sixianjiao junction. Makou on the West River and Sanshui on the North River are the controlling stations of water and sediment discharges. In this study, the collected hydrological data in the PRD is used to analyze the change of the diversion ratio at the Sixianjiao junction. A 3D integrated model of currents and salinity will be established taking water levels and discharges at Sanshui and Makou as the upper boundary condition. The response of the salt flux to the changes of river discharge and tidal mixing will be investigated based on the model results. The contribution of different driving forces on salinity distribution is studied by mechanism decomposition. This research will provide scientific basis for the prediction and early warning of saltwater intrusion in the PRD, and for the safety of the freshwater supply in the surrounding regions.

河口盐通量是陆海相互作用研究中关于气候变化和人类活动对流域及河口产生环境效应这一研究热点的重要基础理论内容之一。本课题将建立多动力因子下珠江河口河网与口外海滨区整体三维水流盐度数学模型，模拟研究径潮动力格局变异下河口盐通量的响应过程，分析主要区域的盐度分布与输移特点；通过对珠江三角洲强潮弱径（虎门）与强径弱潮（磨刀门）两个分汊口处断面的ADCP走航测量，描述流速、流量及盐度断面分布的高精度时空变化特征，探讨断面侧向斜压梯度力对复杂水流结构产生和发育过程的影响；根据动量方程分解计算主要驱动力，分析分汊口处不同驱动力对盐通量的贡献率和转变过程，合理解释河口盐度异常现象的动力机制。河口盐通量的变化影响着河口的类型与特性，因此研究成果对河口海岸的动态演化及其邻近海域生态环境的变化，具有十分重要的意义。

珠江河口是世界上地形最复杂的河口之一，近几十年来受到河道挖沙、航道疏浚、围垦造地等人类活动的影响，珠江口的径潮动力条件发生了很大变化。本项目研究了径潮动力格局变异下，珠江河口的水流、盐度、咸潮上溯的响应过程及机理分析。通过对所收集的水文资料、地形资料以及现场全潮观测进行数据分析，总结了近年来上游高要、石角、博罗水位流量的变化，下游虎门、磨刀门的潮位过程和盐度变化。同时建立了多动力因子下珠江河口河网与口外海滨区整体水流盐度数学模型，对模型进行了水位、流速、流量、盐度的验证。基于模型结果，探讨了珠江河网主要分汊口分流对不同径流量、不同分潮、地形下切的响应；定量分析了上边界径流量、地形、下边界潮差以及海平面上升对珠江口咸潮界位置的影响；通过指数函数拟合了磨刀门、洪奇门、虎门咸潮上溯距离分别对主要节点落潮平均流量、下边界潮差的关系，相关性均较高。对模型进行了多组敏感性试验，揭示了珠江口盐度的时空分布及其对径流、潮汐和风的响应。通过通量机制分解，定量计算了不同动力因子对河口盐通量的贡献，探讨了河口盐度输移机理，解释了珠江河口水体和盐度潮周期平均输运分离异常现象的动力机制。研究成果对河口海岸的动态演化及其邻近海域生态环境的变化具有重要意义，对于珠江河口枯季咸潮上溯的预测与预防具有较大的实际指导意义。