长江倒灌对鄱阳湖水动力特征影响的数值模拟

Simulation of the impact of the reverse flow from Yangtze River on the hydrodynamic process of Lake Poyang

长江水倒灌是鄱阳湖的一个重要现象,是江湖作用的具体体现.利用环境流体动力学开源代码(EFDC)建立鄱阳湖的二维水动力模型,并借助染色剂模块和水龄模块,分析鄱阳湖全年的水动力变化过程、倒灌现象及其影响.数值模拟结果精确地验证倒灌的发生、持续时间和倒灌流量,显示倒灌时期湖区水力梯度、湖流逆向的特点.顶托作用强于鄱阳湖盆地作用时是倒灌发生的条件,通过计算倒灌发生的临界流量并与实际来流进行对比,本文提出新的倒灌判定条件,可以准确地预测倒灌和预估倒灌流量,且利用2007 2009年的测量数据验证了其可靠性.通过在赣江入流设置染色剂的方法,模拟获得2008年4次倒灌入流水体在湖区的占据面积.顶托作用和倒灌造成湖水不能外泄甚至逆流,增加湖区水体的水龄,通过数值模拟并与水力停留时间进行对比,估算出湖湖水水龄的增加时间.

The reverse flow from the Yangtze River is an important phenomenon of the Lake Poyang,embodying the interaction between river and lake. In this paper,a 2D model of the Lake Poyang based on the Environmental Fluid Dynamics Code（ EFDC） is established to study the hydrodynamic process,and the reverse flow from the Yangtze River is investigated in favor of the dye module and water age module. The reverse flow appears when the blocking effect of the Yangtze River becomes stronger than the basin effect of Lake Poyang. By calculating the critical flux of the reverse flow and contrasting it with the observed inflow,we propose a new discriminated condition for the reverse phenomenon,which can accurately predict the occurrence and estimate the flux of reverse flow,as validated by the observed data of three years from 2007 to 2009. Using this method to set colouring agent at the inflow of the Ganjiang River,the occupying areas from the Yangtze River are obtained by the simulation of 2008. The blocking effect and the reverse flow of Yangtze River are found to enlarge the water age by preventing the outflow of water from the lake,and the increased time can be estimated by comparing the simulated water age with hydraulic retention time.