长江三峡库区污染混合区的有限元模拟

Finite element simulation of pollutant mixing zones in streams entering the Three Gorges Reservoir

为进一步弄清长江三峡水库修建对库区水质的影响 ,确定库区的环境容量 ,需要针对库区主要城市排污口及重要支流汇流口附近污染混合区进行计算。建立了求解浅水流动及其污染物输移扩散的分步有限元格式。采用 k- ε紊流模型确定紊动应力和污染物质扩散系数。对长江和嘉陵江汇流口附近的流场和浓度场进行了模拟。利用实测资料对模型进行了率定和验证。选取了桃花溪和李家沱两个典型排污口 ,对建库前后的污染混合区范围进行了预测 ,分析了建库前后污染混合区的变化。计算结果表明 :建库后污染混合区的面积有较大增加 ,需要采取必要的措施来控制水体污染 。

Water runoff from urban drainage systems into rivers and pollutant mixing in those rivers should be analyzed to determine the water quality and the environmental capacity of reservoir areas after completion of the Three Gorges Project. A fractional step finite element scheme was used to solve the shallow water flow and pollutant transportation equations for river systems, especially the junctions of rivers. The turbulent viscosity and pollutant diffusion coefficients were determined using the k-ε turbulence model. The numerical models were validated using observed data for both the velocity distributions and the pollutant concentration distributions near the junction of the Yangtze and Jialing Rivers. Data for the Taohuaxi and Lijiatuo outlets was used to predict changes in the pollutant mixing zones before and after the Three Gorges Project was built. The results show that the pollutant mixing zones near the outlets will increase after the project is completed, so proper measures are needed to control water pollution and to protect the water quality in the reservoir areas.