北方城市大型景观水系水体循环净化的数值模拟

NUMERICAL SIMULATION ON WATER PURIFICATION BY CIRCULATING ENGINEERING OF A LARGE LANDSCAPE WATER SYSTEM IN NORTHERN CITIES IN CHINA

静湖是中新天津生态城最大的景观湖,并连通故道河及惠风溪等水体一起形成了生态城独特的水生态系统,是北方城市大型景观水系的代表,其水环境改善和保障问题受到较大关注。在对生态城静湖水系水体循环净化设施建设和水质提升工程运行方案实施等重点调查分析的基础上,运用Delft3D FM构建静湖水系数值模型模拟水体水动力、水质演变过程,分析评估了工程运行对水质指标的改善效果。结果表明:静湖水系水质受降雨影响明显,对比汛前、汛后各河段水质浓度变化发现,汛后COD、TP浓度可升高10%,部分河段甚至升高60%,汛后NH_(3)-N降低20%-30%;通过设置补水、拆除隔离坝、增加循环泵和排水泵等工程措施,静湖水系水动力条件得到较大改善,NH_(3)-N、TP基本能达到GB 3838—2002《地表水环境质量标准》Ⅳ类水标准,ρ(NH_(3)-N)可降低3%-25%,ρ(TP)可降低6%-50%。工程措施应综合考虑水环境本底、污染源治理、水利设施运行等多因素共同制定水质提升策略。

Jinghu Lake is the largest landscape lake in Sino-Singapore Tianjin eco city. It connects Gudao River and Huifeng River to form a unique water ecosystem, which is the representative of large-scale landscape water system in northern cities. Thus, the water system environment attracted great attention. Based on the investigation and analysis of the construction of water circulation purification facilities and the implementation of water quality improvement projects in Jing water system, Delft3 D FM model was built to study the hydrodynamic and water quality evolution process in Jing water system under different engineering schemes, whose results were further evaluated to verify the engineering effect on water quality improving. The results indicated that the water quality of Jing water system was obviously affected by rainfall. By comparing the changes of water quality before and after the flood season, the concentration of COD and TP increased by 10% after the flood season, even increased by 60% in some river sections, but the NH_(3)-N decrease by 20%-30% after the flood season. Furthermore, through the engineering measures, such as setting up water replenishment, removing isolation dam, and installing circulating pump & drainage pump, the hydrodynamic condition of Jing water system was greatly improved, and NH_(3)-N and TP generally met the requirements of class Ⅳ water standard, for that NH_(3)-N was reduced by 3%-25%, and TP was reduced by 6%-50%. Engineering measures should take water environment background, pollution source control, water conservancy facilities operation and other factors into account, to develop water quality improvement strategy.