Evaluation of the effect of water diversion on improving water environment in plain river network under the multi-objective optimization

Abstract

引调水是改善平原河网地区水环境的重要方法之一，通过构建太湖流域走马塘东南片平原河网区一维水动力水质数学模型，研究不同引调水方案对区域水环境改善效果，确定引调水过程中的异质性因子.从决策目标、水质指标、空间指标3个层面综合考虑，构建环境效益与经济效益结合的多目标函数及评价体系，对引调水方案进行评估优选.结果表明：引调水流量较大时，能够在一定程度上改善区域水环境状况，规划方案下引调水5 d后，高锰酸盐指数、氨氮、总磷的平均改善率分别为30.7%、22.2%、26.4%；引调水时，区域河网中不同空间点位、不同水质指标之间的水质改善过程与效果都存在一定异质性；引调水水量、调度模式及污染源分布都会对调水后的河网区水质产生差异性影响；本研究建立的多目标评价体系较现有方法能够有效涵盖引调水中存在的异质性因子，从多个目标层面优选引调水方案，实现水量水质综合优化调控，为平原河网地区水环境长效管理与科学决策提供理论参考.;Water diversion is a significant method to improve the water environment in the plain river network area. Through building up the one-dimensional hydrodynamic and water quality model of the plain river network area of southeast Zoumatang of Taihu Basin, the effect on water environment of different water diversion schemes was simulated, and the heterogeneous factors in the process were determined. A multi-objective function and evaluation system combining environmental benefits and economic benefits were constructed from three aspects, including decision-making, water quality indexes and spatial indexes, and the water diversion schemes were evaluated and optimized. The results show that: (1) With a larger flow, water diversion can improve the regional water environment to some extent. After 5 days of water diversion under the planning schemes, the average improvement rates of COD_Mn, ammonia nitrogen and total phosphorus were 30.7%, 22.2% and 26.4%, respectively. (2) Heterogeneity existed in the process and effect of water quality improvement in different spatial points and water quality indexes in the river network during water diversion. (3) The water quantity and dispatching mode of water diversion as well as distribution of pollutants all have different effects on the water quality in the river network. (4) Compared with the existing method, the multi-objective evaluation system of water diversion established in this research can effectively cover the heterogenous factors and evaluate and optimize different water diversion schemes from multiple objectives, therefore can achieve comprehensive optimization and control of water quantity and quality, and provide theoretical reference for long-term management and scientific decision-making of water environment in the plain river network area.