生物滞留系统内部植物-土壤-排水设施协同促渗机理与效应研究

The LID-bioretention is an effective way to reduce the risk of urban flood disaster and runoff non-point source pollution, which promotes rainwater infiltration and purification through the synergistic effects of plants and soils in the system. In areas with poor soil permeability, the internal drainage will be added in the bottom and form a high permeable area to intercept and discharge rainwater, which considerably accelerates the migration of water and pollutants in the system. However, the synergistic mechanism of plant-soil-drainage on enhancing rainwater infiltration within bioretention and constraints of optimal drainage volume, configuration and effect of drainage remain inexplicit. This study will conduct the indoor large-scale variable slope soil trough experiment and adopt numerical simulation method to concentrate on studying this synergistic mechanism. The objectives are: considering whether the drainage in the bottom is equipped or not, to expound the spatial and temporal changes of water and pollutants in the bioretention with the various combinations of different rainfall accumulation depths, plant types, soil properties and so on; to clarify the mechanism of plant-soil on infiltration in non-drainage-system and the threshold setting condition in drainage-system; to reveal the promoting infiltration mechanism and effect of plants and soils in collaboration with drainage, and the determination basis and method of the optimal conveyance capacity of drainage; to explore the optimal configurations of bioretentions by multi-objective optimization algorithm. The research results are expected to provide technical support for urban storm water resources management and "Sponge City" construction.

低影响开发生物滞留系统是降低城市暴雨洪涝灾害和径流面源污染风险的有效途径，通过系统内部植物、土壤的耦合作用来促进雨水入渗和净化。对土壤渗透性较差的地区，还会增设底部排水设施，形成高透水区域，截留和排放入渗雨水，极大的促进系统内部水分和污染物的运移。然而关于生物滞留系统内部植物-土壤-排水设施协同促渗机理，排水设施最佳过流能力、构型、效应等的约束因子与机制尚不明确。本项目拟运用室内大型变坡土槽实验和数值模拟方法，考虑设置与不设置底部排水设施的情景，研究不同降雨积水深度、植物类型、土壤性质等多方案组合下生物滞留系统内部水分、污染物的时空动态变化，明确无排水设施时系统内部植物-土壤耦合促渗机理及排水设施设置的阈值条件，揭示排水设施存在时与植物、土壤的协同促渗机理及排水设施最佳过流能力，提出基于多目标优化算法的系统最佳构型的依据和方法。研究成果以期为城市雨洪资源管理和“海绵城市”建设提供技术支撑。

城市暴雨洪涝减灾技术和径流面源污染治理已经成为我国社会经济可持续发展中迫切需要解决的关键问题，低影响开发作为新兴的城市雨洪资源调控策略，通过系统内部植物、土壤的耦合作用来促进雨水入渗和净化。对土壤渗透性较差的地区，还会增设底部排水设施，形成高透水区域，截留和排放入渗雨水，极大的促进系统内部水分和污染物的运移。然而关于生物滞留系统内部植物-土壤-排水设施协同促渗机理，排水设构型、效应等的约束因子与机制尚不明确。本项目通过综合运用室内试验和数值模拟等方法，（1）对不同排水设施构型（是否设置排水设施、不同管径开孔收集管、不同孔径开孔收集管、有无储水层以及不同储水层深度）的生物滞留系统开展降雨径流水量调控模拟试验，在连续监测生物滞留系统进水、排水以及溢流过程的基础上，对比评估各系统下渗能力；（2）通过监测不同峰型、不同峰现时间的径流过程条件下，生物滞留系统下渗能力的变化特征，分析不同径流条件下各生物滞留系统下渗能力的变化规律，揭示径流特征及降雨特征对不同生物滞留系统下渗能力的影响机制，总结不同排水设施生物滞留系统下渗能力对各径流过程的响应机制；（3）在HYDRUS模型中引入排水设施的重要相关参数，南京市区2年一遇降雨为例，以单因素扰动分析法，分析变水头入渗条件下土壤水力参数的敏感性，定量描述土壤水力参数变化对生物滞留系统下渗能力的影响。研究成果以期为城市雨洪资源管理和“海绵城市”建设提供技术支撑。