基于优先流控制的绿色屋顶植物-人工基质结构优化研究

As an important engineering technology for urban stormwater management in the construction of “Sponge City” in China, green roofs have drawn a lot of attention. The structural component substrate layer in an extensive green roof designed specifically for stormwater management purpose has light density, high porosity, shallow profile depth and strong interaction with plant root system, which will lead to preferential flow. Occurrence of preferential flow in the substrate layer will weaken stormwater management performance of green roofs as well as other ecological services. The study focus on scientific questions “the interaction between plant and substrate” and “occurrence and development of preferential flow in plant-substrate system”. Hydraulic properties of suitable substrates and root system distributions of plants with different water demands are quantified by a series of lab tests. The occurrence and movement of preferential flow in different plant-substrate systems are investigated by using dyeing tracer experiment, solute penetration experiment and multiple-domain water movement model. Based on comprehensive analysis of environmental factors such as rainfall, initial water content and plant-substrate system corresponding to non-preferential flow and preferential flow, the dominant factor causing preferential flow can be identified and optimal design of plant-substrate system targeted at preferential flow control in green roofs will be proposed. The results are able to provide theoretical and technical support for green roofs design, application and development.

绿色屋顶作为城市雨水管理和我国海绵城市建设的重要措施之一，近年来受到广泛关注。用于暴雨管理的简易式绿色屋顶结构层人工基质容重小、孔隙多、剖面深度浅、与植物根系交互作用强，存在优先流风险。优先流发生会削弱绿色屋顶的降雨径流管理能力及其它生态服务功能。本研究围绕绿色屋顶植物-人工基质相互作用机制、植物-人工基质优先流发生及运移规律等科学问题，通过室内检测，量化适用于简易式绿色屋顶人工基质的水力特性及景天属植物的根系分布特征，采用染色示踪实验、溶质穿透实验结合多孔运移模型等方法，研究不同植物-人工基质组合中优先流发生及其运移规律，系统分析降雨、含水率、植物-人工基质等环境因子对优先流发生发展的影响，揭示诱发植物-人工基质结构优先流的主控因子，构建基于优先流控制的植物-人工基质结构优化的设计方法，为我国海绵城市建设中绿色屋顶的设计、应用、发展提供理论和技术支撑。

绿色屋顶作为城市雨水管理和我国海绵城市建设的重要措施之一，近年来受到广泛关注。但用于暴雨管理的简易式绿色屋顶植物-人工基质结构中存在优先流风险。为控制优先流，本项目基于水文学、渗流理论及植物学理论，采用控制实验及数值模拟相结合的方法开展研究。量化简易式绿色屋顶不同设计变量（如植物种类、人工基质种类及厚度等）下人工基质水力特性及植物根系分布特征，分析植物与人工基质的交互作用；通过室内控制实验，得到不同植物-人工基质组合在不同降雨、含水率条件下优先流发生及其运移规律；通过模拟分析，确定诱发植物-人工基质结构优先流的主控因子并进行基于优先流控制的植物-人工基质结构优化设计。研究表明，（1）两种景天属植物垂盆草、佛甲草的根长密度、根表面积密度、根体积密度等根系特征的差异性，由人工基质厚度和种类共同作用所致；对于有植物根系的人工基质而言，人工基质种类和厚度均对饱和导水率有显著影响，但二者的交互作用没有显著影响；不同植物及厚度下珍珠岩基质的水分特征曲线参数不同而蛭石基质的水分特征曲线参数相同。（2）在实验及模拟条件下，优先流普遍发生；降雨强度、植物类型、基质厚度及植物类型与基质厚度的交互作用对珍珠岩基质优先出流量及发育程度均有显著影响；降雨强度和基质厚度对于蛭石基质优先出流量有显著影响、基质厚度对蛭石基质优先流发育程度有显著影响。（3）根系的存在可以降低珍珠岩基质优先流发育，但对蛭石基质影响甚微；基于优先流控制，推荐应用种植佛甲草的10 cm珍珠岩基质作为武汉市绿色屋顶建设。结果可为我国海绵城市建设中绿色屋顶的设计、应用、发展提供理论和技术支撑。