基于宏观水文本构关系的城市下垫面降水产流物理机制研究

Due to the high variability of the urban underlying surface and the complex spatial relationship between the permeable surface and impermeable surface, the physical mechanism of the runoff generation over urban underlying surface is a difficult topic in urban hydrology field. The project takes the Liangshui river basin as research object, which is located in the Beijing City. Based on the detailed monitoring of Fangzhuang and Yizhuang experimental areas, a numerical model couples with the Saint Venant equation for surface runoff and Richards equation for soil water movement is developed and validated. By taking into account the range of meteorological forcing factors and the spatial variability of underlying surface conditions, a large number of numerical experiments are carried out in the typical subcatchments using the proposed numerical model. By statistical analysis of the experiment results, The constitutive relation of runoff generation in subcatchment scale is conducted. By coupling the proposed constitutive equation with the pipe network and river channel confluence model, a phisical-based urban hydrological model with coordinated scale is built. The aim of the project is to quantitative describing the physical mechanism of runoff generation over urban underlying surface, and explore the law in increasing scale between misco-grid, subcatchment and basin. The project is of great significance for scientific understanding of the formation process of urban flooding, and also has important reference value for flood control and disaster reduction and sponge city construction in the capital by exploring the runoff generation mechanism of the Liangshui River.

由于城市下垫面高度的空间变异性和不透水面透水面之间错综复杂的空间关系，下垫面降水产流物理机制是城市水文科学研究的难点。项目以北京市凉水河流域为研究对象，结合方庄和亦庄两个实验小区的精细化监测，从描述微观尺度产汇流过程的数学物理方程出发，构建适用于城市下垫面的产汇流数值模型；通过考虑气象强迫因子的取值范围和下垫面条件的空间变异性，采用数值模型在典型汇水单元进行大量随机试验，在统计分析的基础上构建汇水单元尺度降水产流过程宏观本构关系；将所建宏观本构方程与管网和河道汇流模型相耦合，构建尺度协调、物理性强的城市分布式水文模型。通过项目研究，探索“微观网格—汇水单元—流域”的产流升尺度规律，实现城市下垫面降水产流物理机制的定量描述，对科学认识城市雨洪形成过程具有重要意义；通过典型区凉水河流域降水产流机制探索，对首都的防洪减灾和海绵城市建设也具有重要的参考价值。

由于高度的空间变异性和不透水面与透水面之间错综复杂的空间关系，城市下垫面产流物理机制成为城市水文科学的难点。研究综合室外水文观测实验和数值模拟试验，深入分析城市下垫面产流的影响机制，构建了适用于城市下垫面的降水产流本构关系。主要成果和结论如下：.（1）辨识了城市下垫面不透水面空间分布对产流机制的影响。在不透水面汇流路径识别的基础上，提出了有效不透水面的界定方法，建立了有效不透水面和总不透水面之间的定量统计关系，辨识了有效不透水面变化对城市产流过程的影响。结果表明，城市化过程中，有效不透水面比例的变化和总不透水面面积呈显著正相关关系；有效不透水面的比例变化在城市化前期对降水产流的影响更为巨大，同时对于稀遇暴雨的影响更为明显。.（2）在北京市昌平区白浮实验基地的室外精细化水文观测实验的基础上，针对完全透水面模式和无效不透水模式两种汇水单元类型，定量分析了不同影响因素对径流过程的影响。实验结果表明：降雨强度、土壤前期含水量的加大，会导致汇水单元产流时间的加快，径流系数的提高；雨峰系数的延后会导致洪峰流量的增大；汇水单元上不透水面积的增加会导致径流系数的显著增加。.（3）综合场地实验和数值实验，构建了汇水单元尺度城市下垫面降水产流本构关系。通过耦合一维垂向土壤水分运动方程和二维地表浅水方程，构建精细尺度的汇水单元产汇流模型；在场地实验结果验证的基础上，通过数值实验识别各种影响因素与径流系数的统计关系，构建了面向不同汇水单元类型的下垫面产流驱动要素与径流系数的宏观水文本构关系。通过对北京市凉水河大红门流域“7.21”暴雨过程的模拟，实现了对本构关系在流域尺度的验证。. 项目的研究结果对于认识我国城市洪涝形成物理机制，推动具有我国自主知识产权的城市水文模型建立具有重要的意义，并在实践上对首都洪涝管理和海绵城市建设具有支撑作用。