城市地表雨洪特征的数值模拟研究（英文）

Numerical study of surface water flooding characteristics in urban environments

摘要

【目的】局部强降雨引发的地表洪水已经成为很多城市洪水的主要形式。真实的城市环境非常复杂，影响地表降雨-产流的因素很多，比如马路宽度、方向和建筑物覆盖率。通过开展大量不同参数组合的数值模拟试验，得到城市地表特征对降雨-产流过程的影响。【方法】具有真实感的地表形态是采用程序化建模软件自动生成的。这款软件通过11个独立参数描述城市地表形态，包括平均街道长度、街道方向、街道曲率、主路宽度、辅路宽度、公园覆盖率等。研究采用具有激波捕捉功能的总变差减少的麦科马克格式求解浅水方程组，得到了大量不同城市地表的降雨-产流过程。研究揭示了影响城市雨洪汇流时间的主要参数。这个汇流时间代表了洪水形成的特征时间尺度。【结果】为了得到普遍适用的结果，研究将计算得到的流域出口的流量过程线归一化，使之不受流域面积、坡度和雨强的影响。因此，无量纲汇流时间取决于12个独立参数，即11个控制城市地表形态的参数和第12个描述地面粗糙程度的曼宁系数。基于多元线性回归的方法，对2 994个数值模拟的结果进行了敏感性分析，定量研究了每个参数对计算结果的影响。【结论】结果表明：地表粗糙度和建筑物覆盖率是影响城市雨洪形成的最主要的两个参数。提出的经验公式描述了各参数对流域无量纲汇流时间的影响。研究成果可以为未来设计具有韧性防洪能力的城市环境和改进现有的排洪系统提供有益的指导。

Abstract

[Objective] Surface water flooding is caused by heavy rainfall, which has been the main type of flooding in many cities across the world. Real urban environments are highly complex, and there are numerous parameters influencing the rainfall-runoff processes, such as road width, orientation and building coverage. The main objective is to perform a parametric study concerning the rainfall-runoff processes in complex urban environments, in order to gain a better understanding of the impact of urban characteristics on the surface runoff. [Methods] Realistic urban layouts are generated by means of procedural modelling software, which parameterises the urban configurations using 11 independent variables, including the averaged street length, street orientation, street curvature, major street width, minor street width, park coverage, etc. A shock-capturing TVD Mac Cormack shallow water equations solver is used to undertake a large number of computational simulations regarding the rainfall-runoff processes over realistic urban layouts. The dominating urban parameters that influence the time of concentration is unveiled, which characterises the timescale of the flood formation. [Results] In order to generalise the research outcomes, the obtained hydrographs at the outlet of the catchment are normalised so that they are independent of the catchment area, slope or rainfall intensity. The dimensionless time of concentration is thus only the functions of 12 independent parameters, including 11 parameters that governing the urban layouts and the Manning roughness coefficient of the ground. A sensitivity analysis, based on the multiple linear regression method, is performed on the 2, 994 simulation cases to quantify the influence of each parameter. [Conclusion] The results show that the ground roughness and the building coverage ratio are the two most important factors that influence the urban flood formation. Their influences on the dimensionless timescale of the urban catchments' response to rainfall are quantified by empirical formulae. The research findings can provide useful guidelines for the design of future flood-resilient urban environments and the improvement of existing drainage systems in cities.

关键词

城市洪水 / 地表洪水 / 浅水方程 / 汇流时间 / 降雨产流过程 / 洪水预报 / 降水 / 人类活动

Key words

urban flooding / surface water flooding / shallow water equation / time of concentration / rainfall-runoff / flood forecasting / precipitation / human activity

基金资助

甘肃省自然资源厅科技开发计划项目(2023-02-08)

英国工程和自然科学研究委员会(EP/ N021614/1)