Numerical study of surface water flooding characteristics in urban environments

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.

Keywords

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

Funding

Technology Research and Development Program, Department of Natural Resources of Gansu Province(2023-02-08)

The Engineering and Physical Sciences Research Council(EP/ N021614/1)