Assessment of Sponge City Flood Control Capacity According to Rainfall Pattern Using a Numerical Model after Muti-Source Validation

Haichao Li,Kazuyoshi Souma,Hiroshi Ishidaira,Yanqi Wei,Jun Magome

doi:10.3390/w14050769

Abstract

Urban floods are a common urban disaster that threaten the economy and development of cities. Sponge cities can improve flood resistance ability and reduce floods by setting low-impact development measures (LID). Evaluating flood reduction benefits is the basic link in the construction of sponge cities. Therefore, it is of great significance to evaluate the benefits of sponge cities from the perspective of different rain patterns. In this study, we investigated the urban runoff of various rainfall patterns in Mianyang city using the Strom Water Management Model (SWMM). We employed 2–100-year return periods and three different temporal rainfall downscaling methods to evaluate rain patterns and simulate urban runoff in Mianyang, with and without the implementation of sponge city measures. After calibration, model performance was validated using multi-source data concerning flood peaks and inter-annual variations in flood magnitude. Notably, the effects of peak rainfall patterns on historical floods were generally greater than the effects of synthetic rainfalls generated by temporal downscaling. Compared to the rainfall patterns of historical flood events, the flood protection capacities of sponge cities can be easily overestimated when using the synthetic rainfall patterns generated by temporal downscaling. Overall, an earlier flood peak was associated with better flood sponge city protection capacity. In this context, the results obtained in this study provide useful reference information about the impact of rainfall pattern on urban flood control by LID, and can be used for sponge city design in other part of China.

Highlights

Urbanization has greatly increased in the past century
Model reliability was quantitatively assessed using the runoff depth derived via water balancing, the simulated annual maximum discharge Rcal of the model using the default parameters (156.7 m3 /s) was underestimated by 17% compared to the estimated runoff
For E2, as the return period increased, the peak and volume reduction rates tended to first increase and decrease in each month. These findings indicate that, under the chi-squared rain pattern, the return periods at which the low-impact development measures (LID) facilities became saturated varied according to the month

Summary

Introduction

Urbanization has greatly increased in the past century. As of 2011, the global urbanization rate was 52.1%; it will reach 67.2% by 2050 [1]. The proportions of populations affected by floods are increasing [2]. China is one of the world’s most urbanized countries; this urbanization is expected to become more pronounced [3]. Heavy rains and floods compromise urban health. Drainage systems are old, while new urban areas have changed the original runoff pattern; the population is concentrated, rendering flooding and waterlogging problems increasingly serious. In recent years, waterlogging has become more common [4]. In 2012, heavy rain on 21 July in Beijing caused

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