Matching analysis of investment structure and urban inundation control function of sponge cities in China

The risk of urban flood inundation has been increasing worldwide. To address this problem, the sponge city strategy has been proposed in China. This study focuses on the issue of urban flood inundation, which is a main problem that the construction of sponge cities seeks to address. The design mode of sponge city flood control and drainage systems (SCFCDSs) is examined, including source control systems (SCSs), stormwater pipe network systems (SPNSs), and over-standard stormwater storage and drainage systems (OSSSDSs). A quantitative method to evaluate flood control and drainage capacity (stormwater equivalent) of SCFCDSs is proposed and applied to quantitatively analyze the matching relationship between investment structure and inundation control function. Based on 18 pilot cities, the stormwater equivalents of the SCSs, SPNSs, and OSSSDSs account for 13.8, 57.7, and 28.6% of the stormwater equivalent of SCFCDSs on average, respectively. On the other hand, the investments in SCSs, SPNSs, and OSSSDSs account for 66.1, 15.0, and 18.9% of the total investment in SCFCDSs on average, respectively. The results show that an unbalanced investment structure and corresponding design standards along with insufficient investment in OSSSDSs are the key factors hindering the effective implementation of urban flood inundation control in sponge cities.