Construction cost-based effectiveness analysis of green and grey infrastructure in controlling flood inundation: A case study

Abstract

Global climate change and rapid urbanization have increased the frequency of urban flooding. In this work, SWMM was used to simulate the implementation of low impact development (LID) practices, drainage network reconstruction, and detention tanks to evaluate potential reductions in flood severity in the TQ subdistrict of SH city, China. Two assessment indexes, construction costs and construction effectiveness, were used to evaluate model results for three scenarios. Construction effectiveness was quantified by reductions in total flood volume and peak flow rate. Results show that LID practices such as permeable pavement and sunken green space mitigate the flooding by reducing total flood volume by 8.6% and decreasing surface runoff by 7.9%, at a cost of $0.34 million. Reconstructing the drainage network reduced total flood volume by 38.4%, which is less than the 46.6% given by detention storage construction. However, the peak flow for drainage network reconstruction decreased by 46.6% and peak flow for detention construction was reduced by 50.1%. Despite the lower peak flows, three nodes experienced flood durations longer than the general guideline of 1 h for network reconstruction, while only two nodes did so with detention tanks. Thus, detention tanks are more effective in reducing the effects of flooding than drainage network reconstruction. Detention tanks are also more cost effective, costing $1.59 million, while network reconstruction cost $1.74 million. While this study considers flood risk reduc-tion only in regard to economics and effectiveness, the benefits extend to the environment, ecology and human populations. Consequently, this paper can be used as a guide for planners and engineers who make flood mitigation decisions in using these techniques for balancing construction costs and effectiveness. This study should be meaningful for urban stormwater system design, planning, and construction in other southeastern cities of China with high water coverage ratios.