A method for determining reasonable water area ratio based on flood risk and cost-effectiveness in Rainy City

Urban flooding is increasingly pervasive, with the decreasing water area in cities and the dreadful impact on people. Therefore, it is necessary to carry out a quantitative evaluation of the area of urban water and analyze the threshold of the reasonable water ratio under different drainage scenarios. In this research, simulations were performed by using the Personal Computer Storm Water Management Model (PCSWMM), and the model parameter calibration method was based on the runoff coefficient as a contribution to meeting the data-poor urban areas. Then, urban flood control standards were divided into four classes, and the rainfall scenario once in 200 years and historical maximum were selected to build future extreme inundation scenarios in the case study. Simultaneously, methods for the reasonable water area ratio estimation were decided. The cost-effectiveness of all possible solutions was examined across the two scenarios based on the assessment method. The results show that the range of reasonable ratios of the water area under traditional planning is 5.78–6.02% to meet the standard of urban drainage. Similarly, the range of reasonable ratios of water area under the LID (low impact development) plan combined with the sponge city concept is 5.63–5.88%.