Emergy Ecological Model for Sponge Cities: A Case Study of China

Abstract Sponge cities have been recognized as the major measures to deal with urban drainage and waterlogging and restore urban water ecology in China. However, the existing evaluation indices could not calculate ecological benefits of the whole sponge city system. The objective of this study is to develop an emergy ecological model for evaluating the ecological benefits and sustainability of the urban stormwater system with a sponge city case in Xiamen, China. To achieve this objective, this study adopts the emergy analysis method and proposed the emergy flow diagrams of grey and green water networks. The results confirmed that the green water network was more sustainable. Additionally, this study selected the Wastewater Reuse Rate and Rainwater Utilization Rate as the variables to optimize the green water network. The analysis results showed that the optimized green water network received significantly better Emergy Index of Sustainable Development (0.82), by setting Volume Capture Ratio of annual rainfall, Wastewater Reuse Rate and Rainwater Utilization Rate at 75%, 40% and 50%, respectively. The case study verified that the proposed emergy model can be used as a generic model to quantitatively evaluate the ecological benefits of sponge cities, and the construction of sponge cities could promote water circulation and improve the sustainability of the system.