Research on Sustainable Evaluation Model of Sponge City Based on Emergy Analysis

Sponge city is a method of managing rain floods, proposed by China to deal with urban waterlogging and the overflow pollution of drainage pipe networks, which indicates a more effective strategy to promote urban sustainable development. Due to the diversity of sponge city construction objectives and the complexity of the developmental system, a unified and effective sustainability evaluation method has not yet been formed. Based on the emergy analysis method, the indicators of ecosystem service, the construction cost, the runoff regulation, and the pollutant reduction of sponge city construction are thus included in the evaluation system, and the sustainable evaluation model of a sponge city is fully constructed. Taking the core area in the south of Haicang in Xiamen City as the studying object, the runoff regulation, and the pollutant reduction indicators, are carefully obtained by using Info Works simulation software. The results showed that: ① the quality of COD (Chemical Oxygen Demand) of pollutants discharged from the research object is 409.8t/a, the total runoff is 3.579 million m3/a, the current annual total runoff control rate is 37.15%, and the current emergy index ESI of sponge city system is 0.05 < 1, which is in an unsustainable state, It is necessary to upgrade and transform the urban underlying surface; ② The transformation intensity of three LID (Low Impact Development) facilities, i.e., concave green space, permeable pavement and green roof, is carefully selected as different construction schemes. When the construction intensity of LID is 25%, the emergy index ESI (Emergy Sustainable Index) = 1.08, which meets the basic requirements of sustainable development; As long as the reconstruction construction intensity is 30%, the growth value of ESI, ΔESI, is the largest, the sustainable growth effect of sponge city construction is the most obvious, and the marginal benefit is the largest; ③ As long as the total annual runoff control rate of the research object is 69–82%, its sustainable energy index ESI should be within the range of 1.39–1.83. If ESI is less than 1.39, this indicates that the total annual runoff control rate of the research area cannot adapt to the planning requirements of 69%.