A Comprehensive Evaluation Method of Cost-Effectiveness of LID Facilities in Sponge City Based on the Life Cycle

Currently, there is a notable issue with high investment and low returns in sponge city construction in China, which hinders the widespread adoption of such initiatives. To mitigate unnecessary investment costs, this study evaluates the life cycle cost (LCC) and the ecological, environmental, security, economic, and social benefits of low impact development (LID) facilities based on a comprehensive cost-effectiveness ratio (B/C_LCC). This method utilizes 11 indices determined through the Delphi method and assigns weights using the analytic hierarchy process (AHP). The method was applied to an area in Zhuzhou City, a sponge city demonstration site, to analyze the cost-effectiveness of individual and combined LID facilities. The results indicate that as the area ratio increases, the comprehensive benefit of individual LID facilities increases gradually, with rain garden (RG) and sunken green space (SGS) showing higher growth rates compared to permeable pavement (PP) and vegetated swale (VS). At a 12% area ratio, the comprehensive benefit ranking is RG, PP, SGS, and VS. Considering LCC, the B/C_LCC value of single facilities was SGS > VS > PP > RG. Among the 16 combined LID facilities designed using an orthogonal experiment, S3, S4, S8, S15, and S16 meet the sponge city construction standards (runoff control rate ≥ 75%). Of these, S4 (3% PP + 12% RG + 12% VS + 12% SGS) meets sponge city standards with the best comprehensive benefit, while S3 (3% PP + 9% RG + 9% VS + 9% SGS) provides the best balance of benefits and costs.