Synergizing flood mitigation and water quality goals through green infrastructure in Dali City, China
Wenhan Feng, Bingyi Zhou, Ziyao Wang, Yifei Wang, Haifeng Jia, Junxu Chen, Jingyu Wang, Xiangzheng Deng, Matthias Garschagen, Liang Emlyn Yang
Abstract
Many cities have implemented strict drainage regulations to preserve the water quality of rivers and lakes; however, these measures can inadvertently exacerbate urban flooding. Dali City, located in southwestern China, faces similar challenges and is exploring governance solutions through the implementation of green infrastructure. This study examines the behaviors of various actors within the water management system and models the effectiveness of green infrastructures interventions in Dali. Our flood simulation experiments based on Storm water management model (SWMM) and Personal Computer Storm Water Management Model (PCSWMM) confirmed the potential of green infrastructure in coordinating water quality preservation and flood management objectives. The combination of 71% green infrastructure deployment rate with gray infrastructure helps to achieve a volume capture ratio exceeding 94% and a pollutant reduction rate of over 60%. However, scenario analyses at various scales indicate that excessively large-scale green infrastructure can reduce the synergistic efficiency of achieving both objectives. Specifically, after reaching an 85% volume capture ratio under typical rainfall conditions, each additional 1% increase in green infrastructure coverage would require an investment of at least 12 million RMB, which is no longer cost-effective. The optimal solution is to implement green infrastructure at 71% coverage while prioritizing its integration with gray infrastructure. Our findings highlight the need to balance technical design with institutional coordination, and we propose a governance framework that integrates hydrological and social processes to enhance policy synergy. This study contributes a case-based perspective from China's planning system, offering transferable insights for other rapidly urbanizing regions.