Optimization framework for urban flood mitigation strategies considering collaborative drainage mechanisms

• An optimization framework for urban flood mitigation strategies is proposed. • A new concept of Micro-Watercourse is introduced to assist in flood management. • Multi-level coupled drainage system improves efficiency and climate resilience. With rapid urbanization, urban flooding has become increasingly severe, challenging conventional drainage systems. This study proposes an optimization framework for collaborative urban drainage that integrates Urban Micro-Watercourses (UMW), Low Impact Development (LID) facilities, and conventional drainage networks into a unified multi-level regulation system. The framework consists of two core modules: (1) an intelligent optimization module for LID facility planning, automatically determining optimal allocation ratios to maximize hydrological control; and (2) a layout optimization module for UMW, dynamically refining the spatial configuration of UMW networks to enhance collaborative drainage capacity. By establishing coordinated coupling among LID facilities, UMW networks, and conventional drainage systems, the framework enables integrated operation and resource sharing across subsystems, improving overall system performance and resilience. The parallelized framework led to a 46.8-fold increase in LID optimization efficiency and a 192.3-fold increase in UMW optimization efficiency. A case study in the Fangzhuang area of Beijing, under extreme rainfall scenarios with 5-, 10-, and 50-year return periods, showed total accumulated water volume reduced by 51.2%–68.1% and overflow points decreased by 18.1%–73.3%. Compared with the optimal LID scheme, the UMW–LID–pipe network coupling further reduced water volume by 7.85%–21.77% and overflow points by up to 64.94%, substantially alleviating pressure on drainage infrastructure. The results demonstrate that the proposed framework provides an innovative and scalable approach for sustainable urban stormwater management and flood resilience.