Abstract: Affected by persistent heavy rainfall from July 23 to 29, 2025, multiple rivers in the Haihe River Basin, including the Chaobai River, Luanhe River and Daqing River, occurred rainstorm floods. Notably, the Chaobai River experienced its largest flood since 1959. Based on flood risk map models and associated outputs, and informed by hydrological monitoring and forecasting results, the flood evolution processes for both the Dongdian Flood Storage and Detention Area under different discharge scenarios of Miyun Reservoir were rapidly simulated. Based on the simulation results, the decision not to activate the Dongdian Flood Storage and Detention Area was accurately determined, and the inundation extent of the Chaobai River under various discharge scenarios was analyzed. The results provided a scientific references for levee patrols, flood defense and personnel evacuation in residential areas such as Zhuangtouyu Village, Xin′anzhuang Village, Yangshan Village along the Chaohe River downstream of Miyun Reservoir, Ning Village, Tuanjie Village, Xinxing Village at the confluence of Chaohe River and Baihe River. This practical application demonstrates that flood risk maps provide a rapid and reliable basis for decisionmaking in flood risk analysis, levee patrolling and emergency evacuation.