Flooding is a major concern in many cities. It can be devastating and cause considerable destructions and fatalities. Real time monitoring of the impact of flooding after rainfalls is often crucial in flooding control. This work studies the feasibility of monitoring city flooding using unmanned drones. Methods that enhance the efficiency of unmanned aerial vehicles (UAVs) are investigated. The results show that an integration of UAV platforms, photogrammetry and geographic information systems provides faster and more precise information on potential flooding areas than traditional techniques. In this research, we have shown the effectiveness of using UAVs to monitor city flooding and water ponding conditions with UAV field tests. In addition, we have developed an algorithm to generate more efficient UAV flying plans when the city is covered with many large buildings. It opens a new direction of research and practice in city flooding control and storm water management.