After the 25-26 Sept 2026 "rain-soaked" 48-hour downpour, Bangkok flooding still came through even though several giant tunnels are finished. Per Governor Chadchart, three main tunnels (Bang Sue, Phra Khanong, Makkasan) give about 150 cubic metres per second. Five completed tunnels total 28.57 km and 255 m³/s. Eight more projects (55.32 km, 370 m³/s) are under construction or awaiting budget, including a 9,561 million baht eastern extension still pending contractor qualification. For a small business in flood-prone districts, plan for drainage to stay slow; check whether your district is on the tunnel list before relying on it.