Despite prolonged heavy rain and high water levels in drainage channels, the city's urban drainage system remained largely stable, according to the Hanoi Technical Infrastructure Management Centre.
No flooding was recorded in central areas or locations where emergency and local flood-control projects have been completed. Vo Chi Cong Street and the Ciputra urban area saw only shallow surface water during heavy rain, which quickly receded as rainfall eased.
Some low-lying areas in western and southwestern Hanoi drained more slowly as high water levels in the Nhue River limited the system's discharge capacity.
Several former flooding hotspots, including Phung Hung, Hang Da Market, Tong Dan, Nguyen Khuyen, Nguyen Trai and parts of the West Lake area, remained free of flooding during the latest downpours.
Other areas that typically took four to 10 hours to drain after heavy rain in 2025 saw water recede within about 30 minutes to two hours this time.
Nguyen Duc Hung, director of the centre, said the results showed improvements in the system's capacity to collect, regulate and discharge stormwater, reducing the extent, severity and duration of flooding.
He said coordinated operation of retention lakes, pumping stations, sluice gates, drains and canals had also helped improve drainage.
However, Hanoi still needs further investment in major drainage facilities, particularly in western and southwestern areas, to cope with extreme rainfall exceeding the system's design capacity.
During the heavy rain on September 17, the city mobilised more than 2,500 workers and over 200 vehicles and pieces of equipment to clear drains, operate pumps and support traffic management.
Pumping stations, sluice gates and retention lakes were operated according to rainfall and water levels. By 2pm, the rain had eased, water had receded at many flooded locations and traffic had largely returned to normal.
Some areas, including sections of Thang Long Boulevard, Trieu Khuc and Tay Mo, remained flooded or were still draining.
Localised flooding also occurred around To Huu and Luong The Vinh streets as prolonged rain and high water levels in drains, canals and nearby retention lakes overwhelmed the system's immediate drainage capacity.
The Dong Bong 2 pumping station was operated at maximum capacity to discharge water into the Nhue River. Floodwater in the area had receded by 2pm, allowing traffic to return to normal.