HANOI, Vietnam (VNExpress): Hanoi's Department of Construction said the downpour seen on Tuesday was the heaviest in decades and far exceeded the capacity of the drainage system, and the flooding could last a week.
Le Van Du, head of its water supply and drainage infrastructure management division, said on Friday that Typhoon Bualoi brought rains on Monday and Tuesday of 120 mm to over 600 mm.
Some spots saw exceptional levels, including 616 mm at O Cho Dua and 503 mm at Hai Ba Trung, he said.
This was the highest in decades, even surpassing the 2008 deluge, he pointed out.
In 2008 there were five straight days of heavy rain from Oct. 31 to Nov. 4.
The National Center for Hydro-Meteorological Forecasting had reported 558 mm in the inner city and 568 mm at Lang station, 642 mm in Long Bien, and 820 mm in Ha Dong. Data from the Hanoi Drainage Company showed 484 mm at Van Ho and 828 mm at Dong Bong.
Both times there had been very heavy rain, but the impacts differed.
In 2008, much of Hanoi was flooded, typically 0.5-0.7 m deep, though waist level in some areas, forcing residents to move around by boat.
The flooding did not just affect certain streets or neighborhoods: In some districts, as they were called then, half the area was under water.
A man receives assistance after falling off his motorbike on a flooded street in Hanoi, on Sept. 30, 2025. -- Photo by VnExpress/Tung Dinh
It persisted for at least three days in most places and more than 10 days in Ngoc Khanh and Thinh Liet wards.
Authorities and relief groups had to use boats to deliver water and food to residents.
This time, the Hanoi Drainage Company recorded up to 116 flooding spots, typically 0.3-0.5 m deep but reaching 1-1.5 m in some places like Duong Dinh Nghe Street (Cau Giay Ward) and Phung Hung Street (Thinh Liet Ward).
Because the rains stopped sooner, the waters receded faster.
By Wednesday evening, there was still flooding in only 11 places, many of them in the Nhue River basin, including roads along Thang Long Avenue, the T-branch of the General Department V and Cau Buou and Trieu Khuc streets.
But as of Thursday morning, the Nhue was still overflowing in Ha Dong, slowing drainage nearby.
Du said: "This is an unusual natural disaster that has greatly affected people's lives. We ask for understanding and sympathy."
The flooding could persist for a week at some locations, he said.
Trinh Ngoc Son, deputy general director of Hanoi Drainage One Member Co. Ltd., said the central drainage system is designed to handle 310 mm of rain falling over two days, while the recent storm dumped more water than that within just a few hours.
More than 2,000 employees were mobilised to operate pumping stations and remove manhole covers to accelerate drainage, but the flooding was unavoidable, he said.
He also pointed to other causes, like detention lakes not being comprehensively upgraded and the shortage of canals and ditches, which could drain some of the water.
Now the city has to speed up work on approved drainage projects like detention lakes, main pumping stations and dredging rivers and streams.
New urban areas need to connect their internal drainage networks to the citywide system.
The department also wants underground water storage tanks built in parks, gardens, and other public places in addition to step-up pumping stations, a common feature in many major cities, to cope with flooding during extreme rains.
Besides, the drainage elevation master plan for until 2045 needs to incorporate climate-change scenarios to enhance resilience to rain events far beyond current design standards.
The recent downpours turned Hanoi's streets into rivers, forcing residents to wade through waist-deep water, walk stranded motorbikes, and even row boats and rafts to get to work and school.
The flooding persisted until Wednesday, with many areas reporting 30-40 cm of water, leading to severe traffic congestion during the morning rush hour. - VNExpress