Why flooding returns to haunt Hanoi after heavy downpours

On May 25, torrential rain flooded Hanoi after a five hour deluge, causing major traffic chaos and leaving low-lying areas submerged for over a day.

A number of officials and experts have expressed their views on the matter that has been haunting Hanoi since the historic downpour in 2008 caused extreme flooding in the city, killing 20 people and causing trillions of VND worth of damage.

According to Pham Ngoc Dang, chairman of the Urban Environmental Association, the main reason for the flooding is because the urban drainage system is outdated, consisting of small pipes with limited capacity that can get blocked easily by sediment buildup.

“Hanoi is 3.5 to 9 meters above sea level, which is higher than Hai Phong and other cities, so the flooding is not due to the terrain,” Dang said.

According to Dang, many lakes in the city have either been filled in or narrowed to make way for housing. Renovation work on canals in the city such as the concrete embankment at To Lich River has also reduced their drainage capacity.

Explaining the frequent flooding in the south and southwest of Hanoi, Dang said the capital has expanded westward where drainage still mainly relies on agricultural irrigation systems and no investment has been made to install bigger drains.

The west of Hanoi used to be rice fields and ponds that naturally made drainage easy, Dang said. However, the area has been concreted in, resulting in a lot of standing water.

An urban area in Ha Dong District was transformed into an isolated island, with 50-60 centimeters of water in some parts. Photo by VnExpress/Duong Trieu

The director of the Hanoi Drainage Company said the sudden rainfall on May 25 exceeded the capacity of the city’s drainage system. Hanoi's 12 districts are divided into four main drainage basins. The To Lich River Basin is in the process of construction and renovation, but Ta Nhue, Long Bien and Ha Dong are all still dependent on agricultural irrigation systems and have no urban drains in place.

In order to improve the situation, Hanoi plans to complete phase 2 of a drainage project. The project was assigned to the management board of the Hanoi Drainage Project and launched in 2008 with total investment of about VND8 trillion in ODA loans from the Japanese government. It was scheduled for completion in December last year.

Due to delays, Hanoi and the Japanese investor agreed to push back the completion date to June 30, 2016. However, issues related to land clearance has left the project largely unfinished, despite there being just a month to go until the new deadline.

People wade through 60cm of water at Xanh Market on Pham Van Truong Street in Cau Giay District. Photo by VnExpress/The Son

“There is not enough evidence to say this was a record storm, but it is very rare to see one with such intensity,” said Le Thanh Hai, deputy director of the Center National Hydrometeorology.

Another meteorological expert said that the total rainfall in one night had exceeded the monthly average. "The 340mm of rainfall recorded in Ha Dong District was only slightly less than the historic flood in 2008."