A second underground reservoir, with a capacity of 1,800 cubic metres, will be constructed beneath the Bac Duong railway underpass in Phu Dong Commune at a cost of around VND 6.7 billion.

The two projects are classified as emergency works aimed at addressing chronic urban flooding. City officials said Hanoi is implementing 10 urgent drainage projects worth nearly VND 5.6 trillion, most of which are expected to be largely completed before the 2026 rainy season.

Hanoi’s first pilot underground reservoir was completed in 2020 at Ly Thuong Kiet Secondary School and has been in operation since late 2021. Authorities said the facility has significantly reduced flooding in the area during heavy rainfall.

Under the city’s long-term master plan, Hanoi is studying large-scale underground infrastructure combining transport and stormwater storage, including a proposed mega-reservoir of about 125 million cubic metres planned for 2036-2045.