To tackle chronic flooding in Hanoi, the city must prioritize large-scale drainage infrastructure  -  including rivers, pumping stations, and discharge canals into the Red River and Day River. Only when a complete drainage route is in place can inner-city flooding be truly resolved.

Within just two weeks, Hanoi has repeatedly found itself submerged after heavy rains. Explaining the issue to VietNamNet, Prof. Dr. Dao Xuan Hoc, President of the Vietnam Irrigation Association and former Deputy Minister of Agriculture and Rural Development, emphasized that urban flood prevention hinges on two main factors: water discharge and drainage.

First, water discharge requires that canals and receiving basins remain lower than the city surface. Second, drainage depends on whether city water can reach rivers through a functional sewer system.

He explained: “Urban rainfall may cause temporary flooding, but drainage should be fast. If a drainage system is designed to handle 70mm/hour, then even after one hour of 70mm rainfall, the streets should dry once the rain stops.”

“If rainfall is double the capacity, water should drain in double the time  -  not over one or two days as we've recently seen. In some cases, flooding lingers for an entire week.”

Such prolonged flooding, according to Prof. Hoc, reflects not local blockages but inadequate macro-level drainage infrastructure  -  meaning there’s simply no path for water to exit the city.

In 2009, the government approved a drainage plan for the Nhue River system, aiming to increase total drainage capacity from 104 cubic meters per second to 504 cubic meters per second  -  nearly a fivefold boost. The plan covered Hanoi’s urban core and surrounding areas, intending to eliminate widespread flooding and reduce severe waterlogging to brief, localized incidents after heavy rain.

However, over 15 years later, the implementation remains far behind schedule.

For instance, the Yen Nghia pumping station, designed to handle 120 m³/s, is complete  -  but the canal that supplies it is not. Yen So station, designed for 140 m³/s, currently operates at only 90 m³/s. The Lien Mac pumping station, expected to handle 170 m³/s, hasn’t even begun construction.

Meanwhile, main drainage rivers in the city  -  To Lich, Kim Nguu, Lu, and Set  -  are only capable of channeling around 90 m³/s, though they were designed for 140 m³/s.

“Instead of dredging and widening drainage channels, we built retaining walls and decorative dams, which restrict the flow,” Prof. Hoc commented.

"We should not rely on underground reservoirs"

In 2019, Hanoi’s Dong Da District launched a drainage upgrade project on Nguyen Khuyen Street, including an underground reservoir at Ly Thuong Kiet Secondary School, which began operation in late 2021.

Hanoi Drainage Company Ltd., the unit managing the system, called it effective and proposed additional underground reservoirs near areas such as Hang Da Market.

However, Prof. Hoc believes this is unnecessary.

“Underground reservoirs are not simple to build. The Yen Nghia pump station handles 120 m³/s  -  imagine the size and cost of a tank that can hold just that much water,” he said.

“Pumping 120 cubic meters per second versus slowly storing the same volume are vastly different solutions. Yes, Tokyo uses underground reservoirs  -  but Hanoi has plenty of rivers and canals. We should use them.”

According to Prof. Hoc, many mistakenly believe flood prevention should begin in the city center. In reality, without external water outlets, internal sewer upgrades have limited effect.

“Hanoi needs to focus on macro-scale drainage: rivers, pumping stations, and canals leading to the Red and Day Rivers, just as the approved plan outlined. Once water has somewhere to go, sewer upgrades inside the city will actually be effective,” he emphasized.

Once the 2009 master plan is fully implemented, Hanoi's drainage capacity will reach 504 m³/s. Even with prolonged, heavy rainfall, flooding in the city will be minor and should recede within 1–2 hours.

“The government has already approved everything. We just need to follow the plan. Once stations like Yen Nghia and Lien Mac are operational and rivers like To Lich, Kim Nguu, Set, and Lu are upgraded to design capacity, flooding in Hanoi will virtually disappear. At most, we’ll see 2–3 minor incidents a year during extreme storms  -  and even those will drain quickly,” Prof. Hoc concluded.

N. Huyen