Hanoi has officially begun diverting water from West Lake through a pipeline system to rejuvenate the polluted To Lich River. However, concerns have been raised over whether this strategy remains viable if West Lake's water levels fall too low.

Was recent flooding caused by the construction of a dam on the river?

W-Ảnh chụp Màn hình 2025 09 11 lúc 16.54.27.png

The To Lich River has turned green again. Photo: N. Huyen

On the night of August 25, heavy rains from Storm No. 5 caused widespread flooding across Hanoi. By the morning of August 26, many streets were submerged, paralyzing traffic. At several long-standing flood-prone zones, water remained for two to three days despite clear weather.

Explaining the slow drainage, Hanoi Drainage Company officials stated that at the time, water levels in rivers such as the Nhue River were extremely high. For instance, the water level at the To Lich River near Cong Moc Bridge reached 4.27 meters, while at the Thanh Liet dam it rose to 4.67 meters.

Nonetheless, some observers blamed the problem on the damming of the To Lich River, suggesting that the newly built dam obstructed water flow and contributed to the flooding.

Addressing these concerns, Truong Quoc Bao, head of the Yen Xa Wastewater Treatment Project Management Unit (under the Hanoi Infrastructure and Agriculture Construction Investment Project Management Board), explained that the dam is designed to maintain the To Lich River's water level at +3.5 meters during the dry season.

During the rainy season, the dam's sluice gates will be raised to over +5.6 meters - approximately 0.4 meters above the river's maximum water level - and will span the full width of the river.

“In principle, the dam does not obstruct water flow on the To Lich River during the rainy season,” Bao emphasized.

He added that when the Thanh Liet sluice gate is opened, the dam's gates will be lowered to block backflow from the Nhue River into the upper To Lich River. This setup enhances the Nhue River’s drainage to the Yen So pumping station and minimizes the impact of upstream water discharges into To Lich.

“According to its operating mechanism, the dam on the To Lich and Nhue Rivers neither obstructs water flow nor increases the risk of flooding in the capital,” Bao confirmed.

When West Lake's water drops, what will happen to the To Lich River?

W-đập dang.jpeg
The dam on the To Lich River does not obstruct water flow. Photo: N. Huyen

Following a short implementation period, Hanoi officially started diverting water from West Lake into the To Lich River on the morning of September 9. The once foul-smelling, pitch-black river now flows green once again - offering hope to residents after years of pollution.

While the public is optimistic that the river can be revived, some are concerned about the availability of water from West Lake during the dry season.

Addressing these concerns, Bao explained that the water transfer system consists of a dedicated pipeline that operates independently from the wastewater channel. Wastewater continues to be diverted to the Yen Xa treatment plant for processing.

“The transfer of water from West Lake to the To Lich River is based on hydrological data, including the water levels of both West Lake and the To Lich River. The process occurs in cycles - not continuously - and helps supply water to To Lich while also draining West Lake during heavy rains,” Bao noted.

As of August 15, construction crews completed the collection of all 245 discharge outlets along the To Lich River, redirecting them to the Yen Xa Wastewater Treatment Plant. The plant currently operates at a capacity of 200,000 cubic meters per day and night - enough to treat all wastewater flowing into the river. By September 20, the treated water will also be added to the To Lich River.

“In addition to the water from West Lake, the treated water from Yen Xa will maintain a daily flow of approximately 200,000 cubic meters in the To Lich River. This will stabilize the water level at 3.5 meters, eliminate foul odors, and significantly improve environmental conditions,” Bao confirmed.

N. Huyen