Professor Dr Nguyễn Quốc Dũng, Standing Vice-Chairman of the Vietnam Large Dams and Water Resources Development Association. — VNS Photo Tố Như

Repeated storms have placed intense strain on Việt Nam’s reservoir system, prompting emergency water releases across several central provinces. In response, experts are considering a mechanism to purchase flood storage capacity as a way to ease pressure and protect downstream communities. Professor Dr Nguyễn Quốc Dũng, Standing Vice-Chairman of the Vietnam Large Dams and Water Resources Development Association, spoke with Việt Nam News reporter Tố Như about the proposal and the challenges ahead.

What makes extreme storms and floods such a serious challenge for Việt Nam’s reservoirs?

Heavy rainfall puts immediate pressure on reservoirs, low-lying areas and irrigation systems. Extended downpours over two to three days reduce the ability of soil, forests and reservoirs to absorb water, sending excess flows directly into river basins and creating high flood peaks. The increasingly common phenomenon of 'double floods' – where a new flood hits before the previous one has receded – poses a particular challenge, as most Vietnamese reservoirs are still operated under a single-flood model that does not account for such events.

Globally, managing double floods relies on advanced forecasting models and sophisticated operational methods to improve prevention and control of large reservoirs.

Recently, many reservoirs designed for 500-year floods are facing events with a 1,000-year probability, far exceeding current standards, which only consider climate change within existing technical models. Việt Nam also lacks a professional hydrology and hydraulics advisory body to guide reservoir operations. In countries like Japan, hydrological agencies directly oversee operations and provide expert advice during the rainy season. If establishing a dedicated agency is not feasible, outsourcing forecasting services to specialised units could provide timely support for critical operational decisions.

In the current situation, how are reservoir monitoring and operations being managed?

I don’t think a separate monitoring programme is necessary for dam operators. Reservoirs, including hydropower ones, are currently managed under the Civil Defence Law. During the flood season, the Ministry of Agriculture and Environment, through the Department of Disaster Prevention and the Civil Defence Office, provides guidance to the provincial Steering Committee for Disaster Prevention.

The authority to order water releases, however, remains with the provincial chairman, depending on the reservoir’s classification, while for some large reservoirs the ministry issues orders directly under the law.

The pressing need now is for a strong advisory system, particularly at the provincial level, where specialised teams like those at the central level are lacking. This requires comprehensive basin data, including topography, hydrological history and flood records, followed by the development of forecasting models. Only with detailed flood scenarios can reservoir operations be calculated and advised accurately. Decisions must be grounded in science and mathematical modelling to ensure both public safety and efficient operation.

Dầu Tiếng Reservoir, covering Tây Ninh, HCM City, and Đồng Nai, releases floodwater. — VNA/VNS Photo

The flood storage capacity purchase has been proposed to balance public safety with economic interests. How exactly does this mechanism operate, and what advantages does it offer to investors?

The proposed mechanism aims to balance hydropower operations with economic efficiency and energy security by using the natural disaster prevention fund to compensate operators when they release water to create flood storage. In practice, the State would be 'purchasing flood storage capacity' from the reservoir owner.

To protect downstream communities, reservoirs must lower their water levels ahead of major storms. But releasing water too early reduces the volume available for power generation. If the anticipated rainfall does not arrive, the operator faces lost revenue. Under the proposed system, the disaster prevention fund would cover this loss, effectively paying for the empty storage space kept for flood protection.

While the idea is not new, Việt Nam’s increasing exposure to extreme weather makes it timely to reconsider as the country seeks a better balance between disaster prevention and economic interests.

Reservoirs operate in three stages during the flood season: early, mid and late. Early in the season, water levels are lowered to create room for floods. Mid-season releases cannot exceed inflows. Late in the season, storage and releases depend on short- and long-term forecasts. In reality, many reservoirs are already close to full by the end of the season, leaving very little capacity for sudden heavy rainfall.

For example, an 800 million-cubic-metre reservoir may have only around 70 million cubic metres, about 10 per cent, left for flood control.

Expanding that buffer to 200 million cubic metres would require lowering water levels earlier. But doing so exposes operators to financial risk if the rains fail to materialise. The proposed 'flood storage purchase' mechanism would offset that loss through the disaster prevention fund, ensuring both public safety and investor protection.

What are the key shortcomings in how reservoirs are currently operated and in the face of increasingly extreme storms and floods, what solutions and strategic directions do you believe are needed to improve reservoir management?

The current shortcomings come from both increasingly extreme weather and the way many reservoirs are designed and operated. A large number still use a single-flood model, even as double-flood events become more frequent. Operating rules also allow very wide discharge ranges, meaning a reservoir might release only a few hundred cubic metres per second in the morning and suddenly increase to several thousand in the afternoon. This may follow regulations, but it leaves downstream communities little time to react.

Hydropower reservoirs, run by private investors, also prioritise electricity generation, so operators often hesitate to lower water levels to create flood storage. The absence of specialised hydrological advisers at the provincial level further complicates decision-making. In contrast, countries like Japan and China have around-the-clock hydrology offices to support timely decisions.

Another challenge is the differing objectives of hydropower and irrigation reservoirs. Hydropower is closely linked to energy security, so lowering water levels always carries the risk of reduced power generation. The proposed 'flood storage purchase' mechanism would compensate operators for this risk, encouraging more proactive cooperation to ensure downstream safety.

Stronger advisory systems, more flexible and transparent operating rules, and better coordination among reservoirs are essential. Việt Nam can learn from international models or outsource hydrological advisory services to fill current gaps. Hydropower and irrigation reservoirs must also work more closely together, with civil defence committees strengthening their coordinating role.

With 70 billion cubic metres of total reservoir capacity – 55 billion in hydropower reservoirs – it is unrealistic to rely on irrigation reservoirs alone for flood control. Compensating operators through the 'flood storage purchase' mechanism would create incentives to lower water levels, protect downstream communities, and maintain economic efficiency.

Recent storms show how exceptional current weather patterns have become: intense, prolonged rainfall saturates low-lying areas and reduces forest absorption, producing successive flood peaks. Under such double-flood conditions, single-flood operating models are no longer sufficient. This makes tighter coordination, clear compensation mechanisms, and robust scientific advice critical for timely, proactive reservoir operations. — VNS

Crops submerged after Đồng Nai 5 Hydropower Plant released water on November 21. — VNA/VNS Photo