Flexible operation of hydropower to regulate floods

During the recent flood caused by storm No. 13, implementing the Prime Minister's telegram and the direction of the Ministry of Agriculture and Environment, Da Nang city directed the hydropower plant to regulate floods more flexibly, ensuring safety for downstream areas.

Hydroelectric reservoirs have been directed to lower the water level before the flood to cut and reduce flooding downstream during the flood caused by the impact of storm No. 13. In the photo: Song Tranh 2 Hydroelectric Reservoir regulates floods downstream of Thu Bon River. Photo: NAM TRAN

Continuously request to lower water level before flood

Faced with the shortcomings of the Inter-reservoir Operation Procedure on the Vu Gia - Thu Bon River Basin revealed in the exceptionally large flood that occurred from October 25 to 30, Da Nang City has requested the Ministry of Agriculture and Environment to supplement the operational scenario when the flood flow to the reservoirs reaches or exceeds the threshold, while the water level in the downstream is still low, then consider operating to lower the reservoir water level or maintain the reservoir water level.

In addition, increase the flood prevention capacity of the largest hydroelectric reservoirs possible at the beginning of the flood season to increase flood reduction capacity downstream...

The Ministry of Agriculture and Environment has urgently proposed immediate measures to overcome the shortcomings in Procedure 1865 in particular and the operation process of reservoirs nationwide in general in the content of Official Dispatch No. 208/CD-TTg dated November 4, 2025 of the Prime Minister on proactive prevention and response to storm No. 13 (Kalmaegi).

At the working session with Da Nang city on the afternoon of November 4, 2025, Director of the Department of Dyke Management and Natural Disaster Prevention (Ministry of Agriculture and Environment) Pham Duc Luan emphasized: "The Prime Minister's dispatch assigned the Ministry of Agriculture and Environment to direct localities to operate flood regulation of reservoirs while waiting for amendments to the reservoir operation procedures".

Pursuant to the direction of the Ministry of Agriculture and Environment at the above-mentioned working session and applying the content of the regulation on switching to the operation mode in abnormal situations of Procedure 1865, on the evening of November 4, the City People's Committee issued Official Dispatch No. 3516/UBND-PTDS requesting hydropower companies to gradually lower the water level in the hydropower reservoirs of Song Bung 2, Song Bung 4, A Vuong, Dak Mi 4, and Song Tranh 2 from full reservoir to the highest water level before the flood in the afternoon and evening of November 6.

On November 5, the City People's Committee continued to issue Official Dispatch No. 3542/UBND-PTDS requesting hydropower companies to continue to organize operations to gradually lower the water level of reservoirs to the lowest flood level for Dak Mi 4 hydropower reservoir and to the flood level for Song Tranh 2 and A Vuong hydropower reservoirs before the night of November 6 (the lowest flood level and the flood level are both lower than the highest water level before the flood).

On November 6, the City People's Committee continued to issue Official Dispatch No. 3583/UBND-KT requesting hydropower companies to continue operating at lower water levels for the three hydropower reservoirs Song Tranh 2, A Vuong and Song Bung 4 before early morning of November 7...

Thanks to the active and drastic request for hydropower companies to lower the water level of the reservoirs, by the evening of November 6, when floods appeared in the Vu Gia - Thu Bon river basin due to the impact of storm No. 13 (Kalmaegi), the reservoirs had a significant flood prevention capacity to operate to cut and reduce floods for the downstream.

On the night of November 6, when the water level of Song Tranh 2 Hydropower Reservoir had been lowered by 6.5m compared to when the reservoir was full, realizing that the flood flow was rising rapidly, Song Tranh Hydropower Company switched to the operation state of cutting and reducing floods for the downstream. The hydropower plant began to operate to cut and reduce floods from the average flow (1,511m3/s) to the peak (2,603m3/s) and the entire later stage of the flood for the downstream with a peak flow cutting rate of more than 53%.

Floods appeared on the Dak Mi 4 hydropower reservoir basin from the afternoon of November 6 when the reservoir water level had just been lowered below the lowest flood level. Due to the flood prevention capacity guaranteed according to Procedure 1865, within 15 hours of the flood, Dak Mi Hydropower Joint Stock Company proactively operated to cut and reduce floods for the downstream by nearly 37 million cubic meters of water, accounting for nearly 52% of the total flood volume to the reservoir with the largest discharge flow of only 1,097m3/s compared to the peak flood flow to the reservoir of 3,281m3/s.

Flexible operation to cut and reduce floods

According to General Director of Dak Mi Hydropower Joint Stock Company Vu ​​Duc Khanh, through monitoring forecast reports, the company determined that this was a thin flood type, so it decided to cut the flood early with a large flood cutting rate, corresponding to cutting 76.4% of the peak flood flow (3,281m3/s).

In addition to effectively cutting the flood peak, during the monitoring process, the water level downstream of Vu Gia River at Ai Nghia reached alarm level 1 in the early morning of November 7 and found that the total flow to Vu Gia was still large (2,038m3/s), which could cause flooding downstream and the rainfall in the Dak Mi 4 reservoir basin decreased, so the company decided to regulate and reduce the spillway discharge to the maximum from this point.

The flood caused by storm No. 13 has left a lesson: the operation of reservoirs in the upstream needs to be flexibly adjusted based on hydrometeorological forecasts and actual operational data so that the reservoirs can coordinate to regulate water with the goal of maximizing the capacity to prevent floods downstream.

Thereby, the lakes were lowered to flood-receiving water level, but the water level of Vu Gia River at Ai Nghia only reached approximately BĐ 2. The process of cutting and reducing floods for the downstream of A Vuong, Song Bung 2, Song Bung 4 and Dak Mi 4 lakes with the total discharge flow to Vu Gia River fluctuated from 2,000 - 2,500m3/s to ensure that the water level at Ai Nghia did not exceed the threshold of 8.5m (water level between BĐ2 and BĐ3).

Deputy General Director of A Vuong Hydropower Joint Stock Company Ngo Xuan The acknowledged: "Operating hydropower plants to regulate floods during the flood season caused by storm No. 13 is to ensure safety for downstream areas."

Mr. Pham Duc Luan said that currently, the Ministry of Agriculture and Environment has assigned the Department of Water Resources Management to coordinate with units and localities to amend the inter-reservoir operation process. With the problems that have been exposed in Process 1865, Da Nang city needs to coordinate with units to adjust this inter-reservoir operation process.

At a recent working session with Da Nang City, Deputy Minister of Agriculture and Environment Nguyen Hoang Hiep said that the operating procedures of reservoirs will be adjusted in an open direction. The Ministry of Agriculture and Environment will propose to the Government a mechanism for operating hydropower plants to regulate floods in order to reduce floods and limit impacts and minimize damage to downstream areas.

Source: https://baodanang.vn/linh-hoat-dieu-hanh-thuy-dien-dieu-tiet-lu-3309637.html