According to Vietnam Electricity Group, the largest flow to Thac Ba Hydropower Plant was 5,620m3/s at 9:00 a.m. on September 10. By 12:15 p.m. on September 11, the flow to the reservoir had decreased to 2,952m3/s, with a total discharge of 2,950m3/s (i.e. balanced inflow - outflow).
The upstream water level of the lake is 59.83m, 1.83m higher than the normal water level and 13.83m higher than the dead water level. Thac Ba Hydropower Plant has opened 3/3 of the sluice gates as directed.
According to Lao Dong's records on September 11, at Thac Ba Hydropower Plant, the water flowed turbulently, white foam was flying, and many water columns tens of meters high flowed down from above.
Ms. Nguyen Thi Xuan (32 years old, Thac Ba, Yen Binh) said that currently, many households living around here have been evacuated to a safe place.
"After hearing the news that the amount of water flowing into the lake exceeded the flood discharge level, my family proactively moved to a higher place. Luckily, Thac Ba Hydropower Plant is still stable today," said Ms. Xuan.
Speaking to Lao Dong Newspaper on September 11, Mr. Nguyen Manh Cuong, Deputy General Director of Thac Ba Hydropower Company, affirmed: "The signal is very positive, the water level in Thac Ba Lake is not expected to increase further. Up to this point, the hydropower reservoir has opened 3 floodgates. The project is still safe, no problem."
Previously, on September 10, Deputy Prime Minister Bui Thanh Son signed an official dispatch to the Secretary and Chairman of the People's Committee of three provinces: Lao Cai, Ha Giang and Yen Bai regarding the implementation of urgent measures to ensure the safety of Thac Ba hydropower dam.
Accordingly, currently, the upstream water level of Thac Ba Lake is at a very high level, the flow to the lake exceeds the lake's designed flood discharge capacity.
To ensure safety for Thac Ba Hydropower Reservoir, the Prime Minister requested the Secretaries and Chairmen of the People's Committees of Lao Cai, Ha Giang, and Yen Bai provinces to directly lead and direct local authorities to review and immediately implement measures to prevent and reduce the flow to Thac Ba Hydropower Reservoir.
The Office of the Government, according to its assigned functions and tasks, shall monitor and urge the implementation of this Official Dispatch.
Recently, Yen Bai province has evacuated 3,186 households with 11,279 people from 24 villages and hamlets in Vinh Kien, Yen Binh, Han Da, Dai Minh communes, and Thac Ba town (Yen Binh district) to ensure people's safety when Thac Ba Hydropower Plant releases floodwaters.
Thac Ba is one of the three largest artificial lakes in Vietnam, located in Luc Yen and Yen Binh districts of Yen Bai province. This is the water supply for Vietnam's first hydroelectric plant.
Thac Ba Lake was formed when the Thac Ba hydroelectric dam was completed in 1971, blocking the Chay River and creating a lake. The lake area is 23,400 hectares, the water surface area is more than 19,050 hectares. The water level ranges from 46 to 58m, holding 3-3.9 billion m3. In addition to the Chay River which is the main water source, Thac Ba Lake also has a large river system such as Hanh Stream, Cat Stream... flowing into it.
