The People's Committee of Lang Son province has just approved a plan to respond to the emergency situation of the Thac Xang hydropower dam and reservoir (Bac Giang 2), in order to ensure the safety of the works and downstream areas.
Thac Xang Hydropower Plant is located on the Bac Giang River, a first-level tributary of the Ky Cung River, in Trang Dinh commune. The project belongs to level III, classified as a dam and large reservoir.
The plant has a capacity of 20 MW, including two units, with an average electricity output of about 90.55 million kWh per year. The lake is nearly 4 km2 wide, with a total capacity of 43.89 million m3. The concrete dam is a maximum of 37 m high, with three spillway gates. The project started in October 2010, stocking water and operating from August 2016.
The downstream area is calculated from the hydropower hub to where the Bac Giang River converges with the Ky Cung River, extending through Trang Dinh, Khang Chien and That Khe communes. The areas at risk of impact are mainly low-lying areas, alluvial grounds and residential areas along the two rivers.
Plan to determine three emergency scenarios. In case of flood discharge when floods occur, designed with a frequency of 1%, about 501.51 ha may be flooded, affecting 1,016 households.
In which, That Khe has 593 houses, Trang Dinh 358 houses and Khang Chien 65 houses located within the calculated flooded area.
The main dam breach scenario when the flood occurs is designed to have the largest impact scope, with 551.66 ha and 1,078 houses. Trang Dinh has the largest flooded area, nearly 319.5 ha; while That Khe has the most affected houses, 613 houses.
If the dam breaks in the dry season, the estimated flooded area is 220.66 ha, affecting 435 houses. The areas to be prepared for evacuation are mainly located along the river, including Coc Bao, Ban Nhan, Doan Ket, Na Chua, Ban A, Na Chu, Keo Lay, Pac Luong, De Tham, Ban Duoc and That Khe market.
The above data is the result of simulation in simulated situations to develop response plans, not to predict incidents that will occur.
According to the approved plan, the plant has installed hydrological stations, cameras and sensors to monitor lake and downstream water levels.
The alarm system has a range of about 5 km, and information is transmitted simultaneously through loudspeakers, telephones, social networks and disaster prevention groups.
When the discharge gate is completely closed, 30 minutes before discharging water, the plant must blow three horns, each time for 20 seconds, 10 seconds apart. Before the water flows through the valve gate, two horns continue to be blown.
If emergency discharge is required to ensure project safety, the signal consists of 5 whistles, each whistle 30 seconds apart, 5 seconds apart. When the water discharge ends, the plant pulls a 30-second whistle.
In emergency situations, people in areas at risk of deep flooding will be moved to hills, mounds or mountainsides safely, without the risk of landslides. Schools, People's Committee headquarters, cultural houses and people's houses in high locations are mobilized as shelters.
The new decision replaces the plan issued in 2021. After 5 years of implementation, the investor must report to the Department of Industry and Trade for the Provincial People's Committee to consider continuing to use or request adjustment.
