Building a flood prevention plan for Ho Chi Minh City when Dau Tieng Lake releases floodwaters

According to this decision, the city has 16 large lakes and dams; 10 medium-sized lakes and dams and 10 small lakes and dams. Large dams have a dam body height of 12-34m and up to 5 dams have a dam body length of more than 1km. The largest designed spillway belongs to Song Ray Lake with a flow rate of up to 2,641m3/s. With a reserve of billions of m3 of water, these dams are contributing greatly to water storage for production, daily life, and regulating the flow of rivers. However, what makes both insiders and public opinion concerned is the operation and flood discharge of Dau Tieng Lake - a very large irrigation lake, not located in the city but will have a huge impact on Ho Chi Minh City in unusual and extreme weather conditions...

According to the design, the overflow discharge of Dau Tieng Lake can reach up to 2,800 m3/s, but in reality, since its operation, Dau Tieng Lake has only discharged 3 large volumes with maximum flows of up to 600 m3/s, 538 m3/s and 400 m3/s. However, these discharges have caused widespread flooding in Ho Chi Minh City and Binh Duong . In recent times, the peak tide measured at the city's monitoring stations has continuously increased, the highest peak tide measured at Phu An station at the end of October was 1m77. Heavy rains occurring in the area are becoming more frequent, a record rain lasting 1.5 hours occurred last May, the rainfall measured in Thu Duc area was 103mm; Cu Chi area was 217mm... Therefore, the city needs to set up a response solution when Dau Tieng Lake operates and discharges floods.

Building a flood prevention plan for Ho Chi Minh City when Dau Tieng Lake discharges floodwaters at full capacity -0 — Flooding due to high tide on a street in Ho Chi Minh City at night.

At the Southern Region Disaster Prevention Conference organized by the National Steering Committee for Disaster Prevention in Ho Chi Minh City previously, the leader of this Steering Committee said that operating Dau Tieng Lake to minimize risks for Ho Chi Minh City is a difficult problem with no solution. The representative of the Dau Tieng irrigation reservoir operator said that, put into operation and use 40 years ago, Dau Tieng Lake has a multi-purpose task of providing water for agricultural production, industry, daily life, and the environment for the provinces of Tay Ninh, Binh Duong, Long An , and Ho Chi Minh City. Before the merger, Dau Tieng Lake also had the task of reducing floods and pushing back salinity for the downstream of the Saigon River. Thanks to Dau Tieng Lake regulating floods, flooding in the downstream of the Saigon River has decreased significantly compared to before the construction of the project, minimizing damage to infrastructure downstream. However, due to the rapid urbanization in the lower Saigon River, flooding of downstream infrastructure every time Dau Tieng Lake discharges floodwaters is a very big problem.

Informing the National Steering Committee for Natural Disaster Prevention at that time, Mr. To Van Thanh, former Chairman of the Board of Directors of the Southern Irrigation Exploitation Company Limited - the unit managing and operating Dau Tieng Lake, had to admit that, due to the impact of climate change, if Dau Tieng Lake releases more floodwater, flooding will become more severe. According to Mr. Thanh, in case of large floods, releasing floodwaters to ensure the safety of the project, but minimizing flooding for downstream areas is also a fierce contradiction that has existed in reality after nearly 40 years of operating the Dau Tieng Lake project.

Dau Tieng Reservoir is operated during the flood season according to Decision No. 3474 of 2020 of the Ministry of Agriculture and Rural Development (now the Ministry of Agriculture and Rural Development) and Decision No. 1985 of 2019 of the Prime Minister. According to the design, the overflow discharge of Dau Tieng Reservoir can reach up to 2,800 m3/s. "In case of a major flood, threatening the safety of the project and requiring a larger discharge than before, what will happen to the flooding problem downstream?" is the question raised by Mr. Thanh himself.

The representative of this unit also admitted that the operation of flood discharge at Dau Tieng Lake currently has many shortcomings. The flood discharge at Dau Tieng Lake is currently facing many risks. Especially in the current situation where there is only one flood discharge route for Dau Tieng Lake, which is the Saigon River. While the flood capacity of the Saigon River section from the foot of the dam to Ben Suc Bridge is quite small. This increases serious flooding every time the discharge flow through the spillway exceeds 200m3/s. In particular, Dau Tieng Lake has no spillway incident. When a huge flood occurs, it will lead to the risk of dam failure while the elevation of the main dam and the auxiliary dam of the lake has not met the safety procedures for the project. In addition, the risk of a valve incident is also very high because there is no emergency valve to promptly block the water flow from the lake to the downstream, causing flooding and uncontrolled loss of water in the lake.

To limit the risks of flood discharge and incidents at Dau Tieng Lake, the Ministry of Agriculture and Rural Development has previously developed plans and emergency response plans for the downstream area of the Saigon River. However, to fundamentally solve the problem of flood discharge at Dau Tieng Lake, ensuring absolute safety for the project and avoiding severe flooding in the downstream area, according to Mr. Thanh, it is necessary to consider the overall groups of construction and non-construction solutions.

In which the lake operation company proposed a solution to invest in additional spillway for Dau Tieng Lake. At the same time, there should be a program and plan to dredge the Saigon River to increase the flood discharge capacity of Dau Tieng Lake, ensuring safety for the headworks and the downstream area of the Saigon River.

Acknowledging the above situation, Mr. Tran Quang Hoai, Deputy Head of the National Steering Committee for Natural Disaster Prevention and Control at that time, also made a recommendation: For Ho Chi Minh City, the operation of Dau Tieng Lake is a problem that currently has no solution. Meanwhile, the Saigon - Dong Nai river basin not only has Dau Tieng Lake, but also has a series of other reservoirs. Therefore, the flood discharge operation of the Saigon - Dong Nai river basin is an extremely difficult and complicated problem. "If a bad situation occurs with Dau Tieng Lake, the risk of flooding will be very high, the damage caused will not be small, and it can even become a disaster for Ho Chi Minh City," Mr. Hoai warned.

Ho Chi Minh City needs to pay due attention and have systematic projects to reinforce the dyke system along the Saigon River as well as dredging projects, clearing the flow and large-scale response plans in case Dau Tieng Lake has to discharge floodwaters at full design capacity.

Source: https://cand.com.vn/doi-song/xay-dung-phuong-an-chong-ngap-cho-tp-ho-chi-minh-khi-ho-dau-tieng-xa-lu--i789073/