Beware of flood discharge from irrigation and hydroelectric reservoirs during the rainy season

Consequences of flood discharge

In the context of climate change, weather developments are becoming more complex and unpredictable, and many extreme phenomena may occur. Due to heavy and prolonged rains, water from upstream flows in large quantities, accumulating in lakes, irrigation and hydroelectric dams. When the threshold is exceeded, the capacity at the elevation is not allowed, the water pressure can cause the dam to break at any time, forcing flood discharge to save the dam and limit the consequences of the dam break.

The impact of storms and tropical depressions often causes heavy rain and high rainfall in the Central provinces in general and Nghe An in particular from late July to November. In particular, September to October are the months with the most storms, floods and inundation.

Recalling the consequences of flood discharge in some lakes, irrigation and hydroelectric dams in Nghe An in recent years so that we can remember and learn lessons such as:

Vuc Mau irrigation lake in Hoang Mai town has a design capacity of 75 million m³water, elevation 21m. During the 2013 storm season, after many days of heavy rain, the water level in the lake exceeded the capacity at elevation 21m. If the flood is not discharged, the water pressure can cause the dam to break, the damage will be immeasurable. Therefore, at 8:00 a.m. on September 30, 2013, Hoang Mai Irrigation Enterprise officially issued Notice No. 92/TB-XNTL to wards, communes and towns in the area to know and take precautions. At 7:00 p.m. on the same day, the first spillway gate was discharged, then the second spillway gate was discharged, and then (from 2-3:00 a.m. on October 1, 2013) the remaining 3 sluice gates were discharged in turn.

Thus, within 8 hours, all 5 sluice gates of Vuc Mau Lake discharged floodwater at full capacity, with a discharge volume of nearly 1 million m3.³/h. The large volume of water discharged in such a short time caused terrible flooding in Quynh Luu district and Hoang Mai town, with some places having water depths of 1 - 3m; washing away houses, buffaloes, cows, pigs, chickens, property,...

Most recently in 2022, on the upper reaches of the Hieu River, there were 3 hydropower plants, including: Nhan Hac, Chau Thang and Nam Po ng. Nghe An Irrigation Department said that in the rainy season of September 2022, the western part of Nghe An had heavy rain, the rain lasted longer than other areas in the province. The above flood discharge process pushed a huge amount of water down to the downstream area, causing deaths, houses being swept away, loss of property and assets of the people, causing great damage to crops...

Thus, although the flood discharge was carried out according to the correct procedure, the flood discharge announcement at 2am left people unable to react in time. Calculating the water flow into the reservoir to regulate the appropriate flood discharge is the responsibility of hydropower plants to ensure the safety of infrastructure, lives and property of people in downstream areas...

Some solutions

Nghe An has 1,061 lakes and irrigation dams and over 21 large and small lakes and hydroelectric dams. Of the current 120 lakes and irrigation dams, they were built too long ago and the quality of the lakes and dams has seriously degraded. This year's storm season is forecast to have a much larger total rainfall than the average of many years. Therefore, the possibility of water flowing into the lakes, irrigation dams and hydroelectric dams will be very high. Therefore, the need to release floodwaters to protect the safety of lakes and dams may occur.

To limit the consequences caused by flood discharge from irrigation and hydroelectric reservoirs during the rainy season, we need to implement the following solutions well:

The first:The management board of reservoirs, irrigation and hydroelectric dams should avoid being subjective and afraid of difficulties. From there, they loosen their direction in implementing measures to prevent and combat natural disasters and floods, and do not fully and promptly calculate technical parameters on the number of rains, the duration of each rain, the measured rainfall, the water flow into the reservoirs and dams every hour and every day, the water level rising every day... to ask for permission from competent authorities to release floodwaters to protect the safety of the reservoirs and dams when the rain continues. This is a task that needs to be done continuously 24/7 during the rainy and stormy season. Otherwise, the consequences will be unpredictable and there will be no time to react.

Monday:During the rainy season in Nghe An, mainly from August to October every year, there will certainly be heavy to very heavy rain, lasting for many days. Therefore, the management boards of lakes, irrigation dams, hydroelectric power plants and irrigation enterprises in the localities need to closely monitor and grasp the ability of water sources to flow into each lake and dam, so that they can proactively plan to gradually release floodwaters when the volume of water in the lake is about to exceed the design capacity, only retaining the amount of safe and necessary water. Do not hesitate to release some water in the lake, especially when it continues to rain heavily and for a long time. If you wait until the dam is about to break before releasing floodwaters through all the gates with a huge flow of water, it will cause serious consequences for the downstream area.

Tuesday:The time of flood discharge should not be when the tide is rising. In the case of Vuc Mau irrigation reservoir in Hoang Mai town, this mistake was made when releasing flood water on September 30 and October 1, 2013. At the same time, after the flood discharge announcement, it should not be released at night, which will cause difficulties for people in evacuating people, property, livestock... in the dark. On the other hand, it should be released slowly so as not to accumulate a huge amount of water at once downstream, which will cause severe flooding in the downstream area if not drained in time.

Wednesday:During the rainy and flood season, the standing committees for natural disaster prevention and control from the province down to the district, commune, town, hamlet, village, etc. are on duty 24/7 and continuously announce on the radio and television system about the flood situation, the risk of inundation, the possibility of storms and storms that may occur. If there is a flood discharge at a lake or dam, it must be announced at least 1/2 day before the flood discharge, and announced many times so that people have time to collect their belongings, move their assets to higher ground, and bring the elderly and children to safety.

Thursday:For people in downstream areas near large lakes, irrigation dams and hydroelectric plants, they must always be proactive and ready to evacuate people and protect property when there is an evacuation order due to flood discharge causing inundation.

Friday:Usually in late August and early September, summer-autumn crops such as rice, corn, beans, peanuts, etc. enter harvest season. In low-lying areas that are prone to flooding during heavy rains and downstream areas near lakes, irrigation dams, and hydroelectric dams, it is necessary to try to quickly harvest summer-autumn crops, especially rice when 85-90% of the grains on the panicle are ripe for immediate harvest.