Mekong River water level is low, Mekong Delta is about to welcome a new wave of saltwater intrusion

According to VNMC, the Mekong Delta provinces are about to experience another wave of deep saltwater intrusion. The reason is that reservoirs on the Lancang River (the upper Mekong River section flowing through China - PV) are at about 50% of their total useful capacity. Of which, large reservoirs such as Nuozhadu reservoir contain about 40% of their capacity (4.4 billion ^m3 ) and reservoirs in the lower Mekong River basin are also containing about 55%.

Nước sông Mekong về ít, ĐBSCL sắp đón thêm đợt xâm nhập mặn mới- Ảnh 1. — Mekong Delta is about to welcome a new wave of saltwater intrusion in the next few days.

With the above conditions, along with the decreasing flow trend on the Mekong mainstream. The flow through Kratie station in March tends to decrease and the water storage in Tonle Sap (Cambodia) is also low, currently only 2.9 billion ^m3 . Therefore, the ability to contribute to the Mekong mainstream is very limited.

The average daily flow to the Mekong Delta through Tan Chau and Chau Doc stations in March will continue to decrease from 4,300 ^m3 /s to about 3,400 ^m3 /s, at a level equivalent to the average of many years but lower than the same period in 2023. The total flow in March through these two stations will likely be about 25 - 35% lower than the same period in 2023.

Water from upstream is low, salinity penetrates deep into river branches in the Mekong Delta in March. The 1‰ salinity boundary penetrates deepest on three major river branches (Hau River, Tien River and Vam Co Tay River) 8 - 12km deeper than the average of many years and 5 - 8km deeper than the salinity intrusion in the same period in March 2023. The 4‰ salinity boundary is 6 - 10km deeper than the average of many years and 4 - 7km deeper than the same period in 2023.

From now until the end of March, there will still be a deep saline intrusion from March 20 to 25 (high tide period in the middle of February of the lunar calendar). Therefore, areas regularly affected by salinity need to closely follow salinity monitoring information and salinity intrusion forecast bulletins to operate appropriate salinity prevention works to take advantage of water storage in the canal system. Because water sources will become increasingly scarce during the dry season, localities need to have plans to take water in rotation on rivers and canals to avoid localized depletion, leading to deeper salinity intrusion.

Hydroelectric dams cause erratic Mekong River flows

The recent weekly newsletter of MDM (Mekong Dam Monitoring Project) details: The drought in China and northern Laos during the 2023 rainy season continues to cause the natural flow of the Mekong River to be lower than normal during the 2024 dry season. The impact of dams is causing water levels across the Mekong River to fluctuate abnormally according to water closures and releases. The general trend since the beginning of the dry season has been that the amount of water released from upstream hydropower dams on the mainstream of the Mekong River is very limited. However, at some times the amount of water released is higher than normal, causing the river water in some places to rise. Specifically, in February, the water level at Stung Treng (Cambodia) doubled compared to normal years.

In general, the water level in the Mekong River basin is generally lower than normal for the same period. In Tonle Sap, the water level is about 30cm lower than normal compared to the same period in many years.