Mekong Dam Monitor (Update for July 1 - 7, 2024)

 

Update for July 1-7

Notable changes on the Mekong in the last week. Visit the Monitor home for more, including Burmese, 中文, Khmer, ພາສາລາວ, ไทย, and Tiếng Việt translation.

SPOTLIGHT Tonle Sap Lake Currently Expanding but Likely to Contract  Last week the Tonle Sap Lake, the world’s largest inland fishery, rose by 1 meter, mostly due to reverse flow moving water from the Mekong mainstream up into the lake. This was one of the largest single week changes in river level observed for the early wet season in recent decades. Reverse flow and the lake’s expansion are critical ecological processes that drive the lake’s robust fish catch. However, a developing drought in China and dam restrictions throughout the lower Mekong are driving river levels downward from Chiang Saen to Stung Treng. Without more rain, we predict that reverse flow phenomenon could temporarily end and lake water could flow back into the mainstream over the next two weeks. In our 2023-2024 annual report, we discussed this “Tonle Sap Accordion” phenomenon where in recent years the lake has expanded and then contracted over short periods until the mid-wet season rains drive a more robust reverse flow volume and lake expansion. The accordion effect is likely linked to the operation of dams throughout the basin, which restrict water in inconsistent ways causing Mekong and Tonle Sap Levels to rise and fall.

Where is the water? More dam restrictions than releases were observed last week, particularly in the downstream. We tracked restrictions at fourteen dams, with the largest at Huangdeng (PRC, 577 million cubic meters), Nuozhadu (PRC, 148 million cubic meters), Nam Ngum 1 (LAO, 195 million cubic meters), and Nam Ngiep 1 (LAO, 223 million cubic meters). We tracked releases at seven dams, with the largest at Xekaman 1 (LAO, 264 million cubic meters), Plei Krong (Vietnam, 123 million cubic meters), and Lower Sesan 2 (CAM, 128 million cubic meters). A net restriction of 639 million cubic meters was observed across the entire basin.

Most Impactful Dams

River Levels Across the mainstream, river levels are trending downward to lower than normal levels.

Chiang Saen Gauge Stung Treng Gauge

Weather & Wetness Drought conditions (orange and red) worsened throughout the entirety of the basin last week. Recently China’s portion of the Mekong has mostly shifted from higher than normal wetness to much lower than normal wetness levels. Drought is intensifying throughout the middle of the basin from Laos through NE Thailand and Cambodia. The Mekong Delta is experiencing above average wetness.