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Hydrology

Upstream flow contributes only a small portion of the total annual flow of the Mekong River. Most of the total flow volume is delivered to the Mekong from tributaries in the Lower Mekong Basin (see Table 1); however, the importance of upstream flow should not be underestimated as dry-season snow melt from China contributes to over 24% of the total flow.

Table 1. Proportional contributions to total Mekong River mean annual flow by river reach, distinguishing those made by the left and right bank tributary systems.

River Reach Left Bank (%) Right Bank (%) Total (%)
China 16 16
China – Chiang Saen 1 3 4
Chiang Saen – Luang Prabang 6 2 8
Luang Prabang – Vientiane 1 2 3
Vientiane – Nakhon Phanom 18 4 22
Nakhon Phanom – Mukdahan 3 1 4
Mukdahan – Pakse 4 6 10
Pakse – Kratie 22 2 24
Tonle Sap 9 9
Total 55 20 100

Flooding

The flood season in the Mekong River Basin lasts from June to November and accounts for 80 to 90% of the total annual flow (MRC 2010). The annual flood season is especially important in the Lower Mekong Basin where it has shaped the environment and its inhabitants.

See the sections on the People and Flood and Drought for more information.

Many of the Mekong’s key ecosystems have developed as a result of seasonal flow fluctuations. The area’s extensive wetland habitats would not exist without the annual flood. Likewise, the life-cycles of many Mekong fish species depend on it. Fish migrate to deep pools in the mainstream to seek refuge during the dry season; later, during the flood season, they migrate back to spawning and nutrient-rich feeding grounds on floodplains.

See the Fisheries section for more information.

Latest News

Mekong water levels to drop due to dam equipment testing in China

The water outflows at the Jinghong hydropower station in China will be reduced by more than 50% due to dam equipment testing from 1 – 4 January 2020, affecting river water levels in Thailand, Lao PDR and Cambodia.

MRC Secretariat, LMC Water Center ink first MOU for better upper-lower Mekong management

Data and information exchange, basin-wide monitoring, and joint assessment on Mekong water and related resources are among the main areas to benefit from a new partnership between the Mekong River Commission Secretariat (MRCS) and Lancang-Mekong Water Res

Cross-border water cooperation and joint environmental monitoring received German support

The German government today provided additional 2 million euro (approx. U$2.2 million) to the Mekong River Commission to increase cross-border water dialogue and cooperation and support efforts in monitoring transboundary environmental impacts from Mekong