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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

Media Release - Mekong leaders reaffirm the Mekong River Commission’s primary and unique role in sustainable development of the Mekong River Basin

As the 3rd Mekong River Commission (MRC) Summit came to a close today, the Siem Reap Declaration was adopted by the MRC member ...

China notified about discharge of Jinghong Reservoir 5 days in advance

MRC received a one-day advance ‘emergency notification’ from China – its dialogue partner – about its planned water discharge from the Jinghong Reservoir to the lower Mekong River tomorrow, aimed to ensure power grid security

Media Release - International conference recommends priorities for the lower Mekong countries to achieve sustainable development agenda

A two-day international conference convened by the Mekong River Commission (MRC) comes to a close today...