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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

The Mekong River Commission is striking a balance between development and protection of the Mekong river

A major infrastructure project on the Mekong mainstream, the Pak Beng Hydropower Project in Oudomxay Province of Laos, is currently undergoing a prior consultation process of the Mekong River Commission (MRC). The Commission is serious about this process

MRC’s 2nd Regional Stakeholder Forum on Pak Beng Hydropower Project addresses stakeholder concerns

5 May 2017, Vientiane Capital, Lao PDR – About 200 participants of various stakeholder groups gathered in Vientiane Capital, Lao PDR for the Mekong River Commission’s (MRC) 2nd Regional Stakeholder Forum of the proposed Pak Beng Hydropower Project.

Mekong and Mississippi River Commissions further collaborate in exchanging water management experiences

Members of the Mekong River Commission Council spent five days in the Lower Mississippi Valley in the United States beginning April 2, 2017 arriving in Memphis, Tennessee and travelled to numerous locations in the region as the guests of the Mississippi R