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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

MRC’s Regional Stakeholder Forum on the Mekong Adaptation Strategy and Action Plan seeks inputs

26 June 2017, Vientiane Capital, Lao PDR – Around eighty participants from various stakeholder groups gathered in Vientiane Capital, Lao PDR for the Mekong River Commission’s (MRC) Regional Stakeholder Forum on the Mekong Adaptation Strategy and Action Pl

Official Prior Consultation for Pak Beng Hydropower Project Reaches its 6-month Milestone

20 June 2017, Vientiane Capital, Lao PDR – Yesterday the Mekong River Commission (MRC) Secretariat organised the Special Session of the MRC Joint Committee (JC) on the proposed Pak Beng Hydropower Project (PBHPP) in Vientiane to conclude the official six-

Laos and Viet Nam’s MRC Council members and ministers meet on the Pak Beng project

Viet Nam’s Minister of Natural Resources and Environment Tran Hong Ha recently visited Lao PDR to meet with Lao Minister of Natural Resources and Environment Sommad Pholsena on the Mekong River Commission prior consultation for the Pak Beng Hydropower Pro