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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

Prior Consultation process starting date for Luang Prabang project agreed

The Mekong River Commission’s Joint Committee Working Group (JCWG) for the Procedures for Notification, Prior Consultation and Agreement (PNPCA) has agreed on the official starting date of a six-month prior consultation process for the 1,460-megawatt Luan

MRC, Morocco concretize cooperation, eying for a regional educational visitor center in Laos

The Mekong River Commission and the Moroccan government last week brought their cooperation in renewable energy and eco-tourism to a new level as they sought to strengthen the existing partnership.

Laos to undertake prior consultation for Luang Prabang hydropower project

The Lao Government will undertake the Mekong River Commission’s prior consultation process for the Luang Prabang hydropower project located between the proposed Pak Beng project on the upstream and the nearly completed downstream Xayaburi project. The run