CJP4W6159-14x20cm.jpg

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 River’s aquamarine hue likely to occur elsewhere due to low flows, bringing possible risks

The extremely low flow, slow drop in the river sediments, and presence of algae on the sand and bedrock river bottom are some of the possible causes why the Mekong River has recently acquired an aquamarine color, says the Mekong River Commission. This phe

MRC ministerial council approves a drought management strategy, other policies, boosting Mekong countries’ ability to prepare for future disaster

Ministerial delegates from the Mekong River Commission (MRC) Council today at their annual gathering in Phnom Penh approved a drought management strategy for 2020-2025, allowing Cambodia, Lao PDR, Thailand and Viet Nam to prepare for and manage drought co

Media advisory: Drought, hydrological condition and other policy issues on top agenda of MRC Council meeting next week

Every year, water and environment ministers of Cambodia, Lao PDR, Thailand and Viet Nam who are members of the MRC Council convene to review and come to mutual conclusion on the management and development of water and related resources of the lower Mekong