STELAR-S2S

the Mekong River

Rising in Tibet, the Mekong drains large tracts of China, Burma, Thailand, Laos, Cambodia and Vietnam before discharging into the South China Sea. The Mekong is one of the world’s largest rivers, ranking within the top 10 when measured in terms of the huge volumes of water (475 km3), and sediment (1.6x108 tonnes) that it delivers to the ocean each year. The Mekong Basin can be divided into two distinct units:

  1. the Upper Mekong Basin (UMB), lying within China, and;
  2. the Lower Mekong Basin (LMB) which extends south of the border between China and Laos.

Compared to other large Asian rivers, the Mekong has not yet been subjected to significant changes in land cover nor widespread dam construction, so its hydrological and sediment regimes remain - for the time-being - quasi-natural. Indeed, the Mekong Basin has the highest levels of biodiversity per unit area anywhere on the planet .

The reach selected as the specific focus of this study stretches for about 220 km between the hydrological station at Kratie to Cambodia’s capital city, Phnom Penh. Dominated by the annual monsoon, the Mekong’s flow regime experiences a prolonged annual flood (May-November) and dry season (December-April), with seasonal flow variations ranging between mean annual minima and maxima of 1900 m3/s and 40400 m3/s, respectively. The bed-material is fine sand, with sand-silt river banks of heights that exceed 15 m. The channel planform comprises single-thread or divided sinuous channels (gradient ~5.0x10-5; width ~1200 m; width:depth ratio ~80) that are unconfined and actively migrating.

the Mekong River drainage basin in SE Asia.

the Mekong River drainage basin in SE Asia

Of key significance to this proposal is that much of the Mekong upstream of Kratie is constrained by bedrock, with very little potential for sediment erosion or storage. As such the upstream reach boundary is strongly coupled to its source areas in the Himalaya and Annamite Mountains, while the downstream limit adjoins the apex of the Mekong Delta. Thus the study reach represents an alluvial sediment ‘transfer’ reach that links upstream source areas to a deltaic sink.