CHARACTERIZATION OF GRAVEL BARS OF THE MEKONG RIVER NEAR THE GOLDEN TRIANGLE OF NORTHERN THAILAND

The Mekong River starts in the Qinghai Province, China near Tibet, the river flows as a border between Laos and Burma and between Thailand and Laos before flowing through Cambodia and finally to the South China Sea through Vietnam. Each of these countries have industrial and agricultural interests for the river; for the people living near the Mekong, the river is a source of subsistence fishing, is widely used for transport and tourism. The Mekong River is also a unique ecological and hydrologic system. With multiple hydroelectric dams and two reservoirs (Xiaowan and Dachaoshan) on the Mekong River in China and continued interest in dam development in Laos for hydropower production, flow changes to the river are inevitable. This study focuses on characterizing gravel bars near Chiang Saen, Thailand, with the purpose of documenting the current size distribution of bed-load gravels and the bed form or texture. The study site consists of two lateral bars on the Laotian side. During bank full flow the river is ~0.6km wide and has an approximate depth of 10m over the gravel bars. Annual peak flows are around 10,000 cubic meters/second and the maximum flow of record is 23,600 cubic meters/second occurring September 3, 1966. The pebble counts yield a D₅₀ of 75mm, and outsized clasts of 250 mm (maximum diameters) conducted on exposed bars during low flows of January, 2004. The gravel bars also exhibit large ripples spaced ~4m with amplitude of 0.5m. Most of the bars and islands in this reach of the Mekong are of fine to medium sand, but these gravel bars are important to local people for harvesting algae and may be an important bed form for fish habitat.