SBR- Content.pmd - INBO

2 - Physical landforms of the Mekong BasinIn the lower part of the basin, the boundaries of the catchment are formed by mountainous extensionsfrom these same uplands. One of these, extending southwards from the Laotian Highlands, forms adiscontinuous range of hills through the Phanh Hoei Range in Northeast Thailand, south to theCardamom Mountains in western Cambodia. The other, more continuous range extends moresoutheasterly from the Laotian Highlands through the Annamite Cordillera in Viet Nam to theBolovens Plateau and the Kontum Massif.The present Mekong River and itstributaries are a related group of rivers,created when the steep slopes of themountains of the region were eroded toform deep ravines and valleys. Prior tothe Pleistocene, the Mekong was not likelyto have been a major river. Its modernconfiguration appears to have been createdas a result of a number of important streamcaptures, including the headwaters of theChao Phraya in Thailand. Changes inelevation of the Korat Plateau andmovements and lava flows on theCambodian Plain during this time furtherIn China, the Mekong River is called the Lancangassisted in the formation of the Mekong.Since physiography and geology have been discussed elsewhere, 3 this account is restricted to abroad overview.1. Lancang River BasinThe Lancang, as the Mekong is called in the Peoples’ Republic of China (PRC), drains from analtitude of 4,970 m on the Tibetan Plateau, where the river rises, down to 310 m at the port at Simao.The topography is steep and the river falls 6.5 m per kilometre. Population density near the headwatersis relatively sparse, increasingdownstream where the river flows throughwider river valleys that range in elevationbetween 1,000 and 3,000 m. Forestclearing for agriculture, rubber plantationsand urban development, combined withsteep topography, have contributed tosignificant soil erosion in this region ofthe basin.Rice terraces line the Mekong inYunnan Province in China9