The Hydrology of the Mekong River
The Mekong rises on the Tibetan Plateau at an altitude of about 5200 m and flows 4800 km southeast to the South China Sea, through six developing countries: China, Myanmar, Laos, Thailand, Cambodia, and Vietnam. The Mekong catchment has an unusual shape. Most catchments tend to have a dendritic form, with the width of the catchment gradually decreasing downstream, producing a characteristic teardrop shape. The Mekong catchment, by contrast, progressively widens down valley so that its widest point is immediately upstream of its delta. The hydrology of the Mekong River is characterized by a huge mean annual discharge; concentrated in an extremely regular wet-season peak. The size of the wet-season peak and its highly predictable timing are the defining characteristics of large tropical monsoonal rivers. In the upper part of the Lower Mekong system, at Vientiane, the flow originating from China and Burma, the so-called Yunnan Component, not only provides most of the dry-season flows, but in addition, most of the floodwater during the majority of years. Even though floods can cause major devastation along the Mekong River, the peak discharge of the largest floods tends to be only about double the size of the bankfull discharge.