SBR- Content.pmd - INBO

State of the Basin Report - 20032. Annual runoffThe mean annual discharge of the Mekong is approximately 475 x 10 9 m 3 . China contributes 16percent of the discharge and Myanmar 2 percent, with the remainder arising from the four countriesof the lower basin (Table 1). About 55 percent of the water in the lower basin arises from themountainous regions along the eastern rim of the basin, with Northeast Thailand contributing only10 percent.Table 1. Approximate distribution of MRB water resources by countryCountry or provinceYunnan Myanmar Lao PDR Thailand Cambodia Viet Nam MekongProvince,River BasinPRCCatchment 22 3 25 23 19 8 100area as %of MRBAverage flow 2410 300 5270 2560 2860 1660 15,060(m 3/ sec)from areaAverage flow 16 2 35 18 18 11 100as % of totalOver the period from 1960 to 1999, discharge at selected stations within the Lower Mekong Basinhas remained relatively constant (Figure 4). The variation of the annual flow from year to year isvery low by world standards. The coefficient of variation (C v) of the annual flow at Chiang Saen is0.2, while the average C vfor rivers with catchments larger than 10 5 km² is 0.33, and the average forrivers with catchments of that size in Asia is 0.28. 2 This means that the river flows tend not to differmuch between high flow years and low flow years. Compared with other rivers, the annual flow ofthe Mekong is relatively predictable and not highly variable.Figure 4. Annual variation in discharge from 1961 to 2000 at Chiang Saen (pink) and Pakse(dark blue).16