Water Use in the Mekong River

摘要

The catchment area of the Mekong River is 790,000 km~2 which is about twice as large as the area of Japan and the length of the main channel is 4,200 km. The population in the basin is 170 million. The basin is shaped like a violin, in which the upstream area of the basin extending through in China and Myanmar (20% of the whole basin) is like the violin's scroll and finger board and the downstream area of the basin (600,000 km~2), connecting four countries, i.e., Laos, Thailand, Cambodia and Viet Nam, is like the sounding board. The climate of the extreme upper reaches of the basin is cold and semi- arid and that of the upper and middle areas is temperate and humid, The lower area, which covers 80% of the total basin, is included in the tropical monsoon zone and has an average annual precipitation of 1,700 mm. Discharges in this river start to increase in May or June, reaching their peak in August or September in the upper reaches and in September or October in the lower reaches. The water level isusually lowest in April, and differs greatly between the rainy and dry seasons, fluctuating by 11 m at Vientiane, 7 m at Phnom Penh, and 2 m in the delta areas of Viet Nam, for example, The slope of the river bed is quite gentle, so that the average velocity during flooding is about 2 m/s; during drought it is 0.5 m/s.