a river in China, Laos, Campuchia (Cambodia) and Vietnam that partially forms the border between Laos and Burma and Thailand; the largest river in Indochina. Length, approximately 4,500 km; basin area, 810,000 sq km.
The Mekong originates in the Tangkula Mountains in the Tibetan highlands. The upper course of the river is called the Dzi Chu; the middle course (in China), the Lantsan Chiang. The river flows into the South China Sea, forming a delta. The Mekong’s main tributaries are, on the right, the Mun and Tonle Sap; on the left, the Wu, Theun, and Sen.
In its upper and middle courses, the Mekong flows mainly through deep gorges, and its channel has many rapids. One of the world’s largest waterfalls, Khone Falls (elevation to 21 m), is situated where the river flows into the plain. The rapids end near the city of Kratie in Campuchia. Below the city of Phnom Penh, the Mekong Delta begins (area, approximately 70,000 sq km); the river divides into two large streams linked by numerous channels. Approximately 75 percent of the Mekong’s total flow passes through the main left stream, the Bassac. The delta projects into the sea in the shape of an arc with a coastline approximately 600 km in length; as a result of the river’s abundant regular flow, the delta’s size increases by 80–100 m a year. The delta is marshy and in many places is covered with mangrove thickets.
The Mekong is fed primarily by rain, and in the upper course also by snow and partly by glaciers. High water occurs in summer and fall. In the river’s middle course, maximum water level is usually recorded in August (in the lower reaches, in October); the lowest flow occurs in April. The fluctuation in water level reaches 10–15 m in the mountains, and up to 10 m on the plain and in the delta. The mean annual flow rate in the middle course, at Vientiane, is 4,600 cu m per sec; the maximum annual flow rate is approximately 21,000 cu m per sec. In the lower course, at Kratie, the mean annual flow rate is 14,800 cu m per sec, with a maximum annual flow rate of 33,000 cu m per sec (some years it reaches 67,000 cu m per sec). The Mekong freezes only in the upper course for 1–2 months. It carries an average of 1.5 cu km of drift a year. Tonle Sap, a lake that is connected with the river by the Tonle Sap tributary, exerts a great regulatory influence on the river’s flow. In the humid season (June-November) the lake fills up with water from the Mekong; in the dry season (November-June), the water level of the river falls lower than that of the lake, which results in an intensive overflow of lake water into the Mekong channel, uncovering vast areas of farmland fertilized with productive silt.
The lower Mekong is used for irrigation. Its extensive flooding is conducive to rice growing. The Mekong’s huge hydraulic power resources (estimated at approximately 75 million kilo-watts) are not much used. The rivers and lakes in the Mekong basin are rich in fish, primarily of the carp family; there are many waterfowl, and crocodiles are still common. The river is navigable year round for 700 km, and for 1,600 km (to Vientiane) during high water. Ocean vessels can reach Phnom Penh (350 km). The cities of Luang Prabang, Vientiane (Laos), and Phnom Penh (Campuchia) are on the Mekong.
A. P. MURANOV