IRRAWADDY RIVER

The Irrawaddy and Mekong river basins and their drainage networks. Burmese Ayeyarwady, principal river of Myanmar (Burma), running through the centre of the country. Myanmar's most important commercial waterway, it is about 1,350 miles (2,170 kilometres) long. Its name is believed to derive from the Sanskrit term airavati , meaning elephant river. From its sources to its numerous mouths, the river flows wholly within the territory of Myanmar. Its total drainage area is about 158,700 square miles (411,000 square kilometres). Its valley forms the historical, cultural, and economic heartland of Myanmar. Raft of logs on the Irrawaddy River, Mandalay, Myanmar. Burmese Ayeyarwady principal river of Myanmar (Burma), transversing the centre of the country and running throughout its entire course within Myanmar territory. It is the country's most important commercial waterway, having a length of about 1,350 miles (2,170 km). The Irrawaddy is formed by the confluence of the Nmai and the Mali rivers, which rise in the glaciers of the high mountains of northern Myanmar. The Nmai, which is larger than the Mali at the confluence, is the eastern branch, and the Mali the western. From their confluence the Irrawaddy flows generally southward, varying in width as it passes through three defiles (narrow gorges) between the confluence and the city of Mandalay. About 40 miles (65 km) downstream from Myitkyina is the first defile. Below Bhamo the river makes a sharp westward swing and cuts through the limestone rocks of the second defile. The hills flanking the river are higher there, but the passage is much shorter. The third defile begins about 60 miles north of Mandalay. Farther downriver the Irrawaddy meanders across the densely populated alluvial flats of the central dry zonethe ancient Myanmar cultural heartlandin a broad, open course. Within the central dry zone the river's major tributary, the Chindwin, unites with the Irrawaddy. Continuing south, the lower course flows through a narrow valley between forest-covered mountain rangesthe Arakan (Rakhine) Mountains to the west and the Pegu (Bago) Mountains to the eastafter which it enters the Andaman Sea through a wide delta. The Irrawaddy's total drainage basin covers approximately 158,700 square miles (411,000 square km). Its annual average discharge is 460,000 cubic feet (13,000 cubic m) per second, but the volume of the river and its tributaries fluctuates greatly through the year owing to monsoonal rains that occur between June and September. The rapid melting of glaciers in the summer adds further to the volume. In general, from December to March the Irrawaddy varies between its lowest level and 5 feet (1.5 m) above it, while from mid-June to mid-October the river is 20 to 30 feet above its lowest level. Commercial steamer service is maintained throughout the year from Henzada on the delta to Bhamo 670 miles to the north. The river ports (Mandalay, Chauk, Prome, and Henzada are among the most important) find it necessary to have separate high- and low-water landing points. In the central dry zone the cultivation of wheat, cotton, and oilseeds dominates, while to the south the Irrawaddy delta comprises one of the world's largest rice-growing areas. Rice, other foodstuffs, petroleum, cotton, and teak logs are the major items transported on the river system. Additional reading Coverage of the Irrawaddy River is found in David I. Steinberg, Burma: A Socialist Nation of Southeast Asia (1982), a concise general survey of the country and territory; Hugh Tinker, The Union of Burma, 4th ed. (1967); Charles A. Fisher, South-East Asia: A Social, Economic, and Political Geography, 2nd ed. (1966); Wilhelm Klein, Burma, 7th ed. (1989), a descriptive guide; and Michael Adas, The Burma Delta: Economic Development and Social Change on an Asian Rice Frontier, 18521941 (1974). Alister McCrae and Alan Prentice, Irrawaddy Flotilla (1978), describes the development of inland water transportation on the river. Thomas R. Leinbach