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Irrawaddy,river, Myanmar: see AyeyarwadyAyeyarwady
, chief river of Myanmar, c.1,000 mi (1,600 km) long, formed by the confluence of the Mali and Nmai rivers in N Myanmar. The combined stream flows south through gorges strewn with rapids past Myitkyina, Bhamo, Mandalay, Pakokku, and Pyay; it
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the largest river in Burma. (Its headwaters are in China.) Length, 2,150 km. Basin area, 430,000 sq km (according to other data, 415,000 sq km).
The Irrawaddy rises in the eastern spurs of the Himalayas and flows mainly from north to south. In its upper course the Irrawaddy and its tributaries flow in deep gorges through jungles and have channels full of rapids. Below the city of Myitkyina the Irrawaddy valley broadens, and the channel becomes 800 m wide. The river then cuts across the western part of the Shan Upland, forming three gorges where the channel is 50–100 m wide and where in places there are whirlpools that constitute a danger to navigation. In its middle and lower course the Irrawaddy crosses the extensive Irrawaddy Plain, where the river forms a broad, terraced valley. A flat, very swampy delta covered with jungles begins 300 km from the mouth of the river. The delta has an area of up to 30,000 sq km (according to other sources, 48,000 sq km); along the coast of the Andaman Sea the delta extends for 240 km and is separated from the sea by a belt of sand dunes. The delta is formed by numerous channels and arms; Rangoon and Bassein are the largest ones and are navigable. The water is muddy, and the river carries about 250 million tons of sediments annually, owing to which the delta is advancing out into the sea at an average rate of 40–50 m a year.
The Irrawaddy has a monsoon regimen. Because of the monsoon rains, the river begins to rise in April and continues to rise until August or September, after which the water begins to drop. The amplitude of fluctuations in water level is 8–11 m, and during high water the width of the river increases in places by four to five times; thus, in the middle course at the city of Mandalay the width of the river changes from 2 km to 10 km. In its lower course the Irrawaddy experiences high tides which reach a height of 4—4.5 m at the city of Rangoon. The average water discharge in the river’s lower course is 13,000–14,000 cu m per sec, but during particularly heavy rains it can reach 40,000 cu m per sec, and sometimes even more. Catastrophic floods are frequent. The river is navigable for a distance of 1,100 km upstream, and for a distance of 1,440 km in the summer (to the city of Bhamo); small boats can ascend to the city of Myitkyina (1,600 km from the mouth). In the middle and lower course the waters of the Irrawaddy and its tributaries are used for irrigation. In its upper course timber is rafted. The river’s tremendous power resources are hardly used at all. The cities of Mandalay, Prome, and Henzada are on the Irrawaddy; Rangoon—Burma’s capital—is in the delta on an arm of the Irrawaddy.
A. P. Muranov