IRRAWADDY or IRAWADI, the principal river in the province of Burma, traversing the centre of the country, and running throughout its entire course in British territory. It is formed by the confluence of the Mali and N'mai rivers (usually called Mali-kha and N'mai-kha, the kha being the Kachin word for river) in 45' N. The N'mai is the eastern branch. The definite position of its source is still uncertain, and it seems to be made up of a number of considerable streams, all rising within a short distance of each other in about 28° 3o' N. It is shown on old maps as the Lu river of Tibet ; but it is now quite certain that the Tibetan Lu river is the Salween, and that the N'mai has its source or sources near the southern boundary of Tibet, to the north-east or east of the source of the Mali. At the confluence the N'mai is larger than the Mali. The general width of its channel just above the confluence is 35o or 400 yards. In the rains this channel is filled up, but in the cold weather the average breadth of the river is from 150 to 200 yards. The N'mai is prac tically unnavigable. The Mali is the western branch. Like the main river, it is called Nam Kiu by the Shans. It rises in the hills to the north of the Hkamti country, in about 27° 50' N. Be tween Hkamti (q.v.) and the confluence it runs in a narrow channel through continuous hills. About 1 m. above the confluence it is 15o yd. wide in January and 17 f t. deep, with a current of 3i m. an hour.
Steam launches can only ascend from Myitkyina to the con fluence in the height of the rains. Native boats ascend to Laikaw or Sawan 26° 2' N., all the year around, but can get no farther at any season. From the confluence the river flows in a southerly direction as far as Bhamo, then turns west as far as the con fluence of the Kaukkwe stream, a little above Katha, where it again turns in a southerly direction, as far as the great bend near Mandalay, where it is joined by the Myit-nge. Thence it follows a westerly course and is joined by the Mu stream—an important source of water for irrigation in the Shwebo district—on the north bank. Beyond Myinmu it again assumes a southerly direc tion and is joined by its chief tributary, the Chindwin, described below. Between the confluence and Mandalay the river varies in width from 5o to 4,00o yards. It is narrowest in the three well known "defiles." The third or upper defile lies between Myit kyina and Bhamo and is entered 3 m. below Sinbo by a channel only about so yd. wide and below this, throughout the defile, it averages about 1 oo yd. wide.
At the "Gates of the Irrawaddy" at Poshaw two prism-shaped rocks narrow the river to so yd., and the water banks up in the middle with a whirlpool on each side of the raised pathway. All navigation ceases here in the floods. The defile ends at Hpatin, and below this the river widens out to a wet-season channel of 2 m., and a breadth in the dry season of about 1 mile. At Sinkan, below Bhamo, the second defile begins. It is not so narrow nor is the current so strong as in the third defile. The narrowest place is more than 10o yd. wide. The hills are higher, but the defile is much shorter. At Shwegu the river leaves the hills and becomes a broad stream, flowing through a wide plain. The first defile is tame compared with the others. The river merely flows between low hills or high wooded banks. The banks are covered at this point with dense vegetation, and slope down to the water's edge. Here and there are places which are almost perpendicular, but are covered with forest growth. The course of the Irrawaddy after receiving the waters of the Myit-nge opposite Sagaing, as far as 17° N. lat., is exceedingly tortuous. Below the junction of the Chindwin and Irrawaddy, the tributary streams throughout the dry belt are but small, though some, especially those in the Minbu district, are important sources of water for irrigation, and others, like the Yaw river, are used for floating teak logs to the main river. At Akauktaung, where a spur of the Arakan hills ends in a cliff 30o ft. high, the river enters the delta, the hills
giving place to low alluvial plains, now protected on the west by embankments. From 17° N. lat. the Irrawaddy divides and sub divides, converting the lower portion of its valley into a network of intercommunicating tidal creeks. It reaches the sea in about 16° N. lat. by nine principal mouths. Practically no water, how ever, now reaches the sea through the western and eastern mouths (the Bassein and Rangoon rivers respectively) though these are the ones used by sea-going ships to reach the ports of Bassein and Rangoon.
The largest tributary of the Irrawaddy is the Chindwin, its entire course being in Burmese territory. It is called Ningthi by the Manipuris. The Chindwin is formed by the junction of the Tanai, the Tawan and the Taron or Turong, but it is still un certain which is the main stream. The Tanai his hitherto been looked on as the chief source. It rises in about 25° 30' N. and 97° E., on the Shwedaung-gyi peak of the Kumon range, 12 m. N. of Mogaung, and flows due north for the first part of its course until it reaches the Hukawng valley, when it turns to the west and flows through the middle of the plain to the end of the valley proper. There it curves round to the south, passes through the Taron or Turong valley, takes the name of the Chindwin, and maintains a general southerly course until it enters the Irrawaddy, after flowing through the entire length of the Upper and Lower Chindwin districts.
The Taron, Turong or Towang river seems to be the real main source of the Chindwin. It flows into the Hukawng valley from the north, and has a swift current with a succession of rapids. Its sources are in the hills to the south of Sadiya, rising from Io,000 to 1 i ,000 ft. above sea-level—mountains that are covered at least with winter snows. Below the Hukawng valley the Chindwin is interrupted at several places by falls or transverse reefs. At the village of Haksa there is a fall, which necessitates transhipment from large boats to canoes. Not far below this the Uyu river comes in on the left bank at Homalin, and from this point downwards the steamers of the Irrawaddy Flotilla Com pany ply for the greater part of the year. The Uyu flows through a fertile and well-cultivated valley, and during the rainy season it is navigable for a distance of i 5o m. from its mouth by steamers of light draught.
The area of the catchment basin of the Irrawaddy is 158,000 sq.m. ; the total length of the main river from its known source to the sea is about 1,30o miles. Throughout its course, except through the defiles, it is full of islands and sandbanks ; its waters are extremely muddy, the mud being deposited partly in the delta, in part being carried far out to sea. The river commences to rise in March ; about June it rises rapidly, and attains its maximum height about September. The total flood discharge is between four and five hundred million metric tons of 37 cubic feet. From Mandalay up to Bhamo the river is navigable a distance of nearly I,000 m. for large steamers all the year round; but small launches and steamers with weak engines are often unable to get up the second defile in the months of July, August and September, owing to the strong current. The Irrawaddy Flotilla Company's steamers go up and down several times a week, but the mails are carried to Bhamo by a ferry-boat from the railway terminus at Katha.
The river Irrawaddy itself supplies no main irrigation works; the great value of the river is as a highway. It is the only means of reaching such important centres as the oilfields of Yenangyaung and Singu, which are served as yet neither by road nor railway. The Irrawaddy is nowhere bridged, though crossed by two steam ferries (at Henzada and at Sagaing) to connect the railway system on either bank. (L. D. S.)