IRAWADI, or IRRAWADDY, the principal river in the province of British Bnrmah, traversing the Pcgu division from north to south. The Irawadi is formed by the junction of two streams whose source is as yet unknown, in about 26° N. let. The chief tributaries are the Mogoung, from the westward, which throws its water into the main stream (here 600 yards wide), in 24° 50' N. lat., and the Shwe li and Kycng-dweng. Shortly after leaving the mouth of the Mogoung it enters the first or upper defile. Here the current is very rapid, and the return waters occasion violent eddies and whirlpools. When the river is at its lowest, no bottom is found even at 40 fathoms. After receiving the Ta-peng from the east, it enters the second defile, which is exceedingly picturesque, the stream winding in perfect stillness under high bare rocks rising sheer out of the water. Farther down the Irawadi, and not far from Mandalay, is the third or lowest defile. The banks are covered at this point with dense vegetation, and slope down to the water's edge ; at places appear almost perpendicular but wooded heights. The course of the Irawadi after receiving the waters of the Myit-uge and Tsagaing, as far as 17° N. let., is exceedingly tortuous ; the British frontier is crossed in 19° 29' 3" N. lat., 95° 15' E. long., the breadth of the river here being mile ; about 11 miles lower down it is nearly 3 miles broad. At Akouk-toung, where a spur of the Arakan hills ends in a precipice 300 feet 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 Irawadi divides and subdivides, converting the lower portion of its valley into a network of intercommunicating tidal creeks. It reaches the sea in 15° 50' N. let. and 95° 8' E. long., by nine principal mouths. The only ones used by sea-going ships are the Bassein and Rangoon mouths. The area of the catchment basin of the Irawadi is 158,000 square miles ; its total length from its known source to the sea is about 900 miles, the last 240 of which are in British territory, As far down as Akouk-toung in Henzada district its bed is rocky, but below this sandy and muddy. It is full of islands and sandbanks; its waters are extremely muddy, and the mud is 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 for 1877 was 466,120,288,940 metre tons of 37 cubic feet. The river is navigable at all seasons by steamers of light draught as high as the first defile, and during the dry season for steamers drawing 6 feet as far as the frontier. The chief tributaries of the Irawadi in British territory are the Tha-litnn (or Theng-dim), the Tha-de, and Thai-lai-dau from the west ; and the Bhwotlay, and Na-weng from the east. Below Akouk-toung on the west and Prome on the east the Irawadi receives no tributaries of any importance..

The broad channel of the Irawadi has always been the sole means of communication between the interior and the seaboard. From time immemorial the precious stones, minerals, &c., of Upper Burmah, Siam, and the Chinese frontier provinces have been brought down by this route. At the present day the great bulk of the trade is in the hands of the " Irrawaddy Flotilla Company," an important English carrying firm ; but native boats still maintain a strenuous competition. The flotilla of the company consists of about sixty vessels, including both steamers and flats. They employ about 1770 hands, European and native, and distribute in wages upwards of £50,000 a year. Their headquarters are at Rangoon, whence steamers run twice a week to Bassein, and also to Mandalay.

The latter service is continued twice a month to Bhamo, about 1000 miles from the sea. The principal articles carried up stream are Manchester piece goods, rice, salt, hardware, and silk. The articles carried down stream are raw cotton, cutch, iudia-rubber, jade, spices, precious stones, timber, earth-oil, and dry crops, such as wheat and pease. The value of the trade either way is roughly estimated at about 11 millions sterling. The total number of native boats on the Irawadi is returned at about 8000. They carry a large proportion of the heavy articles of commerce, especially cutch and earth-oil.