THE IRRAWADDY DELTA
Delta ID # 16
Irrawaddy River Delta, Myanmar, Asia
LOCATION LAT. 15°54’N, LONG. 94°53’E
LANDMASS DRAINED MYANMAR, ASIA.
BASIN OF DEPOSITION GULF OF MARTABAN (INDIA OCEAN)
CLIMATE TROPICAL RAINFOREST (Am)
AIR TEMP RANGE 20°C TO 30°C
TIDAL AMPLITUDE 5.5 M
MEAN WAVE HEIGHT LOW
DISCHARGE WATER 36000 M3/S, SEDIMENT 265X106 TONS/YR
DRAINAGE BASIN AREA 3.418X105 KM2
ID 7133049000006350, PATH 133 ROW 49
IMAGE ACQUIRED APRIL 4, 2000
Contributed by Professor James Coleman, LSU. From: Coleman and Huh, 2004.
The Irrawaddy River is located in the country of Myanmar (formerly known as Burma) and is formed in the north by the confluence of the Mali and Nmai rivers. The drainage basin is located in the northern part of Myanmar and has an area of 404,100 sq. km. The river originates in the north-south trending Tebasserun-Shon fold belt. From its headwaters, the river flows generally south for 1,295 km.. Near the town of Henzada it branches into several mouths, forming an extensive delta, and empties into the Andaman Sea. The average elevation of the drainage basin is 898 m and relief in the basin is quite high, with an average relief of 353 meters. Maximum elevation is 4,433 m and minimum elevation is 30 m. Tributaries are quite dense in the drainage basin and stream density is 0.21 km stream length per 500 sq km (Figure 52). The basin is located in a tropical climate and average annual rainfall is quite high, some 1,684 mm per year, with a maximum of 3,529 and a minimum of 665 mm. The rainy months are June through August and coincide with the seasonal monsoons.
The alluvial valley is well defined and the upper channel of the river is braided in nature. Further south, the river displays meandering tendencies and has numerous small tributaries entering the main river channel. The most active region of the delta is located on the western edge of the delta plain (Figure 53 and Plate 15). The delta comprises an area of 20,571 sq. km. and average discharge is approximately 12,564 cu m/sec, with a peak discharge of 36,000 cu m/sec. The delta is located in a tropical rainforest and sediment delivery is extremely high, the river delivering 265 x 106 tons per year to the coast. Tidal range is extremely high, some 2.71 meters in amplitude resulting in an extremely dense network of tidal channels (Figure 53). Mangrove forest cover is dense and dominates the vegetation in the lower delta. Average offshore slope is quite low ((0.02 degrees) and thus wave action along the front of the delta is moderate, and only small beaches are present along the fringes of the distributaries. The RMS wave height is 1.42 m and wave power was calculated to be 0.193 x 107 ergs/sec/meter of coast. A well-developed series of beach ridges flank the southeastern edge of the delta and represent reworking of deltaic deposits by the dominant southeastern swell. Much of the delta plain is cultivated in rice fields and the delta is one of major rice-growing regions of the world. The light pink areas on the image represent agricultural land and make up a large portion of the delta surface. The active delta region is approximately three times the size of the inactive delta region in the central and eastern part of the delta plain. There are approximately 10 active river mouths and distributary density is 0.17 km stream length per 500 sq km, quite low for a delta of this size. The shoreline of the delta is quite long compared to the width of the delta, shoreline length being about 1.7 times the delta width. Based on analysis of bathymetric charts, the subaqueous delta is quite large, probably resulting from the heavy sediment load delivered to the coast. The ration of the area of the subaerial/subaqueous delta is 0.09.