Irrawaddy River
The Irrawaddy River is the principal river of Myanmar, running through the centre of the country. Myanmar's most important commercial waterway, it is about 1,350 miles long. Originating from the confluence of the N'mai and Mali rivers, it flows from north to south before emptying through the Irrawaddy Delta in the Ayeyarwady Region into the Andaman Sea. Its drainage basin of about covers 61% of the land area of Burma, and contains five of its largest cities.
As early as the sixth century, the river was used for trade and transport, and an extensive network of irrigation canals was developed to support agriculture. The river is still of great importance as the largest commercial waterway of Myanmar. It also provides important ecosystem services to different communities and economic sectors, including agriculture, fisheries, and tourism.
In 2007, Myanmar's military dictatorship signed an agreement for the construction of seven hydroelectric dams, yielding a total of 13,360 MW, on the N'mai and Mali Rivers, including the 3600 MW Myitsone Dam at the confluence of both rivers. Environmental organisations have raised concerns about the project's ecological impact on the river's biodiverse ecosystems. Animals potentially impacted include the endangered Irrawaddy dolphin and the critically endangered Ganges shark.
Names
The name "Irrawaddy" is derived from Pali. Irāvatī or Airāvatī is the name of the elephant mount of Sakka and Indra in Hinduism. Saka is an important deva in Buddhism and elephants were often a symbol for water and were used as the name for several other rivers, such as the Achiravati. It can also be based on Iravati, who birthed the mythological elephant. The Irrawaddy gives its name to the Irrawaddy dolphin, which is found in the lower reaches of the river and known to help fishers who practice cast-net fishing. Though called the Irrawaddy dolphin, it has been also found in the Bay of Bengal and the Indian Ocean.During the Age of Discovery, the Irrawaddy was also known to European explorers as the Pegu as the main river of the Hanthawaddy kingdom, itself known as Pegu after its capital, now romanized as Bago. The modern Pegu or Bago River is a separate river, tributary to the Yangon.
After Rudyard Kipling's poem, the river is sometimes referred to as 'The Road to Mandalay'.
Physiography
The Irrawaddy River bisects Myanmar from north to south and empties through the nine-armed Irrawaddy Delta into the Andaman Sea.Defiles
Between Myitkyina and Mandalay, the Irrawaddy flows through three well-marked defiles:- About downstream from Myitkyinā is the first defile.
- Below Bhamo the river makes a sharp westward swing, leaving the Bhamo alluvial basin to cut through the limestone rocks of the second defile. This defile is about wide at its narrowest and is flanked by vertical cliffs about high.
- About north of Mandalay, at Mogok, the river enters the third defile. Between Katha and Mandalay, the course of the river is remarkably straight, flowing almost due south, except near Kabwet, where a sheet of lava has caused the river to bend sharply westward.
Leaving this plateau at Kyaukmyaung, the river follows a broad, open course through the central Dry Zone – the Bamar people's ancient cultural heartland – where large areas consist of alluvial flats. From Mandalay, the river makes an abrupt westward turn before curving southwest to unite with the Chindwin River, after which it continues in a southwestern direction. It is probable that the upper Irrawaddy originally flowed south from Mandalay, discharging its water through the present Sittaung River to the Gulf of Martaban, and that its present westward course is geologically recent. Below its confluence with the Chindwin, the Irrawaddy continues to meander through the petroleum producing city of Yenangyaung, below which it flows generally southward. In its lower course, between Minbu and Pyay, it flows through a narrow valley between forest-covered mountain ranges—the ridge of the Arakan Mountains to the west and that of the Pegu Yoma Mountains to the east.
The Irrawaddy Delta
The delta of the Irrawaddy begins about above Hinthada and about from its curved base, which faces the Andaman Sea. The westernmost distributary of the delta is the Pathein River, while the easternmost stream is the Yangon River, on the left bank of which stands Myanmar's former capital city, Yangon. Because the Yangon River is only a minor channel, the flow of water is insufficient to prevent Yangon Harbour from silting up, and dredging is necessary. The relief of the delta's landscape is low but not flat. The soils consist of fine silt, which is replenished continuously by fertile alluvium carried downstream by the river. As a result of heavy rainfall varying from a year in the delta, and the motion and sediment load of the river, the delta surface extends into the Andaman Sea at a rate of about per year.Hydrography
Due to monsoonal rains, which occur between mid-May and mid-October, the volume of the Irrawaddy and its tributaries varies greatly throughout the year. In summer, the melting of the snow and glaciers in Northern Burma add to the volume. The average discharge near the head of the delta is between a high of and a low of per second. The discharge can be as high as 40,393 cubic meter per second in the rainy season. Over a year, the discharge averages. Further North, at Sagaing, the shows a 38% decrease in discharge compared to where the river enters the delta. it also silted up around 278 tons of sand every year.Variation between high and low water levels is also great. At Mandalay and Prome, a range of has been measured between low-water level and flood level respectively. Because of the monsoonal character of the rain, the highest point is recorded in August, the lowest in February.
This variation in water level makes it necessary for ports along the river to have separate landing ports for low- and high-water. Still, low water levels have caused problems for ports along the river, as in the Bamaw–Mandalay–Pyay sectors, the shallowest point is as shallow as.
Within the basin, the average population density is 79 people/km2. For these people, the river supply amounts to 18,614 m3 per person per year.
Sediments to the Sea
Collectively, the modern Ayeyarwady and Thanlwin There is little modern sediment accumulating on the shelf immediately off the Ayeyarwady River mouths. In contrast, a major mud wedge with a distal depocenter, up to 60 m in thickness, has been deposited seaward in the Gulf of Martaban, extending to ~130 m water depth into the Martaban Depression. Further, 2) There is no evidence showing that modern sediment has accumulated or is transported into the Martaban Canyon; 3) There is a mud drape/blanket wrapping around the narrow western Myanmar Shelf in the eastern Bay of Bengal. The thickness of the mud deposit is up to 20 m nearshore and gradually thins to the slope at −300 m water depth, and likely escapes into the deep Andaman Trench; 4) The estimated total amount of Holocene sediments deposited offshore is 1.290 trillion tons. If we assume this has mainly accumulated since the middle Holocene highstand Unlike other large river systems in Asia, such as the Yangtze and Mekong, this study indicates a bi-directional transport and depositional pattern controlled by the local currents that are influenced by tides, and seasonally varying monsoons winds and waves.Ecology
No complete and precise list of all the fish in the Irrawaddy river basin currently exists, but in 1996 it was estimated that there are about 200 species. In 2008, it was estimated that the Irrawaddy ecoregion is home to 119–195 species of fish found nowhere else in the world. Several new species of fish have been described from the Irrawaddy river basin in recent years, and it is likely that undescribed species remain.Among the most well-known species in the river is the Irrawaddy dolphin, a euryhaline species of oceanic dolphin with a high and rounded forehead, lacking a beak. It is found in discontinuous sub-populations near sea coasts and in estuaries and rivers in parts of the Bay of Bengal and South-East Asia.
Along the north–south course of the Irrawaddy River, a number of notably different ecoregions can be distinguished.
Northern Mountains
The streams of the Nmai and Mali that form the Irrawaddy originate in high and remote mountains near the border with Tibet. This part of Myanmar, which extends north from Myitkyina and the Irrawaddy confluence, lies entirely outside the tropics. Rain falls at all seasons of the year, but mostly in the summer. The valleys and lower hill ranges are covered with tropical and subtropical evergreen rainforest instead of monsoon forest. This region is characterised by subtropical and temperate forests of oak and pine are found at elevations above. This evergreen forest passes into sub-tropical pine forest at about feet. Above, are forests of rhododendrons, and that in turn into evergreen conifer forest above feet.The Central Basin and Lowlands
The Irrawaddy river basin covers an approximate area of 255. The Central Basin consists of the valley of the middle Irrawaddy and lower Chindwin. It lies within the 'dry zone' and consists almost entirely of plains covered with the teak-dominated Irrawaddy moist deciduous forests ecoregion, which surrounds dry forest patches in drier areas. The central basin receives little rain although it does flood quickly during the July–October storms. The one meteorological factor which does not vary greatly, and which is the most important for plant life, is atmospheric humidity. This is always high, except in the winter in certain localities. Humidity usually does not fall below 75% and is 90% or more for long periods during the summer. Another feature is the prevalent southerly summer winds which erode the soil of the basin.The natural habitats of this central zone have been much altered for farming and there are few protected areas.