Manas River - Geography

Geography

The Manas River valley formed by the Manas river system encompasses territory in Bhutan (eastern Bhutan) and India with a total drainage area of 41,350 square kilometres (15,970 sq mi). It is called the Drangme Chhu, flows in southwesterly direction from Arunachal Pradesh in India. It has three major branches: the Drangme Chhu, Mangde Chhu, and Bumthang Chhu that cover most of eastern Bhutan, with the Tongsa and Bumthang valleys also forming part of its catchment. The area drained in Bhutan territory is 18,300 km2 and is bound by the geographical coordinates 26°13′01″N 90°37′59″E / 26.217°N 90.633°E / 26.217; 90.633. A part of the main stem of the river rises in the southern Tibet before entering into India at Bumla pass at the northwestern corner of Arunachal Pradesh.

The river flows through Bhutan in a south-west direction between two ranges of the Lower Himalayas in V-shaped gorges and enters into Assam in India in to the south-central foot hills of the Himalayas. The valley opens up in the foot hills; marked by the formation of swamps and marshes in the plains. The upper catchment is snow bound while the middle and lower catchment are thickly forested.

The river system as a whole in Bhutan constitutes a length of 3,200 kilometres (2,000 mi), the main stem of the river is the Manas or Gongri river, which originates in the West Kameng District of Arunachal Pradesh in India and after flowing in a south westerly direction (the rivers in Bhutan generally flow from northwest to southwest) enters Bhutan near Tashigang. At Tashigong, it is joined by the Kulong Chu, which rises in the northern Himalaya snow ranges of Bhutan. At Tashigong, the bed width of the river is about 550 metres (1,800 ft) and river bed elevation is 606 metres (1,988 ft). The river Kulong Chu is formed by two rivers namely, the Tongsa (Mangde) Chu that rises in northern Bhutan near Kula Kangri Peak where the elevation is 1,666 metres (5,466 ft) and the Bumthang River, also called Murchangphy Chu; the combined stream joins the Manas river.

The Lhobrak, or Kuri Chhu, is the main central tributary of the Manas. It is the only river that rises north of the Great Himalayas and it joins the Manas in southern Bhutan; further downstream of the combined stream joining at the Tongsa Chu. Here, the river bed level is 121 metres (397 ft). After flowing in a generally south-westerly direction for about 29 km in Bhutan, the Aie river enters In India in to the Goalpara district of Assam at the village of Agrong. From here, it follows a meandering course for about 75 kilometres (47 mi) and outfalls into the Brahmaputra near Jogigopa. Aie River, which rises in the Black mountains at an altitude of about 4,915 metres (16,125 ft) near the village of Bangpari, is about 110 kilometres (68 mi) in length. The total length of the Manas measured along its longest tributary the Kur is 376 kilometres (234 mi), out of which about 104 kilometres (65 mi) lies in India.

The river valley in the foothills is surrounded by small meadows located among thickly deciduous forested foothills with many rivulets, streams and natural drainage channels related to the river system. In the lower reaches of the river, there are many smooth sandy stretches populated with trees.

The foot hills in Bhutan and India known as Terai and the Duars (A Sanskrit word meaning "passes" or "gates"), which encompass 15–30 kilometres (9.3–19 mi) stretch of the foot hills and which are very fertile. Each Duar (with elevation varying from 100 metres (330 ft) to near sea level as they join the Brahmaputra river) is named after a stream or hemmed between two streams. Some part of the Duars in Bhutan was under British control. The fertile lands have been developed into tea estates and paddy fields.