Brahmaputra-Jamuna River System

Brahmaputra-Jamuna River System is one of the three major river systems of Bangladesh. Brahmaputra-Jamuna and old brahmaputra, with their main tributary tista, and a good number of small tributaries and distributaries constitute the largest floodplain of Bangladesh. Excepting for a small portion in the north, the entire floodplain lies within the pleistocene terrace regions. The floodplain and the Pleistocene terraces almost completely cover two of the six administrative divisions of the country, rajshahi and dhaka.

The brahmaputra enters Bangladesh east of Bhabanipur (India) and northeast of kurigram district. It first flows south and then turns southeast and travels through the madhupur tract to meet the meghna near Bhairab bazar. The river seems to be much younger than the ganges. Along with the Meghna, it is making a major contribution to the building up of the delta. Among the major rivers, Brahmaputra-Jamuna is the most energetic and has the highest stream power. This river, despite having a smaller drainage basin than the Ganges, has a steeper slope, a larger discharge, and higher sediment transport and higher sediment content.

The Brahmaputra-Jamuna drains the northern and eastern slopes of the himalayas, and has a catchment area of 5,83,000 sq km. Its tributaries and distributaries include two right-bank tributaries and two left-bank distributaries. The right-bank tributaries are the Tista and Atrai-Gur rivers and the two left-bank distributaries are the abandoned course of the Brahmaputra now known as the Old Brahmaputra and the dhaleshwari. In the true sense of the term, Old Brahmaputra and Dhaleshwari are the loop channels carrying a small part of the Brahmaputra-Jamuna flow to the Upper Meghna river.

In the beginning of the 19th century (1830), the Brahmaputra began to flow below Bahadurabad along the jamuna due mainly to recent faulting. This faulting is a minor adjustment related to the last orogeny and is still active. The Jamuna meets the Ganges at goalandaghat, and together down the confluence takes the name of the padma and joins the Meghna at chandpur. The total length of the river from its source in southwestern Tibet to the mouth in the bay of bengal is about 2,850 km (including Padma and Meghna up to the mouth). Within Bangladesh territory, Brahmaputra-Jamuna is 276 km long, of which Brahmaputra is only 69 km.

The Tista is, by far, the largest tributary of the Brahmaputra-Jamuna system and issues from the western side above the bifurcation point of the Old Brahmaputra and the Jamuna. Up to the close of the 18th century, it flowed into the Ganges but after the destructive floods of 1787, in which a large part of rangpur was laid waste, it suddenly turned east and joined the Brahmaputra just south of Chilmari. Since then, it has kept more or less to this channel. The frequent changes of its course have left a legacy in the shape of numerous stagnant cut-off channels west of Rangpur, most of which are known as Mora (dead) or Budi (old) Tista. The present channel of the Tista makes its entry into Bangladesh north of dimla and travels 177 km before it meets the Brahmaputra, and varies from 300m to 550m in width. The Tista Barrage project, a 615m long barrage, 2,470m long closure dam, flood embankment of about 80 km was completed in 1997-98.

West of Tista are the ghaghat, Dhaljan, Jamuneshwari and Sarbamangala. The Ghaghat is a distributary of the Tista. It flows past Rangpur and Gaibandha towns and joins the Brahmaputra a few kilometres north of Fulchhari Ghat. A distributary of the karatoya known as the bangali flows south from Gaibandha. The Ghaghat is for the most part a sluggish stream, choked with weeds. Its flow varies from 50 to 2,500 cusec. The Bangali has a larger flow, varying from 400 to 21,000 cusec.

North of the Tista, two more small tributaries, the dharla and the dudhkumar, meet the Brahmaputra from the west. Both streams originate from the foothills of the Himalayas. The Dharala is a swift river in the rainy season, but a braided clear stream in winter. In its upper course, it is known as the jaldhaka or Singimari. In Rangpur district, it has a small tributary, the Nilkumar, formerly a large river. The Dharala has low and shelving banks and is particularly liable to changing its course. In 1947 it completely diluviated the old site of Kurigram town. The Dudhkumar, known in its upper course as the Sankosh, is a small river. It flows southeast and falls into the Brahmaputra. The major part of the river lies within India.

The Old Brahmaputra takes off from the left bank of the Brahmaputra or the Jamuna to the north of Bahadurabad. Flowing more or less southeast it passes by [[Jamalpur District|jamalpur]] and mymensingh towns and falls into the Meghna at Bhairab Bazaar. The river has no tributary coming from the northeast. Several small distributaries, viz, bangshi, banar, Sirkali and Satia, however, flow out from it. The Bangshi runs more or less south to join the turag and together fall into the buriganga near Dhaka. The Banar, Sirkali and Satia converge to flow together as the shitalakshya and meet the Dhaleshwari close to munshiganj.

The Karatoya is the longest and largest tributary of the Jamuna and originates in a marsh in Baikunthapur in Jalpaiguri district of India. It receives a number of tributaries on the Indian side. It was formerly the main channel of the Tista and was perhaps a distributary of the Brahmaputra. The Karatoya changes its name to atrai from khansama upazila and crosses the barind tract lengthwise all the way to fall into the baral that connects the Ganges with the Jamuna at bera upazila of pabna district.

The part of the Karatoya that passes through Rangpur carries very little water and falls into the Bangali river. The Bogra-Karatoya rises from mithapukur, flows past bogra town and meets the Bangali that links the Rangpur-Karatoya with the Bogra-Karatoya. The Dinajpur-Karatoya was connected with the Rangpur-Karatoya north of Khansama, but at present very little water passes down that channel. The Jamuneshwari-Karatoya flows in slight meanders south-southeast to gobindaganj upazila where the main stream turns east through the Katakhali and falls into the Bangali. The portion of the former river that runs through shibganj upazila remains dry most of the year and effectively separates the Rangpur-Karatoya from the Bogra-Karatoya. The latter flows past Bogra town and runs south, till it joins the Bangali to make the Phuljhor river, which falls into hurasagar. The discharge of the Bogra-Karatoya has declined rapidly since the construction of the Brahmaputra Right Bank Embankment. The fourth part, the Pabna-Karatoya, is a moribund riverbed near Handial. Various other channels are also pointed out as those of the old Karatoya.

West of the Rangpur-Karatoya and the Bogra-Karatoya is the Jamuna, here called the Little Jamuna, to distinguish it from the main Jamuna. The Little Jamuna originates in Jalpaiguri, flows south through eastern dinajpur and western Bogra districts, and falls into the Atrai in naogaon district. The Tulshiganga and Chhiri Nadi, both of which drain the eastern Barind, are its principal tributaries.

The Dhaleshwari, the largest distributary of Jamuna, takes off from the Parbati to join the Shitalakshya which in turn meets the Meghna at Munshiganj. The Dhaleshwari soon bifurcates and its southern arm flows south of manikganj and joins the main stream that flows north of Manikganj 48 km southeast. This southern arm, the Kaliganga, now carries more water than the Dhaleshwari itself. North of their confluence the Dhaleshwari again bifurcates, the southern arm retaining the name, while the northern is called the Buriganga. It flows past Dhaka and joins the Dhaleshwari at Fatulla. The Shitalakshya joins the Dhaleshwari at narayanganj and the joint flow meets the Meghna at Shaitnol. [Masud Hasan Chowdhury and Md Mahbub Murshed]

Bibliography Abdul Wazed, Bangladesher Nadimala (Rivers of Bangladesh, in Bangla), Dhaka, 1991; FH Khan, Geology of Bangladesh, University Press Limited, Dhaka, 1991; Haroun Er Rashid, Geography of Bangladesh, University Press Limited, Dhaka, 1991; Hugh Brammer, The Geography of the Soils of Bangladesh, University Press Limited, Dhaka, 1996; Bangladesh Bureau of Statistics (BBS), 1998 Statistical Year Book of Bangladesh, BBS, Dhaka, 1999.