Old Brahmaputra River a river that originates from the left bank of the brahmaputra to the north of Bahadurabad. Flowing more or less to the southeast it passes by Jamalpur and Mymensingh towns and falls into the meghna at Bhairab Bazar. River shifting has been a characteristic feature of the bengal basin, affecting small sections or even the entire river. The most dramatic was the shifting of the courses of the tista, Brahmaputra and lower ganges river channels as evident from maps prepared hundreds of years ago. James rennell produced the most accurate map back in 1760. According to this map, the Brahmaputra at that time was flowing a course east of the madhupur tract, presently known as the Old Brahmaputra. The lower part of the Brahmaputra channel between Dhaka and Mymensingh subsequently was silted up diverting the Old Brahmaputra flow to shitalakshya river and then to the dhaleshwari and Meghna rivers southeast of Dhaka.

The Old Brahmaputra acquired its present course between the Madhupur Tract and the barind tract in the year 1787. In that year the river shifted its course and was named the jamuna. This shifting followed a major flood in the same year. The severe earthquake reported from Mymensingh region in 1782 may also have contributed to this shift. The shifting of the Old Brahmaputra, along with other major shifting rivers, is now considered the effect of neotectonic activities in recent times. The shifting process seems to have taken place over a period of 30 years. The Old Brahmaputra floodplain stretching from the southwestern corner of the Garo Hills along the eastern rim of the Madhupur Tract down to the Meghna river exhibits a gentle morphology composed of broad ridges and depressions. soils of this geomorphic unit are more oxidised and darker than soils developed in the last 200 years on the Young Brahmaputra Floodplain. groundwater in the unit has a characteristic chemical composition. [Kazi Matinuddin Ahmed]

See map in brahmaputra-jamuna river system.