Jamuna River The Brahmaputra-Jamuna is the second largest river in Bangladesh and one of the largest rivers in the world, flowing through Tibet, China, India and Bangladesh. Actually Jamuna is the downstream course of the brahmaputra which took place after the earthquake and catastrophic flood between 1782-1787. Presently the Brahmaputra continues southeast from Bahadurabad (Dewanganj upazila of Jamalpur district) as the old brahmaputra and the river between Bahadurabad and Aricha is the Jamuna, not Brahmaputra. The Hydrology Directorate of the bangladesh water development board (BWDB) refers to the whole stretch as the Brahmaputra-Jamuna.
It originates in the Chemayung-Dung glacier, approximately at 31'30'N and 82'0'E, some 145 km from Parkha, an important trade centre between lake Manassarowar and Mount Kailas. The Brahmaputra is known as the Dihang in Assam Himalayas before it comes into the Great Plains of Bengal. It enters Bangladesh through Kurigram district (at the border of Kurigram Sadar and Ulipur upazilas). The total length of the Tsangpo-Brahmaputra-Jamuna river up to its confluence with the Ganges is about 2,700 km. Within Bangladesh territory, Brahmaputra-Jamuna is 276 km long, of which Jamuna is 205 km.
The width of the river varies from 3 km to 20 km but the average width is about 10 km. In the rainy season the river is nowhere less than five kilometres broad. The river is in fact a multi-channel braided pattern. Channels of many different sizes, from hundreds of meters to kilometres wide, and of different patterns including braiding, meandering and anastomosing pattern in the country. It is, through most of its course within Bangladesh, studded with bars (chars) many of which are submerged during the rainy season and makes a single water channel. Thus, by breadth alone, this river qualifies as one of the largest in the world. The width/depth ratios for individual channels of the Brahmaputra vary from 50:1 to 500:1. The gradient of the river in Bangladesh is 0.000077, decreasing to 0.00005 near the confluence with the Ganges.
The catchment of the mighty Brahmaputra-Jamuna river is about 5,83,000 sq km of which 293,000 sq km are in Tibet, 241,000 sq km in India and only 47,000 sq km within Bangladesh. The drainage area above Bahadurabad is 536,000 sq km. This is the widest river system in the country flowing north-south. There are gauges and discharges records for this river at Bahadurabad, where amount represents the flow entering Bangladesh plus those of the dudhkumar, the dharla and the tista, and minus those of the Old Brahmaputra and bangali. The discharge during the rainy season is enormous, averaging 40,000 cumec, by which measure it ranks with the Amazon, Congo, La Plata, Yangtse, Mississippi and meghna as one of the seven largest rivers. The highest recorded flood was 98,600 cumec in August 1988.
Average annual flow at Bahadurabad is estimated to be 501 million acre-feet. August has always been the month when widespread flooding has been most likely. Floods from May to July are usually due to the Brahmaputra-Jamuna and Meghna. From August to October due to the combined flows of those river and the Ganges. As a rule, the flow of the Brahmaputra-Jamuna is more erratic than that of the Ganges. The gradient of the Jamuna averages 1:11,850 which is slightly more than that of the Ganges. The Jamuna discharges a large volume of water and at the same time brings in huge amounts of sediments. During the rainy season it brings down something like 1.2 million tons of sediment daily, and the annual silt runoff at Bahadurabad is estimated at 735 million tons.
It has four major tributaries: the Dudhkumar, the Dharla, the Tista and the Karatoya-Atrai system. The first three rivers are flashy in nature, rising from the steep catchment on the southern side of the Himalayas between darjeeling in India, and Bhutan. Of all the distributaries, the Old Brahmaputra is the longest and was actually the course of the present Brahmaputra some 200 years ago.
Recently a 4.8-km long bridge has been constructed over the Jamuna for linking the eastern and western parts of Bangladesh. The eastern edge of bangabandhu jamuna multipurpose bridge lies in Bhuapur upazila of Tangail district and the western end in Sirajganj Sadar upazila of Sirajganj district. Apart from quick movement of goods and passenger traffic by road and rail, it has facilitated transmission of electricity and natural gas, and integration of telecommunication links. The bridge was opened for traffic on 23 June 1998. A considerable volume of river training work was done to keep the river within the bridge instead of a flood-width of 14 km at the bridge site.
The Jamuna is braided in nature. Within the braided belt of the Jamuna, there are lots of chars of different sizes. An assessment of the 1992 dry season Landsat image shows that the Jamuna contained a total of 56 large island chars, each longer than 3.5 km. There were an additional number of 226 small island chars, varying in length between 0.35 and 3.5 km. This includes sandy areas as well as vegetated chars. In the Jamuna, the period between 1973 and 2000, chars have consistently appeared in the reaches opposite to the Old Brahmaputra offtakes, north and east of Sirajganj and in the southernmost reach above the confluence with the Ganges. In entire Bangladesh during 1981 to 1993, a total of about 7,29,000 people were displaced by riverbank erosion. More than half of the displacement was along the Jamuna. [Masud Hasan Chowdhury]
See map in brahmaputra-jamuna river system.