Posts
Barind Tract largest Pleistocene physiographic unit of the bengal basin, covering an area of about 7,770 sq km. It has long been recognised as a unit of old alluvium, which differs from the surrounding floodplains. In Bangla, it is spelled and pronounced as Varendra Bhumi. Geographically this unit lies roughly between latitudes 240200N and 250350N and longitudes 880200E and 890300E. This physiographic unit is bounded by the karatoya to the east, the mahananda to the west, and the northern bank of the ganges to the South. A lower fault scarp marks the eastern edge of the Barind Tract, and the little jamuna, atrai and Lower Punarbhaba rivers occupy fault troughs. The western part of this unit has been tilted up; parts of the western edge are more than 15m higher than the rest of the tract and the adjoining Mahananda floodplain. The southern part of the main eastern block of the Barind Tract is tilted down towards the southwest and passes under lower Atrai basin sediments in the south. The Barind Tract covers most parts of the greater dinajpur, rangpur, pabna, rajshahi, bogra, joypurhat and naogaon districts of Rajshahi division.
The Barind Tract lies in the monsoon region of the summer dominant hemisphere. The tropic of cancer lies south of this region. The climate of the area is generally warm and humid. Based on rainfall, humidity, temperature and wind pressure the weather condition is classified into four types, such as, (a) pre-monsoon, (b) monsoon, (c) post-monsoon and (d) winter. Rainfall is comparatively little in this region, the average being about 1,971 mm. It mainly occurs during the monsoon. Rainfall varies from place to place as well as year to year. For instance, the rainfall recorded in 1981 was about 1,738 mm, but in 1992 it was about 798 mm only. This region has already been designated as drought prone. Its average temperature ranges from 350C to 250C in the hottest season and 90C to 150C in the coolest season. Generally this region is rather hot and is considered semi-arid. In summer, some of the hottest days experience a temperature of about 450C or even more in Rajshahi area, particularly in lalpur upazila. In winter it falls to about 50C in some places of Dinajpur and Rangpur districts. So this older alluvium region experiences extremes that are clearly in contrast to the climatic condition of the rest of the country.
Physiographically this region is divided into three units. These are Recent Alluvial Fan, Barind Pleistocene, and Recent Floodplain. These morphologic units are separated by long, narrow bands of recent alluvium. The floodplain of the Mahananda flanks the west side while the Karatoya delineates the eastern margin. The punarbhaba, Atrai and Old Jamuna with headwaters in the foothills of the himalayas have cut across the Pleistocene and their floodplains separate the units. These and numerous other streams are responsible for the development of a broad Piedmont alluvial plain, which delineates the northern flank of the Tract. The Tista alluvial fan is located to the north of the area. This fan surface of the Himalayan foothills has a slope of approximately 0.43m/km and it overlaps the Barind, which has essentially a flat or somewhat domed surface. South of the Barind Tract are the Recent Floodplains, with a southerly slope of about 0.06m/km.
In the Barind region, three distinct channel patterns are observed. In the north there is a great number of small braided streams, which have built a broad piedmont alluvial plain along the foothills of the Himalayas. The major rivers of these alluvial plains are the Atrai and the Punarbhaba, with entrenched valleys. On the Pleistocene unit, there are numerous small entrenched, tightly meandering streams, which have developed an overall dendritic pattern and flow into the major north-south rivers of the Barind unit. There are some major valleys that separate the Pleistocene unit into some north-south elongated units. These valleys are followed by some major rivers, such as the Mahananda in the west, the Karatoya in the east, the Atrai and the Punarbhaba in between. The largest unit is bounded by the river Punarbhaba and the Atrai. Another large unit is bounded by the Karatoya and the Little Jamuna. Many small channels, mostly of dendritic pattern, flow through the individual units.
However, it is very interesting that the course of the Karatoya is controlled by a southeast trending fault. In the late 17th century, the major stream of this region was tista which, near Jalpaiguri, branched and followed the course of the Depa-Punarbhaba to the west, the Atrai due south and the Little Jamuna to the southeast. All of these rivers discharged into the Ganges. Of these rivers, the Atrai seems to have been the major channel in the late 17th century with the Punarbhaba as the second most important. But now the Tista, Karatoya and Atrai flow into the jamuna (brahmaputra). The river courses, particularly of the Tista, changed suddenly in 1787 during a major flood. This change could have been accompanied by renewed uplift and tilting of the Barind surface. At the present time, the Punarbhaba, Atrai and Little Jamuna still carry some flood flow but they generally can be considered as antecedent streams carrying mainly local runoff water of the uplifted Barind area.