Shifting Courses and River Capturing of Himalayan Drainage

The river capturing and shifting courses are typical phenomena very common in the Himalayan drainage area. River capturing is mainly caused by the headward erosion of the river (which joins and captures the water of its neighbouring stream) and is very common in hilly regions like the Himalayas.

Similarly due to level topography and gentle slope in the Great Plains rivers adopt meadering courses, swing in their valleys and often change their course (during floods due to increased quantity of water the streams try to straighten in their courses).

Earth movements do have their role in affecting these processes. Following is a brief account of some such shifting courses and river capturing observed in the Great Plains during the recent past.

Ancient Saraswati river, which provided abode for early Aryan settlers, presents a typical example of shifting courses and river capturing. Descending from the Himalayan ranges its intial course was passing near Churu (about 2000 to 3000 BC) and the Luni River was its tributary. It gradually shifted towards west till it joined the Satluj (a tributary of the Indus River) near Ahmadpur (Bimal Ghose et al, 1979).

Later on the water of its upper course was captured by a tributary of the Ganga River as a result of which its lower course became dry. This gave birth to the Yamuna River which is today an important tributary of the Ganga system.

Even today the dry valley of the Saraswati River is found in Rajasthan area in the form of Ghagghar valley. Similar shifting has also been observed in the rivers of the Punjab during the historical past. The records of the third century B.C. show that the Indus flowed more than 130 km east of its present course, through the now practically dry beds of a deserted channel, to the Rann of Kachchh which was then a gulf of the Arabian Sea. Later on it gradually shifted towards the west and occupied the present position. During the reign of Akbar the Great the Chenab and Jhelum joined the Indus near Ouch but their present conflu­ence lies near Mithankot, about 100 km downstream of the old place. Similarly Multan was formerly located along the Ravi River but today it is situated 60 km south of its confluence with the Chenab. About 250 years ago the Beas River changed its old course, whose traces are still found between

Montgomery and Multan, and joined the Satluj river near Sultanpur. In the early part of the Christian era the Satluj had more easterly course and independ­ently discharged its water into the Arabian Sea.

There are numerous examples of shifting courses in the rivers of Bengal and Assam. The city of Gaur located along the bank of the Ganga flour­ished as capital of the Pala dynasty of kings for 700 years. Suddenly the Ganga took a westerly shift in its course and the city was deserted.

In the Bengal delta there are evidences that the Ganga has shifted its course towards the east. Previously its main current flowed through the Hugli River and met the sea near Sagar Island. Now it goes to Bangladesh (called Padma) and joins the Jumna and Meghna before merging into the Bay of Bengal.

In the upper and middle Ganga plain the river appears to have shifted its course southward as is evidenced by the occur­rence of numerous ox bow lakes north of its left bank. The Tista river of North Bengal has also changed its courses frequently.

Initially it used to meet the Ganga River near Jaffar flowing through the Purnabhaba river of Barind region. During the floods of 1787 it suddenly adopted a new course and joined the Brahmaputra.

About 250 years ago the Brahmaputra flow­ing through Mymensingh was discharging its waters into the Meghna River. In due course of time it straightened its course and joined the Ganga (Padma) river forming a new stream called Jumna.

A feeble channel of the Brahmaputra is still flowing along the same old course and retains the old name. This change in the river course was associated with 30 m rise in Madhupur forest area between 1720-1830 A.D. Even the entry of the Brahmaputra to the plains of Assam is also the outcome of the process of river capturing.

According to the geologists during early days the Tsangpo river of Tibet taking an easterly course used to join Irrawaddy River through the Chindwin which was then a large river transporting huge quantity of water. Later on a small river flow­ing along the southern slopes of the Himalayas through its headward erosion captured the water of the Tsangpo River and, thus, helped in the evolution of the stream of Brahmaputra.

Similarly Kapili, a tributary of the Brahmaputra, has captured the waters of the Meghna river of East Bengal. In those days the Meghna originated from the Barail Ranges (between Meghalaya and Manipur) and flowing southward it used to empty its waters in the eastern part of the Bay of Bengal. But Kapili, through headward erosion, captured its northern course.

The Lumding-Haflong Pass is an evidence of this left valley. In a similar way Dhansiri capturing the water of a tributary of the Kapili River has helped in the formation of a new river called Jumna.

There can be numerous causes responsible for the shifting courses of the rivers. These include gentle slope of the Great Plains, meandering courses

It appears that Jumna or Yamuna is a new name given to a river arising out of river capturing of the rivers, straightening of the river course during the floods, upliftment of the Delhi-Sirhind plateau region, downwarping of the Malda Gap, rise in the Madhupur forest area and uplift of the Barind area.