Evolution of the Himalayan Drainage

The Evolution of the Himalayan Drainage

Geologists do not all agree on how the Himalayan rivers evolved, but a widely accepted view holds that a single mighty river once ran the entire length of the Himalaya. This river, called the Shiwalik or Indo-Brahma, is believed to have flowed from Assam through Punjab and onward to Sind, finally emptying into the Gulf of Sind near lower Punjab. This is thought to have happened during the Miocene period, roughly 5 to 24 million years ago.

The evidence for this theory lies in the remarkable continuity of the Shiwalik range itself, along with its lacustrine (lake-formed) origin. The alluvial deposits found there — sands, silt, clay, boulders and conglomerates — all point to a long-lived river system rather than a series of separate, smaller rivers.

Over time, the Indo-Brahma river was dismembered into three main drainage systems:

• the Indus and its five tributaries in the western part;
• the Ganga and its Himalayan tributaries in the central part;
• the stretch of the Brahmaputra in Assam and its Himalayan tributaries in the eastern part.

Two major geological events caused this split. The first was the Pleistocene upheaval in the western Himalayas, which included the uplift of the Potwar Plateau (the Delhi Ridge). This uplift acted as a water divide between the Indus and Ganga drainage systems. The second was the down-thrusting of the Malda gap area, lying between the Rajmahal hills and the Meghalaya plateau, during the mid-Pleistocene period. This diverted the Ganga and Brahmaputra systems to flow towards the Bay of Bengal.

The River Systems of the Himalayan Drainage

The Himalayan drainage consists of several river systems, but the three major ones are the Indus, the Ganga and the Brahmaputra.

The Indus System

The Indus is one of the largest river basins in the world, covering an area of 11,65,000 sq. km, of which 321,289 sq. km lies in India. Its total length is 2,880 km, with 1,114 km within India. Also known as the Sindhu, it is the westernmost of the Himalayan rivers in India.

The Indus originates from a glacier near Bokhar Chu (at 31°15' N latitude and 81°40' E longitude) in the Tibetan region, at an altitude of 4,164 m in the Kailash Mountain range. In Tibet it is known as 'Singi Khamban', or Lion's mouth. After flowing northwest between the Ladakh and Zaskar ranges, it passes through Ladakh and Baltistan. It cuts across the Ladakh range, forming a spectacular gorge near Gilgit, and enters Pakistan near Chilas in the Dardistan region.

The Indus receives a number of Himalayan tributaries: the Shyok, the Gilgit, the Zaskar, the Hunza, the Nubra, the Shigar, the Gasting and the Dras. It emerges from the hills near Attock, where the Kabul river joins it on the right bank. Other right bank tributaries — the Khurram, the Tochi, the Gomal, the Viboa and the Sangar — all originate in the Sulaiman ranges. Flowing southward, the Indus receives the Panjnad a little above Mithankot. The Panjnad is the name given to the five rivers of Punjab: the Satluj, the Beas, the Ravi, the Chenab and the Jhelum. The Indus finally discharges into the Arabian Sea, east of Karachi. In India, it flows through the Union Territories of Ladakh and Jammu and Kashmir.

The five tributaries of the Indus deserve individual attention:

The Jhelum rises from a spring at Verinag, situated at the foot of the Pir Panjal in the south-eastern part of the Kashmir valley. It flows through Srinagar and the Wular lake before entering Pakistan through a deep narrow gorge, joining the Chenab near Jhang in Pakistan.

The Chenab is the largest tributary of the Indus. It is formed by two streams, the Chandra and the Bhaga, which join at Tandi near Keylong in Himachal Pradesh; hence it is also known as Chandrabhaga. It flows for 1,180 km before entering Pakistan.

The Ravi rises west of the Rohtang pass in the Kullu hills of Himachal Pradesh and flows through the Chamba valley. Before entering Pakistan and joining the Chenab near Sarai Sidhu, it drains the area between the south-eastern part of the Pir Panjal and the Dhauladhar ranges.

The Beas originates from the Beas Kund near the Rohtang Pass at an elevation of 4,000 m above mean sea level. It flows through the Kullu valley, forming gorges at Kati and Largi in the Dhaoladhar range, and enters the Punjab plains where it meets the Satluj near Harike.

The Satluj originates in the 'Raksas tal' near Mansarovar at an altitude of 4,555 m in Tibet, where it is known as Langchen Khambab. It flows almost parallel to the Indus for about 400 km before entering India, coming out of a gorge at Rupar. It passes through the Shipki La on the Himalayan ranges and enters the Punjab plains. The Satluj is an antecedent river — it existed before the Himalaya rose and has cut its course through the rising mountains. It is a very important tributary as it feeds the canal system of the Bhakra Nangal project.

The Ganga System

The Ganga is the most important river of India, both for its basin and its cultural significance. It rises in the Gangotri glacier near Gaumukh (3,900 m) in the Uttarkashi district of Uttarakhand, where it is known as the Bhagirathi. It cuts through the Central and Lesser Himalayas in narrow gorges. At Devprayag, the Bhagirathi meets the Alaknanda; from this point onward, the combined river is known as the Ganga.

The Alaknanda has its source in the Satopanth glacier above Badrinath. It consists of the Dhauli and the Vishnu Ganga, which meet at Joshimath or Vishnu Prayag. The Pindar joins the Alaknanda at Karna Prayag, while the Mandakini or Kali Ganga meets it at Rudra Prayag.

The Ganga enters the plains at Haridwar. From here it flows first south, then south-east and east, before splitting into two distributaries, the Bhagirathi and the Padma. The river has a length of 2,525 km, shared by Uttarakhand (110 km), Uttar Pradesh (1,450 km), Bihar (445 km) and West Bengal (520 km). The Ganga basin covers about 8.6 lakh sq. km in India alone.

The Ganga river system is the largest in India, with a number of perennial rivers originating in the Himalayas in the north and non-perennial rivers originating in the Peninsula in the south. The Son is its major right bank tributary. The important left bank tributaries are the Ramganga, the Gomati, the Ghaghara, the Gandak, the Kosi and the Mahananda. The river finally discharges into the Bay of Bengal near the Sagar Island.

The major tributaries of the Ganga are:

The Yamuna is the westernmost and longest tributary of the Ganga. It has its source in the Yamunotri glacier on the western slopes of the Banderpunch range (6,316 m) and joins the Ganga at Prayag (Allahabad). The Chambal, the Sind, the Betwa and the Ken join it on its right bank — these originate from the Peninsular plateau — while the Hindan, the Rind, the Sengar and the Varuna join it on its left bank. Much of its water feeds the western and eastern Yamuna and the Agra canals for irrigation.

The Chambal rises near Mhow in the Malwa plateau of Madhya Pradesh and flows northwards through a gorge up to Kota in Rajasthan, where the Gandhisagar dam has been constructed. From Kota it traverses down to Bundi, Sawai Madhopur and Dholpur, finally joining the Yamuna. The Chambal is famous for its badland topography, called the Chambal ravines.

The Gandak comprises two streams, the Kaligandak and the Trishulganga. It rises in the Nepal Himalayas between the Dhaulagiri and Mount Everest, draining the central part of Nepal. It enters the Ganga plain in the Champaran district of Bihar and joins the Ganga at Sonpur near Patna.

The Ghaghara originates in the glaciers of Mapchachungo. After collecting the waters of its tributaries — the Tila, Seti and Beri — it comes out of the mountain, cutting a deep gorge at Shishapani. The river Sarda (Kali or Kali Ganga) joins it in the plain before it finally meets the Ganga at Chhapra.

The Kosi is an antecedent river with its source to the north of Mount Everest in Tibet, where its main stream, the Arun, rises. After crossing the Central Himalayas in Nepal, it is joined by the Son Kosi from the west and the Tamur Kosi from the east. It forms the Sapt Kosi after uniting with the river Arun.

The Ramganga is a comparatively small river rising in the Garhwal hills near Gairsain. It changes its course to the southwest after crossing the Shiwalik and enters the plains of Uttar Pradesh near Najibabad, finally joining the Ganga near Kannauj.

The Damodar occupies the eastern margins of the Chotanagpur Plateau, where it flows through a rift valley and finally joins the Hugli. The Barakar is its main tributary. Once known as the 'sorrow of Bengal', the Damodar has now been tamed by the Damodar Valley Corporation, a multipurpose project.

The Sarda or Saryu rises in the Milam glacier in the Nepal Himalayas, where it is known as the Goriganga. Along the Indo-Nepal border it is called Kali or Chauk, and it joins the Ghaghara.

The Mahananda rises in the Darjiling hills and joins the Ganga as its last left bank tributary in West Bengal.

The Son is a large south bank tributary, originating in the Amarkantak plateau. After forming a series of waterfalls at the edge of the plateau, it reaches Arrah, west of Patna, to join the Ganga.

The Brahmaputra System …