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Of the total land surface of India, 90 per cent drains into the Bay of Bengal and the remaining drains into the Arabian Sea. Only a very small percentage of the area has an inland drainage system.
The Bay of Bengal and the Arabian Sea drainage systems are separated along a distinct divide which lies approximately along the Sahyadris, Amarkantak, Aravallis and the Satluj- Yamuna divide.
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The drainage of the Indian subcontinent has adjusted itself with the evolution of three main geomorphological entities, namely the Northern Mountains, the Northern Plains and the Peninsular Plateau. On the basis of their origin, the river systems of the subcontinent can be divided into two classes—the Himalayan rivers and the Peninsular rivers. The Indus, Ganga and Brahmaputra river systems comprise the Himalayan group while the major rivers in the peninsular systems are the Narmada, Tapti, Mahanadi, Godavari, Krishna and Cauveri.
A Comparative Analysis of Himalayan and Peninsular Rivers:
The Himalayan Rivers drain high mountain regions and descend deep slopes. The peninsular rivers, on the other hand, drain a senile topography. The Himalayan rivers are characterised by their youthful nature forming deep gorges, carved out by millions of years of the erosional activity along” with the uplift of the Himalayas. These rivers continue to perform intense erosional activity, which is evident from huge loads of sand and silt transported by them annually.
The major rivers—the Indus, Brahmaputra and Satluj—are of antecedent origin while the Kosi, Gandak and Ghaghra exhibit river capture. The peninsular rivers, in contrast, are basically matured rivers. The east flowing streams form deep valleys and have graded courses throughout, while the west flowing ones are swift and have narrow valleys. Overall, the peninsular rivers have straight and generally linear courses.
The Himalayan Rivers are free to form their courses and follow a dendritic pattern. These rivers have very large basins. The Indus drains approximately 2.5 lakh square kilometres within the Himalayan region alone. Himalayan reaches are very tortuous for the Himalayan Rivers, but, over the plains, they display a strong meandering tendency and often shift their beds.
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The peninsular rivers, having little erosional activity to perform, follow natural trends and joints in rocks. Superimposed drainage and river capture are common where there is difference in rock structure. Hard rock-bed and the predominantly non-alluvial’ character of the plateau surface hardly allow any significant meandering.
The Himalayan Rivers derive their water flow from melting snow, rainfall and springs in the Terai region and, therefore, are perennial in nature. But they are not free from seasonal variations. The peninsular rivers are completely rain-fed. During summer, the small ones become dry while the large ones have a low discharge.
The Himalayan Rivers are suitable for irrigation purposes because Of their perennial nature and the easily penetrable soil of the region which allows canals to be dug here. The peninsular rivers, on the other hand, are more suited for the generation of hydro-electricity; this is especially true of the west flowing ones. The seasonal nature of these rivers reduces their value as sources of irrigation.
Evolution of River System:
Himalayan Rivers:
These rives originate on the southern slopes of the Tibetan highlands and after following the main Himalayan axis for some length (the Indus, Satluj towards the west and the Brahmaputra towards the east), they bend southwards along the syntaxian bend cutting through Himalayan ridges, forming deep gorges and descend on to the Northern Plains.
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Deep gorges formed by the Indus, Satluj, Alaknanda, Gandak, Brahmaputra and Kosi indicate that these rivers are older than the mountains themselves and have continued to flow all through the building phase of the Himalayas, their banks rising steeply while the beds went lower and lower, thus defining the profile of a deep gorge. This type of drainage, which is not consequent to a topography but exists prior to its origin, is called antecedent drainage.
Indo-Brahm Theory:
One school of geologists attribute the evolution of the present-day north Indian drainage to changes produced in the drainage pattern of an original mighty stream called the Indo-Brahm.
According to some geologists, initially, the region of the Ganga plains was drained by a mighty stream flowing from Assam towards Punjab and incorporating the present courses of the incorporating the present course of the Brahmaputra, Ganga, Indus and finally emptying itself into a gulf situated at the present location of Sind.
Evidence of massive deposition work by this stream—’Indo-Brahm’ or ‘Shivalik’—is to be seen in the deposited strata of the Shivalik ranges whose young, detrital deposits point to recent deposition activity. This mighty stream then got dismembered partly due to the Pleistocene upheavals of western Himalayas including lifting of the Potwar plateau, and partly due to the headward erosion by tributaries in lower regions.
The dismemberment gave birth to the rivers of the present with a reversed flow pattern and the Ganga annexing the Yamuna as its tributary (the Yamuna must have been a south-west flowing tributary of the Indus). This exchange of tributaries between the Ganga and the Indus has continued till recent times. Thus, according to this theory, the Indo:Brahm was the parent stream from which the present river systems of northern India have evolved.
But, the Indo-Brahm theory is challenged on many grounds:
(i) It is not necessary to visualise such a mighty stream to explain the occurrence of Shivalik alluvial deposits and rock beds.
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(ii) The depositional history of the Ganga delta and the evidence in Assam do not go along well with this concept. The Rajmahal-Garo gap alluvium should have been laid over a long period of time than that suggested by the Indo-Brahm theory.
(iii) The evidence of the Tipam sandstone of Assam which were deposited in an estuary, situated too close to the source of the Indo-Brahm, also poses serious difficulty in the acceptance of this theory.
Peninsular Rivers:
These rivers have acquired maturity as suggested by broad, largely graded and shallow valleys and the fact that they have existed for a longer period than the Himalayan rivers, with the exception of limited reaches of some of the rivers where recent faulting has occurred. The beds generally have a subdued gradient, as the erosional forces do not act laterally.
Most of the peninsular rivers flow eastwards, as the main watershed runs through the Western Ghats close to the west coast (Fig. 13.17). The notable exceptions are the Narmada and Tapti which flow westwards in troughs, which are not of their own making. These facts are explained by assuming that the Western Ghats were the original watershed and their subsidence below sea has disturbed the generally symmetrical plan of the rivers on either side of the original watershed.
A second major distortion was introduced during the Himalayan upheaval when the northern flank of the peninsular block was subjected to subsidence and consequent trough-faulting. The Narmada and Tapti rivers flow in such trough-faults and have courses consequent to their general trend. During the course of their alluvial activity, they seem to have filled the original cracks with their detritus. This largely explains the lack of alluvial and deltaic deposits in their valleys.
Why there are no deltas along the west coast?
The season of increased volume of water (carrying silt and eroded material) coincides with the period when the south-west monsoon is active; this generates waves in the opposite direction, thus scouring away the depositions and ruling out the formation of deltas.
A General Survey of Drainage Systems:
Let us now study the physical characteristics and the usability of the country’s major river systems. The Indian River systems can be studied under the Himalayan and the peninsular categories (Fig. 13.17).
Himalayan Rivers:
The Himalayan mountain complex is the source of the following three drainage systems:
1. The Indus system
2. The Ganga system
3. The Brahmaputra system
1. The Indus System:
The Indus rises in Tibet at an altitude of 5,180 metres near the Mansarovar Lake. With a total length of 2,880 km, the Indus is one of the world’s largest rivers. It has a catchment area of 1,165,000 square kilometres, of which 3, 21,290 square kilometres lies within India. It flows through a spectacular gorge cutting through the Kailash ranges and enters Jammu and Kashmir.
From here, it flows through Ladakh, Baltistan and Gilgit and descends down to the plains at Attock. In India, it flows for a length of 709 km. Its tributaries include the Gartang, Zaskar, Dras, Shyok, Shingar, Nubra, Gilgit arid Hunza in Jammu and Kashmir, Kabul and tributaries in foothills near Attack and south of Attock—Kurram, Toch and Zhob-Gomal. Then, there are well-known Punjab tributaries—the Jhelum, Chenab, Ravi, Beas and Satluj.
The Jhelum rises in Verinag at the foothills of pir Panjal and its drainage area in India is 28,490 square kilometres. It flows through the Kashmir valley and Lake Wular before entering Pakistan through a narrow gorge.
The Chenab is the largest of all the Indus tributaries and is formed by two streams Chandra and Bhaga which rise in the snow-covered Himachal Mountains near Kulu. Its drainage area in India is 26,755 square kilometres.
The Ravi also rises in Kulu hills, near Rohtang Pass, of Himachal Pradesh and drains 5,957 square kilometres in India.
The Beas originates at a place called Beas Kund near Rohtang Pass in the Himachal hills. In its early stages, its valley is called the Kulu valley. Since some of its tributaries originating from the southern side of the Great Himalayas are snowfed, it has a relatively larger volume of water even during the long dry season. It joins the Satluj near Harike after flowing for a distance of 615 km. It drains an area of 25,900 square kilometres in India.
The Satluj originates from the Rakas Lake situated at an altitude of 4,555 metres in Tibet. The Rakas Lake is connected with the Mansarovar Lake by a stream. The Satluj enters India through Shipki La. Before entering the Punjab plains, it cuts a deep gorge through Nainadevi Dhar ranges. A dam has been constructed across this gorge near village Bhakra.
This dam is called the Bhakra Dam and the reservoir which it forms is called the Gobind Sagar Lake. The Satluj drains 24,087 square kilometres in India and is of immense economic value for the Punjab plains.
2. The Ganga System:
The Ganga river basin, with an area within India of 8, 61,404 square kilometres, is the largest in the country. This river basin drains the middle part of the Himalayas in the north, the northern part of the Indian plateau (roughly, north of the line running along the Vindhya Range, the Amarkantak Plateau and the watershed lying to the east of Subarnarekha) in the south and the Ganga plain in between. The Ram Ganga, Gomati, Ghaghra, Gandak and the Kosi are the Ganga’s major left-bank, tributaries and the Yamuna and the Son, its major right- bank tributaries.
The Ganga rises in the Gangotri glacier in Uttarakhand. Its two main headstreams— Bhagirathi and Alaknanda—meet at Devaprayag, from where onwards it is called the Ganga. Its total length is 2,510 km, and it drains 9, 51,600 sq. km. Of its length in the plains, the longest stretch lies in Uttar Pradesh, and the rest of it lies mostly in Bihar and West Bengal. Beyond Farakka, the mainstream of the Ganga flows southeast into Bangladesh and is known as the Padma.
From Farakka, a bifurcation channel runs southwards through the deltaic plain on to the sea. In this reach, the river is known as Bhagirathi- Hooghly and receives minor plateau streams such as Dwarka, Ajay, Rupnaryan and Haldi. Before falling into the Bay of Bengal below Chandpur in Bangladesh, the Padma receives the Brahmaputra, known here as the Jamuna and Meghna. The stretch from Allahabad to Haldia port, has been declared as the National Inland Waterway No.l.
The Yamuna is the most important tributary of the Ganga and it rises at the Yamnotri glacier in Uttarakhand. From its source upto Allahabad, where it meets the Ganga, the Yamuna’s length is 1,376 km and it drains an area of 3, 59,000 square kilometres. Important towns such, .as Delhi, Mathura and Agra are situated on the Yamuna’s banks. The Chambal, Betwa and Ken are the major tributaries of the Yamuna.
The headwater of the Ghaghra, the Karnali, is of trans-Himalayan origin and crosses the western part of the Nepal Himalayas through deep and narrow gorges. It joins the Ganga near Chapra. It is a large river choked with silt which keeps shifting its course.
The Ram Ganga rises in the Kumaon Himalayas and enters the Ganga Plains near Kalagarh. It joins the Ganga near Kannauj.
The Gandak rises near the Sino-Nepal border and joins the Ganga at Sonpur. It drains an area of 9,540 square kilometres. The Gandak also keeps shifting its course and is notorious for its floods.
The Kosi has its sources in the Himalayan heights of Sikkim, Nepal and Tibet. It drains 21,500 square kilometres in India and joins the Ganga below Bhagalpur. The river has shifted its course westwards by 112 km-during the last 200 years converting 7,000-8,000 sq km of cultivable land into wasteland.
The Son is a right-bank tributary of the Ganga which, after rising from the Amarkantak Plateau, joins the Ganga near Patna. It drains an area of 71,900 square kilometres.
The Damodar which actually meets the Bhagirathi-Hooghly in West Bengal, rises in the hills of Chhotanagpur Plateau. It drains an area of 22,000 square kilometres. Formerly referred to as the ‘Sorrow of Bengal’ on account of its floods, the Damodar has transformed itself into a boon to West Bengal after the completion of the Damodar valley multi-purpose project.
3. The Brahmaputra System:
The Brahmaputra rises in a glacier, about 100 km south-east of the Mansarovar lake in Tibet. Before entering India, it is called the Tsang-Po in Tibet. Chinese maps show it as Yarlung Zangbo Jiang. It crosses the Assam Himalayas under the name of Dihang. The total length of the Brahmaputra in India is 2,900 km, and it drains an area of 2, 40,000 square kilometres -in India. The Subarnasiri, Bhareli and Manas are its main right-bank tributaries and the Dibang, Luhit, Buri Dihang, Dhansiri and Kapili are its left-bank tributaries.
The catchment areas of these streams receive heavy rainfall during the monsoons, as a result of which the Brahmaputra becomes slow- moving and silt-laden. Its channel is braided and it is notorious for floods and erosion of its banks. Recurrent floods hamper not only navigation through the river but also the establishment of large towns on its bank. The Brahmaputra enters Bangladesh near Dhubri. The stretch from Sadiya to Dhubri has been declared as the National Inland Waterway No.2.
Peninsular Rivers:
The Western Ghats are the main watershed in the peninsula and the major rivers are the east-flowing ones. These rivers are characterised by huge deltas at their mouths, while the west-flowing ones are small with no deltas at their mouths. The Narmada and the Tapti are unusually large west-flowing rivers, flowing through troughs which have been formed due to faulting.
East-Flowing Peninsular Rivers:
The Mahanadi rises in the Sihawa range in Chhattisgarh. It is 857 km long and drains an area of 1, 41,600 square kilometres in Chhattisgarh, Orissa, Bihar and Maharashtra. The left-bank tributaries of the Mahanadi include the Seonath, Hasdo, Mand and lb, while the Jonk, Ung, Tel are among the right-bank tributaries.
After crossing the Eastern Ghats through a gorge, it divides itself into distributaries at Cuttack. The smaller basins of Subarnarekha, Brahmani and Baitarni are interposed between the Ganga and Mahanadi basins. The Brahmani is known as South Koel in its upper reaches in Jharkhand.
These rivers draining the eastern parts of the peninsula have drainage and discharge patterns similar to the Mahanadi. The Brahmani is 800 km long with a drainage area of 39,000 square kilometres. The Subarnarekha is 395 km long with a catchment area of 19,500 square kilometres. The Baitarni has its source region in the Keonjhar Plateau in Orissa.
The Godavari basin is the largest river system in the peninsula and second only to the Ganga system in India. It rises in the Nasik district of Maharashtra, and drains and area of 3, 12,812 square kilometres, half of which lies in Maharashtra. Besides Maharashtra, the basin is shared by Madhya Pradesh, Karnataka, Orissa and Andhra Pradesh.
The Godavari flows for a length of 1,465 km and is often referred to as Vridha Ganga or Dakshina Ganga because of its large size and extent. The major tributaries of the Godavari are the Pravara, Purna, Manjra, Penganga, Wainganga, Wardha, Pranhita, Indravati, Maner and Sabari.
The Krishna is the second largest east-flowing river. It rises from a spring near Mahabaleshwar in Maharashtra. Its total length of 1,400 km is shared by Maharashtra, Karnataka and Andhra Pradesh. The Krishna drains an area of 2, 58,948 square kilometres. The Bhima and Tungabhadra are the two most important tributaries of the Krishna, besides the Koyna, Ghataprabha, Malaprabha, Musi (Hyderabad is situated on its bank), Muneru, Yerla, Panchganga and Dudhganga.
The Pennar basin lies between the Krishna basin and the Cauveri basin, and drains an area of 55,213 square kilometres, most of which lies in Karnataka. Its principal tributaries are the Jayamangali, Kunderu, Sagileru, Chitravati, Papagin, and Cheyyeru.
The Cauveri rises in the Brahmagir rage of the Western Ghats. It flows for a length of 800 km before falling into the Bay of Bengal near Kaveripattinam. It drains an area of 87,900 square kilometres, which is shared by Kerala, Karnataka and Tamil Nadu. The Cauveri basin is one of the most developed regions of India from the point of view of power and inigation. Ninety to ninety-five per cent of the total potential in these two spheres has already been exploited.
The left-bank tributaries of the Cauveri include the Herangi, Hemavati, Shimsha and Arkavati, and the right-bank tributaries include the Lakshamantirtha, Kabini, Suvarnavati, Bhawani and Amravati.
West-Flowing Rivers:
The Narmada rises near Amarkantak in Madhya Pradesh and flows for 1,300 km, while draining an area of 98,796 square kilometres, most, of it lying in Madhya Pradesh. The Narmada basin is characterised by the lack of development of the tributary streams. The Narmada valley is gorge-like and full of rapids and waterfalls between Handia and Mandhata.
The Kapildhara and Dhvandhar are the most important waterfalls. The Orisan is the major tributary and others include the Burhner, Banjar, Shar, Shakkar, Dudhi, Tawa on the south and the Hiran, Barna and the Kolar on the north.
The Tapti is the second largest west-flowing peninsular river. It rises in the Betul district of Madhya Pradesh and while flowing for a length of 724 kilometres, it drains an area of 65,145 square kilometres in Madhya Pradesh, Maharashtra and Gujarat. The left-bank tributaries of the Tapti are Purna, Veghar, Girna, Bori and the Panjhra and those joining it on the right bank are the Aner, Betul, Ganjal, Arunavati and Gomai.
The north-western flank of the plateau is drained by the Sabarmati and the Mahi. The Sabarmati rises in the Aravalli hills and flows for a length of 300 km. It drains an area of 21,674 square kilometres in Gujarat and Rajasthan. The Mahi rises in the east of Udaipur and drains an area of 34,842 square kilometres while flowing for a length of 533 km in Madhya Pradesh, Rajasthan and Gujarat.
There are also a large number of coastal streams draining the narrow coastal plains on the western edge of the peninsula. There are as many as 600 tiny streams which drain the western face of the Western Ghats alone. The most important among these are the Mandovi, Zuari and Rachol in Goa; Kalinadi, Gangavalli-Bedti, Sharavati, Tadri and Netravati in Karnataka; Beypore, Ponnam, Bharatapuzha, Periyar and Pamba in Kerala.
All these streams have carved out narrow valleys with steep gradients and often descend to the plains in the form of cascades and waterfalls. The famous Jog Falls (271 metres) is on the Sharavati River.
