Overview
Antecedent drainage is a discordant river system, one whose course does not fit the structure it crosses, that existed before the land it now crosses was lifted up, and that kept its course by cutting downward as fast as the land rose. Superimposed drainage, the other discordant type, is a river that first took its course on a cover of younger rock, then kept that course after erosion stripped the cover away and exposed older rock of a different structure beneath. Indian rivers show both stories, and river capture adds a third, in which one stream is diverted into the bed of its neighbour.
Accordant and Discordant Drainage and the Evolution of Indian Rivers
Accordant and Discordant Drainage: Meaning and Types
A drainage system is accordant if its pattern correlates with the structure and relief of the land it flows over, and discordant if it does not. Discordant drainage has two main types, antecedent and superimposed, and a mixed type called ante-position drainage combines the two. In antecedent drainage a river's power to cut downward matches the rate of tectonic uplift. In superimposed drainage the system first develops on a surface of younger rock, denudation removes that surface, and the river carries on over what looks like a new surface but is really older rock.
Why Drainage Evolution Explains the Anomalies of the Indian Map
The drainage pattern of an area is the outcome of the geological time period, the nature and structure of rocks, topography, slope, the amount of water flowing and the periodicity of flow. Pattern names such as dendritic or trellis describe shape; they do not explain why the Indus crosses the highest mountains on Earth, why the Narmada flows west when the Peninsula slopes east, or why the Chambal cuts through ridges instead of going round them.
Evolution answers these questions, and it separates two histories: The Himalayan network, which has evolved through a long geological history that is still unfolding, and the older Peninsular network.
Genetic Classification of Streams: Consequent, Subsequent and Others
Consequent, Subsequent, Resequent, Obsequent and Insequent Streams
Streams can be classified by how their course relates to the original slope of the surface and to the rock beneath. Antecedent and superimposed rivers are defined against these terms, because their courses do not fit the present slope and rock structure.
A consequent stream is one whose course is a direct consequence of the original slope of the surface on which it developed; it follows the slope of the land. A subsequent stream has its course set by selective headward erosion along weak strata; it develops after the original stream and follows weak rock belts instead of the original relief. A resequent stream follows the original relief but at a lower level, flowing down a course set by the underlying strata in the same direction, and is generally a tributary of a subsequent stream.
An obsequent stream flows opposite to the consequent drainage. An insequent stream has an almost random, usually dendritic course, formed by headward erosion on horizontally stratified belts or homogeneous rocks, and is not controlled by the original slope.
| Stream type | What sets its course | Relation to original slope |
|---|---|---|
| Consequent | Original slope of the surface | Follows it |
| Subsequent | Selective headward erosion along weak strata | Independent of the original relief |
| Resequent | Underlying strata, at a lower level | Same direction, lower level |
| Obsequent | A slope facing against the original slope | Flows the other way |
| Insequent | Headward erosion on uniform rock or horizontal beds | Not controlled by it |
One river can carry more than one label. The Chambal rises within about 16 km of the Narmada and is described as a consequent stream on the Mesozoic surface, superimposed on the scarps and cutting straight through them, with subsequent tributaries on the softer shales.
Antecedent Rivers in India and Their Himalayan Gorges
How an Antecedent River Keeps Its Course
An antecedent stream maintains its original course and pattern despite changes in the underlying rock and topography. The process runs in three steps.
- A river flows over a surface and develops a pattern suited to it.
- Slow tectonic uplift raises a ridge across its path; as long as the river's downcutting matches the uplift, the ridge cannot block it, and the river erodes through the rising ridge to form a steep-walled gorge.
- The river keeps its original pattern even though it now crosses a landscape that would normally produce a different one, such as a trellis pattern.
The Himalaya began to form between 40 and 50 million years ago when India and Eurasia collided, and the range is still rising. The corner regions around Nanga Parbat and Namcha Barwa are rising fastest, at an estimated 7 millimetres per year. Rivers that cross the range there have been cutting through rock that is still lifting beneath them.
Antecedent Rivers of the Himalaya Compared
Several Himalayan rivers are antecedent. They flowed south from the Tibetan side before the ranges rose and cut their gorges as the land lifted.
| River | Where it breaches the range | What marks it |
|---|---|---|
| Indus | Bends sharply after the Nanga Parbat massif | Indus Gorge 4,500 to 5,200 m deep near Nanga Parbat |
| Sutlej | Enters India through the Shipki La | A gorge it leaves at Rupar; source at Raksas Tal, 4,555 m |
| Kosi | Main stream Arun rises north of Mount Everest, then crosses the Central Himalaya in Nepal | Passes through the Chatra Gorge |
| Gandak | Kali Gandaki gorge between Dhaulagiri and Annapurna | River bed at 2,520 m lies 5,571 m below Annapurna I |
| Brahmaputra | Cuts a gorge around Namcha Barwa as the Tsangpo | Canyon walls of about 5,000 m on each side |
| Subansiri | Crosses the ranges into Arunachal Pradesh | Source in Tibet; right-bank tributary of the Brahmaputra |
The Kali Gandaki gorge is the second deepest canyon in the world when depth is measured from the river to the highest peaks on either side, after the Tsangpo canyon.
The Brahmaputra at Namcha Barwa
The Tsangpo flows east for nearly 1,200 km through a dry, flat region of southern Tibet, then carves a deep gorge in the eastern Himalaya around Namcha Barwa (7,755 m) and emerges as the Siang or Dihang. It enters India west of Sadiya town in Arunachal Pradesh, receives the Dibang and the Lohit, and from there is called the Brahmaputra.
The canyon is among the deepest on land: It averages about 5,000 m in depth around Namcha Barwa and reaches 6,009 m at its deepest point; in some places it is more than 5,300 m from top to bottom, three times deeper than the Grand Canyon. Across the gorge the river falls from about 2,900 m near Pei to the Indian border at about 660 m.
The canyon itself is explained by the river's antecedent course, since the river existed before the Himalaya and has kept cutting down while they rose. Below the canyon it widens to as much as 20 km on the Assam plain.
The Indo-Brahma River and the Dismemberment of Himalayan Drainage
The Shiwalik or Indo-Brahma River Hypothesis
Opinion differs about how the Himalayan rivers evolved, but the most widely accepted account is that a mighty river called the Shiwalik or Indo-Brahma traversed the entire length of the Himalaya from Assam to Punjab and onwards to Sind, and finally discharged into the Gulf of Sind near lower Punjab during the Miocene period, some 5 to 24 million years ago. Two lines of evidence support the view:
- Continuity of the Shiwalik: The Shiwalik deposits are remarkably continuous along the length of the range.
- Lacustrine origin and deposits: The Shiwalik beds are of lacustrine origin and consist of sands, silt, clay, boulders and conglomerates.
The Shiwaliks are the lowest sub-range of the Himalaya, built from sediments washed off the rising mountains into a foreland basin during the Neogene, between 23 and 2.6 million years ago, which is consistent with a long river carrying that material.
How One Great River Became Three Systems
In time the Indo-Brahma river was dismembered into three main drainage systems. The Pleistocene upheaval in the western Himalaya, including the uplift of the Potwar Plateau, acted as the water divide between the Indus and the Ganga systems. Down-thrusting of the Malda gap between the Rajmahal hills and the Meghalaya plateau during the mid-Pleistocene diverted the Ganga and the Brahmaputra to flow towards the Bay of Bengal.
| System | Section of the old river it inherited | What divided it |
|---|---|---|
| Indus and its five tributaries | Western part | Pleistocene uplift in the western Himalaya |
| Ganga and its Himalayan tributaries | Central part | Water divide with the Indus; Malda gap to the east |
| Brahmaputra in Assam and its Himalayan tributaries | Eastern part | Malda gap down-thrust |
The divide between the two systems also has an older history. The Punjab rivers, including the Sutlej, are thought to have drained east into the Ganga until about 5 million years ago, in the Pliocene, before the Pleistocene uplift that now separates the Indus and the Ganga.
Superimposed Drainage System: How the Pattern Is Inherited
How Superimposed Drainage Forms on Older Rock
A superimposed stream forms over horizontal beds that overlie folded and faulted rock of varying resistance. It forms in three steps.
- The stream develops its course on the cover of horizontal beds.
- It cuts down through those beds and, on reaching the rock below, keeps its course and pattern as it erodes the underlying rocks, despite their different character.
- It erodes a gorge through the resistant bed and continues to flow as before.
The result is a river that appears to ignore the structure of the ground it crosses, cutting across ridges that a river developed on that rock would have gone around. The cover that guided its first course has been removed by denudation and no longer shows. One way of understanding why this happens comes from the cycle of erosion: A large, mature river becomes insensitive to rock type and structure, which may explain the existence of superimposed streams.
The Chambal and the Older Peninsular Rivers
Among Peninsular rivers the Chambal is the standard example. It is a river of the Ganga system that rises in the northern part of the Peninsula, and its basin is bounded by the Vindhyan ranges on the south, east and west and by the Aravallis on the north-west. It is described as superimposed on the Vindhyan scarps, through which it cuts straight, and as an anterior river, that is, one much older than the main system it now joins, the Yamuna and the Ganga.
The Chambal, Betwa and Son also complicate the simple Himalayan and Peninsular division of Indian drainage, because they rise in the northern Peninsula, belong to the Ganga river system, and are much older in age and origin than the rivers that rise in the Himalaya. The Son rises near Pendra, just east of the Narmada's headwaters, and its lower valley is geologically an extension of the Narmada valley.
Difference Between Antecedent and Superimposed Drainage
Comparing the Two Discordant Types
| Basis | Antecedent drainage | Superimposed drainage |
|---|---|---|
| Origin | River predates the uplift | Drainage forms on a younger rock cover |
| What changes | Land rises across the river's path | Cover is removed by denudation |
| How the course survives | Downcutting matches uplift | Pattern is carried down onto the older rock |
| Landform | Gorge cut through a rising ridge | Gorge cut through a resistant bed |
| Setting in India | Himalaya: Indus, Sutlej, Brahmaputra, Kosi, Gandak | Peninsula: Chambal |
| Age relation | Older than the mountain | Younger than the rock beneath, older than its present valley |
The two differ in what happened to the land. If the land rose across the river, the river is antecedent. If a covering layer was removed and the river kept its old course over the exposed rock, it is superimposed. In both cases the river's pattern does not match present structure, which is why both are discordant.
River Capture (River Piracy): Meaning, Causes and Indian Examples
What River Capture Is and How It Happens
River capture, also called stream capture or river piracy, is the diversion of a stream or river system from its own bed into the bed of a neighbouring stream. The dry valley left behind by the original stream is a wind gap. The extra water in the capturing stream may accelerate erosion and encourage a gorge. River capture happens in six ways:
- Tectonic movement: Earth movements change the slope of the land and tip a stream out of its former course.
- Natural damming: A landslide or ice sheet blocks the channel and turns the water into a neighbouring valley.
- Headward erosion: One stream valley cuts upward into another.
- Lateral erosion: A meander cuts through the higher ground that divides adjacent streams.
- Karst: Streams sink or flow underground and reappear in a nearby valley.
- Glacier retreat: Meltwater is redirected to a different stream.
Sutlej and Yamuna: Course Changes in the Ghaggar-Hakra Region
In pre-Harappan times the Ghaggar was a tributary of the Sutlej. Tectonic movements later changed the slope of the land and turned the Sutlej from the south-east to the south-west, towards the Indus, leaving the Ghaggar-Hakra as a system of monsoon-fed rivers that ends in the Thar Desert. Estimates of when this happened range from before 8000 BCE to about 2000 BCE, and recent work places the shifts of both the Sutlej and the Yamuna well before the Harappan age, so the Sutlej was captured by the Indus long before the Harappan cities rose.
The Yamuna has a similar history. The present Sarsuti river, which rises in the Shiwalik hills on the Himachal and Haryana border and merges with the Ghaggar near Pehowa, is a palaeochannel of the Yamuna. The Yamuna changed its course to the east because the slope of the Earth's crust shifted through plate tectonics. The Ghaggar-Hakra channel is connected to palaeochannels of both the Sutlej and the Yamuna.
Kosi Fan Shifts and the Allah Bund of 1819
Not every change of course is a capture. The Kosi alluvial fan shows lateral channel shifting of more than 120 km during the past 250 years, through at least twelve major channels. On 18 August 2008 the Kosi picked up an old channel it had abandoned more than 100 years earlier, and about 95 per cent of its water flowed through the new course. The river moved within its own fan and did not take over a neighbour's drainage.
The Allah Bund is a different case. The Rann of Kutch earthquake of 16 June 1819 produced a zone of uplift about 80 km long, 6 km wide and 6 m high to the north of a subsided area, and it dammed the Nara river; the natural dam is called the Allah Bund. It blocked the Nara without diverting it into a neighbouring river, so it is damming, not capture.
Evolution of the Peninsular Drainage and the Old Water Divide
Why the Peninsular Drainage Is Older
The Peninsular drainage system is older than the Himalayan one. Its broad, largely graded shallow valleys and the maturity of its rivers show it. Most Peninsular rivers have a fixed course, no meanders and non-perennial flow. The Western Ghats, running close to the western coast, act as the water divide between the major Peninsular rivers that discharge into the Bay of Bengal and the small rivulets that join the Arabian Sea. Most major Peninsular rivers flow from west to east; the Narmada and the Tapi, which flow west through rift valleys, are the exceptions.
The Peninsula is formed of very ancient gneisses and granites, and the land slopes from west to east, as the flow of its rivers also shows. The Western Ghats arose along the west coast when India separated from the African continent.
Three Events That Shaped Peninsular Rivers
Three major geological events in the distant past shaped the present drainage of Peninsular India:
- Subsidence of the western flank: The western flank sank and was submerged beneath the sea in the early Tertiary period. This disturbed the symmetrical plan of the rivers on either side of the original watershed.
- Himalayan upheaval: When the Himalaya rose, the northern flank of the Peninsular block subsided and trough faulting followed. The Narmada and the Tapi flow in these trough faults and fill the original cracks with their detritus, so these rivers lack alluvial and deltaic deposits.
- Tilting of the block: A slight tilt of the Peninsular block from the north-west to the south-east gave the entire drainage its orientation towards the Bay of Bengal in the same period.
Narmada and Tapi: Rivers in Rift Valleys
The Narmada rises on the western flank of the Amarkantak plateau at about 1,057 m and flows in a rift valley between the Satpuras in the south and the Vindhyas in the north. It forms a gorge in marble rocks and the Dhuandhar waterfall near Jabalpur, flows for about 1,312 km and meets the Arabian Sea south of Bharuch in a broad estuary 27 km long.
The Narmada valley is a graben, a block of crust that dropped relative to the blocks on either side, bounded by the Narmada North fault and the Narmada South fault, which parallel the river's course. The Vindhya and Satpura blocks rose as horsts relative to the graben.
The Tapi originates near Multai in Betul district of Madhya Pradesh, is 724 km long, drains 65,145 sq km and also flows to the west.
Fossils along the two valleys are similar, which suggests that the Narmada and the Tapi may have been confluent about 3 million years ago and that recent earth movements decided their separate fates.
Why Western Ghats Rivers Build Estuaries, Not Deltas
The western coastal plain is a narrow, submerged belt, and the rivers that cross it do not form deltas. The west coast is a high rocky retreating coast on which erosional forms dominate, while the east coast is a low sedimentary coast on which depositional forms dominate. The western slope of the Ghats is steeper than the eastern slope, so the streams have only a short fall from the crest to the sea.
Large rivers that bring plentiful sediment build deltas along low sedimentary coasts, and that is why the broad eastern coastal plain has well-developed deltas of the Mahanadi, Godavari, Krishna and Kaveri. The Narmada, as a rift-valley river, forms an estuary instead of a delta.
Previous Year UPSC‑CSE Questions
Each Prelims question is explained option by option, and each Mains question comes with an answer outline.
- UPSC Prelims 2026Identify the river of the Indian sub-continent on the basis of the following information:
- It has an antecedent drainage system.
- It flows through three countries.
- It originates in the Tibetan Plateau and is an important river for irrigation.
- It does not form distributaries.
Select the answer from the following:
How to approach this Prelims question
Approach: Test each river against the clues. The Brahmaputra, the Indus and the Sutlej are all antecedent, rise on the Tibetan side and are important for irrigation, so the Teesta goes out first. The last clue decides among the three: The Brahmaputra splits into distributary branches in Bangladesh, and the Indus ends in a large delta in Sindh, while the Sutlej joins the Chenab to form the Panjnad, which joins the Indus, so it has no distributaries of its own.
Trap to watch: The Indus also rises in Tibet and crosses three countries; only the absence of distributaries separates it from the Sutlej.
Why each option is right or wrong:
- (a) Brahmaputra: Wrong. It is antecedent and crosses China, India and Bangladesh, but in Bangladesh it splits into distributary branches.
- (b) Indus: Wrong. It is antecedent and rises in Tibet, but it ends in a large delta in Sindh, with distributaries.
- (c) Sutlej: Correct. It is antecedent, rises at Raksas Tal in Tibet, crosses China, India and Pakistan, feeds the Bhakra Nangal canals and ends by joining the Chenab.
- (d) Teesta: Wrong. It rises in the eastern Himalaya at Pauhunri, not on the Tibetan Plateau.
Answer: (c) Sutlej. The Sutlej is the antecedent, Tibet-born river of three countries that ends in a confluence, not a delta.
- UPSC Prelims 2026Consider the following assertion: In the Pleistocene period either the Yamuna once flowed into the Indus, or the Sutlej flowed into the Yamuna and one major tributary of either had shifted from the Ganga to the Indus or vice versa. Which of the following is/are the basis of the above assertion?
- The Nadi-Sukta of the Rigveda
- The explorations of the Sutlej and the Yamuna by Robert Bruce Foote
- The presence of the same species of dolphins in both the Indus and the Ganga river systems
Select the answer using the code given below:
How to approach this Prelims question
Approach: The assertion is about the Pleistocene, which ended about 11,700 years ago, so only evidence that dates from that period can support it. The Ganges and Indus river dolphins were long treated as one species, as the question treats them, and were described as separate species only in 2021; they are estimated to have diverged about 5,50,000 years ago, within the Pleistocene, which fits a time when the two systems were linked. The Nadi-Sukta of the Rigveda was composed far later and lists the rivers of its own time, and Robert Bruce Foote's work as a geologist and archaeologist concerned prehistoric sites and collections, not this river link.
Trap to watch: The Rigveda names the Yamuna and the Sutlej, which makes item 1 look relevant, but it dates from long after the Pleistocene.
Why each option is right or wrong:
- (a) 1 only: Wrong. The Rigveda dates from long after the Pleistocene and lists the rivers of its own time.
- (b) 2 only: Wrong. Foote's work concerned prehistoric sites and collections, not the Pleistocene link of the two river systems.
- (c) 1 and 2: Wrong. Neither item can date a Pleistocene shift of rivers.
- (d) 3: Correct. The dolphins of the Indus and the Ganga, then treated as one species, diverged about 5,50,000 years ago, inside the Pleistocene.
Answer: (d) 3. Only the dolphin evidence dates from the Pleistocene.
- UPSC Prelims 2013The Narmada river flows to the west, while most other large peninsular rivers flow to the east. Why?
- It occupies a linear rift valley.
- It flows between the Vindhyas and the Satpuras.
- The land slopes to the west from Central India.
Select the correct answer using the codes given below:
How to approach this Prelims question
Approach: Test each statement as a cause of the westward flow, not just as a true fact.
- Statement 1 gives the cause: The Narmada flows in a rift valley, a graben bounded by faults.
- Statement 2 is true as a description, since the river flows between the Vindhyas and the Satpuras, but it only names the blocks that frame the rift, not a separate cause.
- Statement 3 is false, because the Peninsula slopes from west to east.
Trap to watch: Statement 2 is a true fact, but it does not explain the westward flow on its own.
Why each option is right or wrong:
- (a) 1 only: Correct. The rift valley between the Satpura and Vindhya blocks guides the Narmada west.
- (b) 2 and 3 only: Wrong. Statement 3 is false, since the general elevation of the Peninsula falls from west to east.
- (c) 1 and 3 only: Wrong. Statement 3 is false.
- (d) None: Wrong. Statement 1 is correct.
Answer: (a) 1 only. The rift valley sets the Narmada's direction.
- UPSC Prelims 2007Assertion and Reason:
- Assertion (A): River Kalinadi is an east-flowing river in the southern part of India.
- Reason (R): The Deccan Plateau is higher along its western edge and gently slopes towards the Bay of Bengal in the east.
How to approach this Prelims question
Approach: Check each claim. The Kali (Kalinadi) of Uttara Kannada rises in the Western Ghats and joins the Arabian Sea near Karwar, so it flows west and the assertion is false. The reason is a true statement: The Deccan is higher in the west and slopes gently east towards the Bay of Bengal.
Trap to watch: Most large Peninsular rivers do flow east, which makes the assertion sound right.
Why each option is right or wrong:
- (a) Both A and R are true and R is the correct explanation of A: Wrong. A is false.
- (b) Both A and R are true but R is not the correct explanation of A: Wrong. A is false.
- (c) A is true but R is false: Wrong. It is the other way round.
- (d) A is false but R is true: Correct. The Kali flows west to the Arabian Sea, and the Deccan does slope east.
Answer: (d) A is false but R is true. The Kali is a west-flowing river, though the plateau slopes east.
- UPSC Prelims 2004Assertion and Reason:
- Assertion (A): West-flowing rivers of Peninsular India have no deltas.
- Reason (R): These rivers do not carry any alluvial sediment.
How to approach this Prelims question
Approach: The assertion is true: The west-flowing rivers end in estuaries, not deltas. The reason is false: The Narmada and the Tapi do carry detritus and fill their trough faults with it. The real reasons are the narrow, steep western belt, the rocky coast and the rift valleys.
Trap to watch: No delta does not mean no sediment; the rivers carry it, but the setting does not let a delta build.
Why each option is right or wrong:
- (a) Both A and R are individually true and R is the correct explanation of A: Wrong. R is false.
- (b) Both A and R are individually true but R is not the correct explanation of A: Wrong. R is false.
- (c) A is true but R is false: Correct. The rivers form no deltas, yet they do carry sediment.
- (d) A is false but R is true: Wrong. A is true.
Answer: (c) A is true but R is false. No deltas, but not for lack of sediment.
- UPSC Mains 2013 GS‑IThere is no formation of deltas by rivers of the Western Ghat. Why?
Answer outline
The outline sets out what the question asks, the main arguments, relevant examples and the direction of the conclusion; it is not a full model answer.
Introduction: The rivers of the Western Ghats end in estuaries, not deltas.
Body (sub-themes to develop):
- Coast: The western plain is a narrow, submerged belt, and the west coast is a high, rocky, retreating coast where erosion dominates.
- Slope: The Ghats stand close to the sea and their western slope is steeper, so the streams are short and swift.
- Rift valleys: The Narmada and the Tapi fill trough faults with their detritus and end in estuaries.
- Contrast: The broad east coast holds the deltas of the Mahanadi, Godavari, Krishna and Kaveri.
Conclusion: Structure, slope and coast type together prevent deltas on the west coast.
Sources
- NCERT: India, Physical Environment (Class XI), Drainage System
- NCERT: India, Physical Environment (Class XI), Structure and Physiography
- NCERT: Fundamentals of Physical Geography (Class XI), Landforms and their Evolution
- USGS: The Himalayas, This Dynamic Earth
- India-WRIS: Narmada basin
- NASA Earth Observatory: Yarlung Tsangpo
- Wikipedia: Antecedent stream
- Wikipedia: Drainage system (geomorphology)
- Wikipedia: Consequent stream
- Wikipedia: Stream capture
- Wikipedia: Wind gap
- Wikipedia: Ghaggar-Hakra River
- Wikipedia: Sutlej
- Wikipedia: Yamuna
- Wikipedia: Chambal River
- Wikipedia: Narmada River
- Wikipedia: Tapti River
- Wikipedia: Kali Gandaki River
- Wikipedia: Yarlung Tsangpo Grand Canyon
- Wikipedia: Namcha Barwa
- Wikipedia: Kosi River
- Wikipedia: Siwalik Hills
- Wikipedia: Allah Bund
- Wikipedia: Kali River (Karnataka)
- Wikipedia: South Asian river dolphin
- Wikipedia: Robert Bruce Foote
- Wikipedia: Rigveda
- Wikipedia: Teesta River
- Wikipedia: Brahmaputra River
- Wikipedia: Indus River
- UPSC: Civil Services Examination question papers
Editorial Disclaimer
This article draws on the current NCERT geography textbooks, India-WRIS, the US Geological Survey, NASA and the documents listed under Sources.
See more of our UPSC articles in Google Search
Add to Preferred Sources