Drainage Systems, Drainage Patterns and River Capture: Terminology for UPSC Geography Optional

Drainage terms describe two things: how a stream network came to lie where it does in relation to slope and structure (the genetic systems), and what shape it makes on the map (the patterns). Read backwards, they let you infer hidden structure, tectonic history and past captures from a topographic sheet, which is exactly what Paper II questions on Himalayan and Peninsular drainage test.

Each entry gives the definition, the controlling structure, a one-line sketch and a named river, Indian first where one exists. UPSC has asked the antecedent drainage of the Himalayas (Paper II, 1996) and river capture in the Himalayas (Paper II, 2016), and Paper II has asked how divides and structure shape Indian drainage patterns (2014, 2017).

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Drainage Systems: How Streams Relate to Slope and Structure

Drainage system vs drainage pattern

A drainage system is a genetic classification of streams by how their courses relate, through time, to the initial slope of the land and to its geological structure (consequent, subsequent, antecedent and so on). A drainage pattern is the geometric arrangement of a stream network in plan (dendritic, trellis, radial and so on). The system answers “why is the river here?”; the pattern answers “what shape does the network make?”.

• Controls: initial slope; structure (folds, faults, joints, dip and strike); rock resistance and permeability; climate and vegetation; history, meaning uplift, burial and capture.
• Concordant and discordant: streams adjusted to slope and structure are concordant (the sequent family); streams that cut across structure, the antecedent and superimposed rivers, are discordant or transverse.
• Examples: the Yamuna is a master consequent within the Dehradun valley yet cuts transversely through the Lesser Himalaya; the east-flowing Peninsular rivers are consequent in system and dendritic in pattern.
• Don’t confuse with: the drainage basin, watershed and divide, which describe area and boundaries, or stream order, which ranks segments.

Sequent drainage

Sequent drainage is the family of streams whose courses follow either the initial slope or structure later exposed by erosion, and so are adjusted to the land they drain: consequent, subsequent, obsequent and resequent streams. They develop broadly in that order as a tilted or folded surface is dissected.

• Sequence: consequents form first down the initial slope; subsequents grow along weak strike belts; obsequents run down scarp faces against the dip; resequents appear in a later cycle on newly exposed structure.
• Key features: right-angled junctions between strike and dip streams; strike vales between ridges; a trellis or annular pattern in plan.
• Examples: the Dehradun valley between the Siwalik and Lesser Himalayan ranges; the Weald of south-east England; the Appalachian Valley and Ridge.
• Sketch: a block diagram of a cuesta with streams labelled C (consequent), S (subsequent), O (obsequent) and R (resequent).

Consequent streams (master, longitudinal and lateral consequents)

A consequent stream is one whose course is a direct consequence of the initial slope of a new land surface, such as an uplifted coastal plain, tilted block, dome, volcano or fold, and so is the first to form there. The largest becomes the master consequent; in folded belts longitudinal consequents follow synclinal axes and lateral consequents run down the fold flanks into them.

• Coined by: John Wesley Powell (1875), in his studies of the Colorado Plateau rivers.
• Key features: parallel courses on a new coastal plain, radial ones on a dome or volcano; synclinal consequents later become the trunks of trellis networks.
• Examples: the Godavari, Krishna and Kaveri follow the eastward tilt of the Peninsula to the Bay of Bengal; the Ganga and Yamuna are the master consequents of the Dehradun valley; short consequents drain the new coastal plains of Konkan and Kerala.
• Sketch: a tilted block with arrows running straight down the slope and one longer arrow labelled “master consequent”.

Subsequent streams

A subsequent stream is a tributary that develops after the consequents, by headward erosion along a belt of weakness such as soft strata, a fault, a shatter zone or a joint set, so that it follows the strike of the rocks, usually at right angles to its consequent. Joseph Beete Jukes first described such valleys in southern Ireland in 1862.

• Formation: gullies on the sides of consequent valleys find weak bands, lengthen along them and gradually become the largest tributaries, often capturing weaker neighbours.
• Key features: long strike vales between ridges; right-angled junctions with the consequent; wide valleys on soft rock.
• Examples: the Asan (flowing north-west to the Yamuna) and the Song (flowing south-east to the Ganga) run along the axis of the Dehradun valley; the Sun Kosi follows the east–west grain of the Lesser Himalaya in Nepal; the strike valleys of the Appalachian Valley and Ridge.
• Sketch: two ridges with a long stream in the soft-rock vale between them, joining a transverse consequent at a right angle.

Obsequent streams

An obsequent stream flows in the direction opposite to the original consequent drainage, typically down the scarp face of a cuesta or ridge against the dip, to join a subsequent. Short and steep, obsequents are the natural agents of headward erosion into the next basin and so of capture across scarps.

• Key features: short courses, steep gradients, small basins, and valleys notched into scarp faces.
• Examples: the north-flowing streams off the northern slopes of the Siwalik ridge into the Dehradun valley, opposed to the south-flowing Ganga and Yamuna; the short streams notching the scarp faces of the Chalk escarpments of the North and South Downs, England.
• Don’t confuse with: resequent streams, which flow with the original slope, not against it.
• Sketch: a cuesta in section with a short arrow down the scarp face (obsequent) and a long arrow down the dip slope (consequent).

Resequent streams

A resequent stream flows in the same direction as the original consequent but develops later, at a lower level, on structure exposed by erosion, typically in a second cycle when streams re-establish themselves in synclines after the relief has been inverted. It follows the dip like a consequent without being inherited from the initial surface.

• Formation: a first cycle turns anticlines into valleys and synclines into ridges (inversion of relief); the region is planed and uplifted; a new cycle excavates the synclines again, and the new streams flowing down the dip are resequent.
• Key features: they lie hundreds of metres below the original surface yet parallel the first consequents; they are common in old, repeatedly uplifted fold belts.
• Examples: second-cycle synclinal streams in the Appalachian Valley and Ridge, where the old fold belt has been planed and rejuvenated more than once (see second cycle of erosion).
• Sketch: a folded section with a dashed original surface and a new stream incised in the syncline far below it.

Insequent drainage

Insequent drainage consists of streams whose courses are controlled neither by the initial slope nor by structure, because the rock is uniform, as in horizontal strata, massive granite, thick basalt flows or deep alluvium. The streams wander in random directions determined by minor local irregularities and branch irregularly, building dendritic networks.

• Key features: no preferred direction; acute, irregular junctions; texture controlled by rainfall and permeability rather than by rock grain.
• Examples: the networks on the granite-gneiss of the central Ranchi plateau and on the flat-lying basalt of the Deccan Traps; the Appalachian Plateau on horizontal strata.
• Don’t confuse with: the discordant antecedent and superimposed streams, which are strongly directed and cross structure for historical reasons.
• Sketch: a small tree-like network drawn over a blank, unpatterned rock symbol.

Antecedent drainage

An antecedent stream is one that existed before an uplift, fold or fault rose across its course and kept that course by cutting down as fast as the land rose, so that it now crosses the uplifted structure in a deep gorge. John Wesley Powell coined the term in 1875 for the Green River’s passage through the Uinta Mountains of Utah.

• Mechanism: uplift must be slow and local relative to the river’s power of incision. If uplift is too fast the river is ponded or diverted and the antecedence is defeated. Tributaries cannot keep pace, so they are left hanging above the trunk gorge.
• Key features: transverse gorges through the highest parts of a range; headwaters on the far, Tibetan side of the range; river terraces warped or tilted where they cross a rising axis; the river older than the structure it cuts.
• Himalayan examples (the 1996 demand): the Indus in its gorge beside Nanga Parbat; the Sutlej, entering India from Tibet near Shipki La; the Kali Gandaki between Dhaulagiri and Annapurna; the Arun, which Lawrence Rickard Wager (1937) used as the type case; the Siang–Brahmaputra around Namcha Barwa. Other rivers, such as the Jhelum and Yamuna, are transverse only to the Lesser and Outer Himalaya.
• Debate and recent research: the alternative is headward erosion and capture, with south-slope rivers cutting back through the range to seize Tibetan streams. A 2024 study argued that the Arun captured a Tibetan catchment about 89,000 years ago, adding perhaps 15–50 m to Everest’s height by isostatic rebound; a 2026 reply attributed the same river-profile evidence to orographic rainfall instead. For the Yarlung–Siang–Brahmaputra, zircon ages from foreland sediments (2014) indicate a Tibetan connection since the Early Miocene, which supports antecedence.
• Sketch: three stages: a river on a plain, a ridge rising across it with the river incising, and a deep gorge through the ridge with hanging tributaries.

Superimposed (epigenetic) drainage

A superimposed (epigenetic) stream is one whose course was established on a cover of younger rocks and then let down by continued incision onto older buried rocks of quite different structure, across which it now flows without adjustment. The course is inherited from a vanished surface; no uplift across the river is required.

• Mechanism: consequent streams form on the cover (flat sediments, lava or a planation surface) and cut through it; on reaching folds, domes or batholiths beneath, they keep their courses and carve gorges across hard ridges.
• Key features: rivers crossing ridges through gorges although easier routes lie alongside; outliers of the old cover nearby; a pattern unrelated to the underlying grain.
• Examples: the Son crossing the Khainjua ridges of lower Vindhyan quartzite on the Rewa plateau, Madhya Pradesh; the Subarnarekha across the Dalma lavas and phyllite hills near Chandil, Jharkhand; the Chambal and Banas are also usually listed. Abroad, the radial drainage of the English Lake District is usually explained as superimposed from a former cover.
• Naming: John Wesley Powell called such valleys superimposed; William John McGee (1888) preferred “superposed”.
• Don’t confuse with: antecedence. An antecedent river is older than the uplift; a superimposed river is older than the exposure of the structure.
• Sketch: a horizontal cover over folded beds with a river incised through the cover and into an anticline.

Drainage Patterns: What the Map Shows

Dendritic pattern

A dendritic pattern is a tree-like branching network in which tributaries of successive orders join at acute angles from all directions. It forms where rocks offer uniform resistance and structure exerts no directional control, as on horizontal strata, massive crystalline rocks, basalt or thick alluvium, and it is the commonest pattern on Earth.

• Controlling structure: none, or uniform.
• Key features: acute confluences pointing downstream; texture fine on impermeable clays and coarse on permeable sandstones.
• Examples: the upper Godavari and Krishna basins on Deccan basalt; the tributaries of the Ganga plain; the Appalachian Plateau on flat-lying strata.
• Sketch: a trunk with branching tributaries, each joining at an acute angle.

Trellis pattern

A trellis pattern is a grid of long, parallel strike streams occupying valleys on weak beds, joined at right angles by short tributaries from the ridges, with the master consequent crossing the ridges through water gaps. It develops on belts of parallel folds or on dipping, alternating hard and soft strata.

• Controlling structure: folded or tilted alternations of resistant and weak rock.
• Key features: evenly spaced parallel subsequents; short, straight tributaries; right-angled junctions; water gaps.
• Examples: the old folded mountains of the Singhbhum belt in the Chotanagpur plateau, Jharkhand, and longitudinal valleys of the Himalaya; the Appalachian Valley and Ridge drained by the Susquehanna and Potomac.
• Don’t confuse with: the rectangular pattern, controlled by joints rather than bedding.
• Sketch: parallel ridges with a long stream in each vale and short tributaries joining at right angles.

Rectangular pattern

A rectangular pattern is a network in which main streams and tributaries make right-angled bends and junctions because they follow two intersecting sets of joints or faults in otherwise uniform rock. Segments are of unequal length and spacing, unlike the regular grid of trellis.

• Controlling structure: joints and faults in massive rock such as sandstone or granite.
• Key features: abrupt right-angled bends in the trunk itself, not only at junctions; straight segments along fractures.
• Examples: the Belan basin on Vindhyan sandstones, south of Prayagraj, Uttar Pradesh, where tributaries join the Belan at right angles along joint planes.
• Don’t confuse with: trellis, which is controlled by the dip and strike of beds and has closely and evenly spaced tributaries.
• Sketch: a stream zig-zagging at right angles along a square grid of joint lines.

Radial pattern

A radial (centrifugal) pattern is formed by consequent streams flowing outward in all directions from a central high point, such as a dome, volcanic cone, residual hill or small plateau, like the spokes of a wheel.

• Controlling structure: a conical or domed initial surface.
• Key features: headwaters close together at the centre; courses diverging outward; often part of an annular pattern on dissected domes.
• Examples: the Amarkantak plateau in the Maikal range, Madhya Pradesh, where the Narmada flows west and the Son and Johila flow north; Parasnath hill in Jharkhand; Mount Abu in Rajasthan; at island scale, the central highlands of Sri Lanka; abroad, Mount Kenya.
• Sketch: a central summit with arrows radiating outward.

Centripetal pattern

A centripetal pattern is formed by streams converging from surrounding higher ground towards a central depression, such as a tectonic basin, crater or lake. It is the reverse of radial drainage and is typical of inland basins.

• Controlling structure: a closed or nearly closed basin.
• Key features: streams ending in a lake, swamp or salt pan; floods concentrate on the basin floor.
• Examples: Loktak lake, Manipur; Sambhar lake, Rajasthan, fed by the Mendha and Rupangarh; the Kathmandu valley, whose streams converge on the Bagmati before it leaves through the Chobhar gorge; abroad, the Lake Chad and Tarim basins.
• Sketch: a closed basin with arrows pointing inward to a central lake.

Annular pattern

An annular pattern is a ring-like arrangement of subsequent streams following concentric belts of weak rock around a dissected dome or basin, linked by short radial consequents. It is essentially a circular trellis.

• Controlling structure: a breached dome with alternating hard and soft beds dipping outward.
• Key features: curved subsequents in concentric vales; radial streams cutting through the ringed ridges; hogback ridges between the rings.
• Examples: the Black Hills of South Dakota, where a ring valley on weak red beds encircles the eroded dome; in India the pattern is rare and confined to small eroded domes.
• Don’t confuse with: the purely radial pattern of an undissected dome.
• Sketch: concentric circles of ridges with curved streams between them and a few radial streams crossing.

Barbed pattern

A barbed pattern is one in which tributaries join the main stream at obtuse angles, pointing upstream like the barbs of a fish-hook. It usually shows that the trunk stream’s direction has been reversed by capture or tilting while its tributaries kept their old orientation.

• Controlling factor: drainage reversal, not rock structure.
• Key features: junctions pointing upstream; hooked tributary mouths close to the confluence.
• Examples: tributaries of the Yarlung Tsangpo upstream of its great bend around Namcha Barwa, read as evidence of reorganisation in the eastern Himalayan syntaxis.
• Significance: one of the plan-view clues to capture, alongside elbows and wind gaps.
• Sketch: a trunk stream with tributaries joining in hooks that point upstream.

Pinnate and herringbone patterns

A pinnate pattern is a feather-like network of many short, nearly parallel tributaries joining a main stream at acute angles, typical of steep slopes on fine, easily eroded material. A herringbone pattern is a trunk stream in a narrow longitudinal valley receiving closely spaced, straight tributaries from both flanking ridges, like the bones of a fish.

• Controlling structure: a narrow valley between steep parallel slopes, or fine-grained erodible deposits.
• Key features: high drainage density; very short, straight tributaries; acute (pinnate) or near right-angled (herringbone) junctions.
• Examples: the upper Narmada and Son in their narrow trough valleys (pinnate); the Jhelum in the Vale of Kashmir, fed from the Pir Panjal and the Great Himalaya (herringbone).
• Sketch: a central stream with dense, short tributaries joining from both sides like a feather or fish spine.

Parallel pattern

A parallel pattern consists of several streams flowing side by side in nearly the same direction down a uniform regional slope, such as a newly emerged coastal plain, a tilted block, a dip slope or a steep mountain front, with few, short tributaries.

• Controlling structure: a uniform slope; it is often an initial pattern that later becomes dendritic.
• Key features: straight, evenly spaced main streams; elongated basins; narrow divides.
• Examples: the short, west-flowing rivers of the Konkan and Kerala coasts descending from the Western Ghats; the seasonal choes of the Siwalik front in Punjab; the Atlantic coastal plain of the United States.
• Sketch: several straight arrows running side by side down a slope to the coast.

Deranged pattern

A deranged pattern is a disorganised network with no consistent direction, full of lakes, swamps and short, interrupted streams, on terrain where drainage has not had time to integrate. It is typical of recently glaciated lowlands mantled by irregular till and of young lava fields.

• Controlling factor: very young, hummocky surface; the pattern records elapsed time, not structure.
• Key features: lakes linked by short channels; poorly defined divides; streams entering and leaving marshes.
• Examples: the Canadian Shield; the lake plateau of Finland; India has no large example.
• Significance: the network integrates as lakes fill or drain, so the pattern gives way to dendritic with time (lakes on till are covered under glacial deposition).
• Sketch: scattered lakes joined by irregular stream segments with no common direction.

River Capture

River capture (river piracy)

River capture is the diversion of the headwaters, or part of the course, of one stream into another whose more vigorous erosion has cut back into its basin. The captor is usually steeper, lower-lying or working on weaker rock, so it pushes the divide back until it intercepts the other stream and draws off its water.

• Mechanisms: headward erosion across a divide, commonest in youth; lateral erosion (abstraction), where a larger stream widening its valley consumes a smaller parallel one; intersection of meanders in old age; underground capture in karst; diversion by ice, lava, tilting or avulsion is related but is not capture in the strict sense.
• Favouring conditions: a steeper gradient, deeper valley, larger discharge, weaker rock and shorter route to base level on one side of the divide.
• Evidence: an elbow of capture, a wind gap, a misfit beheaded stream, barbed tributaries, a knickpoint below the elbow and gravels of the captured river stranded on the old divide.
• World examples: much of the upper Danube sinks near Immendingen and reappears at the Aach spring, flowing to the Rhine through Lake Constance, an underground capture still in progress.
• Himalayan and Indian examples (the 2016 demand): the Arun capture debate (see antecedent drainage); the narrow divide between the Song and Asan in the Dehradun valley, where capture of the upper Yamuna by the Ganga system has been predicted; the steep west-flowing Savitri cutting back towards the Krishna headwaters at Mahabaleshwar. The Sutlej abandoned the Ghaggar–Hakra course between about 15,000 and 8,000 years ago, whether by avulsion on its fan or by capture is debated; the Teesta’s 1787 switch from the Ganga system to the Brahmaputra was an avulsion, not a capture (see avulsion). The 1919 “Indobrahm” hypothesis of Edwin Hall Pascoe and Guy Ellcock Pilgrim, a single Siwalik river later dismembered by capture, is no longer accepted.
• Sketch: two plan-view stages, before and after, showing the divide retreating, the elbow, the wind gap and the beheaded stream.

Elbow of capture, captor, captured and beheaded streams

The captor (pirate) stream is the one that does the capturing; the captured stream is the upper course now diverted into it; the elbow of capture is the sharp bend, often near a right angle, where the captured stream turns into the captor’s valley; and the beheaded stream is the lower remnant of the victim, cut off from its headwaters.

• Key features: the elbow is often followed by a gorge and knickpoint, because the captor is steeper; the beheaded stream shrinks and becomes misfit; the divide jumps upstream; a connecting tributary may reverse its flow.
• Example: near Immendingen, south-west Germany, the Danube’s sinks act as an underground elbow: the captured water turns towards the Aach and the Rhine, while the beheaded Danube below runs dry on many days of the year.
• Exam use: name all four parts on the capture sketch; the elbow and the wind gap just below it are the two field clues examiners look for.
• Sketch: a plan view marking E (elbow), the captor, the captured headwaters, the wind gap and the beheaded stream.

Wind gap and water gap

A water gap is a narrow, steep-sided notch through which a river crosses a ridge; a wind gap is a similar notch with no river flowing through it, usually the abandoned valley of a stream beheaded by capture. Water gaps can also be cut by antecedent or superimposed rivers.

• Formation: a river crossing a resistant ridge deepens a gap as the land around it lowers; if the river is captured upstream, the gap is left dry and stranded above the new drainage.
• Key features: wind gaps often carry river gravels on their floors; their floor heights record the level of the former valley and help correlate old surfaces.
• Examples: the Delaware Water Gap through Kittatinny Ridge and the Wind Gap in Blue Mountain, both in Pennsylvania; in India, the gorges cut by the superimposed Son through the Khainjua ridges are water gaps.
• Don’t confuse with: a col, a saddle between peaks that need never have carried a river.
• Sketch: a ridge with one notch containing a river (water gap) and another dry notch at a higher level (wind gap).

Misfit stream

A misfit (underfit) stream is one too small for the valley it occupies, its meanders far smaller than the valley’s own bends or its channel dwarfed by the valley width, because its discharge has fallen since the valley was cut, through capture, diversion or climatic change.

• Causes: beheading by capture; diversion by avulsion or ice; lower discharge after a wetter climate, which George Harry Dury (1964) showed to explain many underfit streams in Britain and the United States.
• Key features: small stream meanders inside large valley meanders; a broad valley floor with a thin modern channel; often a wind gap upstream.
• Examples: the River Evenlode in the Cotswolds, England, Dury’s classic case; the present Ghaggar, a seasonal monsoon-fed river following the broad palaeochannel built by the Sutlej before about 8,000 years ago (see palaeochannels).
• Sketch: a wide meandering valley outline with a much smaller meandering channel inside it.

PYQs Built on These Terms

• Drainage pattern in Peninsular India is a result of its geological structure and topography. Elaborate. (Paper II, 2017)
• Explain the shifting of river courses and river capturing in the Himalayas. (Paper II, 2016)
• How is drainage pattern determined by the water divide? (Paper II, 2014)
• Examine the origin and characteristics of the antecedent drainage system of the Himalayas. (Paper II, 1996)

Frequently Asked Questions

What is the difference between antecedent and superimposed drainage?

An antecedent river is older than an uplift and keeps its course by cutting down as the land rises across it, like the Indus or Sutlej through the Himalaya. A superimposed river is older than the exposure of the structure it crosses; it was let down from a vanished cover, like the Son across the Khainjua ridges.

What is the difference between trellis and rectangular drainage patterns?

Both show right-angled junctions, but trellis drainage follows the strike of alternating hard and soft beds in folded or tilted strata, with long, evenly spaced parallel streams. Rectangular drainage follows intersecting joints or faults in uniform rock, so even the trunk stream bends at right angles and segments vary in length.

How can river capture be recognised in the field?

Look for a sharp elbow where a stream turns abruptly into a neighbouring valley, a dry wind gap just below it, a beheaded stream now too small for its valley, a knickpoint or gorge below the elbow, and gravels of the captured river stranded on the old divide.

Why are the Himalayan rivers called antecedent?

Rivers such as the Indus, Sutlej, Kali Gandaki, Arun and Brahmaputra rise north of the highest ranges yet cross them in deep gorges, which suggests they were flowing before the ranges rose and cut down as uplift proceeded. Some workers argue instead for headward erosion and capture, and the debate over the Arun remains open.

What is the difference between a wind gap and a water gap?

A water gap is a notch through a ridge that still carries a river, as at the Delaware Water Gap. A wind gap is a similar notch left dry, usually because the stream that cut it was beheaded by capture upstream, and it often keeps old river gravels on its floor.

Which Indian rivers show radial and centripetal drainage?

The Amarkantak plateau is the standard radial case: the Narmada flows west and the Son and Johila flow north from the same upland. Loktak lake in Manipur and Sambhar lake in Rajasthan are standard centripetal cases, where streams from surrounding uplands converge on a central depression.