Which drainage pattern is commonly found in Ganga plains and Assam Valley, characterized by wide plains, gentle slopes, heavy rains and large number of tributaries?
- (a)Antecedent drainage pattern
- (b)Dendritic drainage pattern
- (c)Radial drainage pattern
- (d)Rectangular drainage pattern
Correct — B, Dendritic drainage pattern.
The stem hands you four descriptors — wide plains, gentle slopes, heavy rains, a large number of tributaries — and asks which pattern those conditions commonly produce in the Ganga plains and the Assam Valley. Read them as a description of the surface, not of the water.
A wide plain built of alluvium has no strong grain to it: the material is broadly similar in every direction, there are no resistant ridges to deflect a stream and no dominant joint set to steer it.
On such a surface a stream and its feeders take the shortest available route downslope, and the network that results branches like a tree — a trunk with progressively smaller tributaries entering it at acute angles, pointing downstream. That is the dendritic pattern, and the rivers of the northern plain are the standard Indian illustration of it.
Heavy rain and a large tributary count matter because they mean the branching is well developed and densely filled in, not because they change its shape.
The idea worth carrying away is that a drainage pattern is a readout of the ground beneath it: uniform material plus a gentle, even slope tends to give dendritic; anything that imposes a direction on the rock — joints, faults, folded bands of alternating hardness, a central dome — bends the network into one of the other named forms.
When a question describes the terrain rather than the river, ask what the terrain permits.
- (a)Antecedent drainage pattern — This is not a plan shape at all, which is what makes it the most seductive wrong answer here.
'Antecedent' classifies a river by its history relative to the land it crosses: the river was already flowing, the range rose across its path, and the river kept pace by cutting down, leaving a deep gorge through the mountains it appears to defy.
Nothing about a wide plain of gentle slope invokes that idea. It is the right answer to a question about Himalayan rivers such as the Indus, the Satluj and the Brahmaputra, which cross the ranges through gorges because they are older than the present uplift — a statement about age and downcutting, not about the branching arrangement of a network.
- (c)Radial drainage pattern — Radial requires a central high point — a dome, a conical peak, a volcanic cone, a compact upland — from which streams run outward in different directions like spokes. The defining feature is divergence away from one summit area.
The Ganga plains and the Assam Valley are the opposite geometry: broad, low surfaces that collect water into a trunk river rather than shed it outward from a centre.
Radial is the right answer to a question about streams rising close together on an upland and dispersing outward — Narmada and Son, which both rise at Amarkantak and flow away in different directions, are the usual Indian illustration.
- (d)Rectangular drainage pattern — Rectangular develops on strongly jointed or faulted rock, where the joint and fault lines form a grid of weaknesses. Streams exploit those lines, so the channels run in straight segments, turn through sharp near-right-angle bends, and tributaries meet the trunk at roughly right angles.
That demands hard, well-jointed bedrock at the surface — precisely what a thick alluvial plain does not offer. It is the right answer to a question describing streams with angular bends over jointed rocky terrain.
Note the neighbouring trap: trellis drainage also has right-angle junctions, but it arises from folded strata with alternating resistant and weak bands rather than from a joint grid, and it is not among the options here.
A drainage pattern is the plan-view arrangement a river and its tributaries make when seen from above, and it is largely inherited from the surface the network grew on.
Where the underlying material is broadly uniform and the slope is gentle and even, water has no preferred line to follow and the network branches freely — a trunk stream with tributaries entering at acute angles that point downstream, the whole thing resembling a tree or the veins of a leaf.
This is the dendritic pattern, and it is the commonest form worldwide for exactly that reason: uniformity is the default, structure is the exception. When the rock does impose a direction, the pattern records it.
A grid of joints and faults produces straight reaches and abrupt right-angle turns (rectangular). Folded belts of alternating hard and soft rock produce long strike-parallel trunks fed by short right-angle tributaries (trellis). A dome or cone sheds streams outward in all directions (radial). A closed basin draws them inward to a centre (centripetal).
Separate from all of these is a second, genetic classification that asks how a river came to cross the ground it crosses rather than what shape its network makes — antecedent, superimposed, consequent, subsequent.
Mixing a term from that second list into a set of plan-form options is a standard way of testing whether a candidate knows the difference.
Drainage patterns sit at the join between physical geography and regional Indian geography, which is why they can be asked either abstractly or, as in this question, through named regions.
The Ganga plains and the Assam Valley are both aggradational surfaces — floors built up by sediment carried down from the mountains — so the surface a network develops on there is young alluvium rather than structured bedrock, and the rivers of the northern plain are the example Indian textbooks reach for when illustrating branching drainage.
The same regions carry other, unrelated labels a candidate may have absorbed: the Brahmaputra in Assam is famous for braiding within its own channel, and stretches of the plains show meandering and ox-bow formation.
Those describe what a single channel does across its floodplain; a drainage pattern describes how the whole network of trunk and tributaries is arranged. Keeping the two scales apart is most of the work in questions of this kind.
- Dendritic drainage is tree-like: a trunk stream with progressively smaller tributaries joining at acute angles that open downstream.
- It typically develops where the underlying rock or sediment is broadly uniform and the land slopes gently and evenly, so no line of weakness steers the streams.
- The rivers of India's northern plain are the standard textbook illustration of a dendritic arrangement.
- Rectangular drainage is associated with strongly jointed or faulted rocky terrain; the channels run in straight segments and turn through roughly right angles.
- Trellis drainage also shows right-angle junctions but arises from folded terrain with alternating resistant and weak bands — it is the pattern most often confused with rectangular.
- Radial drainage runs outward from a central high point such as a dome or conical peak; Narmada and Son both rise at Amarkantak and flow away in different directions.
- Centripetal drainage is the inverse of radial: streams converge inward towards a basin or depression.
- Antecedent belongs to a different classification — it describes a river older than the uplift it crosses, which maintained its course by downcutting and so passes through a gorge in the range. Himalayan rivers including the Indus, the Satluj and the Brahmaputra are described this way.
- Braiding and meandering describe the behaviour of one channel across its floodplain, not the plan arrangement of a whole network.
Five of the six entries describe the shape of a network; the last describes a river's history. The options in this question mix the two lists, so the first move is to notice that only three of them are plan forms at all.
- Latching on to 'heavy rains' and 'large number of tributaries' and reaching for braided or deranged — neither is on the list, and neither is what those phrases are doing. Rainfall and tributary count control how densely a pattern is filled in, not what shape it takes.
- Treating antecedent as if it were a fourth plan form. It answers 'how did this river come to cross this range', not 'what shape does this network make'. A candidate who has not separated the two classifications can talk themselves into it.
- Letting 'Assam Valley' trigger the Brahmaputra's braided channel. Braiding is what one channel does on its floodplain; the question asks about the arrangement of a whole network of tributaries.
- Confusing rectangular with trellis because both feature right-angle junctions. The cause is the discriminator — a joint and fault grid for rectangular, folded alternating strata for trellis.
- Choosing radial because the plains receive water from the surrounding mountains. Radial means streams diverging outward from a central high, not converging from the margins.
Two shapes are visible in the material to hand. One is description-to-name, as here and in the CDS 2024 item: the characteristics are listed — uniform rock, regular slope, veins-on-a-leaf, acute-angle junctions — and you supply the label.
The other, which this question uses, seeds the option list with a term from the genetic classification, so that a candidate who has memorised names without sorting them into their two families can be pulled off the plan-form track.
Beyond these two, the same distinction can also be probed by pairing a pattern with an Indian region or river and asking whether the match holds, or by mixing in channel-scale terms such as braiding or meandering to see whether you notice the change of scale.
CDS_GK_2024_I_Q472024The same target and the same keyed concept — dendritic — reached from the opposite direction. CDS supplies the textbook descriptors in the abstract (commonest pattern, uniform rock type and regular slope, a plan like the veins on a leaf, tributaries joining at an acute angle) and asks for the name, so a candidate who has memorised the definition can answer without knowing any region. UKPSC instead names two Indian regions and describes their terrain, requiring you to translate 'wide plains, gentle slopes' into 'uniform material with no directional control' yourself. The option sets differ in a way that matters: CDS keeps all four choices inside the plan-form family (dendritic, radial, trellis, centripetal), whereas UKPSC replaces trellis and centripetal with rectangular and with antecedent — and antecedent belongs to the genetic classification, not the plan-form one, which is the extra discrimination the UKPSC item demands.
UPSC_2013_GS1_Q152013Shares the underlying principle — that relief and structure govern how rivers run — but tests it on a single river's direction rather than on a network's shape. The UPSC item asks why the Narmada flows west when most large peninsular rivers flow east, and the answer turns on its occupying a linear rift valley: a structural control so strong that it overrides the regional slope. That is the complement of this UKPSC question, where the absence of any such control on a uniform alluvial plain is exactly what permits free branching. The differences are real and worth stating: UPSC names no pattern and expects no pattern vocabulary, it is a statement-evaluation item on the peninsular block rather than a single-word identification on the northern plains, and it concerns one channel's course rather than the arrangement of a trunk and its tributaries.
- practice — not a real PYQ
A drainage network shows long straight channel segments that turn through abrupt near-right-angle bends, with tributaries meeting the trunk at roughly right angles. Which control best explains this arrangement?
- (a)A thick, uniform cover of alluvium on a gentle, even slope
- (b)A strongly jointed and faulted rocky terrain whose lines of weakness the streams exploit
- (c)A central dome from which streams flow outward in different directions
- (d)An enclosed basin towards which all streams converge
Answerb — Rectangular drainage is produced where a grid of joints and faults offers the easiest lines of erosion, so the channels adopt the grid's geometry and turn through sharp angles.(a) is the classic dendritic setting: uniform material with no directional weakness gives freely branching, acute-angle junctions, not right angles.
(c) describes radial drainage, defined by divergence outward from a central high, which says nothing about angular bends. (d) describes centripetal drainage, defined by convergence into a closed basin. Only (b) supplies a reason for right angles.
- practice — not a real PYQ
Several Himalayan rivers, including the Indus and the Satluj, cross the ranges through deep gorges because they were already flowing along their courses before the ranges were uplifted and cut down as the land rose. Such rivers are described as:
- (a)Consequent
- (b)Subsequent
- (c)Antecedent
- (d)Superimposed
Answerc — Antecedent is precisely the term for a river older than the uplift across its path, which maintained its course by downcutting and so passes through the range in a gorge.(a) consequent describes a stream that simply follows the slope of the original land surface, with no implication of predating an uplift. (b) subsequent describes a tributary that develops later along a line of weak rock, usually along the strike, and is a product of the structure rather than older than it.
(d) superimposed describes a course impressed from a former overlying cover and then let down onto a buried structure it does not match — the river is younger than the structure it crosses, which is the reverse of what the stem states. Only (c) fits a river that predates the uplift.
- practice — not a real PYQ
A drainage network branches like a tree, with tributaries joining the main stream at acute angles that open downstream. Such a pattern typically develops where:
- (a)Folded strata place resistant and weak bands alternately across the region
- (b)The underlying material is broadly uniform and the land slopes gently and evenly
- (c)Streams converge inward on a depression that has no outlet
- (d)A conical peak sheds streams outward in every direction
Answerb — Free branching with acute-angle junctions is what happens when nothing in the ground imposes a direction, so uniform material on a gentle, even slope is the setting for dendritic drainage.(a) describes the trellis setting: alternating hard and soft folded bands force long strike-parallel trunks with short right-angle tributaries, not acute-angle branching.
(c) describes centripetal drainage, defined by inward convergence rather than by any junction angle. (d) describes radial drainage, defined by outward divergence from a central high. Only (b) explains why the junctions are acute and the branching unconstrained.