MPSC 2022 Prelims Paper-I · Question 6 of 100

Correct — option (2). Three of the four terms belong to the family of streams classified by their relation to the underlying structure, and the fourth belongs to a different classification altogether, which is where the question is most easily cracked. Braided at (d) describes a channel pattern, not a structural relationship: where a river carries more load than it can move, has a variable discharge and banks of loose material, it deposits bars in mid-channel and divides and rejoins around them, producing exactly the maze of interconnected channels described at (iv). No other clue in the second column can mean this, and no other item in the first column can be described by it, so (d) pairs with (iv) and that pairing alone identifies option (2) as the answer. The remaining three confirm it. A consequent stream at (a) is the first stream to establish itself on a newly emerged or newly uplifted surface, and it takes the direction the surface itself gives it, which is what (ii) says when it speaks of flow controlled by the original slope. A subsequent stream at (c) develops afterwards, not on the original slope but along a line of weakness that erosion has exposed, cutting its valley where the softer bed outcrops and usually joining the consequent at a sharp angle; that is (i). An obsequent stream at (b) is the one that runs the other way, down the steep face left by that erosion and therefore against the dip of the beds, which is (iii). The completed pairing is (a)-(ii), (b)-(iii), (c)-(i), (d)-(iv), the row printed at option (2).

• (1)(a) - (iv), (b) - (ii), (c) - (iii), (d) - (i) — This row gives the consequent stream the maze of interconnected channels at (iv), which is a description of a braided channel pattern and has nothing to do with the way a stream relates to the slope or the structure beneath it. A consequent stream is defined by its direction — it takes the slope of the land as first formed — and a stream may be consequent whether it flows in one channel or in fifty. The row then leaves the braided stream at (d) with the outcrop clue at (i), which is the description of a subsequent stream. What makes this row worth studying is the speed with which it can be killed: the braided pairing is the one clue in the question that a candidate can be certain of, and any row that spends (iv) elsewhere is finished before the other three pairs are even read.
• (3)(a) - (iv), (b) - (i), (c) - (ii), (d) - (iii) — This row repeats the error of giving the maze of interconnected channels to the consequent stream, and adds to it by making the braided stream the one that flows against the dip of the rock. Neither statement can stand. Flowing opposite to the dip is the definition of an obsequent stream, a structural description that concerns the attitude of the beds beneath the channel, whereas braiding is a matter of sediment load, discharge variability and bank material and is found on rivers in every structural setting — the Kosi in north Bihar and the Brahmaputra in Assam are the standard Indian examples. The row also gives the subsequent stream the original-slope clue that belongs to the consequent. Every pair in it is wrong, and the braided test disposes of it at once.
• (4)(a) - (ii), (b) - (iii), (c) - (iv), (d) - (i) — This is the row built to defeat a candidate who checks the first half of the list and stops. It correctly gives the consequent stream the original slope at (ii) and the obsequent stream the opposite-to-dip clue at (iii), which are the two pairs most candidates can do, and then reverses the last two: it gives the subsequent stream the braided maze at (iv) and the braided stream the outcrop clue at (i). Both are wrong. A subsequent stream is defined by structure — it follows the outcrop of a weaker bed, which is why it is also called a strike stream — while braiding is a channel pattern produced by load and discharge. The habit that defeats this row is to verify every pair in a matching item, and to be most careful about the last ones, since a setter who leaves the easy pairs intact has done so deliberately.

Streams are classified in two independent ways and the question mixes them, so the classifications are worth separating. The first is genetic, that is by the relation of the stream to the structure it flows over. The consequent stream is the original one, following the slope of the land as it first emerged from the sea or was uplifted. As it cuts down it exposes beds of different hardness, and tributaries develop along the weaker outcrops at right angles to it; these are subsequent or strike streams. Short streams then flow down the steep scarp faces into the subsequent valleys, and because the scarp faces the opposite way from the dip these are obsequent streams; where a stream flows in the same direction as the consequent but at a lower level, on a bench cut into the weaker bed, it is called resequent. Two further terms belong to the same family: an antecedent stream is one that existed before the uplift and cut down fast enough to maintain its course across it, which is how the Indus, Sutlej and Brahmaputra cross the Himalaya, and a superimposed stream is one that established its pattern on a cover of rock since removed and now cuts incongruously into the structure beneath. The second classification is by channel pattern — straight, meandering, braided and anastomosing — and it depends on gradient, sediment load, discharge and the strength of the banks rather than on structure. Braiding belongs to this second scheme.

Fluvial geomorphology is a standing item in the MPSC physical geography block, and the Commission likes the four-by-four match because it can test four definitions in a single question. The particular trick used here is to place a term from one classification among three from another, which rewards a candidate who has organised the chapter rather than merely memorised its definitions. It also supplies the anchor: because the odd term out has a description no other term could take, the pairing is settled in a few seconds and three rows fall together. That method — find the clue that can only belong to one item, pair it, and strike out every row that disagrees — is the correct way to attack any matching question, and it is far quicker than working through the pairs in printed order. The second lesson is in option (4), which reverses only the two pairs a weaker candidate would not check. Verifying a row to the end costs a few seconds and is the difference between a mark gained and a quarter mark lost, since a wrong answer in this paper carries a deduction of a quarter of the marks for the question.

• A consequent stream is the first stream to develop on a newly formed or newly uplifted surface, and its direction is controlled by the original slope of that surface.
• A subsequent stream develops later along a line of weakness, cutting its valley where a softer bed outcrops, and it usually joins the consequent stream at a sharp angle; it is also called a strike stream.
• An obsequent stream flows in the direction opposite to the dip of the rocks, typically down a scarp face into a subsequent valley; a resequent stream flows in the same direction as the consequent but at a lower level.
• A braided channel is one that divides and rejoins around mid-channel bars, forming a maze of interconnected channels; it develops where sediment load is heavy, discharge variable and banks easily eroded, as on the Kosi and the Brahmaputra.
• Antecedent streams predate the uplift they cross and cut down to maintain their course, as the Indus, Sutlej and Brahmaputra do across the Himalaya; superimposed streams inherit a pattern from a cover of rock since removed.

• Treating braiding as a structural category, when it is a channel pattern controlled by sediment load, discharge and bank material rather than by the attitude of the rocks
• Confusing the subsequent stream, which follows the outcrop of a weaker bed, with the obsequent stream, which runs against the dip down a scarp face
• Checking only the pairs you are confident about and accepting a row that reverses the two you are not, which is exactly how option (4) is constructed
• Reading the two side-by-side columns as though the printing paired them, when in a matching question the adjacency is layout and asserts nothing

Drainage and stream classification appear in MPSC papers as matching items of this kind, as one-line definition questions asking what a named stream type is, and as application questions asking which Indian river illustrates a term — the Indus and Brahmaputra for antecedence, the Kosi for braiding and channel shifting, the trellis pattern for the folded ranges. The Commission also likes to pair the genetic terms with drainage patterns in the same question, so the two schemes should be learnt side by side and kept distinct. A compact preparation is a single page carrying the six genetic types with a one-line definition and an example each, the four channel patterns with their controls, and the standard drainage patterns with the structure each indicates.

No directly related past PYQ was found.

• practice — not a real PYQ

  A stream that flows in a direction opposite to the dip of the rock beds, usually down a scarp face into a subsequent valley, is called

  • (a)a consequent stream
  • (b)a resequent stream
  • (c)an obsequent stream
  • (d)an antecedent stream

  Answer(c) an obsequent stream — the name records that it runs against the dip. A consequent stream follows the original slope of the land, a resequent stream flows in the same direction as the consequent but at a lower level on a bench cut in weaker rock, and an antecedent stream is one older than the uplift it crosses, having cut down fast enough to keep its course.

• practice — not a real PYQ

  A braided channel pattern is most likely to develop where

  • (a)the river carries a heavy sediment load, has a variable discharge and easily eroded banks
  • (b)the river flows over hard, resistant rock in a narrow gorge
  • (c)the river flows against the dip of the underlying beds
  • (d)the river is tidal and enters the sea through a funnel-shaped mouth

  Answer(a) The river carries a heavy sediment load, has a variable discharge and easily eroded banks — the excess load is dropped as mid-channel bars, and the flow divides and rejoins around them to give the maze of interconnected channels. The Kosi in north Bihar and the Brahmaputra in Assam are the standard Indian examples, and braiding is a channel pattern rather than a structural relationship.