Radial drainage pattern

Topic: Drainage System of India: Rivers, Basins and Patterns · NCERT: Class 11, Ch 3 "Drainage System"

Meaning

A radial drainage pattern is one where rivers start on a high central point, such as a hill, dome or plateau top, and flow outward in all directions, like the spokes of a wheel. The pattern shows the shape of the land: a high centre with slopes falling away on every side. In India, the Amarkantak plateau shows it best, and it is the source of some of the largest rivers of Peninsular India.

Explanation

What a drainage pattern is

• A drainage pattern is the shape that a river and all its tributaries make on a map. (A tributary is a smaller stream that joins a bigger river.)
• Three things decide the shape:
• Slope: which way the land tilts, and how steeply.
• Rock structure: whether the rock is the same everywhere, or has folds, faults, joints, hard bands and soft bands.

• History: how old the land surface is, and what has happened to it, such as uplift, folding or glaciation.

• A river slowly adjusts to the rock under it. So the pattern shows the hidden geology underneath [2].

• NCERT names four patterns: dendritic, radial, trellis and centripetal. Radial is the one controlled mainly by slope from a high centre.

How radial drainage forms (cause → process → result)

• Cause: a high centre.
• A dome, a volcanic cone or a raised plateau top stands above the land around it.

• The ground slopes down on every side of this high point.

• Process: water runs downhill, away from the centre.

• Rain that falls on the high centre flows down whichever slope it lands on.

• Each slope gets its own stream, and these streams cut valleys as they flow.

• Result: rivers flow out like spokes.

• Seen on a map, the streams spread outward from one centre, like the spokes of a wheel.
• The rivers can end up in different river systems and even different seas.

Conditions it needs

• A raised centre. It needs a clear high point, such as a hill, dome, volcanic cone or plateau top.
• Slopes on all sides. The land must fall away in many directions, not just one.
• Not too worn down. On volcanic cones, the pattern stays clear only if the cone has not been eroded too much [2]. Once erosion has cut deep into a dome, streams may start following rings of weak rock instead, which gives the annular pattern [2].

Amarkantak: how the spokes fan out

Direction	River	Where it goes
West	Narmada	Arabian Sea. It is the largest west-flowing river of Peninsular India [4]
North	Son	Joins the Ganga as a right-bank tributary
East and south	Mahanadi headwaters, e.g. the Arpa	Mahanadi system, then the Bay of Bengal

• So rain from one plateau reaches two different seas: the Arabian Sea in the west and the Bay of Bengal in the east (the Son's water reaches the Bay through the Ganga).

Where it occurs

• World setting: radial drainage is typical of volcanic cones, as long as the cone has not been worn down too much [2].
• India's classic example: the Amarkantak plateau
• Location: in the Maikal (Maikala) range, on the Madhya Pradesh–Chhattisgarh border.
• Source of the Narmada: the Narmada rises in the Maikala range near Amarkantak, in Anupur district, Madhya Pradesh, at about 1,057 m [4].
• Rivers: the Narmada flows west, the Son flows north, and the Mahanadi headwaters (e.g. the Arpa) flow east and south.
• Narmada basin edges: the Vindhyas to the north, the Maikala range to the east, the Satpuras to the south and the Arabian Sea to the west [4].
• Protected area: the plateau lies in the Achanakmar–Amarkantak Biosphere Reserve, which is part of UNESCO's Man and the Biosphere (MAB) network. It is one of the least disturbed and most ecologically varied landscapes in Chhattisgarh and Madhya Pradesh [5].

Don't confuse with

• Centripetal drainage: this is the opposite of radial. In centripetal drainage, streams flow inward from all sides into a central lake or depression (a low hollow in the land), as at Loktak Lake, Manipur and Sambhar Lake, Rajasthan. Radial flows outward from a high centre.
• Annular drainage: both form around a dome. In radial drainage, rivers flow straight out from the dome. In annular drainage, they curve around it in rings, following weak rock on an eroded dome [2].
• Dendritic drainage: a tree-like pattern, where tributaries join the main river at acute angles (less than 90°) on uniform rock, as in the rivers of the northern plain. It spreads over a wide area. It does not fan out from one high point.
• Parallel drainage: many short streams run side by side down one steep slope, as in the short Western Ghats rivers. Radial streams flow in all directions, not just one.

Prelims Hooks

• Radial = outward from a high centre, like the spokes of a wheel. Centripetal = inward to a low centre. NCERT Exercise 2 tests this pair directly.
• Amarkantak (Maikala range, Anupur district, MP, about 1,057 m) → Narmada flows west, Son flows north, Mahanadi headwaters (e.g. Arpa) flow east and south [4].
• The Narmada is the largest west-flowing river of Peninsular India. Its basin lies between the Vindhyas (north) and the Satpuras (south) [4].
• The Son is a right-bank tributary of the Ganga that rises in the Amarkantak area.
• Radial drainage is classically found on volcanic cones. Centripetal drainage is found in craters and enclosed desert depressions [2] [3].
• Trap: Loktak and Sambhar are examples of centripetal, not radial, drainage. Rings of streams around an eroded dome are annular, not radial [2].

Mains Points

• Radial headwater zones are "water towers" (GS-I / GS-III):
• Amarkantak feeds the Narmada, the Son and the Mahanadi system.
• If its forest is damaged, inside the Achanakmar–Amarkantak Biosphere Reserve [5], river flows could drop across several states, from Madhya Pradesh and Chhattisgarh downstream.

• This makes a case for protecting the catchment (the area that collects rainwater for a river) and for states managing these river basins together.

• Patterns record landform and geology (GS-I):

• A radial pattern on a map points to a raised centre, such as a dome, cone or plateau top.

• Reading drainage patterns on maps and topographical sheets helps in understanding relief and rock structure.

• Planning use (GS-III):

• Rivers that start together on one high centre run into different basins and seas, so water sharing involves many states.
• The pattern also affects where dams, canals and interlinking projects (such as Ken–Betwa) can be placed.

Related concepts

• Drainage pattern
• Dendritic drainage pattern
• Trellis drainage pattern
• Centripetal drainage pattern
• Amarkantak plateau

Read more

• Drainage patterns