Drainage Patterns

Drainage Pattern is the pattern formed by the streams, rivers, and lakes in a particular drainage basin. The pattern created by stream erosion over time reveals characteristics of the kind of rocks and geologic structures in a landscape region drained by streams.

The drainage pattern is governed by the topography of the land, the gradient of the land, and whether a particular region is dominated by hard or soft rocks.

The article aims to discuss the types of drainage pattern which hold relevance for various competitive exams as well as the IAS Exam.

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Types of Drainage Patterns

Based on the shape and formation of river patterns, there are different drainage patterns. Broadly it is classified into two types –

1. Discordant Drainage pattern
2. Concordant Drainage pattern

Types of Drainage Pattern – Discordant Drainage Pattern

1. It does not correlate to the topology or geology of the area.
2. The river in the discordant drainage pattern follows its initial path irrespective of the changes in topography.
3. Further classified into two types – Antecedent and Superimposed.

• Antecedent Drainage –
  • Also called inconsequent drainage.
  • A part of a river slope and the surrounding area gets uplifted and the river sticks to its original slope, cutting through the uplifted portion like a saw forming deep gorges like [Vertical erosion or Vertical down cutting].
  • Examples of antecedent rivers or drainage – Indus, Sutlej, Brahmaputra, and other Himalayan rivers.
• Superimposed drainage – 
  • Also called superinduced drainage or epigenetic drainage.
  • a river flowing over a softer rock stratum reaches the harder basal rocks but continues to follow the initial slope.
  • The stream has enough erosive power that it cuts its way through any kind of bedrock, maintaining its former drainage pattern.
  • It exhibits discordance with the underlying rock structure as it originally developed on a cover of rocks that have now disappeared and retains their courses unaffected by the newly exposed structures.
  • Examples of Superimposed drainage or rivers  – The Damodar, the Subarnarekha, the Chambal, the Banas, and the rivers flowing at the Rewa Plateau.

Types of Drainage Pattern – Concordant Drainage Pattern

1. It correlates to the topology and geology of the area.
2. The path of the river is highly dependent on the topography and the slope of the river.
3. These are the most commonly found drainage systems and are classified into two types – Consequent drainage rivers and Subsequent drainage rivers.

• Consequent Drainage Rivers
  • A consequent drainage system is when the river follows the general direction of the slope.
  • Rivers of Peninsular India such as the Godavari, Krishna, and Cauvery are consequent rivers descending from the western ghats and flowing into the Bay of Bengal.
• Subsequent River System
  • A subsequent river is streams that have generally developed after the original stream (Consequent River)
  • It is a tributary stream that is eroded along an underlying belt of non-resistant rock after the main drainage pattern has been established.
  • For example – Chambal, Sind, Ken, Betwa, Tons, and Son are the subsequent drainage rivers and meet the Yamuna and the Ganga at right angles (the main drainage).

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Given below are the types of drainage patterns under the consequent and subsequent drainage systems –

1. Dendritic drainage pattern– 
   • also known as pinnate drainage, looks like the branching of a tree, found in regions with homogenous material.
   • These develop in areas where the rock such as granite, gneiss, volcanic rock, and sedimentary rock which has not been folded (or unconsolidated material) beneath the stream has no particular fabric or structure and can be eroded equally easily in all directions.
   • It develops in a terrain which has uniform lithology, and where faulting and jointing are insignificant.
   • These are by far the most common and a few examples are Indus, Godavari, Mahanadi, Cauvery, and Krishna.
2. Parallel drainage pattern-
   • A pattern of rivers caused by steep slopes with some relief. It is formed where there is a slope. The tributaries run parallel to each other in a uniformly sloping region.
   • Example – Rivers of lesser Himalayas and the small and swift rivers originating in the Western Ghats that flow into Arabian Sea.
3. Trellis Drainage Pattern–
   • patterns look similar to the common garden trellis. These develop where sedimentary rocks have been folded or tilted and then eroded to varying degrees depending on their strength.
   • In this type, the short subsequent streams meet the main stream at right angles.
   • Through soft rocks differential erosion paves the way for tributaries.
   • Examples include – old folded mountains of the Singhbhum (Chotanagpur Plateau).
4. Rectangular Drainage Pattern–
   • The main stream bends at right angles and the tributaries join at right angles creating rectangular patterns.
   • These are found in regions that have undergone faulting. It develops in the area that have very little topography and a system of bedding planes, fractures, or faults that form a rectangular network.
   • Example – streams found is the Vindhyan Mountains of India.
5. Radial Drainage Pattern–
   • Develops around a central elevated point where the streams radiate outwards from a central high point.
   • The tributaries from a summit follow the slope downwards and drain down in all directions.
   • Examples – Rivers like Narmada, Son and Mahanadi originating from Amarkantak Hills flow in different directions. Also, the Girnar Hills (Kathiwar, Gujarat), and Mikir Hills of Assam forms radial draingae pattern.
6. Centripetal Drainage Pattern–
   • The streams converge from all sides in the low lying basisns.
   • Stream flows towards a central depression.
   • It is similar to the radial drainage system, with the only exception that radial drainage flows out where as the  centripetal drainage flows in.
   • Examples include streams of Ladakh, Tibet, and the Baghmati and its tributaries in Nepal.
7. Deranged Drainage Pattern-
   • There is no coherent pattern to the rivers and lakes.
   • Develop from the disruption of a pre-existing drainage pattern.
   • Example – the glaciated valleys of Karakoram
8. Angular Drainage Pattern-
   • These pattern are formed where bedrock joints and faults intersect at more acute angles.
   • This pattern is common in Homalayan Foothhill region.
9. Annular Drainage Pattern-
   • When the upland has an outer soft stratum, the radial streams develop subsequent tributaries which try to follow a circular drainage around the summit.
   • Though these are uncommon drainage pattern in India but Pithoragarh (Uttarakhand), Nilgiri Hills in Tamil Nadu and Kerala are a few example of such drainage pattern.
10. Barbed Drainage Pattern – 
    • Arun River (Nepal), a tributary of the Kosi is a good example of this type of drainage pattern.
    • This pattern is developed where the confluence of a tributary with the main river is characterized by a discordant junction, as if the tributary intends to flow upstream and not downstream.
    • It is the result of capture of the main river which completely reverses its direction of flow, while the tributaries continue to point in the direction of former flow.

Consider the following statements:

1. Drainage patterns are governed by the topography of the land.

2. There are only 2 types of drainage patterns.

Which of the following statements are correct:

a) 1 only

b) 2 only

c) Both 1 and 2

d) None of the above

Answer: a

The above details would help candidates prepare for UPSC 2024.