Image credit fanshare.com

Image credit fanshare.com

ZIMSEC O Level Geography Notes: Drainage Patterns.

  • Drainage pattern is a term that refers to the way in which a river and its tributaries arrange themselves in the drainage basin.
  • The drainage pattern evolves over a long period of time and is affected by such factors as the underlying rock, the slope of the land, the existence or nonexistence of faultlines and tectonic movements.
  • The most common drainage patterns are: trellis, dendritic, radial, centripetal and parallel.

Trellis

Trellis drainage. Image credit wvc.edu

Trellis drainage. Image credit wvc.edu

  • Sometimes known as rectangular drainage pattern.
  • It is formed where streams join the main river at right angles.
  • The trellis pattern develops in areas of alternate hard and soft rocks.
  • The main river (also known as the consequent stream) follows the dip of the rocks down the slope after an initial uplift.
  • The tributaries (also known as the subsequent streams) which develop along the soft rock join the main stream at right angles.
  • These tributaries are at times joined by their own tributaries at more or less right angles.
  • Streams that flow against the dip of the rock strata are called obsequent streams.
  • In Zimbabwe Trellis drainage is found in the Chimanimani mounts.
  • Trellis drainage also occurs along fault lines and rectangular joints.
  • In eroded fold mount areas.
  • Due to headward erosion by streams.

Dendritic

Image credit wvc.edu

Image credit wvc.edu

  • The word dendritic comes from the Greek dendron meaning tree.
  • In dendritic drainage patterns the streams join one another in a shape that looks like the branches of a tree.
  • These streams eventually end up as one big river (the trunk).
  • The tributaries join each other at acute angles.
  • It is commonly found in areas with a uniform rock structure resulting in uniform erosion.
  • It is also found in areas which have gentle slopes.

Radial

Image credit wvc.edu

Image credit wvc.edu

  • Is formed where streams drain from a central highland in all directions.
  • It is also known as centrifugal and divergent drainage.
  • It is common in areas with conical hills and/or domes for example volcanic cones and other conical landforms.
  • Streams radiating from these areas can later end up forming other patterns as the flow downstream and meet up with other tributaries.
  • In Zimbabwe these type of drainage pattern is found in areas that have granite domes still covered by soil.

Centripetal or convergent drainage

Convergent Drainage

Convergent Drainage

  • Is found in areas where rivers drain towards a central inland lake, swamp or depression.
  • It is in essence an inland drainage system e.g. as in the case of the Dead Sea.
  • It is common in inland depressions such as faulted intermontane (between mountains) basins, calderas as well as in arid and semi-arid areas.

Parallel.

Parallel drainage. Image credit MediaWiki

Parallel drainage. Image credit MediaWiki

  • Rivers and tributaries flow downhill together in a more or less parallel pattern.
  • It is the simplest and most basic drainage pattern.
  • It occurs on newly uplifted land or land that is gently sloping allowing rivers and tributaries to flow in parallel channels.
  • Examples include the Zambezi and its tributaries.

To access more topics go to the Geography Notes page.

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