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

• 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

• 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

• 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

• 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

• 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.

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