UPSC IdeAS: World Geography: River Drainage Patterns & Erosion Processes

River Drainage Patterns

If the rocks are composed of homogeneous beds of uniform resistance to erosion, the tributaries will join the main stream obliquely as insequent streams
The drainage pattern so evolved will be tree like in appearance & therefore termed as Dendritic drainage
Most of the rivers of the Indo-Gangetic Plains are of dendritic type

Rectangular drainage patternis found in regions that have undergone faulting.
Rectangular drainage develops on rocks that are of approximately uniform resistance to erosion, but which have two directions of jointing at approximately right angles.
The joints are usually less resistant to erosion than the bulk rock so erosion tends to open the joints and streams eventually develop along the joints.
The result is a stream system in which streams consist mainly of straight line segments with right angle bends and tributaries join larger streams at right angles.
A typical example of this drainage pattern is found is the Vindhyan Mountains of India.

Trellis drainage develops in folded topography like that found in the Appalachian Mountains of North America.
Rocks are made up of alternate layers of hard & soft rocks, hence tributaries tends to follow the pattern of rock structure
A trellis drainage pattern occurs when tributaries join a main stream and erode a valley at approximately right angles in a pattern that resembles a garden trellis.
The old folded mountains of the Singhbhum (Chotanagpur Plateau) have a drainage of trellis pattern

It is a pattern characterized by outflowing rivers, away from a central point, analogous with the spokes of a wheel.
It tends to develop on the flanks of a dome or a volcanic cone.
A good example of a radial drainage pattern is provided by the rivers originating from the Amarkantak Mountain.
Rivers like Narmada, Son and Mahanadi originating from Amarkantak Hills flow in different directions and are good examples of radial pattern.
Radial drainage patterns are also found/in the Girnar Hills (Kathiawar, Gujarat), and Mikir Hills of Assam

When a river flows it carries with it eroded materials which can be divided into 3 distinct types

Materials in Solution	Minerals which are dissolved in water
Materials in Suspension	Suspension of Sand, Silt & Mud in water
The Traction Load	Coarser materials such as pebbles, stones, rocks & Boulders

The ability of river to move the various grades of materials depends greatly on the volume of the water, velocity of the flow & size, shape and weight of the load
It is said that by doubling the velocity of a river, its transporting power is increased by more than 10 times.

Mechanical grinding of river’s traction load against the banks & bed of the river.
The rock fragments hurdle against the sides as well as bottom of the river leading to lateral & vertical corrasion

Lateral corrasion is sideways erosion which widens the V shaped valley.

Vertical corrasion is the downward action which deepens the river channel.

Chemical action of water on soluble or partly soluble rocks with which river come into contact
For ex. in case of Calcium carbonate

Wear & tear of transported material among them when they roll and collide into one another