what is drainage
Drainage is the outflow of water through the system of natural rivers
what is drainage pattern?
A drainage pattern is a layout that a river and its tributaries, or set of rivers, make on the earth’s surface. Some of the common river drainage patterns include dendritic river pattern, trellised river pattern, radial river pattern and centripetal river pattern
The following are hints to follow when you describe drainage in topographical map
- Divide the map into drainage basins using compass directions. Note that the drainage basin is an area drained by single river system.
- In each drainage basin explain the drainage pattern which the river system in the basin take. The common river drainage pattern are
- For each drainage basin explain how the rivers drain the relief region i.e highlands, lowlands and plateaus. at this part state the direction of the flow of the river, where the river is pouring its water and whether the area is well drained or not. The area is well drained when there is no swamps or marshlands and is not well drained when is waterlogged areas.
Dendritic drainage pattern
dendritic drainage pattern require the following condition to be formed:
- rock should be uniformly resistant to erosion
- this pattern is not dependent on geology
characteristics of dendritic drainage pattern
- the pattern is tree shaped
- the tributaries join the main stream at acute angles
example of rivers with dendritic pattern include tigela, mooi and umgeni in the south Africa
Radial drainage pattern
radial drainage pattern is formed on dome shaped hill, conical hill, mesa or butte
characteristic of radial drainage pattern
streams radiate outwards from the central high point.
example of areas with radial drainage pattern includekoffiebus and teebus in south africa
Trellis drainage pattern
requirement for trellis drainage pattern to be formed
- parallell ranges of fold mountains or alternate layers of hard and soft rock
- a strong main stream
- the pattern is dependent on the relief and the geology of the area
charateristics of the trellised drainage pattern
- tributaries meet the main stream at the right angles
- the main stream cut gaps through the mountains
example of areas with trellis drainage pattern include beffels river at laingsburg in south africa
Centripetal drainage pattern
this type of drainage pattern is formed on a central basin or a low lying area such as a lake or a marsh
characteristics of centripetal drainage pattern include:
- streams radiate inward from a sorrounding higher area
- it is opposite of radial drainage pattern
example of centripetal drainage pattern is flatter parts of namaqualand in south africa
parallel drainage pattern
characteristics of parallel drainage pattern
- the main streams flows parallel (or nearly) to each other
- the tributaries enters the main stream at very small angles
An example of an area with a parallel drainage pattern is tributaries of the steelport river in Limpopo
ractangular drainage pattern
this occurs in a well-jointed rock with joints exposed at the surface
characteristics of rectangular drainage pattern
- rivers flows in exposed joints
- rivers and tributaries have right angled bends
An example of areas with rectangular drainage pattern is rivers in Waterberg (Limpopo)
deranged drainage pattern
this type of drainage pattern occur in geologically young areas
characteristics of deranged drainage pattern
- haphazard pattern
- numerous lakes and swamps
- streams enters and leaves swamps and lakes randomly
example of areas with deranged drainage patterns are recently glaciated areas such as the Canadian shield
factors that influence the development of river drainage pattern
The slope of the land
The direction of the river Flow is generally guided by the direction of the slope since the flow of the water is controlled by gravitational force.
There are rivers whose flow is exclusively determined by the direction of the slope.
Difference in rock resistance or hardness
As the river erodes its channel, the nature of the bedrock becomes significant in determining how deep the river channel will become.
If the river encounters a very resistant rock outcrop in its path, it may have to change its direction to circumvent it despite the nature of the slope.
The rock structure along the river’s profile.
At certain stages in the course of the river, The arrangement of rock layers may influence the direction that the river takes.
The river may change its direction due to the direction of the strike of an exposed rock layer despite the general direction of the flow.