Define drainage pattern ? Explain the factors affecting drainage pattern and types of drainage patterns
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Answer:
In a drainage basin, a number of factors such as topography, soil type, bedrock type, climate and vegetation cover influence input, output and transport of sediment and water (Charlton, 2008). These factors also influence the nature of the pattern of water bodies (Twidale, 2004).
The main river along with its tributaries develops a river system or a drainage system. The area on the earth's surface, which is drained by a single river system, is called a drainage basin or river basin. The relief feature which separates two river basins is called a water- shed or water-divide.
The main river and its tributaries within a drainage basin form certain patterns, called the drainage pattern. The shape of the drainage pattern depends on the (1) slope of the land, (2) underlying rock structure, (3) climatic conditions in the area and (4) human activities. The main types of drainage patterns are dendritic, trellis, rectangular and radial. A combination of several patterns can be seen in the same river basin.
1. The Dendritic Drainage Pattern: The word 'dendritic' has been derived from the Greek word dendron, meaning a tree. In this pattern, the main river is like the trunk of a tree and the tributaries join the main river like the branches of a tree. This pattern develops, where the river channel follows the slope of the land. It is the most common type of drainage pattern.
2. The Trellis Drainage Pattern: It is a rectilinear pattern, which develops in areas where hard and soft rocks occur parallel to each other. In this pattern the main river follows the direction of general slope, while the tributaries flow in the direction of strike. The tributaries meet the main stream at almost right angles.
3. The Rectangular Drainage Pattern: In this drainage pattern, the tributary streams join the main river at almost right angles. It resembles the trellis drainage pattern. But it develops in those areas where the joints in the rock structure form a rectangular pattern. In the rectangular pattern, the streams are more closely spaced than in the trellis pattern.
4. The Radial Drainage Pattern: In this pattern, the streams radiate or flow in different directions from a central peak or dome-like structure, like the spokes of a wheel. The streams follow the slope of the land.
A stream flowing in the direction of the slope or as a consequence of the slope is called the consequent stream. The rivers which existed before the formation of the Himalayas and have cut their courses southwards by making gorges in the mountains are known as the antecedent rivers.