Key Drainage Terminology
Specific channels that carry the flow of water are termed ‘drainage,’ and a ‘drainage system’ is the network of these channels.
When a river collects water from a specific region, this area is termed its “catchment area.”
A ‘drainage basin’ designates the region drained by a river and its tributaries.
We call the boundary line that separates one drainage basin from another the ‘watershed.’
Large rivers’ catchments are often termed “river basins,” whereas smaller rivulets and rills are commonly referred to as “watersheds.” Note that river basins cover more extensive areas compared to watersheds.
The drainage pattern within an area is shaped by various factors, including geological time periods, rock composition and structure, topography, slope, water volume, and flow regularity.
Drainage Patterns: Geometric Arrangements of Streams
- Dendritic: Resembling the branches of a tree with numerous twigs. This type of pattern is known as dendritic drainage. The northern plain rivers are examples of dendritic drainage.
- Radial: Radial drainage patterns form when rivers originate from a central point, typically a hill, and flow outward in all directions. For instance, rivers originating from Amarkantak exhibit this pattern.
- Centripetal: A centripetal drainage pattern occurs when rivers discharge their waters from various directions into a central lake or depression. Loktak Lake in Manipur is an example of this pattern.
- Trellis: Trellis drainage patterns develop when primary tributaries of main rivers flow parallel to each other, and secondary tributaries join them at right angles. This pattern is observable in rivers in the upper part of the Himalayan region.
Indian Drainage System
The Indian drainage system can be categorized based on various factors:
1. Orientation to the Sea:
- Arabian Sea Drainage: Rivers in this category discharge their waters into the Arabian Sea. They are geographically separated from the Bay of Bengal drainage by natural features, including the Delhi Ridge, the Aravallis, and the Sahyadris.
- Bay of Bengal Drainage: Rivers in this group, including the Ganga, Brahmaputra, Mahanadi, and Krishna, flow towards the Bay of Bengal. This category encompasses about 77% of the drainage area in India.
2. Size of Watershed:
- Major River Basins: Comprising watersheds with more than 20,000 sq. km of catchment area, this category includes prominent basins like the Ganga, Brahmaputra, and Krishna, among others.
- Medium River Basins: Encompassing catchment areas ranging from 2,000 to 20,000 sq. km, this category includes basins like Kalindi and Periyar.
- Minor River Basins: These basins feature catchment areas of less than 2,000 sq. km and include numerous rivers found in regions with low rainfall.
Indian Drainage System Classification
The Indian drainage system is broadly classified into two major groups:
1. Himalayan Rivers: Rivers originating from the Himalayas constitute this group.
2. Peninsular Rivers: Rivers that flow within the Indian peninsula belong to this category.