Drainage Pattern

Drainage refers to the flow of water through clearly defined channels that move in various directions, draining water from different regions. The water’s direction and flow are influenced by factors like rocks, geological structure, slope, topography, and flow speed. Rivers in India have adapted to land’s physical conditions through three major physiographic divisions, which are studied in India’s physiography.The drainage system consists of a network of tributaries and a main river that collect surface water and direct it towards seas, lakes, or other water bodies. These systems also help in the formation of plains.

Rivers drain water from catchment area, forming drainage basins.
Watersheds separate drainage basins from each other.
Larger rivers like Ganga or Brahmaputra have basins acting as significant land catchment areas.

Types of Drainage Systems:

Drainage systems are classified into two main types:

1. Subsequent Drainage System: This type of drainage follows the natural slope and geological structure of the land. Several kinds of streams are connected to this system:
   
   • Inconsequent or Antecedent Streams: These rivers, like the Indus and Ganga, existed before major geological changes. They continue their courses even after mountain uplifts, creating gorges.
   • Consequent Streams: These rivers are formed in alignment with the original slope of the land. An example is most of the rivers in Peninsular India.
   • Subsequent Streams: These streams develop after the consequent streams and join them at right angles. Examples include the Chambal, Sind, and Betwa rivers.
   • Obsequent Streams: These rivers flow in the opposite direction to the consequent streams but meet at right angles.
   • Resequent Streams: These streams follow the direction of the main river but join it at a right angle.
2. Non-Subsequent Drainage System: This system does not follow the regional slope or geological structure of an area, indicating a more complex development of the river system.
   

Drainage Patterns:

A drainage pattern is the arrangement of streams within a drainage basin. Rivers are connected by tributaries, which form distinct patterns influenced by the type of rocks in the drainage basin. The major types of drainage patterns are:

• Dendritic Pattern: This pattern looks like the branches of a tree, with smaller branches joining larger ones. It forms in areas with uniform rock types and little faulting or jointing. An example is the rivers of the Indo-Gangetic plains.
• Trellis Pattern: This is a rectangular pattern where primary rivers run parallel to each other, and secondary rivers meet them at right angles. Example: Singhbhum region of the Chhotanagpur plateau.
• Radial Pattern: In this pattern, rivers radiate out from a central point, like the spokes of a wheel. Example: Amarkantak range.
• Centripetal Pattern: In this pattern, rivers flow towards a central point, such as a lake or depression. An example is the Loktak Lake in Manipur.

Classification of Drainage Systems in India:

India’s drainage system is classified into different categories based on water discharge and the size of drainage basins:

1. Discharge into the Bay of Bengal vs. the Arabian Sea:
   
   • Bay of Bengal: About 77% of India’s drainage area, including major rivers like the Ganga, Brahmaputra, Mahanadi, and Krishna, flows towards the Bay of Bengal.
   • Arabian Sea: Approximately 23% of the drainage, including rivers like the Indus, Narmada, Tapti, Mahi, and Periyar, drains into the Arabian Sea.
2. By Size of Watershed:
   
   • Major River Basins: These have catchment areas larger than 20,000 square kilometers and typically receive high rainfall. Examples include rivers in the north of the Tropic of Cancer, and others between the Tropic of Cancer and 20°N latitude, as well as several rivers in Peninsular India.
   • Medium River Basins: These have catchment areas between 2,000 and 20,000 square kilometers and receive medium rainfall. They contribute to 7% of the total runoff.
   • Minor River Basins: These have catchment areas smaller than 2,000 square kilometers and account for 8% of the total runoff.