Drainage System Class 11 Notes Geography Chapter 3 - CBSE

• A river drains the water collected from a specific area called its ‘catchment area’. An area drained by a river and its tributaries is called a drainage basin. The boundary line separating one drainage basin from the other is known as the watershed.
• On the basis of discharge of water (orientations to the sea), it may be grouped into :

(i) The Arabian Sea drainage; and

(ii) The Bay of Bengal drainage.

• Nearly 77% of the drainage area consisting of the Ganga, the Brahmaputra, the Mahanadi, the Krishna, etc. are oriented towards the Bay of Bengal, while 23% comprising the Indus, the Narmada, the Tapi, the Mahi, and the Periyar systems discharge their waters in the Arabian Sea.
• On the basis of the size of the watershed, the drainage basins of India are grouped into three categories :

(i) Major river basins with more than 20,000 sq. km of catchment area. It includes 14 drainage basins such as the Ganga, the Brahmaputra, the Krishna, the Tapi, the Narmada, the Mahi, the Penner, the Sabarmati, and the Barak.

(ii) Medium river basins with catchment area between 2,000–20,000 sq. km incorporating 44 river basins such as the Kalindi, the Periyar, and the Meghna.

• The Indus System is one of the world’s largest river basins, with a total size of 11,65,000 km² (in India, it is 321,289 km² ) and a length of 2,880 km (in India, it is 1,114 km).
• The Ganga System rises in the Gangotri glacier near Gaumukh (3,900 m) in the Uttarkashi district of Uttarakhand. Here, it is known as the Bhagirathi. It cuts through the Central and the Lesser Himalayas in narrow gorges. At Devprayag, the Bhagirathi meets the Alaknanda; hereafter, it is known as the Ganga. The Alaknanda has its source in the Satopanth glacier above Badrinath.
• The Alaknanda consists of the Dhauli and the Vishnu Ganga which meet at Joshimath or Vishnu Prayag. The
  other tributaries of Alaknanda such as the Pindar joins it at Kama Prayag while Mandakini or Kali Ganga meets
  it at Rudra Prayag.
• One of the world’s biggest rivers is the Brahmaputra. The Kailash range’s Chemayungdung glacier, which is close to the Mansarovar lake, is where it first appeared. It gets a large number of tributaries as it travels through the Assam valley for 750 km. The Burhi Dihing and Dhansari (South) are its main left-bank tributaries, but the Subansiri, Kameng, Manas, and Sankosh are significant right-bank tributaries. An earlier river is the Subansiri, which originates in Tibet.
• The peninsula’s rivers are mature, wide, and shallow valleys are heavily graded as evidence. Except for Narmada and Tapi, most of the main rivers in the peninsula run from west to east. The Ganga river system includes the Chambal, Sind, Betwa, Ken, and Son, originating in the peninsula’s northern section. The other significant river systems in the Peninsular drainage are the Mahanadi, Godavari, Krishna, and Kaveri.
  Peninsular rivers are distinguished by their stable path, lack of meanders, and seasonal water flow.
• There are some problems in river water usage. Some of these are:

(i) No availability in sufficient quantity
(ii) River water pollution
(iii) A load of silt in the river water
(iv) The uneven seasonal flow of water
(v) River water disputes between states
(vi) Shrinking of channels due to the extension of settlements towards the thalweg