CH 3 DRAINAGE

• The term ‘drainage’ describes the river system of an area. Small streams flowing from different directions come together to form the main river, which ultimately drains into a large water body such as a lake or a sea or an ocean.
• The area drained by a single river system is called a drainage basin. Any elevated area, such as a mountain or an upland which separates two drainage basins, is known as a water divide.
• Indian rivers are divided into two major groups: Himalayan rivers and Peninsular rivers
• Most Himalayan rivers are perennial, meaning they have water throughout the year
• Peninsular rivers are seasonal and their flow depends on rainfall
• Himalayan rivers like the Indus and Brahmaputra originate from the north of the mountain ranges
• Peninsular rivers mostly originate in the Western Ghats and flow towards the Bay of Bengal
• Himalayan rivers have long courses from their source to the sea
• Peninsular rivers have shorter and shallower courses compared to Himalayan rivers
• Major Himalayan rivers: Indus, Ganga, Brahmaputra
• A river system consists of a river and its tributaries
• Indus River:

  • One of the longest rivers in the world, with a total length of 2900 km
  • Rises in Tibet near Lake Mansarovar
  • Enters India in the Ladakh district of Jammu and Kashmir, forming a gorge
  • Joined by the Satluj, Beas, Ravi, Chenab, and Jhelum near Mithankot in Pakistan
• Ganga River:

  • Source called 'Bhagirathi', fed by Gangotri Glacier, joined by Alaknanda at Devaprayag in Uttarakhand
  • Emerges from mountains to plains at Haridwar
  • Joined by major tributaries like Yamuna, Ghaghara, Gandak, and Kosi
  • Length of over 2500 km
  • Northernmost point of Ganga Delta is Farakka in West Bengal
  • Bhagirathi-Hooghly flows southwards through deltaic plains to Bay of Bengal
  • Mainstream flows southwards into Bangladesh, joined by Brahmaputra, known as Meghna downstream, flowing into Bay of Bengal forming Sundarban Delta
• Brahmaputra River:

  • Rises in Tibet east of Mansarowar Lake
  • Slightly longer than Indus
  • Takes a 'U-turn' at Namcha Barwa (7757 m), enters India in Arunachal Pradesh as Dihang
  • Dihang joined by Dibang, Lohit, and other tributaries to form Brahmaputra in Assam
• Main water divide in Peninsular India is formed by the Western Ghats
• Major rivers of the Peninsula, such as the Mahanadi, the Godavari, the Krishna, and the Kaveri, flow eastwards and drain into the Bay of Bengal
• The Narmada and the Tapi are the only long rivers which flow west and make estuaries
• Narmada Basin:

  • Rises in the Amarkantak hills in Madhya Pradesh
  • Flows through a deep gorge at the ‘Marble Rocks’ near Jabalpur
  • At Dhuadhar Falls, the river jumps over steep rocks
  • Basin covers parts of Madhya Pradesh and Gujarat
• Tapi Basin:

  • Rises in the Satpura ranges in the Betul district of Madhya Pradesh
  • Basin covers parts of Madhya Pradesh, Gujarat and Maharashtra
• Godavari Basin:

  • Largest Peninsular river with a length of about 1500 km
  • Rises from the slopes of the Western Ghats in the Nasik district of Maharashtra
  • Basin covers parts of Maharashtra, Madhya Pradesh, Odisha and Andhra Pradesh
  • Known as the Dakshin Ganga
  • Joined by tributaries such as the Purna, the Wardha, the Pranhita, the Manjra, the Wainganga and the Penganga
• Mahanadi Basin:

  • Rises in the highlands of Chhattisgarh
  • Length of the river is about 860 km
  • Drainage basin shared by Maharashtra, Chhattisgarh, Jharkhand, and Odisha
• Krishna Basin:

  • Rises from a spring near Mahabaleshwar
  • Length of the river is about 1400 km
  • Drainage basin shared by Maharashtra, Karnataka and Andhra Pradesh
• Kaveri Basin:

  • Rises in the Brahmagri range of the Western Ghats
  • Total length of the river is about 760 km
  • Basin drains parts of Karnataka, Kerala and Tamil Nadu
• Smaller rivers flowing towards the east include:

  • The Damodar
  • The Brahmani
  • The Baitarni
  • The Subarnrekha
• India has many lakes that differ in size and characteristics
• Most lakes are permanent
• Some lakes contain water only during the rainy season
• Some lakes are the result of the action of glaciers and ice sheets
• Some lakes have been formed by wind, river action, and human activities
• Lakes in India are attractive to tourists in places like Srinagar and Nainital
• Different types of lakes in India include:

  • Ox-bow lakes formed by meandering rivers across floodplains
  • Lagoons formed by spits and bars in coastal areas, such as Chilika Lake, Pulicat Lake, and Kolleru Lake
  • Seasonal lakes in regions of inland drainage, like the Sambhar Lake in Rajasthan used for salt production
  • Freshwater lakes in the Himalayan region, mostly of glacial origin
  • The Wular Lake in Jammu and Kashmir, the largest freshwater lake in India formed by tectonic activity
  • Other important freshwater lakes like Dal Lake, Bhimtal, Nainital, Loktak, and Barapani
• Importance of Lakes:

  • Lakes help regulate the flow of a river
  • Prevent flooding during heavy rains
  • Maintain an even flow of water during the dry season
  • Can be used for developing hydel power
  • Moderate the surrounding climate
  • Maintain the aquatic ecosystem
  • Enhance natural beauty
  • Provide recreation
• Role of Rivers in the Economy:

  • Rivers have been of fundamental importance throughout human history
  • Water from rivers is a basic natural resource essential for various human activities
  • Rivers are used for irrigation, navigation, and hydropower generation
• River Pollution:

  • Growing demand for water from rivers is affecting water quality
  • Rivers are getting polluted due to untreated sewage and industrial effluents
  • Concern over rising river pollution led to the launching of various action plans to clean the rivers