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Geography: Class 11 (Part 1) — Chapter 3: Drainage System

Introduction to Drainage Concepts

The flow of water through well-defined channels is known as drainage, and the network of such channels is called a drainage system. The drainage pattern of an area is determined by geological time period, nature and structure of rocks, topography, slope, amount of water flowing, and the periodicity of the flow.

Key Geographical Terms

  • Catchment Area: The specific area from which a river drains the water collected.
  • Drainage Basin: An area drained by a river and its tributaries.
  • Watershed: The boundary line separating one drainage basin from another. While river basins cover larger areas, watersheds are smaller in scale and apply to small rivulets and rills.

Important Drainage Patterns

Pattern TypeDescriptionExample
DendriticResembles the branches of a tree.Rivers of the northern plains.
RadialRivers originate from a hill and flow in all directions.Rivers originating from the Amarkantak range.
TrellisPrimary tributaries flow parallel to each other and secondary tributaries join them at right angles.Appalachian region, parts of old fold mountains.
CentripetalRivers discharge their waters from all directions into a lake or depression.Loktak lake in Manipur.
Classification of Indian Drainage Systems

The Indian drainage system can be classified based on different criteria, including discharge orientation, watershed size, and mode of origin.

Based on Discharge of Water (Orientation to the Sea)

The Indian drainage is divided into two major groups, separated by the Delhi ridge, the Aravalis, and the Sahyadris:

$$\text{Discharge Ratio} = 77\% \text{ (Bay of Bengal)} : 23\% \text{ (Arabian Sea)}$$
  • Bay of Bengal Drainage: Nearly 77 percent of the drainage area (Ganga, Brahmaputra, Mahanadi, Krishna, etc.) is oriented towards the Bay of Bengal.
  • Arabian Sea Drainage: Nearly 23 percent of the drainage area (Indus, Narmada, Tapi, Mahi, Periyar) discharges into the Arabian Sea.

Based on the Size of the Watershed

CategoryCatchment Area SizeNumber of Basins / Examples
Major River BasinsMore than 20,000 sq. km14 basins (Ganga, Brahmaputra, Krishna, Tapi, Narmada, Mahi, Pennar, Sabarmati, Barak, etc.)
Medium River Basins2,000 to 20,000 sq. km44 basins (Kalindi, Periyar, Meghna, etc.)
Minor River BasinsLess than 2,000 sq. kmFairly good number of rivers flowing in low rainfall areas.

Based on Mode of Origin and Characteristics

  • Himalayan Drainage: Perennial rivers fed by both glaciers and precipitation.
  • Peninsular Drainage: Non-perennial, rain-fed rivers with fixed courses and absence of meanders.
The Himalayan Drainage System

The Himalayan drainage system has evolved through a long geological history and includes three major river basins: the Indus, the Ganga, and the Brahmaputra.

Evolution of Himalayan Drainage

Geologists believe that during the Miocene period (5-24 million years ago), a mighty river called the Shiwalik or Indo-Brahma traversed the entire longitudinal extent of the Himalayas from Assam to Punjab, discharging into the Gulf of Sind. Over time, this river was dismembered into three main systems due to the Pleistocene upheaval in the western Himalayas (uplift of Potwar Plateau/Delhi Ridge) and the down-thrusting of the Malda gap.

The Indus System

One of the largest river basins in the world, with a total length of 2,880 km (1,114 km in India).

  • Origin: Glacier near Bokhar Chu in the Tibetan region (Kailash Mountain range) at an altitude of 4,164 m. Known as Singi Khamban (Lion's mouth) in Tibet.
  • Course: Flows northwest between Ladakh and Zaskar ranges, cuts a spectacular gorge near Gilgit, and enters Pakistan near Chilas.
  • Tributaries: Himalayan tributaries include the Shyok, Gilgit, Zaskar, Hunza, Nubra, Shigar, Gasting, and Dras. Right bank tributaries from Sulaiman ranges include Khurram, Tochi, Gomal, Viboa, and Sangar.
  • The Panjnad: The collective name for the five rivers of Punjab: Satluj, Beas, Ravi, Chenab, and Jhelum.

The Ganga System

The most important river basin of India, stretching over 2,525 km.

  • Origin: Rises as the Bhagirathi from the Gangotri glacier near Gaumukh. It meets the Alaknanda at Devprayag, from where it is known as the Ganga.
  • Tributaries:
    • Right Bank: Yamuna (longest tributary, originates from Yamunotri glacier), Son.
    • Left Bank: Ramganga, Gomati, Ghaghara, Gandak, Kosi (the 'Sorrow of Bihar'), and Mahananda.
  • Namami Gange Programme: An Integrated Conservation Mission approved in June 2014 to abate pollution, conserve, and rejuvenate the National River Ganga.

The Brahmaputra System

  • Origin: Chemayungdung glacier of the Kailash range near Mansarovar lake.
  • Course: Flows eastward longitudinally through southern Tibet as the Tsangpo (meaning 'the purifier'). It enters India near Namcha Barwa as the Siang or Dihang.
  • Tributaries: Left bank: Dibang (or Sikang), Lohit, Burhi Dihing, and Dhansari. Right bank: Subansiri, Kameng, Manas, and Sankosh.
  • Enters Bangladesh near Dhubri and is known as the Jamuna before merging with the Padma.
The Peninsular Drainage System

Older than the Himalayan drainage system, characterized by broad, largely-graded shallow valleys and mature rivers.

Evolution of Peninsular Drainage

  1. Subsidence of the western flank of the Peninsula during the early Tertiary period, submerging it below the sea.
  2. Upheaval of the Himalayas causing subsidence of the northern flank of the Peninsular block, leading to trough faulting (where the Narmada and Tapi flow).
  3. Slight tilting of the Peninsular block from northwest to southeast, orienting the major drainage towards the Bay of Bengal.

Major Peninsular Rivers

RiverOriginLengthKey Features / Tributaries
MahanadiSihawa, Raipur (Chhattisgarh)851 kmFlows through Chhattisgarh and Odisha into the Bay of Bengal.
GodavariNasik district (Maharashtra)1,465 kmLargest Peninsular river, also called Dakshin Ganga. Tributaries: Penganga, Indravati, Pranhita, Manjra.
KrishnaNear Mahabaleshwar in Sahyadri1,401 kmSecond largest east-flowing Peninsular river. Tributaries: Koyna, Tungbhadra, Bhima.
KaveriBrahmagiri hills, Kogadu (Karnataka)800 kmPerennial-like flow due to dual monsoon rainfall. Tributaries: Kabini, Bhavani, Amravati.
NarmadaAmarkantak plateau (Madhya Pradesh)1,312 kmFlows westward in a rift valley between Satpura and Vindhyan ranges; forms Dhuandhar waterfall.
TapiMultai, Betul (Madhya Pradesh)724 kmWestward flowing river draining parts of Maharashtra, MP, and Gujarat.
LuniNear Pushkar (Rajasthan)EphemeralLargest river system of Rajasthan, west of Aravali; terminates in the Rann of Kuchchh.
Usability and Issues of River Water

Indian rivers carry massive volumes of water, but distribution is highly unequal across time and space, leading to simultaneous floods and droughts.

Key Challenges

  • Water Pollution: Caused by domestic sewage, industrial effluents, agricultural runoff, and cultural practices (immersion of statues, cremation on banks).
  • River Water Disputes: Inter-state conflicts over water sharing due to seasonal scarcity.
  • Siltation: High load of silt reduces channel capacity, leading to shifting courses (e.g., Kosi).

Proposed Solutions

Inter-basin water transfer schemes have been proposed to divert surplus water to water-deficit basins. Examples include:

  • Periyar Diversion Scheme
  • Indira Gandhi Canal Project
  • Kurnool-Cuddapah Canal
  • Beas-Satluj Link Canal
  • Ganga-Kaveri Link Canal