Drainage System
Class 11 · Geography
4 ideas in Class 11 Geography, explained in plain words, with games and quizzes to practise.
Drainage Concepts, Patterns and Basins
Part of: Ideas and Evolution
Water moving through defined channels is called drainage, and the full network of channels is a drainage system. The area a river collects water from is its catchment, large catchments are river basins and small ones are watersheds, and the line dividing two basins is the water divide. Patterns include tree-like dendritic channels, radial streams flowing out in all directions, trellis grids joining at right angles, and centripetal streams gathering into a lake. About 77 per cent of India drains to the Bay of Bengal and 23 per cent to the Arabian Sea.
Why it matters. These terms are the vocabulary of every river discussion. Once learners can name patterns and basins, they can read river maps, argue about floods and judge water-sharing plans sensibly.
Key words
- Drainage
- : The flow of water through well-defined natural channels.
- Catchment area
- : The land area from which one river gathers its water.
- River basin
- : The large catchment of a big river with all its tributaries.
- Watershed
- : The small catchment of a rivulet, also the line dividing two basins.
- Water divide
- : A ridge or high line sending rain to different seas on either side.
Try it in two minutes
- Draw a tree branch and ask your child which drainage pattern it resembles.
- Sketch streams leaving a hilltop in all directions and name the pattern.
- Ask your child to sort Ganga, Periyar and a local stream into major, medium and minor basins.
- Trace the Delhi ridge, Aravalis and Sahyadris and ask which seas the two sides drain to.
Try at home. Ask your child to watch rainwater lines on a sloping courtyard and sketch the pattern they form.
Evolution of the Himalayan Drainage
Part of: Ideas and Evolution
Geologists picture a mighty Indo-Brahma river that once ran the whole length of the Himalaya into the Gulf of Sind, 5 to 24 million years ago. Later upheavals in the west and the sinking of the Malda gap split it into the Indus, Ganga and Brahmaputra systems. Himalayan rivers run all year on snowmelt plus rain, carve gorges and valleys in the hills, then wind through plains with meanders and shifting beds. The sediment-heavy Kosi jumps course so often it is called the sorrow of Bihar.
Why it matters. This story explains why three giant systems share one birth and why floods and shifting channels trouble the plains. It links plate movement, rain and human suffering in one chain.
Key words
- Perennial river
- : A river that carries water through all seasons of the year.
- Antecedent river
- : A river older than the mountains it cuts through, keeping its old path.
- Gorge
- : A deep narrow passage carved by a river through hard rock.
- Meander
- : A winding loop formed by a mature river swinging over its plain.
- Silt load
- : The sand and mud a river carries and drops along its course.
Try it in two minutes
- Draw one long westward river and cut it into three with two pushes to model the split.
- Ask your child why snow plus rain keeps these rivers flowing all year.
- Compare a gorge in the hills with a meander in the plains using sketches.
- Discuss why the Kosi's heavy sediment load forces it to change course.
Try at home. Ask your child to explain how the Potwar uplift and the Malda gap together redirected two great rivers.
Indus, Ganga and Brahmaputra Systems
Part of: Great Rivers and Water Use
The Indus, or Sindhu, starts at the Bokhar Chu glacier near Mansarovar at 4164 m, runs 2880 km in all with 1114 km in India, gathers the Panjnad five of Punjab plus the Kabul, and reaches the Arabian Sea. The Ganga begins at the Gangotri glacier, becomes the Ganga where Bhagirathi meets Alaknanda at Devprayag, runs 2525 km with a basin of 8.6 lakh sq. km, and meets the sea near Sagar Island. The Brahmaputra starts at the Chemayungdung glacier, crosses Tibet as the Tsangpo, dives through a deep gorge, and braids across Assam before joining the Padma.
Why it matters. These three systems water the most crowded farmlands of South Asia. Knowing their tributaries and junctions helps learners trace floods, canals and holy cities to their river roots.
Key words
- Tributary
- : A smaller river that joins and feeds a larger one.
- Distributary
- : A branch that splits away from the main river near its mouth.
- Confluence
- : The meeting point of two or more rivers or streams.
- Panjnad
- : The combined flow of the Satluj, Beas, Ravi, Chenab and Jhelum.
- Glacier source
- : A mass of ice whose meltwater gives birth to a river.
Try it in two minutes
- Trace all three systems from source to sea on one map with three colours.
- Ask your child to recite the five Panjnad rivers from memory.
- Mark Devprayag, Prayag and Sagar Island and say what happens at each.
- Compare the Indus length in India with its total length.
Try at home. Ask your child to list the Ganga states in order and add up their kilometre shares to reach 2525.
Peninsular Rivers and the Use of River Water
Part of: Great Rivers and Water Use
Peninsular rivers are older and rain-fed: they keep fixed courses, show no meanders and shrink in the dry season. The Godavari, Krishna, Mahanadi and Kaveri flow east to the Bay of Bengal, while the Narmada, Tapi and Luni run west through rift valleys or desert. India's water arrives unevenly, so one region floods while another goes dry; rivers also carry silt and city and factory waste. Linking surplus basins to deficit ones is debated as one answer.
Why it matters. Most of peninsular India depends on these seasonal rivers. Understanding their limits plus the pollution load helps learners debate dams, links and clean-up drives with facts.
Key words
- Estuary
- : A wide drowned river mouth where fresh and sea water mix.
- Ephemeral river
- : A stream that flows only in the rainy season and dries up after.
- Silt
- : Fine mud and sand carried and dropped by flowing water.
- Water sharing
- : Dividing river water fairly between states, farms and cities.
- River linking
- : Joining basins with canals to move surplus water to dry areas.
Try it in two minutes
- Sort the Mahanadi, Godavari, Krishna, Kaveri, Narmada and Tapi by the sea they reach.
- Ask why the Narmada forms an estuary while the Godavari builds a delta.
- List three sources of river pollution from the chapter.
- Debate whether carrying flood water to dry basins is easy or hard.
Try at home. Ask your child to find the shares of the Krishna basin across three states and check that they add to one hundred.
What your child will practise
- Drainage Concepts, Patterns and Basins: Ocean Quick Fire (Quick Fire)
- Evolution of the Himalayan Drainage: Jungle Puzzle (Clue Puzzle)
- Evolution of the Himalayan Drainage: Jungle Quick Fire (Quick Fire)
- Indus, Ganga and Brahmaputra Systems: Candy Quick Fire (Quick Fire)
- Peninsular Rivers and the Use of River Water: Desert Puzzle (Clue Puzzle)
- Quiz: Drainage Concepts, Patterns and Basins (8 questions)
- Quiz: Evolution of the Himalayan Drainage (8 questions)
- Quiz: Indus, Ganga and Brahmaputra Systems (8 questions)
- Quiz: Peninsular Rivers and the Use of River Water (8 questions)