NCERT Solutions for Class 11 Geography Chapter 3: Drainage System (NCERT 2026–27)

These Class 11 Geography Chapter 3 solutions cover Drainage System from India: Physical Environment, the NCERT textbook for the 2026–27 session. The chapter explains what drainage and a drainage system are, how drainage basins and watersheds are defined, the major drainage patterns (dendritic, radial, trellis, centripetal), and the two great systems of India — the Himalayan drainage (the Indus, the Ganga and the Brahmaputra systems with their tributaries) and the Peninsular drainage (the Mahanadi, Godavari, Krishna, Kaveri, Narmada, Tapi and others). Below you get step-by-step answers to every NCERT exercise question, clear notes on key terms, extra practice, MCQs, Assertion–Reason and FAQs.

Class: 11 Subject: Geography Book: India: Physical Environment Chapter: 3 Chapter Name: Drainage System Session: 2026–27
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Class 11 Geography Chapter 3 – Overview

Chapter 3, Drainage System, begins by defining drainage as the flow of water through well-defined channels and the network of such channels as a drainage system. The area drained by a river and its tributaries is a drainage basin, separated from the next by a watershed. Indian drainage is grouped by orientation to the sea (the Bay of Bengal drainage carrying about 77 per cent of the area, and the Arabian Sea drainage about 23 per cent), by size of the watershed (major, medium and minor basins), and most importantly by mode of origin into the Himalayan drainage and the Peninsular drainage. The chapter traces the evolution of both systems (the mighty Indo–Brahma or Shiwalik river; the subsidence, upheaval and tilting that shaped the Peninsula), describes the Indus, Ganga and Brahmaputra systems with their tributaries in detail, and then the major Peninsular rivers — the Mahanadi, Godavari, Krishna, Kaveri, Narmada, Tapi and Luni. It ends by discussing the extent of usability of river water and the idea of inter-basin water transfer.

Key Concepts & Terms

Drainage: the flow of water through well-defined channels (rivers, nalas and channels) that drain the excess water of an area.

Drainage system: the network of such channels. The drainage pattern of an area is the outcome of geological time period, the nature and structure of rocks, topography, slope, amount of water and the periodicity of flow.

Catchment area: the specific area from which a river drains the water it collects.

Drainage basin: an area drained by a river and its tributaries; the catchments of large rivers are called river basins.

Watershed: the boundary line separating one drainage basin from another. Watersheds are small in area (catchments of rivulets and rills) while basins cover larger areas.

Drainage patterns: Dendritic (tree-branch-like, e.g. rivers of the northern plain); Radial (rivers flowing in all directions from a hill, e.g. the Amarkantak range); Trellis (primary tributaries parallel, secondary ones joining at right angles); Centripetal (rivers discharging from all directions into a lake or depression).

Himalayan drainage: the Indus, Ganga and Brahmaputra basins; fed by both snowmelt and precipitation, so the rivers are perennial; they form gorges, V-shaped valleys, meanders, ox-bow lakes, flood plains, braided channels and deltas, and frequently shift course (e.g. the Kosi).

Peninsular drainage: older than the Himalayan; broad, graded, shallow valleys; rivers have fixed courses, almost no meanders and largely non-perennial flow; most (except the Narmada and Tapi, which flow in rift valleys) flow west to east into the Bay of Bengal.

Antecedent rivers: rivers older than the relief they cross, which kept their course by cutting gorges as the land rose — e.g. the Satluj, the Kosi, the Subansiri.

Panjnad (Panchnad): the combined name of the five rivers of Punjab — the Satluj, the Beas, the Ravi, the Chenab and the Jhelum — which join the Indus a little above Mithankot.

Other key terms: Delta (a low-lying triangular depositional landform where a river splits into distributaries at its mouth, e.g. the Ganga delta); Estuary (a funnel-shaped tidal mouth where the river meets the sea without splitting, e.g. the Narmada and Tapi); Namami Gange Programme (the integrated mission to clean and rejuvenate the Ganga).

NCERT Exercises — Full Solutions

All questions below are reproduced verbatim from the NCERT textbook’s end-of-chapter Exercises. Answers are original, written in exam-ready style.

1. Choose the right answer from the four alternatives given below.

(i) Which one of the following rivers was known as the ‘Sorrow of Bengal’? (a) The Gandak    (b) The Son    (c) The Kosi    (d) The Damodar

ANSWER (d) The Damodar. The Damodar, flowing through a rift valley along the eastern margin of the Chotanagpur Plateau, was once known as the ‘Sorrow of Bengal’ for its destructive floods. It has since been tamed by the multipurpose Damodar Valley Corporation. (Note: the Kosi is called the ‘Sorrow of Bihar’.)

(ii) Which one of the following rivers has the largest river basin in India? (a) The Indus    (b) The Brahmaputra    (c) The Ganga    (d) The Krishna

ANSWER (c) The Ganga. The Ganga system is the largest river basin in India, draining about 8.6 lakh sq. km within India alone, with a large number of perennial and non-perennial tributaries from both the Himalayas and the Peninsula.

(iii) Which one of the following rivers is not included in ‘Panchnad’? (a) The Ravi    (b) The Chenab    (c) The Indus    (d) The Jhelum

ANSWER (c) The Indus. The ‘Panchnad’ (Panjnad) is the combined name of the five rivers of Punjab — the Satluj, the Beas, the Ravi, the Chenab and the Jhelum. The Indus is the master river they finally join, so it is not counted among the five.

(iv) Which one of the following rivers flows in a rift valley? (a) The Son    (b) The Narmada    (c) The Yamuna    (d) The Luni

ANSWER (b) The Narmada. The Narmada flows westward in a rift valley between the Satpura range in the south and the Vindhyan range in the north. (The Tapi too flows in a rift valley.) Such rivers lack large deltas and form estuaries.

(v) Which one of the following is the place of confluence of the Alaknanda and the Bhagirathi? (a) Vishnu Prayag    (b) Rudra Prayag    (c) Karan Prayag    (d) Deva Prayag

ANSWER (d) Deva Prayag (Devprayag). At Devprayag the Bhagirathi meets the Alaknanda, and from this confluence the combined river is known as the Ganga.

2. State the differences between the following.

(i) River Basin and Watershed

ANSWER Both are areas drained by a river system, but they differ mainly in size:
River BasinWatershed
The catchment of a large river is called a river basin.The catchments of small rivulets and rills are called watersheds.
Covers a much larger area.Small in area.
Example: the Ganga basin.Example: the catchment of a small stream or rill.
Both, however, are marked by unity — what happens in one part directly affects the whole unit — which is why they are treated as appropriate micro, meso or macro planning regions. (In the strict sense, ‘watershed’ also means the boundary line separating two basins.)

(ii) Dendritic and Trellis drainage pattern

ANSWER
Dendritic patternTrellis pattern
Resembles the branches of a tree.Has a rectangular, grid-like arrangement.
Tributaries join the main river at acute (irregular) angles.Primary tributaries flow parallel to each other and secondary tributaries join them at right angles.
Develops where the rock structure is uniform; example — the rivers of the northern plain.Develops where rocks of differing hardness alternate (folded/faulted terrain).

(iii) Radial and Centripetal drainage pattern

ANSWER
Radial patternCentripetal pattern
Rivers originate from a hill or dome and flow outward in all directions.Rivers flow inward from all directions and discharge their waters into a lake or depression.
Water moves away from a central high point.Water converges towards a central low point.
Example — rivers originating from the Amarkantak range.Example — rivers draining into a central lake/basin (an interior drainage).

(iv) Delta and Estuary

ANSWER
DeltaEstuary
A triangular depositional landform built where a river splits into many distributaries at its mouth.A funnel-shaped tidal mouth where the river meets the sea as a single channel.
Formed when the river deposits large quantities of sediment; the load is laid down.Formed when the sediment is carried out to sea (often due to a rift valley/steep gradient or strong tides).
Land area grows seaward; very fertile.No major new land is built; tidal water enters far inland.
Example — the Ganga–Brahmaputra delta.Example — the Narmada and Tapi estuaries.

3. Answer the following questions in about 30 words.

(i) What are the socio-economic advantages of inter-linking of rivers in India?

ANSWER Inter-linking transfers surplus water from flood-prone basins to water-deficit ones, controlling floods and droughts together. It expands irrigation and food production, provides drinking water, generates hydro-power, improves inland navigation and creates rural employment.

(ii) Write three characterstics of the Peninsular river.

ANSWER (1) They have fixed courses with an almost complete absence of meanders. (2) Most flow non-perennially, depending on monsoon rainfall. (3) Most (except the Narmada and Tapi) flow from west to east into the Bay of Bengal through broad, shallow, graded valleys.

4. Answer the following questions in not more than 125 words.

(i) What are the important characteristic features of north Indian rivers? How are these different from Peninsular rivers?

ANSWER Features of north Indian (Himalayan) rivers: They rise in the snow- and glacier-fed Himalayas, so they are perennial, carrying water all year from both snowmelt and rainfall. In their mountain courses they cut deep gorges and V-shaped valleys; on entering the plains they develop strong meanders, frequently shift their courses (the Kosi, ‘sorrow of Bihar’) and form depositional features such as ox-bow lakes, flood plains, braided channels and large deltas. They have very large basins and are youthful, actively eroding rivers. How they differ from Peninsular rivers: Peninsular rivers are older and mature, with broad, graded, shallow valleys. They are largely non-perennial (rain-fed), have fixed courses with hardly any meanders, and smaller basins. Most flow west to east into the Bay of Bengal (the Narmada and Tapi being rift-valley exceptions flowing west). Thus Himalayan rivers are perennial, meandering and course-shifting, while Peninsular rivers are seasonal, stable and non-meandering.

(ii) Suppose you are travelling from Haridwar to Siliguri along the foothills of the Himalayas. Name the important rivers you will come across. Describe the characteristics of any one of them.

ANSWER Travelling eastward from Haridwar to Siliguri along the Himalayan foothills, you would cross (roughly in order) the Ganga (at Haridwar), the Ramganga, the Sarda (Saryu/Kali), the Ghaghara, the Gandak, the Kosi, and the Mahananda near Siliguri. Characteristics of the Kosi: The Kosi is an antecedent river whose main stream, the Arun, rises to the north of Mount Everest in Tibet. After crossing the Central Himalayas in Nepal it is joined by the Son Kosi (west) and the Tamur Kosi (east), forming the ‘Sapt Kosi’ after uniting with the Arun. It brings a huge quantity of sediment from its upper reaches and deposits it in the plains; this blocks its channel, so the river frequently changes its course — earning it the name the ‘sorrow of Bihar’ for its devastating floods.

Extra Practice Questions

Short Answer Type Questions

Q1. Define drainage and drainage system.

ANSWERThe flow of water through well-defined channels is called drainage, and the network of such channels is called a drainage system. The pattern depends on geology, rock structure, topography, slope, amount of water and periodicity of flow.

Q2. On what bases can the Indian drainage system be classified?

ANSWERIt can be classified (i) by discharge/orientation to the sea — Arabian Sea drainage and Bay of Bengal drainage; (ii) by the size of the watershed — major, medium and minor river basins; and (iii) by mode of origin — the Himalayan drainage and the Peninsular drainage (the most accepted basis).

Q3. Why are the Himalayan rivers perennial while most Peninsular rivers are not?

ANSWERHimalayan rivers are fed by both the melting of snow/glaciers and by rainfall, so they carry water throughout the year. Most Peninsular rivers depend only on monsoon rainfall, so they have little water in the dry season and are non-perennial.

Q4. What is an antecedent river? Give two examples from this chapter.

ANSWERAn antecedent river is one that is older than the relief it crosses and kept its original course by cutting deep gorges as the land was uplifted. Examples from the chapter include the Satluj, the Kosi and the Subansiri.

Q5. Name the three major geological events that shaped the Peninsular drainage.

ANSWER(1) Subsidence and submergence of the western flank of the Peninsula in the early Tertiary period; (2) the upheaval of the Himalayas, which caused subsidence and trough-faulting on the northern flank (the Narmada and Tapi fill these troughs); and (3) a slight tilting of the Peninsular block from north-west to south-east, orienting most rivers towards the Bay of Bengal.

Long Answer Type Questions

Q1. Describe the Indus system and its tributaries.

ANSWERThe Indus (Sindhu) is one of the largest river basins of the world and the westernmost Himalayan river of India. It originates from a glacier near Bokhar Chu in Tibet at about 4,164 m in the Kailash range, where it is called ‘Singi Khamban’ (Lion’s mouth). Flowing north-west between the Ladakh and Zaskar ranges, it passes through Ladakh and Baltistan, cuts a gorge near Gilgit, and enters Pakistan near Chilas. Its Himalayan right-bank tributaries include the Shyok, Gilgit, Zaskar, Hunza, Nubra, Shigar, Gasting and Dras; near Attock it receives the Kabul, and further down the Khurram, Tochi, Gomal, Viboa and Sangar from the Sulaiman ranges. Above Mithankot it receives the ‘Panjnad’ — the combined Satluj, Beas, Ravi, Chenab and Jhelum — before discharging into the Arabian Sea east of Karachi. In India it flows through Ladakh and Jammu & Kashmir.

Q2. Give an account of the Ganga system and its major tributaries.

ANSWERThe Ganga is India’s most important river by basin size and cultural significance. It rises as the Bhagirathi from the Gangotri glacier near Gaumukh (3,900 m) in Uttarkashi, meets the Alaknanda at Devprayag (where it becomes the Ganga), and enters the plains at Haridwar. It flows about 2,525 km, splitting near its mouth into the Bhagirathi and the Padma, and discharges into the Bay of Bengal near Sagar Island; its basin covers about 8.6 lakh sq. km in India. Its major right-bank tributary is the Son. Its left-bank tributaries include the Ramganga, Gomati, Ghaghara, Gandak, Kosi and Mahananda. The Yamuna, its longest and westernmost tributary, rises in the Yamunotri glacier and joins it at Prayag; the Yamuna in turn receives the Chambal, Sind, Betwa and Ken (right bank, from the Peninsula). The Ganga is thus fed by rivers from both the Himalayas and the Peninsula.

Q3. Discuss the extent of usability of Indian river water and the measures suggested to improve it.

ANSWERIndian rivers carry huge volumes of water each year, but it is unevenly distributed in both time and space. Perennial rivers flow all year, while non-perennial rivers nearly dry up in the lean season; during the monsoon much water is wasted in floods and runs to the sea, and floods in one region coexist with drought in another. The chief problems in using river water are insufficient quantity where needed, pollution, silt load, uneven seasonal flow, inter-state river disputes and the shrinking of channels by encroachment of settlements. Suggested measures include inter-basin water transfer by linking rivers (e.g. the Beas–Satluj, Periyar Diversion, Indira Gandhi Canal and proposed Ganga–Kaveri link), building storage dams and canals to even out seasonal flow, rainwater harvesting, and pollution-control programmes such as the Namami Gange Programme and the Yamuna cleaning campaign to make rivers pollution-free.

MCQs & Assertion–Reason

1. The boundary line separating one drainage basin from another is called the:

(a) catchment    (b) watershed    (c) delta    (d) thalweg

2. Approximately what percentage of India’s drainage area is oriented towards the Bay of Bengal?

(a) 23%    (b) 50%    (c) 77%    (d) 90%

3. The drainage pattern that resembles the branches of a tree is called:

(a) trellis    (b) radial    (c) centripetal    (d) dendritic

4. The Indus originates from a glacier near Bokhar Chu in the:

(a) Pir Panjal range    (b) Kailash range    (c) Dhauladhar range    (d) Sahyadri

5. The Bhagirathi and the Alaknanda meet to form the Ganga at:

(a) Haridwar    (b) Karna Prayag    (c) Devprayag    (d) Rudra Prayag

6. The largest Peninsular river system, also called the ‘Dakshin Ganga’, is the:

(a) Krishna    (b) Mahanadi    (c) Godavari    (d) Kaveri

7. In Tibet the Brahmaputra is known as the Tsangpo, which means:

(a) the purifier    (b) Lion’s mouth    (c) the sorrow    (d) the great river

8. Which river is the largest tributary of the Indus?

(a) The Jhelum    (b) The Ravi    (c) The Chenab    (d) The Beas

9. The Luni, the largest river system of Rajasthan, finally drains into the:

(a) Arabian Sea    (b) Rann of Kuchchh    (c) Bay of Bengal    (d) Sambhar lake

10. The Narmada and the Tapi are exceptions among Peninsular rivers because they:

(a) are perennial    (b) flow west into the Arabian Sea through rift valleys    (c) form large deltas    (d) have meandering courses

Answer key: 1-(b), 2-(c), 3-(d), 4-(b), 5-(c), 6-(c), 7-(a), 8-(c), 9-(b), 10-(b).

For each Assertion–Reason question, choose: (A) Both true and the Reason correctly explains the Assertion; (B) Both true but the Reason is not the correct explanation; (C) Assertion true, Reason false; (D) Assertion false, Reason true.

A-R 1. Assertion: Himalayan rivers are perennial.

Reason: They are fed both by the melting of snow and by precipitation.

A-R 2. Assertion: Most Peninsular rivers flow from west to east.

Reason: The Western Ghats act as the water divide and the Peninsular block tilts towards the south-east.

A-R 3. Assertion: The Narmada forms a large delta at its mouth.

Reason: The Narmada flows in a rift valley and meets the Arabian Sea in a broad estuary.

A-R 4. Assertion: The Kosi frequently changes its course in the plains.

Reason: It brings a huge quantity of sediment from its upper reaches and deposits it, blocking its channel.

A-R 5. Assertion: A watershed covers a larger area than a river basin.

Reason: Watersheds are the catchments of large rivers while basins are the catchments of small rivulets.

Answer key: 1-(A), 2-(A), 3-(D), 4-(A), 5-(D).

Exam Tips & Common Mistakes

How to score full marks in this chapter

Memorise the three bases of classifying Indian drainage (orientation to the sea, size of watershed, mode of origin) and the four drainage patterns with one example each. For the Himalayan systems, learn the source, important tributaries and final sea for the Indus, Ganga and Brahmaputra; the ‘Panjnad’ five rivers and the prayags (Vishnu, Karna, Rudra, Deva Prayag) are favourite one-mark questions. For the Peninsular systems, keep a quick table of source, length and the sea/sea-mouth for the Mahanadi, Godavari, Krishna, Kaveri, Narmada and Tapi. Always present comparison questions (basin vs watershed, dendritic vs trellis, delta vs estuary) as a two-column table with an example.

Common mistakes to avoid

  • Calling the Kosi the ‘Sorrow of Bengal’ — it is the ‘Sorrow of Bihar’; the Damodar is the ‘Sorrow of Bengal’.
  • Including the Indus among the ‘Panchnad’ — the five are the Satluj, Beas, Ravi, Chenab and Jhelum.
  • Saying the Narmada and Tapi form deltas — they flow in rift valleys and form estuaries.
  • Confusing a delta (river splits into distributaries) with an estuary (single funnel-shaped tidal mouth).
  • Mixing up radial (water flows outward) with centripetal (water flows inward to a depression).
  • Stating that a watershed is larger than a river basin — it is the opposite.

Frequently Asked Questions

What is Chapter 3 of Class 11 Geography (India: Physical Environment) about?

Chapter 3, Drainage System, explains drainage and drainage systems, drainage basins, watersheds and drainage patterns, and describes the two great Indian systems — the Himalayan drainage (Indus, Ganga, Brahmaputra) and the Peninsular drainage (Mahanadi, Godavari, Krishna, Kaveri, Narmada, Tapi), along with the usability of river water.

What is the difference between the Himalayan and Peninsular drainage systems?

Himalayan rivers are perennial (snow- and rain-fed), youthful, form deep gorges and large meandering courses with deltas, and frequently shift course. Peninsular rivers are older and mature, largely non-perennial (rain-fed), have fixed courses with almost no meanders, broad shallow valleys, and mostly flow west to east into the Bay of Bengal.

Which is the largest river basin in India?

The Ganga river system has the largest basin in India, draining about 8.6 lakh sq. km within the country, fed by perennial and non-perennial rivers from both the Himalayas and the Peninsula.

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