This MCQ module is based on: Drainage Concepts & the Himalayan River Systems
TOPIC 6 OF 17
Drainage Concepts & the Himalayan River Systems
🎓 Class 11
Social Science
CBSE
Theory
Ch 3 — Drainage System
⏱ ~25 min
🌐 Language: [gtranslate]
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Chapter 3 · Drainage System — Concepts & the Himalayan Rivers
Every drop of rain that falls on India eventually finds its way into a channel — a nala, a stream, a tributary, a great river. Why does some water race east to the Bay of Bengal while another hurries west to the Arabian Sea? Why do Himalayan rivers carry water all year while many Peninsular rivers shrink in summer? This part introduces the basic ideas of drainage — basins, watersheds, patterns — and then traces the three giants of north India: the Indus, the Ganga and the Brahmaputra.
3.1 Drainage — The Vocabulary of Flowing Water
You have surely seen water hurrying through streams, nalas and channels during the rainy season, draining off the land. Without these channels, low-lying areas would be permanently flooded; wherever channels are blocked or poorly defined, flooding becomes a regular hazard. The flow of water through well-defined channels is what geographers call drainage, and the network of those channels together is called a drainage system.
📖 Core Definition
The drainage pattern of an area is the outcome of four interacting controls: the geological history of the area, the nature and structure of the rocks, the topography and slope, and the amount and periodicity of water flowing. Two regions with similar rocks but different slopes will produce different drainage patterns.
3.1.1 Catchment, Basin and Watershed
A river collects water from a specific stretch of land called its catchment area?. The whole area drained by a river along with all of its tributaries is called a drainage basin?. The line of higher ground that separates one basin from another is the watershed?. The catchments of large rivers (the Ganga, the Brahmaputra) are usually called river basins, while those of small rivulets and rills are called watersheds. The difference is mostly one of scale — watersheds are small, basins are large.
🧭 Why Basins Matter for Planning
River basins and watersheds are bound by unity — what happens in one part of a basin (deforestation, dam-building, pollution) directly affects the rest. That is why basins and watersheds are accepted as the most appropriate units for micro, meso and macro planning regions in India.
3.1.2 Three Ways to Classify Indian Drainage
Geographers slice India's drainage in three different ways depending on the question they want to answer.
| Basis of Classification | Categories | Key Numbers |
|---|---|---|
| Discharge of water (which sea?) | (i) Bay of Bengal drainage; (ii) Arabian Sea drainage | ~77% of drainage area flows to Bay of Bengal; ~23% to Arabian Sea |
| Size of watershed | (i) Major basins (>20,000 sq km); (ii) Medium basins (2,000–20,000 sq km); (iii) Minor basins (<2,000 sq km) | 14 major basins; 44 medium basins; many minor basins |
| Mode of origin / character | (i) Himalayan drainage; (ii) Peninsular drainage | Most-accepted scheme used by NCERT |
The water-divide between the Bay of Bengal and Arabian Sea drainages is formed by the Delhi Ridge, the Aravalis and the Sahyadris. The Bay of Bengal side carries the Ganga, the Brahmaputra, the Mahanadi, the Krishna and others; the Arabian Sea side carries the Indus, the Narmada, the Tapi, the Mahi and the Periyar.
3.1.3 The Four Important Drainage Patterns
When you look at a topographic sheet, the network of channels usually falls into one of four classic shapes. Each shape is a fingerprint of the underlying geology and slope.
Dendritic — like a Tree
Tributaries branch like the limbs of a tree. Example: rivers of the Northern Plain.
Trellis — Grid-Like
Primary tributaries flow parallel; secondary tributaries join at right-angles — typical of folded-and-faulted ridge-and-valley terrain.
Radial — From a Hill
Rivers flow outward in all directions from a central high. Example: rivers rising on the Amarkantak range.
Centripetal — Inward to a Lake
Rivers from all directions discharge into a central depression or lake.
LET'S EXPLORE — Spot the Pattern
Bloom: L3 Apply
Open the topographic sheet given in Chapter 5 of Practical Work in Geography — Part I (NCERT). Pick out at least one example each of dendritic, trellis and radial drainage. For each, sketch a small inset on tracing paper and write a one-sentence justification linking the pattern to the slope or rock structure shown by the contour lines.
✅ Pointers
Dendritic patterns develop where the rocks are uniform and the slope is gentle — the river goes wherever gravity takes it. Trellis patterns appear where there are alternating hard and soft rock bands forming parallel ridges. Radial patterns betray a central dome or volcanic hill from which streams descend in all directions.
3.2 Indian Drainage — Himalayan vs Peninsular
The Indian drainage system is the joint outcome of three major physiographic units (the Himalayas, the Northern Plain and the Peninsular Plateau) plus the nature of precipitation. On the basis of mode of origin, nature and characteristics, the rivers are grouped into the Himalayan drainage and the Peninsular drainage. (A few rivers — Chambal, Betwa, Son — are actually older than most Himalayan rivers, but this scheme is still the most accepted classification, and we will follow it here.)
Himalayan: Perennial
Fed by both monsoon rain and melting snow, so they carry water all year. Pass through deep gorges and form V-shaped valleys.
Peninsular: Mostly Seasonal
Fed only by rainfall — many shrink to a trickle during the dry season. Their valleys are broad, shallow and graded.
Plains: Meanders & Deltas
After leaving the mountains, Himalayan rivers slow down on the plains — forming ox-bow lakes, flood plains, braided channels and large deltas.
Peninsular: Fixed Course
Flowing over rigid Archaean rocks, Peninsular rivers rarely change course. The Narmada and Tapi flow in fault-controlled rift valleys.
3.3 Evolution of the Himalayan Drainage
How did the present Himalayan rivers come to be? Geologists are not unanimous, but the most widely accepted view is that a single Indo-Brahma (or Shiwalik) river? once ran along the entire foot of the Himalayas — from Assam through Punjab and onwards into Sind — discharging into the Gulf of Sind during the Miocene period, roughly 5 to 24 million years ago. The remarkable continuity of the Shiwalik deposits, their lacustrine origin and the alluvial fill (sands, silts, clays, boulders, conglomerates) all support this idea.
During the Pleistocene upheaval in the western Himalayas, this single river was dismembered into three separate drainage systems:
🧭 The Three Children of the Indo-Brahma
(i) The Indus and its five tributaries — in the western part.(ii) The Ganga and its Himalayan tributaries — in the central part.
(iii) The Brahmaputra of Assam with its Himalayan tributaries — in the eastern part.
The break-up was driven by the uplift of the Potwar Plateau (Delhi Ridge), which became the water-divide between the Indus and Ganga systems, and by the down-thrusting of the Malda gap between the Rajmahal hills and the Meghalaya plateau in the mid-Pleistocene, which sent both the Ganga and the Brahmaputra towards the Bay of Bengal.
3.4 The Indus System
The Indus is one of the largest river basins of the world. Its total basin covers about 11,65,000 sq km (321,289 sq km of which lies inside India). The river itself is 2,880 km long in total — 1,114 km of which flow through India. It is the westernmost of the great Himalayan rivers.
The Indus rises near Bokhar Chu (31°15' N, 81°40' E) at an altitude of 4,164 m in the Kailash Mountain range of Tibet. There it is called Singi Khamban (Lion's Mouth). Flowing north-west between the Ladakh and Zaskar ranges, it crosses Ladakh and Baltistan, cuts a spectacular gorge across the Ladakh range near Gilgit, and enters Pakistan near Chilas in the Dardistan region. Inside India, it passes through the Union Territories of Ladakh and Jammu & Kashmir.
3.4.1 Tributaries of the Indus
On the right bank, the Indus picks up several Himalayan tributaries — the Shyok, Gilgit, Zaskar, Hunza, Nubra, Shigar, Gasting and Dras. Near Attock, the Kabul river joins from the right. Other right-bank tributaries — the Khurram, Tochi, Gomal, Viboa and Sangar — all originate in the Sulaiman ranges. A little above Mithankot, the river receives the Panjnad — the combined flow of the five rivers of Punjab.
📖 The Panjnad — Five Rivers of Punjab
The Panjnad is the joint name given to the five great left-bank tributaries of the Indus: Satluj, Beas, Ravi, Chenab and Jhelum. The Indus finally discharges into the Arabian Sea east of Karachi.
| River | Source | Key Features |
|---|---|---|
| Jhelum | Verinag spring, foot of Pir Panjal, Kashmir | Flows through Srinagar & Wular Lake; joins Chenab near Jhang. |
| Chenab | Tandi (Keylong, HP) — confluence of Chandra & Bhaga | Largest Indus tributary; flows 1,180 km before entering Pakistan; also called Chandrabhaga. |
| Ravi | West of Rohtang Pass, Kullu hills (HP) | Drains the Chamba valley; joins Chenab near Sarai Sidhu. |
| Beas | Beas Kund near Rohtang Pass (4,000 m) | Forms gorges at Kati and Largi; meets Satluj near Harike. |
| Satluj | 'Raksas Tal' near Mansarovar (4,555 m), Tibet — known as Langchen Khambab | Flows ~400 km parallel to Indus, comes out of a gorge at Rupar; antecedent river; feeds the Bhakra Nangal canal system. |
🌍 Antecedent Drainage
An antecedent river? is one that existed before the mountain it cuts through was uplifted. As the land rose, the river kept cutting downward at the same pace, sawing a deep gorge through the rising rock. The Satluj (Shipki La gorge) and the Subansiri are textbook Indian examples.
3.5 The Ganga System
The Ganga is India's most important river, both by basin size and by cultural significance. It rises from the Gangotri glacier near Gaumukh (3,900 m) in the Uttarkashi district of Uttarakhand, where it is called the Bhagirathi. After cutting through narrow gorges in the Central and Lesser Himalayas, the Bhagirathi meets the Alaknanda at Devprayag — and from that confluence onward the river is called the Ganga.
The Alaknanda itself rises in the Satopanth glacier above Badrinath. It is formed by the union of the Dhauli and the Vishnu Ganga at Joshimath (Vishnu Prayag). Other tributaries of the Alaknanda — the Pindar joins at Karna Prayag, and the Mandakini (Kali Ganga) joins at Rudra Prayag. The Ganga finally enters the plains at Haridwar.
📖 Ganga — The Numbers
Total length: 2,525 km. Shared by Uttarakhand (110 km), Uttar Pradesh (1,450 km), Bihar (445 km) and West Bengal (520 km). Indian basin area: about 8.6 lakh sq km — the largest river basin in India. Below Farakka the river splits into two distributaries — the Bhagirathi (Hugli) and the Padma — and finally discharges into the Bay of Bengal near Sagar Island.
3.5.1 Tributaries of the Ganga
The right-bank tributary Son rises on the Amarkantak plateau and joins the Ganga at Arrah, west of Patna. The major left-bank tributaries are the Ramganga, Gomati, Ghaghara, Gandak, Kosi and Mahananda. Important right-bank tributaries from the Peninsula — the Chambal, Sind, Betwa and Ken — actually join the Ganga's longest tributary, the Yamuna.
| Tributary | Source | Notes |
|---|---|---|
| Yamuna | Yamunotri glacier, western slope of Banderpunch (6,316 m) | Western-most & longest tributary; meets Ganga at Prayag (Allahabad). |
| Chambal | Near Mhow, Malwa plateau (MP) | Flows through a gorge above Kota (Gandhisagar dam); famous for Chambal ravines (badland topography); joins Yamuna. |
| Gandak | Nepal Himalayas, between Dhaulagiri & Mt. Everest | Two streams — Kaligandak & Trishulganga; joins Ganga at Sonpur near Patna. |
| Ghaghara | Glaciers of Mapchachungo | Cuts deep gorge at Shishapani; joined by Sarda; meets Ganga at Chhapra. |
| Kosi | North of Mt. Everest, Tibet (Arun) | Antecedent river; forms Sapt Kosi after joining Son Kosi & Tamur Kosi; called the 'Sorrow of Bihar' for shifting course frequently. |
| Ramganga | Garhwal hills near Gairsain | Enters UP plains near Najibabad; joins Ganga near Kannauj. |
| Damodar | Eastern Chotanagpur Plateau | Flows through a rift valley; main tributary Barakar; once 'Sorrow of Bengal' — now controlled by the Damodar Valley Corporation. |
| Sarda (Saryu) | Milam glacier, Nepal Himalayas (Goriganga) | Called Kali or Chauk along Indo-Nepal border; joins the Ghaghara. |
| Mahananda | Darjiling hills | Last left-bank tributary of the Ganga in West Bengal. |
| Son | Amarkantak plateau | Major right-bank tributary; forms waterfalls at the plateau edge. |
📜 Did You Know? — Namami Gange Programme
Approved by the Union Government in June 2014 as a "Flagship Programme", the Namami Gange Programme is an Integrated Conservation Mission with twin objectives — abatement of pollution and rejuvenation of the National River Ganga. Its main pillars include sewerage treatment infrastructure, river-front development, river-surface cleaning, biodiversity, afforestation, public awareness, industrial-effluent monitoring and the 'Ganga Gram' initiative.
Approved by the Union Government in June 2014 as a "Flagship Programme", the Namami Gange Programme is an Integrated Conservation Mission with twin objectives — abatement of pollution and rejuvenation of the National River Ganga. Its main pillars include sewerage treatment infrastructure, river-front development, river-surface cleaning, biodiversity, afforestation, public awareness, industrial-effluent monitoring and the 'Ganga Gram' initiative.
3.6 The Brahmaputra System
The Brahmaputra, one of the largest rivers of the world, has its origin in the Chemayungdung glacier of the Kailash range, near Lake Mansarovar. From there it flows eastward longitudinally for nearly 1,200 km across the dry, flat plateau of southern Tibet, where it is known as the Tsangpo ("the purifier"). Its major right-bank tributary in Tibet is the Rango Tsangpo.
The river then carves a deep gorge through the Central Himalayas near Namcha Barwa (7,755 m) and emerges into India under the name Siang (or Dihang) just west of Sadiya in Arunachal Pradesh. Flowing south-west, it is joined by its main left-bank tributaries — the Dibang (Sikang) and the Lohit — and only after this triple confluence is it called the Brahmaputra.
3.6.1 Through the Assam Valley
In its 750 km journey through the Assam valley, the Brahmaputra picks up many tributaries:
- Major left-bank tributaries: Burhi Dihing and Dhansari (South).
- Major right-bank tributaries: Subansiri, Kameng, Manas and Sankosh.
- The Subansiri originates in Tibet and is an antecedent river.
The Brahmaputra enters Bangladesh near Dhubri and turns south. There the Tista joins it on the right bank, after which the river is called the Jamuna. It finally merges with the Padma and pours into the Bay of Bengal as part of the world's largest delta.
⚠️ Why the Brahmaputra Floods so Often
The Brahmaputra is famous for floods, channel-shifting and bank-erosion. The reason is structural: most of its tributaries are themselves large rivers that carry enormous sediment loads, fed by the very heavy rainfall in the catchment. As a result, the channel is constantly being raised and re-routed by deposition.
India's Three Himalayan River Systems — Schematic
Bloom: L2 UnderstandFigure 3.1: A simplified diagram showing how the Indus drains to the Arabian Sea while the Ganga and Brahmaputra finally unite in Bangladesh and discharge into the Bay of Bengal.
3.7 Comparing the Three Systems
How do the three Himalayan giants compare in length? The chart below puts the numbers side by side. Note that "length" here means the total length of the main river — including the portions that flow outside India.
Figure 3.2: Total length (km) of selected Himalayan-system rivers. The Indus and Ganga are within ~350 km of each other; the Chenab — though only a tributary — is itself longer than many independent rivers.
THINK ABOUT IT — Why a 'Sorrow'?
Bloom: L4 Analyse
The Kosi is called the 'Sorrow of Bihar' and the Damodar was once called the 'Sorrow of Bengal'. Both names refer to repeated, devastating floods — yet only one of them rises in the Himalayas. In 4–5 sentences, explain why a Himalayan river like the Kosi behaves so differently from a Peninsular river like the Damodar, and why both could nevertheless become 'sorrows'. Reflect on how the Damodar Valley Corporation may have helped tame the Damodar.
✅ Pointers
The Kosi carries an enormous sediment load from the rapidly rising Himalayas. When that load is dumped on the Bihar plains, it blocks the channel, forcing the river to break out and shift sideways — sometimes by tens of kilometres. The Damodar instead flows through a structural rift valley with hard rocks; its flooding came from heavy monsoon rain plus poor channel capacity, and so could be controlled by a multipurpose scheme of dams and reservoirs.
📋
Competency-Based Questions — Drainage Concepts & Himalayan Rivers
Case Study: Aanya is on a school trip from Devprayag to Allahabad along the Ganga. At Devprayag she sees two greenish-blue streams meeting; further downstream she watches the river enter a flat plain at Haridwar; near Allahabad she watches another major river join from the right. Her teacher reminds her that India's drainage can be classified by sea, by basin size, or by mode of origin — and that the Ganga shares both natural and cultural significance with hundreds of millions of people.
Q1. The two streams meeting at Devprayag are:
L1 RememberAnswer: (B) — At Devprayag, the Bhagirathi (which rises at Gaumukh from the Gangotri glacier) meets the Alaknanda (which rises from the Satopanth glacier above Badrinath). Below this confluence the river is called the Ganga.
Q2. The river joining the Ganga from the right at Allahabad is the Yamuna. Which of the following is NOT a tributary of the Yamuna?
L2 UnderstandAnswer: (D) — The Chambal, Sind, Betwa and Ken (all rising on the Peninsular plateau) join the Yamuna on its right bank. The Kosi is a left-bank tributary of the Ganga itself, not of the Yamuna.
Q3. About 77% of India's drainage area drains into the Bay of Bengal and about 23% into the Arabian Sea. Which natural feature divides the two?
L3 ApplyAnswer: (B) — The water-divide between Bay of Bengal and Arabian Sea drainage runs along the Delhi Ridge, the Aravalis and the Sahyadris. The Vindhyas and Satpuras are part of the rift-valley system but are not the principal east–west divide.
HOT Q. Design a 1-page poster on "Why Himalayan Rivers Are Perennial". Include three causes (precipitation, snow-melt, basin geology), one diagram (long profile + tributaries), and one suggested management measure for the lean season. Briefly explain why a Peninsular river usually fails the same 'perennial' test.
L6 CreateHint: Cause 1 — heavy summer monsoon over the Himalayas. Cause 2 — melting of permanent snow and glaciers in summer when monsoon rain is not yet at peak. Cause 3 — large catchment with many tributaries spreading rainfall events through the year. Management: storage reservoirs (Bhakra, Tehri) to release water during the dry months. Peninsular rivers depend solely on monsoon rainfall in a much shorter window, so they shrink badly in winter/summer.
⚖️ Assertion–Reason Questions — Drainage & Himalayan Rivers
Options:
(A) Both A and R are true, and R is the correct explanation of A.
(B) Both A and R are true, but R is NOT the correct explanation of A.
(C) A is true, but R is false.
(D) A is false, but R is true.
(A) Both A and R are true, and R is the correct explanation of A.
(B) Both A and R are true, but R is NOT the correct explanation of A.
(C) A is true, but R is false.
(D) A is false, but R is true.
Assertion (A): The Satluj is described as an antecedent river.
Reason (R): It existed before the rise of the western Himalayas and continued to cut down through them as they were uplifted, producing a deep gorge near Shipki La and at Rupar.
Answer: (A) — Both A and R are true, and R is the correct explanation. An antecedent river is one that pre-dates the mountain it crosses; its erosive power kept pace with uplift, sawing a near-vertical gorge through the rising rock.
Assertion (A): The Ganga has the largest river basin in India.
Reason (R): The Ganga drains all the rainfall that falls on the Western Ghats and the Eastern Ghats.
Answer: (C) — A is true: the Ganga basin covers about 8.6 lakh sq km in India, the largest in the country. R is false: the Ganga drains the southern Himalayan slopes and the northern face of the Peninsula via tributaries like the Chambal and the Son; it does not drain the Western or Eastern Ghats.
Assertion (A): The Brahmaputra is famous for floods, channel shifting and bank erosion.
Reason (R): Most of its tributaries are themselves large rivers that bring enormous sediment loads from a high-rainfall catchment.
Answer: (A) — Both A and R are true, and R correctly explains A. Heavy sedimentation raises the bed, reduces channel capacity and forces the river to overflow or shift, producing exactly the flood-and-erosion behaviour described.
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