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Drainage System – Class 11 Geography notes, important questions and MCQs

NCERT Class 11 Geography, chapter 17. Notes, key terms, important questions with answers and MCQs.

Chapter overview

A drainage system is the flow of water through well-defined channels, and the area drained by a river and its tributaries is its drainage basin. Indian rivers are divided into the Himalayan rivers and the Peninsular rivers. Himalayan rivers such as the Indus, Ganga and Brahmaputra are perennial, while Peninsular rivers such as the Godavari, Krishna, Kaveri and Mahanadi depend mainly on rainfall. Drainage patterns include dendritic, trellis, radial and centripetal.

Drainage patterns and basins

A watershed or water divide separates two drainage basins; the Western Ghats are the main water divide of peninsular India.
Drainage patterns include dendritic (tree-like, as in the northern plains), trellis, radial (rivers flowing outward from a central hill, such as the Amarkantak region) and centripetal (rivers flowing into a lake or depression).
About 77% of India's drainage area flows into the Bay of Bengal and about 23% into the Arabian Sea.

Himalayan and Peninsular rivers

The Indus rises near Lake Mansarovar in Tibet; its tributaries include the Jhelum, Chenab, Ravi, Beas and Satluj. The Ganga rises at Gangotri as the Bhagirathi and joins the Alaknanda at Devprayag; the Yamuna joins it at Prayagraj. The Brahmaputra rises in Tibet as the Tsangpo and enters India through Arunachal Pradesh.
Most Peninsular rivers flow east into the Bay of Bengal and form deltas (Mahanadi, Godavari, Krishna, Kaveri); the Narmada and Tapi flow west through rift valleys and form estuaries.
Himalayan rivers are perennial, meander in the plains and have large basins; Peninsular rivers are seasonal, flow in shallow valleys and have smaller basins.

Key terms

Drainage basin: the area drained by a river and its tributaries
Water divide: an elevated area separating two drainage basins
Dendritic pattern: a tree-like drainage pattern
Estuary: the funnel-shaped mouth of a river where tides mix fresh and salt water
Perennial river: a river that flows throughout the year

Important questions with answers

What is a water divide?2 marks

A water divide is an elevated area, such as a ridge or mountain range, that separates two neighbouring drainage basins, so that rivers on either side flow in different directions. The Western Ghats form the main water divide of peninsular India.

Why are Himalayan rivers perennial?3 marks

Himalayan rivers are fed both by rainfall and by the melting of snow and glaciers in the high mountains. Even in the dry season, melting snow keeps them flowing, so they have water throughout the year.

Compare the Himalayan and Peninsular rivers.5 marks

Himalayan and Peninsular rivers differ in several ways. The Himalayan rivers, such as the Indus, Ganga and Brahmaputra systems, originate in the snow-covered Himalayas and are perennial because they are fed by both rain and melting snow and glaciers. They have large basins and long courses, cut deep gorges in the mountains, and in the plains they meander, change courses and form floodplains, ox-bow lakes and large deltas such as the Ganga–Brahmaputra delta. They are in a youthful stage and carry large amounts of silt. The Peninsular rivers, such as the Mahanadi, Godavari, Krishna and Kaveri, originate in the Peninsular plateau, mainly in the Western Ghats, and depend largely on monsoon rainfall, so their flow is seasonal. They have smaller basins and shorter courses, flow in broad, shallow, graded valleys over hard rocks, and are older, mature rivers. Most flow east and form deltas in the Bay of Bengal, while the Narmada and Tapi flow west through rift valleys into the Arabian Sea and form estuaries. Himalayan rivers are more useful for irrigation and navigation in the plains, while Peninsular rivers have good potential for hydroelectricity because of their falls.

Quick revision

Drainage basin, water divide, patterns.
Himalayan rivers: Indus, Ganga, Brahmaputra systems.
Peninsular rivers: east-flowing deltas; Narmada and Tapi estuaries.
Perennial versus seasonal.

Exam tips

Make a table comparing Himalayan and Peninsular rivers.
Mark the major rivers and their mouths on a map.

Practice MCQs

The area drained by a river and its tributaries is its
1. delta
2. floodplain
3. estuary
4. drainage basin
Show answer
Answer: (d) drainage basin. It is separated by water divides.
The Ganga rises at
1. Yamunotri
2. Gangotri
3. Amarkantak
4. Mansarovar
Show answer
Answer: (b) Gangotri. It is called the Bhagirathi there.
A tree-like drainage pattern is called
1. radial
2. dendritic
3. trellis
4. centripetal
Show answer
Answer: (b) dendritic. It is common in plains.
Which river flows westward into the Arabian Sea
1. Narmada
2. Krishna
3. Godavari
4. Mahanadi
Show answer
Answer: (a) Narmada. It flows through a rift valley.
The Bhagirathi and Alaknanda meet at
1. Haridwar
2. Prayagraj
3. Devprayag
4. Rishikesh
Show answer
Answer: (c) Devprayag. From there the river is called the Ganga.
The Brahmaputra is known in Tibet as the
1. Dihang
2. Meghna
3. Jamuna
4. Tsangpo
Show answer
Answer: (d) Tsangpo. It enters India in Arunachal Pradesh.
Why do the Narmada and Tapi form estuaries and not deltas
1. they carry heavy silt
2. they are perennial Himalayan rivers
3. they flow into the Bay of Bengal
4. they flow through rift valleys with hard rock and little silt deposit at the mouth
Show answer
Answer: (d) they flow through rift valleys with hard rock and little silt deposit at the mouth. Tides also remove sediment.
Rivers flowing outward in all directions from a central dome form a
1. dendritic pattern
2. trellis pattern
3. radial pattern
4. centripetal pattern
Show answer
Answer: (c) radial pattern. The Amarkantak area is an example.

All chapters of Class 11 Geography

Written by Kundali IQ from standard, well-established facts to help with revision. This is not an official NCERT publication; always read your textbook too.