NCERT Class 9 Chapter 3: Drainage

NCERT Class 9 Drainage

 Very Short Answer Type Questions. [1 Mark]

  1. What is drainage?

Ans. Drainage is a term signifying the river system of an area.

2. What are narrow and not very deep rivers called?

Ans. Narrow and not very deep rivers that are small in size are called streams, creeks and brooks.

3. What do you understand by the term tributaries?

Ans. Small rivers that join big rivers are called tributaries.

4. What are distributaries?

Ans. Distributaries are streams or rivers that branch off and flow away from the main river.

5. What is the river?

Ans. A river is any natural stream of fresh water that flows in a definite channel.

6. What is the drainage basin?

Ans. The area of land from which a river collects water is called its drainage basin.

7. What is a river system?

Ans. A river along with its tributaries or distributaries is called a river system. In this, small rivers flowing from different directions come together to form a river system, for example, the Ganga, the Indus, etc.

8. Name the world’s largest river system in the world.

Ans. The Amazon basin is the world’s largest river system.

9. Which is the largest river system in India?

Ans. The Ganga basin is the largest river system in India.

10. What is a dendritic pattern?

Ans. A dendritic pattern consists of a single mainstream with tributaries joining like branches of a tree.

11. When is a trellis pattern formed?

Ans. A rectangular pattern is formed when a long river is joined by short flowing streams, approximately at right angles.

12. Into how many types are Indian river systems classified?

Ans. On the basis of origin, the Indian river systems are classified into two groups – (i) the Himalayan rivers and (ii) the Peninsular rivers.

13. What is a perennial river?

Ans. A river that flows throughout the year is called a perennial river.

14. What is a seasonal river?

Ans. A river that flows only in the rainy season is known as a seasonal river.

15. Mention the types of rivers is found in India.

Ans. There are two types of rivers in India—the Himalayan rivers and the Peninsular rivers.

16. Write the names of important peninsular river systems.

Ans. Some of the peninsular river systems are the Mahanadi and Godavari, the Narmada and Tapi, and so on.

17. Where does the rectangular pattern develop?

Ans. This pattern develops on a strongly jointed rocky terrain like limestone.

18. Where do most of the Peninsular rivers originate and where do they flow?

Ans. Most of the rivers of Peninsular India originate in the Western Ghats and flow towards the Bay of Bengal.

19. What kind of a drainage pattern is formed when tributaries join rivers at almost right angles?

Ans. Radial pattern

20. Which drainage pattern develops on a strongly jointed rocky terrain?

Ans. Rectangular drainage pattern

21. In which course of the river do meanders form?

Ans. In the lower course.

22. Which one of the following drainage pattern does the Ganga river form?

Ans. The Dendritic pattern

23. Which factors control the drainage system of the Indian subcontinent?

Ans. The broad relief features of the subcontinent mainly control the drainage systems of the Indian subcontinent.

24. How many drainage patterns are studied?

Ans. There are four common patterns in which rivers flow. These are: (i) Dendritic (ii) Trellis (iii) Rectangular and (iv) Radial.

25. What is the Trellis pattern?

Ans. In this pattern, its tributaries join the main river almost at right angles. This pattern develops where the hard and soft rocks lie parallel to each other, e.g. the Narmada Basin.

26. What is Radial pattern?

Ans. This pattern develops when streams flow in different directions from a central peak. Example of this type of river pattern is the Yamuna basin.

Short Answer Type Questions. [3 Marks]

1. What is water divide or watershed?

Ans. Water divide or a watershed refers to a high mountain or a plateau or a higher ground that separates two drainage systems. For example, Ambala city is located in the water divide between the Indus and the Ganga river system.

2. List the three Himalayan river systems in India.

Ans. The three Himalayan river systems are (i) the Indus river system in Punjab, (ii) the Ganga river system in north India (iii) and the Brahmaputra river system in the north-east of India.

3. What do you understand by drainage pattern?

Ans. When streams within a drainage basin flow in a certain way, it is known as the drainage pattern. This pattern depends on the slope of the land, the nature of rocks and the climatic conditions of the area.

4. Describe the Dendritic pattern.

Ans. The Dendritic pattern generally follows the slope of the land. The mainstream with its tributaries resembles like the branches of a tree, e.g. the Ganga river system, the Godavari river system and the Krishna river system.

5. What is a canyon?

Ans. A canyon is nothing more than a valley with extremely steep sides. One of the famous canyons in the Grand Canyon in Arizona. It is over a mile deep in many spots and ranges from 2 to 18 miles across.

6. What are watersheds or divides?

Ans. Rivers are separated from each other by heights of land. These heights called divides, decide the slopes of the land and the direction in which the water will flow. Sometimes these divides are called watersheds because they decide in which direction the rainwater will flow.

7. What are perennial and non-perennial rivers?

Ans. The rivers that flow throughout the year are termed as perennial rivers. They have more or less even flow throughout the year, e.g., the Ganga, the Brahmaputra, etc. The rivers that do not flow throughout the year are termed as non-perennial rivers. They are seasonal rivers that flow mainly during the rainy season and dwindle during the dry period, e.g., the Subarnarekha.

8. Give reasons why the Himalayan region consists of perennial rivers.

Ans. The rivers of the Himalayan region are perennial in nature. During monsoon, the Himalayas receive very heavy rainfall and the rivers discharge heavy flow of water. During dry periods the rivers are fed by the melting snow and glaciers of the lofty Himalayan range. Hence, the Himalayan rivers flow throughout the year.

9. Write any three differences between a tributary and a distributary.

Ans. The three basic differences between tributaries and distributaries are as follows:

Tributary Distributaries
(i) Tributaries can be found in three stages of the river–upper, middle and lower. (i) It is only found in lower courses of the river.
(ii) It is useful for irrigation and transportation all through. (ii) It only provides a network of transport in the lower course.
(iii) It brings water and silt from its catchment area. (iii) It deposits silt in its course.

the river gets blocked with silt which forces the river to open branches. The Bhagirathi-Hooghly is a distributary of the river Ganga. The main function of the distributary is to distribute water through newly opened channels.

III. Long Answer Type Questions. [5 Marks]

1. What is a gorge? In what type of terrain does a gorge form?

Ans. A gorge is a very steep-sided, narrow river valley. It is found in the mountains in the upper courses of the rivers. They are nearly I-shaped in appearance.

In the upper course, the river is very swift as it descends down the steep slopes of the mountains. Vertical corrosion or down cutting is the predominant action of the river here. In areas where the rocks are very hard or resistant, the valley that develops is narrow and the sides are steeply rising almost vertically. Such narrow river valleys are called gorges,

for example, the Indus Gorge, the Brahmaputra Gorge, etc. Gorges are features of youthful topography. In the Himalayas where the land has been uplifted in the recent geological period, gorges are common.

2. What are the salient features of the Himalayan Rivers?


Himalayan rivers Peninsular rivers
These rivers originate from the glaciers of the Himalayas. These rivers flow through the Peninsular plateau.
These rivers are perennial as they flow throughout the year. They are non-perennial or seasonal rivers. They are rainfed rivers.
They are rainfed and snow-fed. These rivers have small basins, short course, swift and shallow valleys.
They have long course, deep gorges and valleys. These rivers perform minimum erosion.
These rivers are engaged in intense erosional activities. They have small meanders, oxbow lakes, deltas or estuaries.
Their rivers have a large basin, huge meanders, oxbow lakes, flood plains and deltas. These rivers are less useful for navigation, e.g. the Mahanadi, the Godavari, the Krishna and the Kaveri rivers.

Describe the fluvial cycle of action of a river.
Ans. A river starts its journey from a source and finally ends its journey into a water body such as a lake or a sea. This is called the mouth of the river. The river covers a long distance from its source to its mouth. This is known as the fluvial cycle. This journey is divided into three stages called courses. These are the Upper course, the Middle course and the Lower course. In each of these stages, the river acts differently. This is due to variation in the slope of the land and the amount of water it carries. Each stage makes different types of landforms.

Name the stages of a river. Describe the Upper Course.
Ans. The first stage is called the Upper Course, or the youthful stage, the second stage is the Middle Course or, the mature stage and the third stage is the Lower Course or the old stage.
The Upper Course
• During this stage, the river flows from a high mountain.
• The river flows swiftly and carries a large volume of water.
• The main work of the river is vertical erosion resulting in deepening of valleys.
• Valley deepening leads to the formation of V-shaped valley, gorges and canyons.
• In areas of hard and soft rocks, the river tumbles down over the hard rock to form a waterfall.
• Canyons are steep-sided valleys with vertical walls on either side, e.g. the Grand Canyon of Colorado.

Explain the features of the Middle Course of a river.
Ans. • During this stage, the river descends from the mountain and flows through the plain.
• The speed of the river decreases and the volume of water also reduces.
• The main work of the river is valley widening, resulting in the formation of meanders. Meanders are S-shaped curves formed in the river course.
• When the river overflows its banks, it erodes the materials from the sides of the valleys, which blocks the river channel to form cut off a portion of a meander known as oxbow lakes.
• Flood plains are formed when the river overflows its banks, depositing fertile sediments.

Discuss the Lower Course of a river.
Ans. • During this stage, the river flows in a levelled plain or a gentle slope.
• The speed of the river becomes extremely slow or sluggish and the volume of water also decreases.
• The main work of the river is the deposition of sediments. This results in the branching of the main river into many channels called distributaries. In between the channels, the sediments spread in a triangular shape to form a delta, e.g. the Sunderban Delta.
This delta is formed by the Ganga and the Brahmaputra rivers.
• Some rivers enter the sea as deep narrow river channel to form an estuary.

What are drainage patterns? Write a brief note on the different drainage patterns.
Ans. In highland areas, small streams flowing from different directions join together to form the main river which ultimately drains into some large water body, a lake, sea or ocean. The main river is joined by a number of tributaries along its course. The streams within a drainage basin form certain patterns called drainage patterns. The patterns formed depend on the (i) slope of the land, (ii) underlying rock structure and (iii) the climatic conditions of the area. Dendritic, trellis, rectangular and radial are the four main types of drainage patterns. When the mainstream with its tributaries has a drainage pattern resembling the branches of a tree, it is known as dendritic drainage pattern. The dendritic pattern develops where the river channel follows the slope of the terrain.
When a river is joined by its tributaries, at approximately right angles, the trellis drainage pattern is formed. A trellis drainage pattern develops where hard and soft rocks exist parallel to each other. A rectangular drainage pattern develops on a strongly jointed rocky terrain. When streams flow in different directions from a central peak or dome-like structure, the radial drainage pattern develops. The radial drainage pattern resembles the spoke of a wheel on the map.