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Solutions, questions, answers, and notes of chapter 7: Drainage which is a part of social science class 9 syllabus of students studying under the Nagaland Board of School Education.

The term drainage describes the river system of an area. Small streams flowing from different directions come together to form the main river, which ultimately drains into a large water body such as a lake or a sea or an ocean. The area drained by a single river system is called a drainage basin.

Image source: NASA / Unsplash

A closer observation on a map will indicate that any elevated area, such as a mountain or an upland separates two drainage basins. Such an upland is known as water divide. The drainage systems of India are mainly controlled by the broad relief features of the subcontinent.

l. Choose the correct answer.

1. The drainage pattern formed by a river or stream in arid areas, where they converge towards a central depression is called

Answer: (a) The centrifugal drainage pattern

2. In which of the following states is the Wular Lake located?

Answer: (a) Rajasthan

3. Which river is also known by the name ‘Dakshin Ganga’?

Answer: (d) Godavari

4. The river Narmada has its source at

Answer: (b) Amarkantak

5. Which one of the following lakes is a saltwater lake?

Answer: (a) Sambhar

6. Which one of the following is the longest river in Peninsular India?

Answer: (b) Godavari

7. Which river formed the Dhuadhar falls?

Answer: (a) Narmada

II. Very Short Answer Type Questions

1. What is a drainage basin.

Answer: The area drained by a single river system is called a drainage basin.

2. Where do the following rivers originate?
(a) Kaveri (b) Brahmaputra (c) Mahanadi (d) Tapi

Answer: (a) Brahmagir Hills, ht. 1,341 m.

(b) About 100 km S.W. of Mansarovar ht. 5,150 m.

(c) Raipur district, Chhattisgarh ht. 442 m.

(d) Rises in Betul district.

3. What is a watershed?

Answer: Watershed is the boundary between two rivers.

4. What is the radial pattern of rivers?

Answer: This has the streams flowing in different directions from a central peak or dome-like structure.

5. What is meant by a water divide? Give an example.

Answer: Rivers are separated from each other by heights of land. These heights are called divides.

6. Name the different stages of rivers.

Answer: The different stages of rivers are:

i. Source of river
ii. Upper course
iii. Middle course
iv. Oxbow lake
v. Lower course
vi. Delta

7. Where do the river Indus and Ganga have their origin?

Answer: Indus has its origins in the Himalayas of western Tibet, near the lake Mansarowar. The Ganga rises in the Himalayas on the Indian side of the Tibet border.

8. Which two peninsular rivers flow towards west

Answer: The Narmada and the Tapi.

III. Short Answer Type Questions.

1. Differentiate between dendritic and trellis pattern of rivers.

Answer: A dendritic patter: This consists of a single mainstream with tributaries joining like the branches of a tree.

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

2. Give any three characteristics of Himalayan rivers.

Answer: Three characteristics of Himalayan rivers are:

i. These rivers have large basins, e.g. Indus Basin.
ii. The rivers passing through the Himalayas create spectacular gorges.
iii. The steep rock-sided deep valleys were created by the down-cutting of the river during the period of the Himalayan uplift.

3. Write a short note on (i) Mahanadi Basin (ii) Kaveri Basi

Answer: (i) Rising in Chhattisgarh, the Mahanadi flows through Odisha to reach the Bay of Bengal for 885 km long river has its drainage basin lying in Chhattisgarh, Jharkhand, Odisha and Maharashtra.

(ii) Kaveri has its source in the Brahmagir range of the Western Ghats. The river reaches the Bay of Bengal after flowing over 800 km. It ends at Kaveripatnam and its basin is shared by Karnataka, Tamil Nadu and Kerala.

4. What is meant by the term ‘inland drainage’?

Answer: A drainage system in which rivers do not flow into the ocean but drain their water into a lake or an inland sea is called inland drainage.

5. Why are rivers important for the country’s economy?

Answer: Rivers are important for the country’s economy because of the following reasons:

i. River valleys provided easy routes and fertile land. This helps in the transportation of goods and agriculture.
ii. Rivers are needed for hydroelectric projects which powers the country.

V. Long Answer Type Questions

1. What is the difference between the peninsular rivers and Himalayan rivers?

Answer: The difference between the peninsular and Himalayan rivers are as follows:

Peninsular rivers Himalayan rivers
Most of these rivers are seasonal and their flow depends on rainfall.These rivers are perennial as they receive water from rainfall and melting ice all the time.
The gentler slopes cause a low intensity of erosional activity as compared to other rivers.These rivers carry out intensive erosional activities upstream and also carry huge loads of sand and silt.
These rivers do not have many meanders as the hard rock bed and lack of silt and sand does not allow them.When in the plains, these rivers form large meanders and depositional features such as flood plains, river cliffs and levees.

2. Write notes on (i) Ganga System (ii) Brahmaputra System (iii) Indus System.

Answer: (i) The Ganga System: The length of the river Ganga is 2510 km. Rising in the Himalayas on the Indian side of the Tibet border, the Ganga’s five headstreams Bhagirathi, Alaknanda, Mandakini, Dhauliganga and Pindar have their origins in Uttarakhand. The Alaknanda and Bhagirathi meet at Devaprayag to form the Ganga. In Bangladesh, Brahmaputra joins Ganga to form the combined stream called the Padma.

(ii) The Brahmaputra System: The Brahmaputra or Yarlung Zangbo is one of the great rivers of southern Asia. The river’s source lies in the Chemayungdung Glacier. The river flows for nearly 1,126 km in an easterly direction. Throughout its upper course, the river is generally known as the Tsangpo. Near Sadiya, Assam, the Dihang changes course to the southwest and is known as the Brahmaputra. After flowing 800 km in this direction it turns south again, going through Bangladesh.

(iii) The Peninsular Rivers: Peninsular India’s main watershed is formed by the Western Ghats. Most of the main peninsular rivers like the Kaveri, Krishna, Godavari and Mahanadi flow eastwards and drain into the Bay of Bengal. These rivers make deltas at their mouths. A large number of small streams flow west of the Western Ghats. The Narmada and the Tapi are the only long rivers that flow west.

3. Where is inland drainage found in India?

Answer: A drainage system in which rivers do not flow into the ocean but drain their water into a lake or an inland sea is called inland drainage. Rajasthan, an arid and semi-arid area in north-western India is where inland drainage occurs the most. Many saltwater lakes are located in this part of the country.

4. 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. [HOTS]


Click here for notes of other chapters of Class 9 Social Science

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