Class 9 Geography Chapter 3 Drainage Important Questions

Class 9 Social Science Geography Chapter 3 Drainage important questions and answers cover the major concepts of the chapter. Solving answers of these important questions help students to revise the Chapter most competently. We prepared these questions with PDF as per the latest NCERT book and CBSE syllabus. Practising these questions before the exam will ensure excellent marks in the exam.

Drainage Class 9 Important Questions and Answers

1. What are perennial and non-perennial rivers? Give reasons why the Himalayan region consists of perennial rivers.

Answer: 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 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.

The rivers of the Himalayan region are perennial in nature. They have their sources in the snow fields and glaciers of the Himalayas which supply water to these rivers throughout the year. During monsoons the Himalayas receive very heavy rainfall and rivers discharge heavy flow of water. During dry periods the rivers are fed by the melting snow and glaciers of the lofty great Himalayan range. Hence, the Himalayan rivers flow throughout the year.

2. Why is the Godavari often referred to as the ‘Dakshin Ganga’? Write a note on the river Godavari and its tributaries.

Answer: The Godavari is the largest Peninsular river. It has a length of 1500 km. It has the largest drainage basin amongst the Peninsular rivers. Its drainage basin covers parts of Maharashtra, Madhya Pradesh, Orissa and Andhra Pradesh. On account of its dominating length and the extent of area it covers, the Godavari is known as the ‘Dakshin Ganga’. The Godavari rises from the slopes of the Western Ghats in the Nasik district of Maharashtra. It flows eastwards and drains into the Bay of Bengal. Nearly half of its drainage basin lies in Maharashtra.

The Godavari is joined by large tributaries–the Wainganga, the Penganga and the Manjra. The Purna, the Wardha and the Pranhita are its other tributaries.

3. How are salt lakes formed? Give examples of salt lakes in India.

Answer: Lakes which have water with high salt content are called salt lakes. They are usually found in the basins of inland drainage in the regions of arid and semi-arid climate. Such lakes are seasonal in nature.

Hollows may be created in the deserts due to the deflation action of the winds. These may reach the groundwater level which seeps out into these depressions. Small shallow lakes are formed which become salt lakes due to excessive evaporation.

Sometimes short, intermittent streams drain into low depression or a desert basin and form temporary lakes. Such short lived lakes also contain high percentage of salts on account of high rate of evaporation.

An example of such saltwater lake is the Sambhar lake of Rajasthan. The water of this salt lake is used for producing salt.

4. What is a lagoon? How does it differ from a lake?

Answer: Lagoon is a stretch of brackish or salt water separated from the sea by a sandbank, bars, reefs, etc. The action of wind and waves along coasts builds spits and bars in the inlets of seas isolating lagoons from the sea. They are commonly found off the deltas of large rivess like the Ganges, the Mahanadi, etc.

The Chilika lake of Orissa, the Pulicat lake of Tamil Nadu and the Kolleru lake of Andhra Pradesh are lagoons.

Strong on shore winds are also capable of pushing the coastal sand dunes along beaches landwards. They may enclose marshy lagoons.
(i) Lagoons are found only in coastal areas, usually near the mouths of rivers, while lakes may be formed in any geographical location, in highlands or in inland basis.

(ii) Lagoons have brackish water while a lake may have fresh water or salty water.

(iii) Lagoons are formed due to wind and wave action in the coasts. Lakes may be of tectonic origin or may be formed due to river action, glacial action, wind. They may also be human-made artificial lakes.

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

Answer: 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 neary 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 in narrow and the sides are steep rising almost vertically. Such narrow river valleys are called gorges.

Thus, gorges are found in mountainous terrain with resistant rocks. They are usually found in the upper reaches of the river in high mountains, e.g. the Indus Gorge, the Brahmaputra Gorge. Gorges are features of youthful topography. In the Himalayas where the land has been uplifted in recent geological period, gorges are common.

6. What type of channel does the river Brahmaputra have? Write a short note on the formation of this type of channel.

Answer: The river Brahmaputra has a braided channel in its entire length in Assam. The northeastern part of India is a region of high rainfall. Assam receives heavy rainfall during the monsoons. This increases the volume of water in the Brahmaputra river. On account of rapid erosion, the river carries a considerable amount of silt. The silt is deposited in the riverbed when the load becomes excessive. As a result the river splits into several complicated channels called braided channels. The channels frequently shift position. Many big and small river islands are located in between the braided channels. The Majuli Island on the Brahmaputra is the world’s largest, riverine island. It has, however, been broken due to floods.

7. Where are India’s most of the freshwater lakes located and why?

Answer: Most of the freshwater lakes of India are located in the Himalayan region. The lofty ranges of the Himalayas are snow covered and have many glaciers. Glacial activity results in the formation of circular hollows lip in the mountains. They are known as Cirques. The melting of the glacial snow in later period forms cirque lakes. As the lakes have water from snow melt they are freshwater lakes, e.g., Pangong lake in Ladakh. Tectonic activity in the Himalayan region also results in the formation of depressions. They are filled with melting snow forming lakes of tectonic origin, e.g., the Wular lake in Jammu and Kashmir, which is the largest freshwater lake in India. The Dal Lake of Srinagar, Bhimtal and Nainital of Uttarakhand, Loktak Lake of Manipur and Barapani Lake of Meghalaya are some other important freshwater lakes. All are located in the Himalayan region and the Purvanchals.

8. What is a river basin? Explain briefly.

Answer: The area drained by a single river system, comprising a main river and its tributaries, is called its drainage basin or river basin. The term drainage describes the river system of an area. Small streams flowing from different directions come together to form the main river. It has number of tributaries and distributaries. The river ultimately drains into a large water body such as a lake or a sea or an ocean. The area drained by the main river, its tributaries and distributaries is termed as the river basin. The river Ganga has the largest river basin in India. The river Indus has a larger river basin but most of it lies outside India.

9. Write a note on the river Krishna and its tributaries.

Answer: The river Krishna rises from a spring near Mahabaleshwar. It flows eastwards to the Bay of Bengal. It has a length of about 1400 km, which makes it the second longest river of Peninsular India after Godavari which has a length of 1500 km. The Tungabhadra, the Koyna, the Bhima, the Ghatprabha and the Musi are important tributaries of the river Krishna. The drainage basin of the river Krishna lies in Maharashtra, Karnataka and Andhra Pradesh.

10. Name the three Himalayan river system. Give two tributaries of each. (CBSE 2010)

Answer: Three Himalayan river systems are :
(i) The Indus river system
(ii) The Ganga river system
(iii) The Brahamaputra river system.

(i) Indus river system – Satluj, Beas, Ravi
(ii) Ganga river system – Yamuna, Ghaghara, Gandak
(iii) Brahmaputra river system – Dibang, Lohit, Kenula.

11. Which of the factors mainly controls the drainage system of the Indian subcontinent? Into which major groups are the Indian rivers divided? Write three points of difference between the two.

Answer: The drainage system of the Indian subcontinent are mainly controlled by the broad relief features. The Indian rivers are divided into two major groups :
(a) The Himalayan rivers and
(b) The Peninsular rivers.

Points of difference :
(a) The Himalayan rivers mostly originate in the Himalayan ranges whereas the Peninsular rivers mostly originate in the Western Ghats
(b) The Himalayan rivers are perennial whereas the Peninsular rivers are seasonal
(c) The Peninsular rivers have shorter and shallower courses in comparison to the Himalayan rivers.

12. Why are lakes of great value to human beings? Explain any three reasons. 

Answer: Lakes are of great value to human beings.
(i) A lake helps to regulate the flow of a river. During heavy rainfall, it prevents flooding. During dry reason, it helps to maintain an even flow of water.
(ii) Lakes are also used for developing hydel power.
(iii) Lakes help develop tourism and provide recreation.

13. Write any three features of the rivers originating in the Himalayas.

Answer: Three main features of the Himalayan rivers are :
(i) Most of them are perennial.
(ii) They have long and deep courses from their source to the sea.
(iii) They perform intensive erosional activity in their upper courses and carry huge loads of silt and sand.

14. What is a lake? How are lakes formed? 

Answer: A lake is an area of water surrounded by land on all sides.
(i) There are lakes which are formed as a result of action of glaciers and ice sheets, while the others have been formed by wind, river action, and human activities.
(ii) Some lakes are formed as a result of the tectonic activity. For example, Wular Lake in Jammu and Kashmir.
(iii) The damming of rivers for the generation of hydel power has also led to the formation of lakes.

15. Which three river systems form the Himalayan river systems?

Answer: The Indus, Ganga and Brahmaputra have formed the three major Himalayan river systems of the country.

16. Describe any three important features of the river Brahmaputra.

Answer: The three important features of the river Brahmaputra are as follows:
(i) It passes through a high rainfall region and therefore carries a large volume of water and silt.
(ii) It has braided channel in its entire length in Assam and forms many riverine islands.
(iii) In rainy season, the river overflows it banks causing widespread floods in Assam and Bangladesh.

17. How does a river affect the economy of a country?

Answer: Water from the rivers is a basic natural resource. It is essential for various human activities. Therefore, river banks have attracted settlers of very ancient times. These settlements in course of time become cities. In India, rivers are used for irrigation, navigation and power generation besides agriculture. The agriculture is the major source of livelihood of the population and hence its role in the economy is a great.

18. What is the name of Brahmaputra in Tibet and Bangladesh? Give one feature of each.

Answer: Brahmaputra is known as the Tsangpo in Tibet and Jamuna in Bangladesh. One important feature of Brahmaputra in Tibet is that it carries a smaller volume of water and less silt as it passes through a cold and dry area in Tibat. In Bangladesh, however, in rainy season the river overflows its banks, carries much water and causeds widespread devastation by floods including siltation in the riverbed.

19. What are the differences between east-flowing and west-flowing rivers of the peninsular plateau?

Answer: The major rivers of the peninsular the the Mahanadi, the Godavari, the Krishna etc. are flowing eastward and merges into the Bay of Bengal. Only the river Narmada and Tapti are flowing towards west and merge into the Arabian Sea. The essential differences between the two rivers are as follows: 

East flowing peninsular riversWest flowing peninsular rivers
(i)The rivers flowing eastward on the peninsular plateau are generally large.(i)The rivers flowing westward on the peninsular plateau are generally small but rivers Narmada and Tapi are exceptions to this.
(ii)These rivers form huge deltas near their mouth(ii)These rivers do not form deltas.  
(iii)These rivers do not flow through trough.(iii)West flowing rivers like Narmada and Tapi flow through troughs which have been formed due to faulting.
(iv)These rivers fall into Bay of Bengal.(iv)These rivers fall into Arabian sea.
(v)The Mahanadi, Godavari, Krishna and Kaveri are east flowing rivers.(v)The Narmada and Tapi are west flowing rivers.

20. What are the causes of river pollution? Suggest some ways to overcome them?

Answer: The main causes of river pollution is dumping of untreated sewage and industrial effluents into the rivers. This affects the quality of water.

21. What is the difference between tributary and the distributary? Write any three points.

Answer: A smaller stream joining with the main stream is known as tributary. A tributary is generally carried water and silt to the main river. River Jamuna is an example of tributary of the river Ganga.

A Distributary is formed at the lower coarse of the river when the main channel of the river get blocked with silt which forced 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.

The three basic differences between tributaries and distributaries are given below :

A stream that flows into a mainstream (or parent) river.A tributary that branches off and flows away from the mainstream or the parent river.
Does not flow directly into a sea, ocean or lakeMay or may not flow directly into a sea, ocean or lake.
Generally found in the upper course of the river.Generally found in the lower course of the river.
Example: Yamuna is the tributary of the Ganga.Example: Hooghly is the distributary of Ganga.

22. What are the causes of river pollution? Suggest some ways to overcome them?

Answer: The main causes of river pollution is dumping of untreated sewage and industrial effluents into the rivers. This affects the quality of water.
(i) Recycling and reuse of waste water is to be done to check waste water.
(ii) Waste water is to be released after proper treatment.
(iii) All outlets of effluents from industrial and domestic sources should be diverted to elsewhere.

23. Describe the three main features of Narmada Basin.

Answer: The river Narmada emerges from the Amarkantak hills in Madhya Pradesh.
(i) It flows towards the west in a rift valley formed due to faulting.
(ii) It creates many picturesque places like the Marble Rocks near Jabalpur and Dhuadhar Falls.
(iii) All the tributaries of the Narmada are very short and most of them join at right angles to the main stream.

25. What are the differences between the Himalayan rivers and the Peninsular rivers?

Answer: The differences between the two main groups of rivers of India are as follows:

The Himalayan riversThe Peninsular rivers
These rivers are perennial that is they have water throughout the year.These rivers are seasonal.
These rivers obtain water from rain as well as from melted snow from high mountains.The flow of these rivers is based on rainfall.
These rivers have large river basinThese rivers have a smaller basin as compared with the Himalayan rivers
The rivers are mainly running in their youth stageThese rivers are considered as old rivers
Two major Himalayan rivers, the Indus and the Brahmaputra originate from the north of the mountain ranges.Most rivers of peninsular region originate in the Western Ghats and flow towards the Bay of Bengal. Godavari and Narmada are the main river system of peninsular rivers.
The main source is from glaciers of the Himalayan mountain rangeThe main source of the river is the peninsular plateau and the central highland
The Himalayan rivers have long duration courses from their source to the sea.These rivers have shorter and shallower courses as compared to Himalayan rivers.

26. Write a note on the Indus Drainage System.

Answer: The Indus is one of the longest rivers of the world. The river Indus rises in Tibet, near lake Mansarovar. Flowing west, it enters India in the Ladakh district of Jammu and Kashmir. A spectacular gorge formed by the Indus marks this part. Several tributaries – the Zaskar, the Nabra, the Shyok and the Hunza – join the Indus in the Kashmir region. The Indus flows through Baltistan and Gilgit and emerges from the mountains at Attock. The tributaries of the Indus – the Jhelum, the Chenab, the Ravi, the Beas and the Satluj – flow partly through Kashmir and Himachal Pradesh and mainly through Punjab. They join together to enter the Indus near Mithankot in Pakistan. The Indus then flows southwards and eventually reaches the Arabian Sea, east of Karachi. The Indus has a total length of 2900 km. The Indus plain has a very gentle slope. A little over onethird of the Indus basin lies in India in the states of Jammu and Kashmir, Himachal Pradesh and Punjab. Major part of its basin lies in Pakistan.

27. Write a note on the Brahmaputra Drainage System.
Name any two major river systems of the Himalayan region. Describe any one in detail.

Answer: The Brahmaputra is one of the longest rivers of the world, but most of its course lies outside India. The river Brahmaputra rises in Tibet east of the Mansarovar lake. The river flows eastwards parallel to the Himalayas in its upper course. It is known as Tsangpo in Tibet. Here it carries smaller volume of water and less silt as it is a cold and dry area. The river takes a ‘U’-turn bend at Namcha Barwa (7757 m) and enters India in Arunachal Pradesh through a gorge. In Arunachal Pradesh, it is known as Dihang. Here it is joined by the Dibang, the Lohit, the Kenula and many other tributaries. The volume of the river increases and it is known as the Brahmaputra in Assam.

The region receives heavy rainfall during the monsoon which increases the volume of water and silt content of the river. Devastating floods are caused by the river in Assam and Bangladesh every year during the rainy season. The deposition of the silt in the riverbed due to the heavy load, leads to the formation of braided channels intervened by riverine islands. The Brahmaputra has a braided channel in its entire length in Assam. Many riverine islands like the Majuli, the world’s largest riverine island, are formed in between the channels. The Brahmaputra is known as Jamuna in Bangladesh. Here it is joined by the Ganga, known here as Padma. Together they form the Ganga-Brahmaputra Delta known as Sunderbans, and discharge into the Bay of Bengal.

28. Write a note on the Ganga Drainage System. (Important)

Answer: The Ganga is the longest and the most important river system of India. It has a total length of over 2500 km. Nearly the entire river basin of the Ganga lies in India with a part of its lower course and delta in Bangladesh.

The headwaters of the Ganga is called the ‘Bhagirathi’. It is fed by the Gangotri Glacier. It is joined by the Alaknanda at Devaprayag in Uttarakhand. At Haridwar, the Ganga emerges from the mountains and enters the plains. The Ganga is joined by a large number of tributaries. The Yamuna, a right-bank tributary of the Ganga, rises from the Yamunotri Glacier, flows parallel to the Ganga and joins it at Allahabad. The Ghaghra, the Gandak, the Kosi and the Sarda are the left-bank tributaries of the Ganga. The other right bank tributaries of the Ganga – the Chambal, the Betwa and the Son – come from the Peninsular uplands. The Ganga and its tributaries form a major portion of the northern plains. On account of water availability and fertile soil, it is the most important agricultural region of India. The Ganga develops large meanders in the plains. The Ganga flows eastwards with the increased volume up to Farakka in West Bengal. The river bifurcates here. Its distributary, the Bhagirathi-Hooghly, flows through the deltaic plains to the Bay of Bengal.

The mainstream flows southwards into Bangladesh. Here it is known as Padma. It is joined by the Brahmaputra. Further downstream it is known as Meghna. Together they form the Ganga- Brahmaputra Delta, also known as Sunderbans delta. It is the world’s largest and fastest growing delta.

29. Write a note on the east-flowing and the west-flowing rivers of Peninsular India.

Answer: The Peninsular Plateau of India is marked by a large number of east-flowing rivers and a few west-flowing rivers. Most of the major rivers of Peninsular India such as the Mahanadi, the Godavari, the Krishna and the Kaveri and their tributaries flow eastwards. They rise from the Western Ghats, the highlands of the Deccan Plateau, flow towards east and drain into the Bay of Bengal. Only two big rivers, the Narmada and the Tapi, with long courses flow westwards in Peninsular Plateau region. They rise from the Satpura range and Amarkantak hills, flow westwards through faults and drain into the Arabian Sea. The coastal plains between Western Ghats and the Arabian Sea are very narrow. Hence, the west-flowing coastal rivers are short and swift flowing. The Sabarmati, Mahi, Bharathpuzha and Periyar are the west-flowing rivers. The Sabarmati and the Mahi originate in the Central highlands and flow into the Arabian Sea. The Western Ghats form the main water divide in Peninsular India. The east-flowing rivers have wide basins. They have dendritic drainage pattern with many tributaries joining them. They form large deltas at their mouths.

The west-flowing rivers flow between highlands and have elongated courses. They have trellis and rectangular drainage pattern. They flow through rift valleys and are fault guided rivers. They form estuaries at their mouths. The west-flowing rivers do not form deltas.

30. Why are rivers important for a country’s economy? 

Answer: Rivers are the lifelines of a nation. Rivers have been of fundamental importance in the settlement and progress of man throughout the human history. The rivers form broad, fertile alluvial plains that have been the cradle of human civilisation. Water from the river is a basic natural resource, essential for various human activities. They provide water for domestic use. Rivers provide water for irrigation that helps to develop agriculture in the surrounding area.
The fertile soil of the riverine plain, abundant supply of water and the flat land provides opportunities for the development of agriculture. In an agricultural country like India, rivers play a major role in shaping the country’s economy. Rivers supply water for industrial use. Rivers provide for a cheap mode of transportation, inland navigation.

Hydro-electricity harnessed from river water supplies power to our industries, to our homes and to our agricultural fields. Integrated water management of rivers through River Valley Projects by building dams provide hydro-electricity, water for irrigation, inland navigation, fishing, recreation etc. Hence, rivers are of prime importance in the flourishing of a country’s economy.

31. What are drainage patterns? Write a brief note on the different drainage patterns.

Answer: In highland areas small streams flowing from different directions and join together to form the main river which ultimately drains into some large waterbody, 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 main stream with its tributaries have 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, 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 rockey 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.

32. Write a note about the causes and remedy of river pollution.
 Explain any three reasons for pollution of rivers in India.
 Discuss any three causes of water pollution. 

Answer: Pollution of rivers by discharge of untreated sewage water and industrial effluents is a big menance. They are changing the life-giving rivers into toxic streams. Dumping of garbage into the streams is another cause of river pollution.

The growing domestic, municipal, industrial and agricultural demand for water from the rivers due to ever increasing population has led to over-exploitation of water. Excessive, uncontrolled use of this main source of freshwater has reduced their volume and has affected the quality of water. Increasing urbanisation and industrialisation has increased the pollution level of many rivers to such a level that the self-cleansing capacity of the river cannot cope up with it. Concern over rising pollution in our rivers led to the launching of various river action plans like the Ganga Action Plan, the Yamuna Action Plan, etc., to clean the rivers. The National River Conservation Plan (NRCP) covers 152 towns along 27 interstate rivers in 16 states. Pollution abatement works are being taken up in 57 towns under it. A million litres of sewage is targeted to be intercepted, diverted and treated.

Citizens should also take up responsibility to prevent river pollution. Garbage should not be disposed in rivers. Industrial waste should not be dumped into rivers. Sewage and industrial effluents should be treated before discharging into rivers.

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