WBBSE Solutions For Class 7 Geography Chapter 5 River Topic B Works Of River And Its Influences On Our Life

WBBSE Chapter 5 River Topic B Works Of River And Its Influences On Our Life Long Question And Answers

Question 1. What are the works of a river in its upper course? Describe the features created in its mountainous stage.
Answer:

Works of a river in its upper course:

The river flows through a mountainous region in its upper course. So its velocity is very high. Its main work is erosion and it also carries the eroded materials along as it flows.

Features created by the river in its mountainous stage:

The main features created by the river in its mountainous stage are-

1. Gorge and canyon:

The river forms a deep and narrow valley in the mountainous region due to intensive vertical erosion. In the moist regions, lateral erosion also takes place along with vertical erosion. This forms a wide, V-shaped valley. This is called a gorge.

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Example: Gorge of River Kali in Nepal.

In certain regions, only vertical erosion takes place. This gives rise to deep l-shaped valleys called canyons. Example: The Grand Canyon of River Colorado is the largest canyon in the world.

2. Waterfall:

• The waterfall is a variation in the general level of a flowing river. When the river flows down a steep slope, its mass of water suddenly jumps downwards.
• When the river reaches a soft bedrock from a resistant bedrock, the soft rocks get eroded quickly farming a steep slope. Here, the river jumps down forming a waterfall.

Example: Shivasamudram Falls on Cauvery and Jog Falls on Sharavati.

3. Plunge pool:

The large hole formed at the foot of a waterfall as a result of continuous striking by water and heavy rocks is called a plunge pool. Its size and depth depend on the height of the waterfall, the volume of water and the volume of the suspended rocks.

Question 2. Describe the features formed in the middle course of the river.
Answer:

Features formed in the middle course of the river:

• In the middle stage, the slope of the land is moderate and so the velocity as well as the energy of the river decreases.
• At this stage, its main work is transportation and deposition.

The main features formed by a river in this stage are:

1. Meander:

In the middle course, the energy of the river decreases due to changes in the slope. If the river faces any obstacle, it begins to move in a winding path called meander. It may also form a hairpin bend.

Example: The Ganga has formed a beautiful bend near Varanasi.

2. Ox-bow Lake:

• When the river moves in meanders, lateral erosion also occurs on the outer banks. Gradually any two bends or loops move near each other and the river straightens its course cutting off from the loops.
• As deposition simultaneously occurs on the inner bank, the loops get clogged and separated. This part resembles a horse-shoe and is, therefore, called a horse-shoe lake or an ox-bow lake.

3. River Island:

• Since the slope of the land is moderate in the middle course of a river, its transportation power decreases. So the river’s load i.e. pebbles, silt, sand and gravel get deposited in the middle or on the two sides of the river.
• Sedimentation takes place and sometimes, island-like structures are formed. These are called river islands. The Majuli Island on the Brahmaputra is a famous river island and is also the largest river island in the world.

4. Wide and shallow valley:

In this stage vertical erosion decreases and the depth of the valley also decreases. However, due to the increase in the volume of water, lateral erosion increases proportionately. This results in the widening of the valley.

Question 3. Describe the features formed in the lower course of the river.
Answer:

Features formed in the lower course of the river:

The main work of the river in the lower course is deposition. The main features formed in this course of the river are-

1. Floodplain:

• The river flows very gently in its lower course. So pebbles, sand and silt get deposited on the river bed which becomes shallow due to deposition. Every year, when the volume of water increases during the rainy season, the river overflows its banks.
• This causes a flood. The sedimentation on the bank that results because the flood water spills over the lands on both banks, makes them very fertile. The plain thus formed on the banks is called a floodplain.

Example: The Ganga forms a floodplain in its lower course.

2. Natural levee:

• Sometimes, the sediments transported during a flood get deposited in a heap on the banks.
• They form natural embankments called levees.
• They are about 2-3 metres higher than the floodplains.

3. Delta:

• When the sand, silt and clay transported by the river get deposited at the mouth, a triangular-shaped structure is formed.
• This is called a delta. As it looks like the Greek letter A, it is named so.

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Question 4. Draw a comparison among the different courses of a river.
Answer:

A comparison among the different courses of a river:

A comparison among the different courses of a river is as follows-

 

Question 5. Write about the influence of rivers on our life.
Answer:

The influence of rivers on our life:

The influence of rivers on our life can be discussed as follows-

1. Rivers are a source of drinking water from times immemorial.
2. Fertile silt deposits on the banks of the rivers are good for agricultural activities.
3. In the industrial sector, river water acts as a raw material.
4. Places on the river banks have moderate climatic conditions in comparison to extreme climatic conditions in areas away from the influence of water.
5. Rivers play an important role in maintaining the balance of our earth’s hydrological cycle. Rivers are one of the main sources of water vapour, which condenses and forms precipitation and carries on the hydrological cycle.
6. Rivers are the natural route of transport and communication between different countries that help in the navigation and transport of trade items.
7. Perennial rivers enhance the irrigation system of the country. Canals, drawn out from the perennial rivers, provide water for irrigation even in the dry season.
8. River deltas are the hotspots for aqua culture, that involves commercial fish farming or pisciculture.
9. Rivers are also used to generate hydroelectricity. The energy of water flowing through a river, spins a turbine to produce electricity.

Question 6. Write about the consequences of human activities on the health of a river.
Answer:

The negative consequences of human activities on the health of a river:

Even though rivers have a very influential effect on human life. Man has never adequately valued this natural resource. Different human activities have often had negative consequences on the health of a river. Like-

1. Multi-purpose river valley projects:

• Dam-building on the rivers might yield short-term benefits but has long-term negative consequences also. Building a dam on the upper reaches of the river results in the drying up of the lower course.
• Again, at times during monsoon, heavy rainfall in the upper reaches causes devastating floods in the lower course along the banks which destroys life and property and hampers the ecosystem.

2. Water pollution due to industrialisation:

• Discharge of industrial wastes into the river water and discharge of fertiliser mixed water from the agricultural fields pollute the rivers
• This water pollution in turn kills the fish in the river.

3. Irrigation on the agricultural fields:

• Daming on the river to divert the river water for irrigation to agricultural fields results in the drying up of the rivers.
• On the other hand, discharged water from agricultural fields carries soil sediments and crop residues along with it.
• These settle on the river beds making them shallow and prone to floods.

4. Urbanisation:

• The expansion of urban settlements on the river banks is mainly due to the increase in demand for the river water.
• This excessive use of river water decreases its volume. Also, the household wastes dumped into the river hugely pollute the river.

Question 7. The majority of the Indian population resides in the Ganga River Basin. Our lives depend on this river. What are the probable consequences if the Ganga dries up?
Answer:

The probable consequences if the Ganga dries up:

River Ganga is the main and the most voluminous river of India. The probable consequences if the Ganga dries up are-

• Scarcity in drinking water: One-third of the Indian population resides in the Ganga Basin and is dependent on the purified water of this river for drinking purposes. If the river dries up, there would be a large scale drinking water scarcity in the country.
• Problem in water transport: The waterways on the Ganga would be rendered useless and thus creating a huge problem in water transport, if the Ganga dries up.
• Shut down of industries: The industries on the banks of the Ganga are hugely dependent on the river water for their manufacturing process. A dried-up river would impact the industries.
• Infertile agricultural fields: The floodplains would run infertile in the absence of water and that would affect the agricultural production.
• Scarcity in groundwater: In the absence of river water, the dependency on groundwater would increase magnanimously. As a result, the groundwater table would rapidly deplete.
• Death of aquatic organisms: If the Ganga dries up, all the aquatic organisms in the water would die, disrupting the ecological balance

Question 8. Compare a gorge and a canyon.
Answer:

The comparison between a gorge and a canyon are given in the table below.

 

Question 9. Write a note on waterfalls.
Answer:

Waterfalls:

• If alternate bands of hard and soft rocks the harder rocks being more resistant remain exist horizontally along the course of the river, protruding outward like an outcrop while the softer rocks are easily eroded.
• When the river plunges over the protruding rock beds, a waterfall is formed.
• Waterfalls are commonly formed along young swift flowing streams.

 

 

Waterfalls form in the upper courses of the rivers because of the steep slope of the land and the presence of faults in the course of the rivers.

• For example, Gersoppa or Jog Falls on the Sharavati River in Karnataka is the second-highest waterfall in India.
• More intensive erosion of the softer rocks in comparison to the resistant rocks makes the harder rocks collapse, disturbing the balance of the waterfall-forming conditions.
• This is called the ‘retreat of a waterfall’.

Question 10. Briefly write about potholes.
Answer:

Potholes:

Potholes are formed when a river cuts directly into its bedrock as a result of vertical erosion and processes of abrasion. Potholes are deepened by spherical or disc-shaped stones which are often found at their bottom.

A spiralling flow of water or turbulence in the pothole rotates these spherical or disc-shaped stones gradually boring into the rock and scooping out the softer rocks.

For example, potholes are found on the bed of River Subarnarekha.

Real-Life Scenarios Involving Flood Management

Question 11. Write a short note on the alluvial fan and alluvial cone.
Answer:

Alluvial fan and alluvial cone:

When a river leaves the mountainous terrain and enters the plain, there is a sudden decrease in the steepness of the land slope and its erosive power.

• This causes the river to deposit its load comprising boulders, pebbles, sand, and silt in a conical manner leading to the formation of an alluvial cone.
• As the river continues to flow over the alluvial cone, it sometimes radiates downslope into a fan-shaped deposit comprising the finer particles called an alluvial fan.
• The sediment content is more in the case of alluvial cones than fans.

 

 

Question 12. Discuss the middle course or plain stage of a river.
Answer:

The middle course or plain stage of a river:

• When the river leaves the mountains and flows over land with relatively low height, it is in the middle course.
• The moderate slope of the land, greater volume of water and moderate velocity of river flow decrease its erosional activity and mainly transport the eroded materials with little deposition along the channel.
• For example, the middle course of the River Ganga extends from Haridwar to Mithipur in Murshidabad.

Question 13. What are the characteristics of a river in its middle course?
Answer:

The characteristics of a river in its middle course are-

1. The moderate slope of the land lowers the speed of the river flow.
2. The volume of water increases as many tributaries join the main channel leading to an increase in the ‘load’ carried by the river.
3. The main work of a river in the middle course is lateral erosion or side-cutting and transportation. The river water here is used for irrigation as well as for navigation.

Question 14. Write a note on meander.
Answer:

Meander:

In the plain stage or middle course of a river there is a sudden decrease in the velocity of water flow.

• The river winds its course the moment it gets the slightest resistance.
• When the river channel winds its course through a series of bends, it forms meanders or loops.
• The term ‘Meander’ has been derived from the winding River Menderes in Asia Minor.

Example: the meandering course of River Ganga can be observed near Varanasi.

 

 

Question 15. Briefly write about sandbars and braided rivers.
Answer:

Sandbars and braided rivers:

In the middle course, the slope of the land becomes moderate and the velocity of the river decreases. So the river deposits the sand, silt etc.carried from the mountains on the valley floor forming sandbars or, the bigger ones eventually form river islands.

• The river gradually becomes shallow due to the extensive formation of sandbars with time.
• Valley widening takes place as a number of tributaries join the main river.
• The water of the main river branches out into several channels due to the presence of sandbars in its course forming a braided river.

Example:

River Brahmaputra is a braided river as it has formed many river islands along its course in Assam of which Majuli is the largest.

Examples of Real-Life Applications of River Knowledge

Question 16. How are river cliffs and slip-off slopes formed?
Answer:

River cliffs and slip-off slopes formed:

A river has two bends or banks- an outside bend or concave bank and an inside bend or convex bank.

• The water dashes straight to the outside bend, eroding it and forming a steep river cliff while the eroded sediments, get transported and are deposited in the inner bend or convex bank forming a gentle slip-off slope.
• The outer bend is therefore the bank of continuous erosion while the inner bend is the bank of continuous deposition.

Question 17. Write about ox-bow lake.
Answer:

Ox-bow lake:

In the plain stage or middle course of a river, since the land has a moderate slope, it winds its course the moment it gets the slightest resistance.

• As the river meanders, its steeper bank gets eroded, while these eroded sediments get deposited on its opposite bank. In this way, meanders become prominent.
• When two such steeper banks come very close to each other, the meander neck is pronounced, making it difficult for the river to follow such a curved course.

 

 

• The river then flows straight, leaving behind a cut-off lake with its ends sealed off by deposition.
• This abandoned channel of water is known as an oxbow lake or horseshoe lake, as it resembles the foot of a horse in shape.

Example: Oxbow lakes are commonly seen in the plain stage of River Ganga.

Question 18. Discuss the lower course or delta stage of a river.
Answer:

Lower course or delta stage of a river:

• When the river flows over extensive level land near its mouth, it is in the lower course.
• Alluvium deposition is the main work of the river in this course caused by gently sloping land.
• The river deposits its load leading to the formation of various small and big deltas.
• Here, the main river channel subdivides itself into numerous channels i.e., distributaries before draining into the ocean or sea.

For example, the lower course of River Ganga extends from Mithipur in Murshidabad to the Bay of Bengal.

Question 19. What are the characteristics of a river in its lower course?
Answer:

The characteristics of a river in its lower course are-

1. In its lower course, the river flowing along gently sloping lands becomes sluggish as the velocity of flow reduces drastically.
2. The main work of the river in this course is deposition. The river deposits its entire bed load comprising alluvium or silt.
3. Before flowing into the ocean or sea most of the rivers develop deltas at their mouths. This stretch of the river is highly navigable.

 

Important Definitions Related to River Works

Question 20. Why is deposition the main work of a river in its lower course?
Answer:

Deposition is the main work of the river in the delta stage or lower course because-

1. Near its mouth, the slope of the land and the velocity of the water flow decreases.
2. The load carried by it increases.
3. It follows a winding course instead of a straight course.
4. Near its mouth, the action of water currents helps in deposition.

Question 21. Write a short note on floodplains and natural levees.
Answer:

Floodplains and natural levees:

• In the lower course, a river carrying pebbles, sand, silt, etc. makes its valley shallower. At times of flood, the volume of water in the river increases and the river then overflows its banks.
• The silt brought by flood water is then spread over the low-lying areas along the channel and further away.
• These result in the formation of floodplains. Floodplains are very favourable for agricultural activities.
• Large deposits of silt or mud on either side of the river often form an elongated deposit which then creates a ridge or embankment. This is called levee.

Example:

Floodplains and natural levees are found along the course of River Ganga near Rajmahal Hills in the state of Jharkhand.

Question 22. What are the causes of frequent floods in the lower course of a river?
Answer:

Floods are frequent in the lower course of a river because-

1. Numerous tributaries joining the main river increase the volume of water near its mouth.
2. As the land slope is gentle, the velocity of river flow decreases.
3. Sand, silt and clay are deposited on the river bed making it shallow.
4. In the rainy season, as the volume of water increases, the river overflows its banks and causes a flood.

Question 23. Briefly write about delta formation.
Answer:

Delta formation:

• In the lower course of a river, the slope of the land is very gentle. This leads to a slow and sluggish flow of water with almost no erosional activities.
• When the river reaches the sea, the fine sediments are deposited at its mouth forming a fan-shaped alluvial land called delta. The word ‘delta’ originated from the Greek letter Δ.

For example, the Ganga-Brahmaputra Delta is the largest delta in the world.

• Due to the obstruction in the river flow caused. by the deposited alluvium, the river may discharge its water through several channels which are known as distributaries.
• The river bifurcates at these deltas and the distributaries flow along its sides.
• Deltas can be further classified into several types depending on the shape they take.

 

 

Question 24. What are the conditions necessary for the formation of a delta?
Answer:

The favourable conditions for delta formation are-

1. Large amounts of sediment should be carried by the river.
2. The coast should be preferably tideless.
3. The sea adjoining the delta should be current less and shallow or else the sediments will disappear in the deep water.
4. There should be no large lake in the river course because the sediments will get deposited in the lake.
5. The wind must blow from the opposite direction.
6. The river must have a long course which will help to collect a large amount of eroded matter as bed load.
7. The river must have a large number of tributaries.

Question 25. What are the causes for the formation of distributaries in the delta stage?
Answer:

In the delta stage, many distributaries form because-

1. At the mouth of the river, the land slope is gentle and the water is shallow. Though the volume of water is more, the velocity is less and the river divides into several channels as soon as any rock obstructs its path.
2. The sand banks obstruct the flow of the river forcing it to branch out into channels.
3. Thus, the sediment load carried by the river paves the way for the formation of its distributaries.

Question 26. What are the reasons for some rivers not forming deltas?
Answer:

The reasons for some rivers not forming deltas are-

•  At the mouth of the river near the sea, river current and rate of transportation decreases while the rate of deposition increases.
• But this rate of deposition should be more than the velocity of the ocean current. If the velocity of the river carrying the eroded materials is more, then the sediments will get carried deep into the sea and not form a delta.
• If the river is not very long it will not have caused much erosion all through its course.
• If the river has a lesser number of tributaries the amount of sediment carried would be less.
• If the river has eroded less in its upper and middle courses the amount of sediment carried would be less.
• If the coast is not sheltered.
• If the wind blows in a direction as that of the river, the sediments will be carried into the sea due to the wind.

For example, west-flowing rivers like Narmada and Tapi do not form deltas.

Question 27. River Ganga is an ideal river.-Give reason.
Answer:

River Ganga is an ideal river:

The main river of India, River Ganga performs erosional activities in its upper course or mountain stage (from Gomukh ice cave near Gangotri Glacier in Kumaun Himalayas to Haridwar in Uttarakhand), transportation activities in its middle course or plain stage (from Haridwar to Mithipur in Murshidabad) and depositional activities in its lower course or delta stage (from Mithipur in Murshidabad to river mouth in Bay of Bengal).

Since River Ganga displays all three courses distinctly it is called an ideal river.

Question 28. Discuss the three courses of River Ganga.
Answer:

The three courses of River Ganga are-

1. The upper course or mountain stage of River Ganga extends from Gomukh ice cave near Gangotri Glacier in Kumaun Himalayas to Haridwar in Uttarakhand.
2. The middle course or plain stage or River Ganga extends from Haridwar in Uttarakhand to Mithipur in Murshidabad.
3. The lower course or delta stage of River Ganga extends from Mithipur in Murshidabad to the river mouth in the Bay of Bengal.

Question 30. What is meant by river valley civilisations?
Answer:

River valley civilisations:

In ancient times, the ease of conducting agricultural activities along the river banks caused the growth and development of human settlements there.

• There were other advantages of living in settlements on the banks of rivers – such as the plentiful supply of water for drinking and other activities, communication through waterways as well as growing trade.
• As the population increased, these settlements developed and transformed into proper towns and cities.
• Throughout history, many civilisations have developed along the rivers.

Example:

Indus Valley Civilisation along River Indus, Chinese Civilisation along River Yangtze and Hwang Ho, Mesopotamian Civilisation along River Tigris and Euphrates and the Egyptian Civilisation along River Nile.

 

Question 31. Fill up the knowledge hive information about the waterfall.

Answers:

1. A waterfall forms along a steep slope, that may have formed, along the course of a river due to an earthquake.
2. The direction of a river changes at the waterfall.
3. A nick point is formed along the course.
4. In a plateau region waterfall may form due to the presence of faults along the course.
5. Waterfalls form where hard and soft rocks lie along the course alternately.
6. If the balance of waterfall forming conditions is disturbed, the waterfall retreats.

Question 32. Think and write down.

Answers:

1. Enhanced erosion
2. Enhanced deposition

Question 33. Fill it up correctly.

Answers:

1. Deposition
2. Erosion
3. Deposition

Question 3.

 

 

Answers:

1. Tributaries
2. Distributaries

Question 34. A diagram of the course of a river is given below. Now mark the works of the river in its different stages as (a), (b) and (c) and the landforms as (d), (e) and (f).

 

 

Answers:

1. Works of the river-(a) erosion and transportation (b) transportation and deposition (c) deposition.
2. Features-(d) gorge, waterfall, rapid (e) meander, ox-bow lake, river island (f) delta, floodplain.

Question 35.

 

Down:

1. Fertile stretch of land lying between two rivers.
2. Sand deposits are found in the middle of the river.

Across:

3. Flooded banks of a river.
4. Winding path of a river.

Answers:

Down: 1. DOAB, 2. SAND BAR
Across: 3. FLOODPLAIN, 4. MEANDER

Question 36.

 

Down:

1. Kettle-like depressions on the river bed.
2. Winding course of a river.

Across:

3. Vertical fall of water in mountainous regions.
4. Longest river of the world.

Answers:

Down: 1. POTHOLE, 2. MEANDER
Across: 3. WATERFALL, 4. NILE

Question 37.

 

1. Where a river meets the sea.
2. River in which water flows throughout the year.
3. River originating from a main river.
4. A highland that makes rainwater runoff to different sides to form rivers flowing in different directions.
5. Deep-cut river valley in a dry region.
6. River water falls from a height along a steep slope to form a ________.
7. Alluvium is deposited along both banks of a river during a flood to form.

 

 

Answers:

1. MOUTH,
2. PERENNIAL,
3. DISTRIBUTARY,
4. WATERSHED,
5. CANYON,
6. WATERFALL,
7. FLOODPLAIN

Question 38. What is an ‘interlocking spur’?
Answer:

• As the river wanders in the mountainous region eroding the landscape, it winds and bends to avoid areas of hard rock along its course.
• This profile of mountains when seen from a distance appears as an interlocked feature like the teeth of a zip known as an interlocking spur.

Question 39. What is the sixth power law?
Answer:

The river processes-erosion, transportation and deposition, are related to one another. The velocity of flowing water controls these riverine processes.

• An increase in the velocity of running water increases the energy of the river while a decrease in the velocity of running water decreases the energy.
• If the velocity of the river increases 2 times then the rate of transportation of the river increases 6 times (2⁶ = 64).
• The proportional relationship between velocity and transportation is called the sixth power law.

The load that can be carried by a river depends on the following factors-

1. The velocity of water flow,
2. The volume of water,
3. Amount of load.

Question 40. Differentiate between an alluvial fan and an alluvial cone.
Answer:

The differences between an alluvial fan and an alluvial cone are listed in the table below-

Question 41. Pour water on sloping surfaces in your yard, in the park or in the school playground. Watch where the water flows. It surely flows from the higher to the lower ground. Now, mark three points ‘A’, ‘B’ and ‘C’ at different heights in the upper reaches of the slope. Pour water at these three points and observe how the water along the three channels flow.

Mark another point ‘D’. Keep a brick a foot down the slope from ‘D’ and pour water on the point. Now, observe how this channel lays out.
Answer:

• If we pour water in the yard, in the park or on a sloping place, we will see that the water starts flowing. The place from where the water starts flowing in the source. and the direction to which the. water is flowing, is the mouth.
• Three points ‘A’, ‘B’, and ‘C’ are marked 6 inches apart at the top of a slope. If we pour water at those three points and wait for a while, we will see that the Slope of the land three streams start flowing from the high to the low end of the slope.

 

 

• These are tributaries because those three streams join with the former stream. Another point ‘D’ is taken. In front of point ‘D’ a little away a brick or a big stone is placed.
• This time, if water is poured from point ‘D’, the flowing water will get obstructed at the brick and then it will bifurcate on both sides of the brick. Thus the distributaries are formed.

Question 42. Can you make out something from the diagram?

 

Answer:

What I could make out from the given diagram are as follows:

1. A general idea about the course of a river from source to mouth and the main works of a river can be established.
2. The slope of the entire river basin is from west to east.
3. Three stages of the river i.e., upper, middle and lower, are clearly noticeable.
4. Narrow valleys in the upper course, meanders in the middle and floodplain estuaries in the lower course are noteworthy here.
5. This river is a perennial one.
6. There are neither tributaries nor distributaries of the river, as found in the diagram.

Question 43. You can fill this up from the college

Answer:

WBBSE Chapter 5 River Topic B Works Of River And Its Influences On Our Life Short Question And Answers

Question 1. Mention the work of the river in its different stages.
Answer:

 

Question 2. Why is erosion an important riverine activity in the mountain stage?
Answer:

• The upper course or mountain stage of a river extends from the source to the foothills of mountains.
• In this stage, the swift-flowing river mainly erodes the rugged mountain terrain and steep land due to the high velocity of the water flow and carries the eroded materials downstream.
• Thus, erosional activities can be distinctly observed in the upper course due to the processes of attrition, solution and corrosion or abrasion.

Question 3. Define the water cycle.
Answer:

Water cycle;

• A river is an important part of the water cycle. Rainwater drains along a river and empties into the sea.
• Water evaporating from the sea and other waterbodies cool down and come back as rain into the rivers.
• This cyclical movement of water is known as the water cycle.

Question 4. What is a V-shaped valley?
Answer:

V-shaped valley:

• In humid regions, rivers in their upper course usually form a V-shaped valley, as a result of extensive vertical erosion along the steep slope of the land and slight lateral erosion due to rainfall.
• The narrow river valley with its steep slopes resembles the English letter ‘V’. It is also known as a gorge.

Question 5. What is an ‘estuary’?
Answer:

Estuary:

• In the delta stage or lower course, if the velocity of the river is high, the sediments are carried into the sea along with the water.
• Thus no delta is formed and the river mouth becomes very wide.
• This wide, funnel-shaped mouth of the river is called an estuary. Example: Tidal rivers of Sundarbans form estuaries.

Question 6. Define an ideal river.
Answer:

Ideal river:

• A river which displays all three stages from source to mouth i.e., upper course or mountain stage, middle course or plain stage and lower course or delta stage is called an ideal river.
• For example, the main river of India, the River Ganga is an ideal river.

Question 7. Identify the course of a river in which the landform shown in the following figure is seen.
Answer:

Upper course of a river.

Question 8. What is meant by transportation by suspension?
Answer:

Transportation by suspension:

• Fine light materials like sand, silt and mud are carried along with the water as the stream flows.
• This is called transportation by the suspension.

Question 9. What is meant by transportation by the solution?
Answer:

Transportation by the solution:

• The minerals present in the rocks eroded by the river get dissolved in the water and are carried along the channel by solution.
• Limestone and salt also dissolve in water and are transported down the channel by solution.

Question 10. What is meant by transportation by dissolving action is the work of fresh water, saltation?
Answer:

Transportation by dissolving action is the work of fresh water, saltation:

• The transportation of eroded particles like small pebbles which make intermittent leaps from the river bed is called saltation.
• In this process, particles are lifted from the river bed, carried short distances downstream, returned to the river bed, lifted again and so on.
• These particles are of intermediate size and too heavy to be suspended load.

Question 11. What is meant by transportation by traction?
Answer:

Transportation by traction:

• Eroded particles that are too heavy for saltation move along the river bed by traction.
• These include coarser materials such as pebbles, stones, rocks and boulders.
• These particles either roll and slide along the river bed or move forward by mutual collision.

Question 12. What is meant by ‘erosion by attrition’?
Answer:

Erosion by attrition:

• Attrition is a form of erosion, in which the bed load is eroded due to friction between itself and the bed.
• The rocks break down into smaller pieces by rubbing against one another and by the pressure of water.
• The pebbles, stones and boulders carried by the river current roll and collide with one another and break into finer particles. Gradually the rocks turn rounder and smoother.

Question 13. What is meant by ‘erosion by solution’?
Answer:

Erosion by solution:

• Erosion by solution takes place due to the action of water on soluble or partly soluble rocks which the river comes in contact with.
• Erosion by dissolving action is the work of fresh water, salt water, and acidic water.

Example:

Calcium carbonate present in limestone gets easily dissolved and eroded by solution when rivers flow through limestone topography.

Question 14. What is meant by ‘erosion by cavitation’?
Answer:

Erosion by cavitation:

• In the upper course of a river, air bubbles form in the water as the river flows at a high speed.
• The air trapped within these bubbles bursts and sends ripples outwards, eroding the river banks by creating cracks in the rocks.

Question 15. What is ‘erosion by hydraulic action’?
Answer:

Erosion by hydraulic action:

• Erosion by hydraulic action is caused by water flowing over the stream bed and bank.
• This flow, coupled with the impact of other smaller forces, easily loosens and erodes smaller alluvial matter, such as gravel, sand, silt and clay.

Question 16. Observe any river near your home and get an idea about its characteristics.
Answer:

I live in Balagarh village of Hooghly district.

1. Name of the river: Hooghly River
2. The volume of water (high/low): High
3. The velocity of water (high/low): Low
4. The slope of the land (steep/gentle): Gentle
5. So, which course of the river are you watching (upper/middle/lower): Lower course

Question 17. What do you mean by the term ‘river processes’?
Answer:

River processes:

A river uses its energy to carry out three main processes-

1. Erosion
2. Transportation
3. Deposition.

In the upper course or mountain stage, the river is in its youth stage and carries out erosional activities on the surrounding landscape. It also transports the eroded materials with little or no deposition. In the middle course or plain stage, the river mainly transports the eroded materials down its channel. There is little lateral erosion. In the lower course or delta stage, the river deposits its bed load along the channel with little transportation.

Question 18. What is meant by river load?
Answer:

River load:

The eroded rock debris carried by a river along its course is known as river load. A river’s load includes rocks, stones, pebbles, sand, and silt, much of which are washed along the river bed.

River load is mainly of three types-

1. Soluble load or dissolved load,
2. Suspended load,
3. The load is carried by saltation and traction or bed load.

Question 19. List the governing factors in the erosion, transportation depositional work of a river.
Answer:

The governing factors in the erosion, transportation and depositional work of a river are-

• The volume of water: The increase or decrease of the volume of water is directly proportional to the rate of erosional and transportation capacity of a river.
• The velocity of water: The velocity of a river directly determines its erosional and transportation capacity.
• The slope of the land: The slope of the land is also directly proportional to the work of the river. The higher is the slope, the higher is the rate of work and vice versa.

Question 20. What are the sources of the energy of a river?
Answer:

The sources of the energy of a river are-

1. Streams flowing through steep slopes have greater energy as compared to ones flowing through gentle slopes.
2. The more is the volume of water in a river, the more is energy and vice-versa.
3. The higher is the stream’s velocity, the higher is the energy and vice-versa.
4. As the bed load carried by the river increases, the energy of the river decreases and vice-versa.

Conceptual Questions on the Cultural Significance of Rivers 

Question 21. What are the factors on which the rate of transportation is dependent?
Answer:

The rate of transportation depends on-

• Volume of water: If the volume of water increases, the rate of transportation by the river also increases.
• Velocity of water flow: If the velocity of the river increases, transportation by the river also increases. The velocity of the river depends on the slope of the land – the velocity of the river increases if the land is steep, thus increasing the rate of transportation.
• The grain size of the sediment load: If smaller and finer particles are carried by the river, transportation is more as compared to that of larger particles.
• Nature of particles: If particles being transported are soluble, the rate of transportation increases.

Question 22. Discuss the upper course or mountain stage of a river.
Answer:

Upper course or mountain stage of a river:

• The upper course or mountain stage of a river extends from the source area of the river in the mountains to the foothills.
• Steepness of the land slope, strong currents and high velocity of water flow in the channel lead to erosional activities along this stretch.

Example: The upper course of River Ganga extends from Gomukh ice cave, near Gangotri Glacier in Uttarakhand to Haridwar.

Question 23. What are the characteristics of a river in its upper course?
Answer:

The characteristics of a river in its upper course are-

1. The river in its youth stage flows through mountainous or plateau regions. The steep slope of the land makes vertical erosion or down-cutting by the river very prominent.
2. Though the ‘load’ of the river is less, transportation takes place due to the high velocity of the water flow.
3. Since the river is swift-flowing, it helps in the generation of hydel power in this course but is unsuitable for navigation.

Question 24. Write a short note on the gorge and Canyon.
Answer:

Gorge and Canyon:

In mountainous regions, laterally eroded V-shaped valleys undergo rapid vertical erosion due to an increase in the velocity of water flow along the steep slopes.

• This deep valley with steeply sloping sides, resembling the English letter ‘V’ is called a gorge. Gorges are a common feature in dry mountainous regions.
• For example, Rivers Indus, Ganga and Brahmaputra have carved deep gorges along their courses in the Himalayas.
• One of the deepest gorges in the world is carved by River Colca in Peru (4,370 m).
• When the snow-fed river passes through rain-less, arid areas, lateral erosion becomes almost insignificant.
• If non-resistant rocks are present at the valley bottom, it leads to rapid down- cutting forming very narrow and deep gorges resembling the English letter ‘I’ called canyons.
• Example: Grand Canyon on River Colorado (1800 m deep) is world famous.

Question 25. What is a canyon or I-shaped valley?
Answer:

Canyon or I-shaped valley:

In arid and semi-arid regions, erosional activities by the river lead to the formation of I-shaped valleys because physical weathering has a more localised effect in arid zones.

• The wind and the water of the river combine to erode and cut away the less resistant rock fragments.
• The freezing and expansion of water and seepage of water into the cracks between the rocks eventually widen the valley.
• Such narrow, deep valleys, resembling the English letter ‘l’ are called canyons.

WBBSE Chapter 5 River Topic B Works Of River And Its Influences On Our Life Very Short Question And Answers

Question 1. Where do you find water flowing faster- on a flat surface or on a slope?
Answer: On a slope.

Question 2. When does water flow faster on slopes- when the volume of water is more or when the volume of water is less?
Answer: When the volume of water is more.

Question 3. Name a river that you have seen flowing in graceful loops.
Answer: River Ganga near Varanasi.

Question 4. In which course is the velocity of a river maximum?
Answer: Upper course.

Question 5. What is an I-shaped river valley called?
Answer: Canyon.

Question 6. What is a V-shaped deep river valley called?
Answer: Gorge.

Question 7. What is the aggregate of solid matter transported by river called?
Answer: River load.

Question 8. What is a fan-shaped depositional feature of a river called?
Answer: Alluvial fan.

Question 9. What is the winding course of a river known as?
Answer: Meander.

Question 10. What is a horse-shoe-shaped lake called?
Answer: Oxbow Lake.

Question 11. In which course of a river does deposition mainly take place?
Answer: Lower course.

Question 12. What is the principal work of the river in its lower course?
Answer: Deposition.

Question 13. What is a feature developed due to the accumulation of sand, silt, etc in the lower course of a river called?
Answer: Floodplain.

Question 14. What is a funnel-shaped river mouth known as?
Answer: Estuary.

Question 15. What is a river comprising three distinct courses known as?
Answer: Ideal river.

Question 16. What is the base level of river erosion?
Answer: Sea level.

Question 17. What are the small holes formed on the surface of rocks due to air bubbles known as?
Answer: Cavitation.

Question 18. What is the wear and tear of transported materials due to mutual collision termed as?
Answer: Attrition.

Question 19. By which process are the very fine rock fragments transported from one place to another?
Answer: Suspension.

Question 20. What is meant by ‘erosion by abrasion or corrasion’?
Answer:

Erosion by abrasion or corrosion:

Abrasion is the wearing away and the breaking up of rock surfaces along the valley sides using bed load (rocks, pebbles, boulders) as the grinding tools.

Question 21. I am a feature formed by a river falling from higher to lower altitudes in the form of steps. Who am I?
Answer: Waterfall

Question 22. I am a kettle-shaped depression on the river bed formed by the whirling motion of water. Who am I?
Answer: Pothole

Question 23. I am a fan-shaped depositional landform at the foothills. Who am I?
Answer: Alluvial fan

Question 24. I follow a winding path along the middle course of a river. Who am I?
Answer: Meander

Question 25. I am a horse-shoe-shaped lake. Who am I?
Answer: Ox-bow lake

Question 26. I am a landform like Δ the 4th letter of the Greek alphabet. Who am I?
Answer: Delta

Question 27. I form on both sides of a river due to flooding. Who am I?
Answer: Floodplain

Question 28. I am a natural embankment formed on both sides of the river due to silt deposition. Who am I?
Answer: Natural Levee

Question 29. I am a funnel-shaped mouth of the river. Who am I?
Answer: Estuary

Question 30. I refer to the volume and velocity of the water flowing in a river. Who am I?
Answer: River Discharge

Question 31. From the last experiment performed, do you find any similarity of that experiment with the concept of tributaries and distributaries?
Answer: Yes, the concept of tributaries and distributaries is exactly similar to the concept of the experiment performed.

Question 32. What is meant by ‘deposition by a river’?
Answer:

Deposition by a river:

When the amount of sediment or bed load of a river exceeds its carrying capacity i.e., capacity < bed load, then the eroded materials are deposited either on the river bed or along its banks.

WBBSE Chapter 5 River Topic B Works Of River And Its Influences On Our Life Find The Odd One Out

Question 1. Luni: Yamuna Amu Darya: Syr Darya
Answer: Yamuna (not an inland river)

Question 2. Indus: Narmada : Rhine: Danube
Answer: Narmada (not an international river)

Question 3. Floodplain : Waterfall: Gorge: Canyon
Answer: Floodplain (not have an erosional feature)

Question 4. Meander: River island: Delta: Ox-bow Lake Answers
Answer: Delta (not a feature of the middle course)

WBBSE Chapter 5 River Topic B Works Of River And Its Influences On Our Life Correct The Following

Question 1. The place where a river originates is called its mouth.
Answer: Source

Question 2. The Ganga originates from the Yamunotri Glacier.
Answer: Gangotri

Question 3. The smaller rivers which join a larger river are called distributaries.
Answer: Tributaries

Question 4. The river which flows through more than one country is called an inland river.
Answer: International

Question 5. The main work of a river in its lower course is erosion and transportation.
Answer: Deposition

Question 6. Almost 50% of the land surface of the earth bears evidence of the work of rivers.
Answer: 60

Question 7. There is no delta at the mouth of the Ganga River.
Answer: Amazon

WBBSE Chapter 5 River Topic B Works Of River And Its Influences On Our Life Fill In The Blanks

Question 1. The youthful age of a river is also known as the ________ stage.
Answer: Mountain

Question 2. Erosional activities are more distinct than depositional activities in the ________ course of a river.
Answer: Upper

Question 3. The main work of a river in its upper course is ________.
Answer: Erosion

Question 4. The two types of river erosion are vertical and ________.
Answer: Lateral

Question 5. Waterfalls are formed in the ________ stage of a river.
Answer: Mountain

Question 6. Narrow, deep river valleys are called ________.
Answer: Gorges

Question 7. Canyons are found in the ________ region.
Answer: Arid

Question 8. When a waterfall descends over a series of rock steps, it is known as a ________.
Answer: Cascade

Question 9. Gersoppa Falls is on the ________ river.
Answer: Sharavati

Question 10. The ________ Falls on River Narmada is located near Jabbalpur.
Answer: Dhuandhar

Question 11. Small holes on the river bed formed due to the drilling action of rock fragments are called ________.
Answer: Potholes

Question 12. Alluvial fans are formed by the river in its ________ course.
Answer: Middle

Question 13. When a river winds its course, it forms a ________.
Answer: Meander

Question 14. Meanders are observed in the ________ course of a river.
Answer: Middle

Question 15. The largest river island of India, ________ is formed by the River Brahmaputra.
Answer: Majuli

Question 16. The mature age of a river is also known as the ________ stage.
Answer: Plain

Question 17. River Ganga is joined by its tributary Kosi in its ________ stage.
Answer: Plain

Question 18. Depositional activities are more distinct’ than erosional activities in the ________ course of a river.
Answer: Lower

Question 19. Wide and shallow valleys are formed in the ________ course of a river.
Answer: Lower

Question 20. The rivers usually form ________ in their old stage.
Answer: Deltas

Question 21. Fluvial landforms are found all over the earth’s surface except in ________ areas.
Answer: Desert and Pola

Question 22. The ________ flowing rivers of India do not form any delta at their mouth.
Answer: West

WBBSE Chapter 5 River Topic B Works Of River And Its Influences On Our Life True Or False

Question 1. The course of an ideal river can be divided into three stages.
Answer: True

Question 2. The main work of a river in its mountain stage is erosion.
Answer: True

Question 3. In arid regions, lateral erosion is high in river valleys because of scanty rainfall.
Answer: True

Question 4. The main work of a river in its middle course is transportation.
Answer: True

Question 5. Interlocking spurs are observed in the middle course of a river.
Answer: False

Question 6. The accumulation of silt, sand, pebbles, etc. on the banks of a river lead to the formation of natural levees.
Answer: True

Question 7. The word ‘meander’ has been derived from the winding river Menderes of Turkey.
Answer: True

Question 8. On a plain-land, erosion of the banks of a meandering river makes the river flow straight forming islands or bars in its path.
Answer: False

Question 9. The stretch from Haridwar to Rajmahal Hills is identified as the upper course of River Ganga.
Answer: False

Question 10. ‘V’-shaped valleys are formed in the middle course of a river.
Answer: False

Question 11. River Brahmaputra forms the largest delta in the world.
Answer: False

Question 12. The meandering course of River Ganga can be seen near Varanasi.
Answer: True

Question 13. Potholes are common along the upper course of River Ganga.
Answer: True

Question 14. Floodplains develop on either side of a river in its lower course.
Answer: True

Question 15. A river flows in a winding course in its mountain stage.
Answer: False

Question 16. The alluvial fans formed by River Ganga are observed near Haridwar.
Answer: True

WBBSE Chapter 5 River Topic B Works Of River And Its Influences On Our Life Scrambled Words

1. NGYOFALBEBA
2. NTCATEAMECHAR
3. VIWARDITEDE
4. NBAERVSIRI
5. RIRENNVALIERPE
6. SIONPODETI
7. OWKEOXLAB
8. DINOOPLFLA

Answers:

1. BAY OF BENGAL
2. CATCHMENT AREA
3. WATER DIVIDE
4. RIVER BASIN
5. PERENNIAL RIVER
6. DEPOSITION
7. OX-BOW LAKE
8. FLOODPLAIN

WBBSE Chapter 5 River Topic B Works Of River And Its Influences On Our Life Match The Columns

Question 1.

Answer: 1. D, 2. E, 3. F, 4. C, 5. B, 6. A, 7. G