Class 9 Social Science (Contemporary India) Chapter 3 Drainage

Key Concept: Indus River System, Ganga River System

b) The Ganga tributaries enrich the soil for agriculture, while the Indus tributaries do not.

[Solution Description]

The Indus River System includes tributaries such as the Zaskar, Nubra, Shyok, Hunza, Satluj, Beas, Ravi, Chenab, and Jhelum, which join together near Mithankot in Pakistan. On the other hand, the Ganga River System has major tributaries like the Yamuna, Ghaghara, Gandak, Kosi, Chambal, Betwa, and Son. The key difference is that the Ganga’s tributaries from the Himalayas, such as the Yamuna, Ghaghara, Gandak, and Kosi, are known for causing floods during the rainy season, enriching the soil for agriculture. In contrast, the Indus tributaries do not have this characteristic. Additionally, the Ganga’s peninsular tributaries like the Chambal, Betwa, and Son have shorter courses and carry less water.

Key Concept: Main Water Divide: Western Ghats

d) Tapi

[Solution Description] The main water divide in Peninsular India is formed by the Western Ghats. Most of the major rivers flow eastwards and drain into the Bay of Bengal. However, the Narmada and the Tapi are the only long rivers that flow westwards and make estuaries.

Key Concept: National River Conservation Plan, Water Resource for Irrigation and Drinking

c) Agriculture and allied activities

[Solution Description]

Improved water quality due to NRCP interventions can have a positive impact on multiple sectors. Agriculture would benefit significantly as clean water is essential for irrigation, leading to higher crop yields and better quality produce. The health sector would also see benefits as clean drinking water reduces the incidence of waterborne diseases, lowering healthcare costs. Industries reliant on water for production processes would experience reduced operational costs and improved efficiency. Additionally, tourism and recreational activities around the river would flourish, contributing to local economic growth. However, agriculture, being the primary source of livelihood for a large portion of the population, would see the most substantial economic benefits from improved water quality.

Key Concept: Indus River System

a) Zaskar

[Solution Description]

The river Indus rises in Tibet, near Lake Mansarowar, and enters India in the Ladakh region. Among its tributaries, the Zaskar joins it in this region. Therefore, the correct answer is the Zaskar.

Key Concept: Origin of the Mahanadi River

c) Chhattisgarh Highlands

[Solution Description] The Mahanadi River originates in the highlands of Chhattisgarh. This is a basic fact mentioned in the syllabus.

Key Concept: The Godavari Basin

d) Godavari

[Solution Description]

The Godavari is the largest Peninsular river with a length of about 1500 km. It drains into the Bay of Bengal and has the largest drainage basin among peninsular rivers. Due to its length and coverage, it is also known as the Dakshin Ganga. Hence, the correct answer is the Godavari.

Key Concept: Ox-bow Lakes, Coastal Lagoons

c) Chilika Lake

[Solution Description]

Coastal lagoons are formed by the action of spits and bars along the coastline. The Chilika Lake in Odisha is a prime example of such a lagoon. Unlike ox-bow lakes, which are formed from river meanders, coastal lagoons are influenced by marine processes.

Key Concept: Origin of Godavari

c) Nasik

[Solution Description]

The Godavari originates from the slopes of the Western Ghats in the Nasik district of Maharashtra.

Key Concept: Natural Lakes, Human-Made Lakes

c) Guru Gobind Sagar

[Solution Description] Guru Gobind Sagar is an artificial lake created by the damming of the Sutlej River as part of the Bhakra Nangal Project. In contrast, Wular, Dal, Nainital, and Loktak are natural lakes.

Key Concept: Natural vs. Artificial Lakes

c) Guru Gobind Sagar

[Solution Description]

Guru Gobind Sagar is a man-made lake formed due to the damming of the Sutlej River as part of the Bhakra Nangal Project. This is explicitly mentioned in the syllabus, which states that the damming of rivers for hydel power generation has led to the formation of lakes like Guru Gobind Sagar.

Key Concept: The Ganga River System

d) Yamuna

[Solution Description]

The river Yamuna rises from the Yamunotri Glacier in the Himalayas. It flows parallel to the Ganga and as a right bank tributary meets the Ganga at Allahabad. This information is provided in the syllabus.

Key Concept: Brahmaputra River System, Environmental Impact

c) Due to the rising riverbed caused by silt deposits

[Solution Description]

The Brahmaputra River carries a large volume of water and considerable amount of silt as it passes through a region of high rainfall in India. The river has a braided channel and forms many riverine islands. The huge deposits of silt on its bed cause the riverbed to rise, leading to frequent overflowing of the banks during the rainy season. This results in widespread devastation due to floods in Assam and Bangladesh.

Key Concept: Inland Navigation, Carbon Footprint

c) 25,000 kg

[Solution Description] To calculate the carbon emission reduction, we multiply the reduction in emissions per tonne-kilometer by the total weight of the goods and the distance traveled.

Carbon Emission Reduction = Emission Reduction per tonne-kilometer * Weight * Distance

Carbon Emission Reduction = 50 grams/tonne-km * 1,000 tonnes * 500 km

Carbon Emission Reduction = 25,000,000 grams

Converting grams to kilograms:

Carbon Emission Reduction = 25,000 kg

Key Concept: Godavari Basin

c) 50%

[Solution Description]

The Godavari basin covers parts of Maharashtra, Madhya Pradesh, Odisha, and Andhra Pradesh. It is mentioned that about 50 per cent of the basin area lies in Maharashtra. Therefore, the correct answer is 50%.

Key Concept: Differences Between Himalayan and Peninsular Rivers

b) They receive water from both rain and melted snow

[Solution Description]

The Himalayan rivers are perennial because they receive water from both rainfall and melted snow from the lofty mountains throughout the year. In contrast, Peninsular rivers are mostly seasonal, depending largely on rainfall. This difference in water sources ensures that Himalayan rivers have a continuous flow, unlike the Peninsular rivers which often experience reduced flow during dry seasons.

Key Concept: Indus Water Treaty

c) 20%

[Solution Description]

The Indus Water Treaty (1960) regulates the sharing of the Indus river system between India and Pakistan. As per the treaty, India is allowed to use only 20% of the total water carried by the Indus river system. This allocated water is primarily used for irrigation purposes in the Indian states of Punjab, Haryana, and parts of Rajasthan.

Key Concept: Godavari Tributaries

b) Purna

[Solution Description]

The Godavari River is joined by several tributaries, including the Purna, Wardha, Pranhita, Manjra, Wainganga, and Penganga. Among the options given, the Purna is one of its tributaries.

Key Concept: Drainage Systems, Types of Drainage Patterns

b) Dendritic Pattern

[Solution Description] A dendritic drainage pattern typically develops in regions with uniformly resistant rock and gentle slopes. This pattern resembles the branching of a tree, with tributaries joining the main stream at acute angles.

Key Concept: Godavari River Basin

c) Maharashtra

[Solution Description]

The Godavari river basin covers parts of Maharashtra, Madhya Pradesh, Odisha, and Andhra Pradesh. Approximately 50\% of the basin area lies in Maharashtra, making it the state with the largest share of the Godavari river basin.

Key Concept: Drainage Basin

a) Ganga

[Solution Description]

The Ganga river is known to have the largest drainage basin in India. It covers a vast area and is one of the most significant river systems on the Indian subcontinent.

Key Concept: Peninsular Rivers

d) Kerala

[Solution Description]

The Godavari river originates from the slopes of the Western Ghats in Maharashtra and drains into the Bay of Bengal. Its drainage basin covers parts of Maharashtra, Madhya Pradesh, Odisha, and Andhra Pradesh. Kerala is not part of the Godavari river basin.

Key Concept: Gorges, Meanders, Oxbow Lakes

b) An oxbow lake

[Solution Description]

In the upper course, a river typically forms gorges due to vertical erosion caused by fast-flowing water. As the river enters its middle course, the slope decreases, and lateral erosion becomes more dominant, leading to the formation of meanders. Over time, these meanders may get cut off from the main river channel, resulting in the formation of oxbow lakes. Therefore, the most likely landform to develop in the middle course of the river is an oxbow lake.

Key Concept: Distributaries: Bhagirathi-Hooghly

c) Bay of Bengal

[Solution Description]

The Bhagirathi-Hooghly is a distributary of the Ganga river that flows southwards through the deltaic plains and empties into the Bay of Bengal.

Key Concept: National River Conservation Plan

c) 1995

[Solution Description]

The National River Conservation Plan (NRCP) was expanded to cover other rivers in 1995, following the initial launch of the Ganga Action Plan in 1985.

Key Concept: Himalayan Rivers

d) They are perennial and form gorges in the mountains.

[Solution Description]

The Himalayan rivers are perennial, meaning they have water throughout the year. They receive water from both rain and melted snow from the mountains. These rivers have long courses and often cut through mountains to form gorges. This makes them distinct from Peninsular rivers.

Key Concept: Tapi River Origin

b) Satpura ranges, Betul district of Madhya Pradesh

[Solution Description] The Tapi river originates in the Satpura ranges, specifically in the Betul district of Madhya Pradesh. This is a direct fact from the syllabus.

Key Concept: River Pollution, Self-Cleansing Capacity

c) The river’s self-cleansing capacity decreases significantly

[Solution Description] When urbanization increases without proper treatment of sewage and industrial effluents, the volume of untreated waste entering the river exceeds its self-cleansing capacity. This leads to higher pollution levels as the river cannot effectively dilute or assimilate the increased pollution load, resulting in degraded water quality and reduced ecological health.

Key Concept: Hydropower Generation, River Regulation

c) 40%

[Solution Description] To find the percentage of the lake’s capacity utilized to prevent flooding, divide the inflow by the total storage capacity and multiply by 100. The calculation is as follows:

$\text{Percentage Utilization} = \left(\frac{200}{500}\right) \times 100 = 40%$

Thus, 40% of the lake’s capacity is utilized to prevent flooding.

Key Concept: Water Storage and Flood Control

c) 100 days

[Solution Description]

To determine how many days it will take for the lake to fill to its maximum capacity during the heavy rainfall event, we need to calculate the net increase in storage per day. The net increase is the difference between the inflow rate and the outflow rate.

Net increase per day = Inflow rate – Outflow rate

Net increase per day = 20 million cubic meters – 15 million cubic meters

Net increase per day = 5 million cubic meters

The total storage capacity of the lake is 500 million cubic meters. To find the number of days required to reach this capacity, we divide the total storage by the net increase per day.

Number of days required = Total storage / Net increase per day

Number of days required = 500 million cubic meters / 5 million cubic meters per day

Number of days required = 100 days

Key Concept: Water Divide

b) Water divide

[Solution Description]

A water divide, such as a mountain or an upland, separates two drainage basins. It acts as a boundary where waters on each side flow into different drainage systems.

Key Concept: Kaveri Basin Tributaries

c) Amravati

[Solution Description]

The Kaveri river has four main tributaries: Amravati, Bhavani, Hemavati, and Kabini. These tributaries contribute to the flow and drainage of the Kaveri basin.

Key Concept: Aquatic Ecosystem

b) By providing habitats and nutrients

[Solution Description]

Lakes provide a habitat for various aquatic organisms, including fish, plants, and microorganisms. They support the food chain by offering nutrients and oxygen, which are essential for the survival of aquatic life. Additionally, lakes help in maintaining water quality by filtering pollutants and sediments, thus ensuring a balanced and healthy aquatic ecosystem.

Key Concept: Direction of Flow and Basins

d) Narmada

[Solution Description]

Most Peninsular rivers flow eastwards and form deltas at their mouths. However, the Narmada and Tapi are exceptions, as they flow westwards and form estuaries instead of deltas. The Godavari, Krishna, and Kaveri flow eastwards and form deltas.

Key Concept: Flow Direction of Narmada

d) West

[Solution Description]

The Narmada river flows towards the west in a rift valley formed due to faulting, as stated in the syllabus.

Key Concept: River Pollution, National River Conservation Plan

b) To reduce the pollution level in rivers

[Solution Description]

The National River Conservation Plan (NRCP) was launched in 1995 to improve the water quality of major rivers in the country through pollution abatement work. This involves reducing the pollution load from domestic, municipal, industrial, and agricultural sources to enhance the overall health and sustainability of these water bodies.

Key Concept: Waterfall Height, Energy Conversion

c) 90 m

[Solution Description]

The potential energy of a unit mass of water at the top of the falls is given by:

$PE = m \cdot g \cdot h$

For a unit mass ($m = 1 kg$), the equation simplifies to:

$PE = g \cdot h$

Given $PE = 882.9 J$ and $g = 9.81 m/s^2$, we can solve for $h$:

$882.9 = 9.81 \cdot h$

$h = \frac{882.9}{9.81}$

$h = 90 m$

Therefore, the height of the falls is 90 meters.

Key Concept: Glacial Origin, Tectonic Activity

c) Tectonic origin

[Solution Description]

The Wular Lake is the largest freshwater lake in India and was formed as a result of tectonic activity. Unlike other lakes in the Himalayan region, which are of glacial origin, Wular Lake’s formation is due to tectonic processes. This distinguishes it from lakes like Bhimtal, Nainital, and Barapani, which are of glacial origin.

Therefore, the correct answer is tectonic origin.

Key Concept: Artificial Lakes, Climate Regulation

b) It stabilizes and moderates the climate

[Solution Description]

Artificial lakes like Guru Gobind Sagar have a moderating effect on the local climate. They help stabilize temperatures by absorbing heat during the day and releasing it slowly at night. This reduces temperature extremes, creating a more temperate environment in the surrounding areas.

Key Concept: Brahmaputra River System, Alternate Names, Geographic Features

c) High rainfall in the Indian region

[Solution Description]

The Brahmaputra River originates in Tibet, where it is called Tsang Po. In Tibet, the region is cold and dry, resulting in less water flow and minimal silt deposition. However, when the river enters India, it flows through a region of high rainfall, especially in Arunachal Pradesh and Assam. This increased rainfall significantly enhances the river’s water volume. Additionally, the heavy rainfall leads to erosion of the riverbanks and surrounding areas, contributing to a large amount of silt being carried by the river. Therefore, the primary reason for the Brahmaputra’s significant increase in water volume and silt deposition as it enters India is the high rainfall in the region.

Key Concept: National River Conservation Plan, Ganga Action Plan

c) To expand the scope to cover other major rivers.

[Solution Description]

The Ganga Action Plan (GAP) was initially launched to address pollution in the Ganga River. However, the need to address pollution in other major rivers across India led to the expansion of GAP into the National River Conservation Plan (NRCP) in 1995. The NRCP aimed to improve water quality in all major rivers through pollution abatement measures.

Key Concept: Tributaries of the Godavari

a) Purna

[Solution Description]

The Godavari is joined by several tributaries including the Purna, Wardha, Pranhita, Manjra, Wainganga, and Penganga. Among these, the Purna is one of the well-known tributaries.

Key Concept: Himalayan Rivers

d) Brahmaputra

[Solution Description]

The major Himalayan rivers are the Indus, the Ganga, and the Brahmaputra. These rivers are long and have important tributaries.

Key Concept: Narmada River Origin

c) Amarkantak hills

[Solution Description]

The Narmada River originates in the Amarkantak hills in Madhya Pradesh.

Key Concept: Domestic Sewage, Treatment Efficiency, Pollutant Removal

c) 135 kilograms per day

[Solution Description]

To determine the daily pollutant removal, we need to calculate the total pollutant mass in the influent and then find $90\%$ of it.

Step 1: Calculate the total pollutant mass in the influent.

The influent pollutant concentration is $300$ mg/L, which is equivalent to $300$ grams per cubic meter. Therefore, the total pollutant mass in the influent is:

$500 \times 300 = 150000 \, \text{grams per day}$

Step 2: Calculate the daily pollutant removal.

The treatment process removes $90\%$ of the pollutants, so the daily pollutant removal is:

$0.9 \times 150000 = 135000 \, \text{grams per day} = 135 \, \text{kilograms per day}$

Key Concept: Water Quality, Fisheries, Economic Impact

b) DO: 4.5 mg/L; Economic Impact: 12%

[Solution Description]

The initial dissolved oxygen (DO) level is 6 mg/L. Industrial discharge reduces it by 25\%, so the reduction is:

$6 \times 0.25 = 1.5 \, \text{mg/L}$

Subtracting this from the original DO level gives:

$6 – 1.5 = 4.5 \, \text{mg/L}$

The new DO level is 4.5 mg/L. Due to the reduced DO level, the fishery’s productivity decreases by 30%. If the community relies on fishing for 40% of its income, the economic impact can be calculated as:

$0.40 \times 0.30 = 0.12 \, \text{(or 12%)}$

Therefore, the community’s income would decrease by 12%.

Key Concept: Drainage Basin

c) An area drained by a single river system into a larger water body

[Solution Description]

A drainage basin is an area where all precipitation or runoff collects and drains into a single river system, eventually flowing into a larger water body like a lake, sea, or ocean. It is defined by its boundaries, which are usually elevated areas such as mountains or uplands that separate it from neighboring basins.

Key Concept: Perennial vs. Seasonal, Drainage Patterns

c) Perennial river with a dendritic drainage pattern

[Solution Description]

The river is perennial because it flows throughout the year. A dendritic drainage pattern indicates that the underlying geology is uniform and the terrain is relatively flat or gently sloping. This pattern resembles the branches of a tree, suggesting no significant structural control over the river’s course.

Key Concept: Role of Lakes in Hydro-Power

b) By storing water and regulating its flow for power generation

[Solution Description] Lakes formed by damming rivers act as reservoirs that store water. During heavy rains, they prevent flooding by holding excess water, and during dry seasons, they release water to maintain a steady flow. This regulated flow is crucial for generating hydro-power consistently throughout the year.

Key Concept: Himalayan Rivers

b) Yamuna

[Solution Description]

The Indus River System consists of several tributaries, including the Zaskar, the Nubra, the Shyok, the Hunza, the Satluj, the Beas, the Ravi, the Chenab, and the Jhelum. These rivers join the Indus at various points along its course. However, the Yamuna is a tributary of the Ganga River System, not the Indus River System.

Key Concept: Impact of Rivers

b) Soil enrichment for agriculture

[Solution Description]

These rivers flood parts of the northern plains every year, causing widespread damage to life and property while enriching the soil for agricultural use as per the syllabus.

Key Concept: Namami Gange Programme, Pollution Abatement

a) Generating electricity through hydroelectric projects

[Solution Description] The Namami Gange Programme was launched with the twin objectives of effective pollution abatement and conservation/rejuvenation of the Ganga river. The programme does not focus on generating electricity from hydroelectric projects or promoting tourism along the river.

Key Concept: Mahanadi River System

b) Highlands of Chhattisgarh

[Solution Description]

The Mahanadi river originates in the highlands of Chhattisgarh.

Key Concept: Basic Concept

c) 1500 km

[Solution Description]

The syllabus mentions that the Godavari river has a length of about 1500 km.

Key Concept: Origin of Krishna River

b) Spring near Mahabaleshwar, Maharashtra

[Solution Description]

The Krishna River originates from a spring near Mahabaleshwar in Maharashtra.

Key Concept: Indus River System

c) Ladakh

[Solution Description]

The Indus river originates in Tibet, near Lake Mansarowar. It flows westward and enters India in the Ladakh region, where it forms a picturesque gorge. Thus, the correct answer is Ladakh.

Key Concept: Kaveri Basin

c) 760 km

[Solution Description] The Kaveri river rises in the Brahmagri range of the Western Ghats and reaches the Bay of Bengal in south of Cuddalore in Tamil Nadu. Its total length is about 760 km.

Key Concept: Economic Importance of Fertile Soil

c) By supporting agricultural activities and ensuring food security

[Solution Description]

The fertile soil deposited by rivers supports agriculture, which ensures food security and provides livelihoods for millions of people. This directly contributes to the economy by sustaining agricultural activities and reducing dependency on food imports.

Key Concept: Brahmaputra River System, U-Turn at Namcha Barwa

b) Presence of the Himalayan range forcing a change in course

[Solution Description]

The Brahmaputra River flows eastwards parallel to the Himalayas until it reaches the Namcha Barwa peak (7757 m). At this point, the river takes a sharp \textquoteleft U\textquoteright turn due to the presence of the Himalayan range, which acts as a natural barrier. This geological feature forces the river to change its course drastically and enter India through a gorge in Arunachal Pradesh.

Key Concept: Kaveri River System, Hydroelectric Power, Shivasamudram Falls

b) Both Assertion and Reason are true, but Reason is NOT the correct explanation of Assertion.

[Solution Description]

The assertion mentions that the hydroelectric power generated from the Shivasamudram Falls is primarily supplied to urban areas like Mysuru and Bengaluru. This is true, as the syllabus explicitly states that the hydroelectric power generated from the falls is supplied to Mysuru, Bengaluru, and the Kolar Gold Field. The reason states that the Shivasamudram Falls is the second biggest waterfall in India and has significant potential for hydroelectric power generation. This is also true, as the syllabus confirms that the river Kaveri makes the second biggest waterfall in India, known as Shivasamudram Falls, and its hydroelectric power is utilized. However, the reason does not directly explain why the power is supplied to specific urban areas; it only highlights the significance of the falls. Therefore, the assertion and reason are both true, but the reason is not the correct explanation of the assertion.

Key Concept: National River Conservation Plan, Ganga Action Plan

b) Yamuna

[Solution Description]

The Ganga Action Plan (GAP) was initially launched in 1985 for the Ganga river. In 1995, the plan was expanded to include other major rivers under the National River Conservation Plan (NRCP). However, the Yamuna river was not initially part of this expansion but was later included under separate initiatives.

Key Concept: River Pollution, Self-Cleansing Capacity

b) 1000 units

[Solution Description]

The initial pollution load is 1000 units. The river reduces pollution by 20\% every 10 km, but gains an additional 200 units of pollution every 10 km.

– After first 10 km:

Pollution reduced = 1000 * 20/100 = 200 units

Remaining pollution = 1000 – 200 = 800 units

Pollution after adding untreated sewage = 800 + 200 = 1000 units

– After second 10 km:

Pollution reduced = 1000 * 20/100 = 200 units

Remaining pollution = 1000 – 200 = 800 units

Pollution after adding untreated sewage = 800 + 200 = 1000 units

– After third 10 km:

Pollution reduced = 1000 * 20/100 = 200 units

Remaining pollution = 1000 – 200 = 800 units

Pollution after adding untreated sewage = 800 + 200 = 1000 units

Thus, the total pollution load after 30 km is 1000 units.

Key Concept: River Origin

c) Yamunotri Glacier

[Solution Description] The Yamuna river originates from the Yamunotri Glacier in the Himalayas.

Key Concept: Indus Water Treaty

c) Punjab, Haryana, and Rajasthan

[Solution Description]

The Indus Water Treaty (1960) specifies that the water allocated to India is used for irrigation in Punjab, Haryana, and the southern and western parts of Rajasthan. Therefore, these are the states that benefit from the treaty.

Key Concept: Indus River System, Brahmaputra River System

c) The Indus flows westwards while the Brahmaputra flows eastwards initially before taking a ‘U’ turn.

[Solution Description]

The Indus River rises in Tibet near Lake Mansarovar and flows westwards into India through Ladakh. It continues through Baltistan and Gilgit, emerging at Attock, and eventually flows southwards to the Arabian Sea. In contrast, the Brahmaputra River originates east of Lake Mansarovar, flows eastwards parallel to the Himalayas, takes a ‘U’ turn at Namcha Barwa, and enters India in Arunachal Pradesh. Thus, the correct statement is that the Indus flows westwards and the Brahmaputra flows eastwards initially before taking a ‘U’ turn.

Key Concept: National River Conservation Plan

c) To improve the water quality of rivers

[Solution Description] The National River Conservation Plan (NRCP) was launched in 1995 with the primary objective of improving the water quality of rivers that are major water sources in the country. This is achieved through the implementation of pollution abatement work, which includes treating sewage and industrial effluents before they are discharged into rivers.

Key Concept: Peninsular Rivers Flow Direction

c) Tapi

[Solution Description]

The Narmada and the Tapi are the two major rivers in peninsular India that flow towards the west and make estuaries. Among the options provided, the Tapi is the correct answer as it flows in a rift valley parallel to the Narmada but is much shorter in length. Its basin covers parts of Madhya Pradesh, Gujarat, and Maharashtra.

Key Concept: Bhagirathi, Gangotri Glacier, Alaknanda

c) 1200 m$^3$/s

[Solution Description]

The total discharge rate of the Ganga immediately after the confluence of the Bhagirathi and Alaknanda rivers can be calculated by summing their individual discharge rates.

Step 1: Identify the discharge rates of the Bhagirathi and Alaknanda rivers.

Discharge of Bhagirathi = 500 m$^3$/s

Discharge of Alaknanda = 700 m$^3$/s

Step 2: Calculate the total discharge rate.

Total discharge = Discharge of Bhagirathi + Discharge of Alaknanda

Total discharge = 500 m$^3$/s + 700 m$^3$/s = 1200 m$^3$/s

Key Concept: Economic Benefits

c) Guru Gobind Sagar

[Solution Description]

Guru Gobind Sagar is a man-made lake formed by the Bhakra Nangal Project, primarily used for hydel power generation.

Key Concept: Tributaries, Flooding, Agricultural Benefits

c) They enrich the soil with nutrients

[Solution Description]

The Ghaghara, Gandak, and Kosi rivers originate from the Nepal Himalayas and carry a significant amount of sediment. When these rivers flood, they deposit this sediment onto the plains. This sediment enriches the soil with nutrients, making it more fertile for agricultural purposes. Hence, despite the damage caused by the floods, they are beneficial for agriculture as they enhance soil fertility.

Key Concept: Lagoons, Spits and Bars

d) Wular lake

[Solution Description]

Lagoons are formed in coastal areas due to the action of spits and bars. Chilika lake, Pulicat lake, and Kolleru lake are examples of lagoons formed by this process. Wular lake, however, is a freshwater lake formed due to tectonic activity and is not a lagoon. Therefore, Wular lake is the correct answer.

Key Concept: Saltwater Lakes: Sambhar Lake

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

[Solution Description] The assertion states that Sambhar lake in Rajasthan is a saltwater lake, which is true as per the syllabus. The reason given is that the water of Sambhar lake is used for producing salt, which is also true and directly explains why it is a saltwater lake. Thus, both assertion and reason are true, and the reason correctly explains the assertion.

Key Concept: Water Divide

b) Vindhya

[Solution Description]

The Vindhya Range acts as a water divide between the Ganga river basin and the Narmada river basin. This elevated region separates these two major drainage systems in India.

Key Concept: The Tapi Basin

c) Satpura ranges, Betul district, Madhya Pradesh

[Solution Description]

The Tapi river originates in the Satpura ranges, specifically in the Betul district of Madhya Pradesh. This information is directly provided in the syllabus.

Key Concept: Formation of the Sundarbans Delta

c) Growth of Sundari trees

[Solution Description] The Sundarban Delta derived its name from the Sundari tree, which grows abundantly in the marshland regions of the delta. This tree is well-adapted to the saline conditions of the deltaic environment.

Key Concept: Brahmaputra River System, Length, Comparison with Indus

c) The Brahmaputra’s drainage basin is more extensive than the Indus.

[Solution Description]

The length of a river is often indicative of its drainage basin size and potential water volume. Since the Brahmaputra is slightly longer than the Indus, it suggests a larger drainage basin and potentially greater water volume. However, other factors like rainfall and tributaries also play a role.

Key Concept: Damodar, Brahmani, Baitarani, Subarnarekha

d) Damodar

[Solution Description]

The Damodar River is known for its significance in the industrial development of the Chota Nagpur Plateau region. It flows through Jharkhand and West Bengal and is often referred to as the “River of Sorrow” due to its frequent flooding. However, it has been harnessed for hydroelectric power and irrigation projects, contributing to the industrial growth of the region.

Key Concept: Role of Rivers in the Economy

b) Developing irrigation systems and hydroelectric projects

[Solution Description]

The greatest long-term impact on agricultural productivity and economic growth would come from investing in irrigation systems and hydroelectric projects. Irrigation systems ensure a consistent water supply for crops, reducing dependency on rainfall and increasing yield. Hydroelectric projects provide clean and sustainable energy, which supports industrial growth and reduces operational costs for farmers. While dams and reservoirs are part of this infrastructure, they alone do not directly address agricultural productivity without complementary irrigation systems.

Key Concept: Flooding in Assam

c) Rising riverbed due to silt deposits

[Solution Description]

The Brahmaputra River carries a large volume of water and considerable silt during the rainy season. The riverbed rises due to silt deposits, and the river frequently shifts its channel, leading to widespread flooding in Assam.

Key Concept: Dhuandhar Falls

b) Jabalpur

[Solution Description]

The Dhuandhar Falls is a notable feature of the Narmada river, where it plunges over steep rocks. This fall is located in Jabalpur.

Key Concept: Freshwater Lakes

d) Wular Lake

[Solution Description]

The Wular lake in Jammu and Kashmir is the largest freshwater lake in India. It is the result of tectonic activity. Other lakes like Dal, Bhimtal, and Nainital are also freshwater lakes but smaller in size compared to Wular lake. Therefore, the correct answer is Wular lake.

Key Concept: Freshwater Lakes, Largest Lake

c) Wular Lake

[Solution Description]

The Wular Lake is the largest freshwater lake in India. It is located in Jammu and Kashmir and was formed due to tectonic activity. Other lakes like Chilika, Sambhar, and Pulicat are either brackish or saltwater lakes. Therefore, among the given options, Wular Lake stands out as the largest freshwater lake formed by tectonic processes.

Key Concept: Krishna River System – Origin

a) A spring near Mahabaleshwar

[Solution Description]

The Krishna River originates from a spring near Mahabaleshwar, as mentioned in the syllabus.

Key Concept: Tributaries, Krishna Basin

c) 600 km

[Solution Description]

The total length of the Krishna river is 1400 km. Before merging with the Tungabhadra, the Krishna river has already flowed for 800 km. After merging, the remaining distance covered by the Krishna river is $1400\,\text{km} – 800\,\text{km} = 600\,\text{km}$. Therefore, the Krishna river covers 600 km after merging with the Tungabhadra.

Key Concept: River Pollution, Self-Cleansing Capacity

c) 785 units

[Solution Description]

Step 1: Calculate the reduction due to self-cleansing after 10 km. The pollution load reduces by 10%, so new pollution load = 500 – (10% of 500) = 500 – 50 = 450 units.

Step 2: After adding untreated sewage at 20 km, the pollution load increases by 200 units. Total pollution load = 450 + 200 = 650 units.

Step 3: At 30 km, the pollution load reduces by 10%. New pollution load = 650 – (10% of 650) = 650 – 65 = 585 units.

Step 4: At 40 km, untreated sewage adds another 200 units. Total pollution load = 585 + 200 = 785 units.