1. Introduction | Class 9 Social Science (Contemporary India) Drainage Easy Notes

Hello students! Welcome to Chapter 3 of your Class 9 Geography syllabus. Whenever we talk about ‘drainage’, we are simply referring to the entire river system of a particular area. Imagine multiple small streams gathering water from various directions and joining together to form one main river. This main river eventually flows into a larger water body, like a lake, sea, or ocean.

The total land area that contributes water to a single river system is known as a ‘drainage basin’. Sometimes, an elevated piece of land like a mountain or a plateau acts as a natural barrier, separating two distinct drainage basins. This elevated land is appropriately called a ‘water divide’. Let’s dive deeper and explore how rivers map the face of our country!

Figure-1: A Water Divide is an elevated area that separates two different drainage basins.

2. Drainage Systems in India

The geography of the Indian subcontinent largely determines how its rivers flow. Based on this, we can broadly classify the Indian river systems into two major categories: the Himalayan rivers and the Peninsular rivers.

These two groups are very different from each other. Himalayan rivers are ‘perennial’, which means they have water flowing through them all year round. They get their water not just from monsoon rainfall, but also from the melting snow of the high mountains. Peninsular rivers, on the other hand, are mostly seasonal. Their water levels depend heavily on rainfall, and during the dry summer months, even the largest of these rivers can have drastically reduced water flow.

3. The Himalayan Rivers

The three most prominent Himalayan river systems are the Indus, the Ganga, and the Brahmaputra. These are mighty, long rivers joined by numerous important tributaries.

The Indus River System starts its journey in Tibet, near Lake Mansarowar, and flows westward into India through Ladakh. It makes spectacular gorges before heading south towards Pakistan, finally meeting the Arabian Sea. Interestingly, under the Indus Water Treaty, India can only use 20% of the total water carried by this massive river system.

The Ganga River System originates from the Gangotri Glacier as the ‘Bhagirathi’ and joins the Alaknanda at Devaprayag. Enlarged by tributaries like Yamuna, Ghaghara, Gandak, and Kosi, it flows eastwards. It eventually joins the Brahmaputra to form the magnificent Sundarban Delta before draining into the Bay of Bengal.

The Brahmaputra River System also rises in Tibet (where it is called Tsang Po). It runs parallel to the Himalayas before taking a sharp ‘U’ turn at Namcha Barwa to enter Arunachal Pradesh. It carries huge amounts of water and silt during the monsoons, often causing floods in Assam and Bangladesh.

4. The Peninsular Rivers

The Western Ghats act as the main water divide for Peninsular India. Most of the major rivers here, like the Godavari, Mahanadi, Krishna, and Kaveri, flow eastwards and drain into the Bay of Bengal, forming fertile deltas.

Figure-2: Map highlighting the East and West flowing rivers of Peninsular India.

The Godavari is the largest of the peninsular rivers and is often referred to as the ‘Dakshin Ganga’ due to its massive size and length. The Mahanadi flows through Odisha, while the Krishna and Kaveri drain parts of Maharashtra, Karnataka, Andhra Pradesh, and Tamil Nadu.

There are two major exceptions: the Narmada and the Tapi. These are the only long peninsular rivers that flow westwards, moving through rift valleys to drain into the Arabian Sea, forming estuaries instead of deltas.

5. Lakes of India

India is home to many beautiful and vital lakes. Some are permanent, while others are seasonal. Most of our freshwater lakes, like the famous Dal lake and Nainital, are located in the Himalayan region and were formed by glacial action. The Wular lake in Jammu and Kashmir is a notable exception; it is the largest freshwater lake in India and was formed by tectonic activity!

We also have saltwater lakes, such as the Sambhar lake in Rajasthan, which is used for salt production. Coastal lagoons like Chilika, Pulicat, and Kolleru lakes are formed by spits and bars in coastal areas. Lakes are incredibly important as they regulate river flow, prevent floods, help generate hydel power, and promote tourism.

6. Role of Rivers in the Economy and River Pollution

Throughout history, rivers have been lifelines for human civilization. Water is essential for drinking, agriculture, navigation, and hydropower generation. This is why our biggest ancient settlements grew along riverbanks and later evolved into the massive cities we see today.

However, increased domestic, municipal, and industrial demands are taking a severe toll on our rivers. Heavy loads of untreated sewage and harmful industrial effluents are being dumped directly into the rivers. This not only pollutes the water but destroys the river’s natural ability to clean itself. To combat this, the government has launched several initiatives, such as the Ganga Action Plan and the National River Conservation Plan (NRCP), aiming to restore the health and purity of our water bodies.

7. Key Takeaways

• A drainage basin is the area drained by a single river system, while a water divide is an upland separating two basins.
• Indian rivers are divided into Himalayan (perennial, snow-fed) and Peninsular (seasonal, rain-fed) systems.
• The major Himalayan rivers are the Indus, Ganga, and Brahmaputra, known for forming huge plains and deltas.
• The Narmada and Tapi are the only major peninsular rivers flowing westwards through rift valleys.
• Godavari is the largest peninsular river, often called the ‘Dakshin Ganga’.
• Lakes are crucial for regulating river flow, supporting ecosystems, and boosting tourism (e.g., Wular, Chilika, Sambhar).
• Rapid urbanization and untreated industrial waste are the leading causes of river pollution in India.

8. Practice Section: Master the Chapter!

Test your knowledge with these carefully crafted questions based on the notes above.

Part A: True or False (10 Questions)

1. Himalayan rivers are mostly seasonal in nature.
2. The area drained by a single river system is called a drainage basin.
3. The river Narmada flows through a rift valley.
4. The Wular lake is a saltwater lake located in Rajasthan.
5. The Godavari is the longest Peninsular river in India.
6. The Indus river originates from the Gangotri glacier.
7. Ambala is located on the water divide between the Indus and the Ganga river systems.
8. The Brahmaputra is known as the Tsang Po in Tibet.
9. The Tapi river flows eastwards and drains into the Bay of Bengal.
10. The Sundarban Delta is formed by the Ganga and Brahmaputra rivers.

Part B: Multiple Choice Questions (10 Questions)

1. Which is the largest river basin in India?
   
   A) Indus basin
   
   B) Ganga basin
   
   C) Brahmaputra basin
   
   D) Godavari basin
2. In which of the following states is the Wular lake located?
   
   A) Rajasthan
   
   B) Uttar Pradesh
   
   C) Punjab
   
   D) Jammu and Kashmir
3. The river Narmada has its source at:
   
   A) Satpura
   
   B) Brahmagiri
   
   C) Amarkantak
   
   D) Slopes of the Western Ghats
4. Which one of the following lakes is a salt water lake?
   
   A) Sambhar
   
   B) Dal
   
   C) Wular
   
   D) Gobind Sagar
5. Which one of the following is the longest river of Peninsular India?
   
   A) Narmada
   
   B) Krishna
   
   C) Godavari
   
   D) Mahanadi
6. Which one amongst the following rivers flows through a rift valley?
   
   A) Mahanadi
   
   B) Tungabhadra
   
   C) Krishna
   
   D) Tapi
7. Where do the rivers Bhagirathi and Alaknanda join to form the Ganga?
   
   A) Haridwar
   
   B) Devaprayag
   
   C) Allahabad
   
   D) Rishikesh
8. Which river is often referred to as ‘Dakshin Ganga’?
   
   A) Kaveri
   
   B) Narmada
   
   C) Godavari
   
   D) Krishna
9. At which mountain peak does the Brahmaputra take a ‘U’ turn to enter India?
   
   A) K2
   
   B) Kanchenjunga
   
   C) Namcha Barwa
   
   D) Nanda Devi
10. Which government initiative was launched in 1985 to clean a major Indian river?
    
    A) National River Conservation Plan
    
    B) Namami Gange
    
    C) Ganga Action Plan
    
    D) Save Narmada Movement

Part C: Short Answer Questions (5 Questions)

1. What is meant by a water divide? Give an example.
2. Why are the Peninsular rivers considered seasonal?
3. Name the two major rivers of India that flow westwards and drain into the Arabian Sea.
4. How are ox-bow lakes formed?
5. Mention two reasons why rivers are getting polluted in India.

Part D: Long Answer Questions (5 Questions)

1. Differentiate between the Himalayan rivers and the Peninsular rivers.
2. Describe the path and features of the Ganga River System.
3. Explain the economic importance of rivers for a country like India.
4. What is the significance of lakes? Explain with examples.
5. Discuss the Godavari basin in detail. Why is it called the ‘Dakshin Ganga’?