Drainage — Study Notes

1. Introduction

The term 'drainage' describes the river system of an area. A river system is made up of a river and all its tributaries, which drain the water from a particular region. The area drained by a single river system is called a drainage basin. The drainage systems of India are among the most important natural features of the country, as they provide water for irrigation, drinking, industry, and transport to millions of people.

The rivers of India are broadly divided into two groups on the basis of their origin: the Himalayan rivers and the Peninsular rivers. The Himalayan rivers are perennial, flowing throughout the year because they are fed by both rain and melting snow from the mountains. The Peninsular rivers are seasonal, depending mainly on rainfall. This chapter describes the major river systems of India, their characteristics, and their importance.

2. Drainage Systems in India

2.1 Himalayan vs Peninsular Rivers

The Himalayan rivers originate from the snow-covered mountains of the Himalayas. They are perennial, meaning they flow throughout the year, and they carry a large amount of water and silt. They are long rivers that flow through deep gorges and form meanders and ox-bow lakes in their plains. The Peninsular rivers, on the other hand, originate from the Peninsular Plateau. They are seasonal, and they have shorter courses. They flow in fixed channels, and their basins are comparatively small.

2.2 The Concept of a Drainage Basin

A drainage basin is the area of land from which a river system collects its water. The boundary line separating one drainage basin from another is called a watershed. In India, the drainage systems are divided into two major groups based on whether they discharge their waters into the Bay of Bengal or the Arabian Sea. Most of the rivers of India, including the Ganga, drain into the Bay of Bengal, while only a few, like the Narmada and the Tapi, drain into the Arabian Sea.

3. The Himalayan Rivers

3.1 The Indus River System

The Indus river rises in the glaciers of the Kailas range in Tibet, near Mansarovar lake. It flows westwards and enters the Indian territory in Jammu and Kashmir, and then flows into Pakistan. Its total length is about 2,900 km, of which about 1,114 km is in India. The main tributaries of the Indus are the Jhelum, the Chenab, the Ravi, the Beas, and the Satluj, which join it from the eastern side. The Indus river system derives its name from the river Indus, and its waters are shared between India and Pakistan.

3.2 The Ganga River System

The Ganga originates from the Gangotri glacier in Uttarakhand, where it is known as the Bhagirathi. It is joined by the Alaknanda at Devprayag, and from there it is called the Ganga. The Ganga is about 2,500 km long. Its headwaters are the Bhagirathi and the Alaknanda. The main tributaries of the Ganga from the northern side are the Yamuna, the Ghaghara, the Gandak, and the Kosi, and from the southern side the Son and the Damodar. The Yamuna, the largest tributary of the Ganga, rises from the Yamunotri glacier and joins the Ganga at Allahabad (Prayagraj). The Ganga flows into the Bay of Bengal through the Sunderban delta, the largest delta in the world.

3.3 The Brahmaputra River System

The Brahmaputra rises in Tibet, where it is known as the Tsangpo, near Mansarovar lake. It enters India through Arunachal Pradesh, where it is known as the Dihang. It is joined by the Dibang, the Lohit, and other tributaries in Assam, and from there it is called the Brahmaputra. It is about 2,900 km long. In Assam, the Brahmaputra forms many riverine islands, of which the Majuli is the largest riverine island in the world. The river is known for its frequent floods, which deposit fertile silt on the plains.

4. The Peninsular Rivers

4.1 The Narmada and the Tapi

The Narmada rises in the Amarkantak hills in Madhya Pradesh. It flows westwards through a rift valley, forming a gorge, and falls into the Arabian Sea near Bharuch in Gujarat. The Tapi rises in the Satpura ranges and also flows westwards through a rift valley to join the Arabian Sea. Both rivers have shorter courses and do not form deltas; they form estuaries instead. The Narmada basin covers parts of Madhya Pradesh and Gujarat.

4.2 The Godavari River System

The Godavari rises in the Nasik district of Maharashtra. It is the longest river of South India, with a length of about 1,465 km. Because of its length and the area it covers, it is also called the Dakshin Ganga (the Ganga of the South). Its basin covers parts of Maharashtra, Telangana, Andhra Pradesh, and Odisha. The Purna, the Wardha, and the Penganga are the main tributaries of the Godavari. It falls into the Bay of Bengal.

4.3 The Krishna River System

The Krishna river rises near Mahabaleshwar in the Sahyadri. It is about 1,400 km long and is the second largest east-flowing river of the peninsula. Its basin covers parts of Maharashtra, Karnataka, and Andhra Pradesh. Its main tributaries are the Tungabhadra, the Koyna, and the Ghatprabha. The Krishna also falls into the Bay of Bengal.

4.4 The Kaveri River System

The Kaveri rises in the Brahmagiri hills in the Kodagu district of Karnataka. It is about 760 km long. Its basin covers Karnataka, Kerala, and Tamil Nadu. The main tributaries of the Kaveri are the Amravati, the Bhavani, and the Hemavati. The Kaveri falls into the Bay of Bengal.

4.5 The Mahanadi

The Mahanadi rises in the highlands of Chhattisgarh. It flows through Odisha and falls into the Bay of Bengal. It is about 860 km long, and its basin covers parts of Chhattisgarh and Odisha.

5. Lakes and Their Importance

Lakes are another important feature of the drainage system. A lake is a water body surrounded by land on all sides. The lakes of India include the Wular lake in Jammu and Kashmir, which is the largest lake of India; the Chilika lake in Odisha, which is the largest saline water lake of India; the Pulicat lake in Andhra Pradesh; the Sambhar lake in Rajasthan, which is the largest salt water lake; and the Pangong Tso in the Ladakh region. Lakes help in regulating the flow of rivers, provide water for irrigation and domestic use, moderate the climate, and support fishing and tourism.

Quick Revision Tables

Table 1: Major River Systems of India

Table 2: Himalayan vs Peninsular Rivers

Table 3: Important Lakes of India

Mind Map

Important Diagrams (SVG)

Diagram 1: Himalayan vs Peninsular Rivers Comparison

Diagram 2: Ganga River System

Common Mistakes

1. Students often say the Ganga originates from the Gangotri glacier directly. The river from the Gangotri glacier is called the Bhagirathi; it becomes the Ganga after meeting the Alaknanda at Devprayag.
2. Many write that the Narmada forms a delta. The Narmada and the Tapi form estuaries, not deltas, because they flow through rift valleys.
3. A common error is to call the Godavari the longest river of India. It is the longest river of South India (Dakshin Ganga); the Ganga is longer overall.
4. Students often say the Indus flows entirely in India. Only about 1,114 km of the Indus is in India; the rest flows through Tibet and Pakistan.
5. Some students say the Brahmaputra is known as the Dihang throughout Assam. It is called the Dihang only when it enters India; it is called the Brahmaputra after joining with the Dibang and the Lohit.
6. It is wrong to say the Wular lake is saline. Wular is the largest freshwater lake of India; the Sambhar lake in Rajasthan is the largest salt water lake.
7. Many students confuse the Chilika (largest saline water lake, in Odisha) with the Sambhar (largest salt water lake, in Rajasthan).
8. Students often forget that the Yamuna rises from the Yamunotri glacier and joins the Ganga at Allahabad (Prayagraj).

Exam Tips

1. Learn the source, length, tributaries, and mouth of each major river — these facts are frequently asked as one-mark questions.
2. Compare Himalayan and Peninsular rivers in a table format for long answers.
3. Memorise the two west-flowing rivers (Narmada, Tapi) that form estuaries, as opposed to the east-flowing rivers that form deltas.
4. For map work, practise marking the rivers Indus, Ganga, Brahmaputra, Godavari, Krishna, Kaveri, Narmada, Tapi, and Mahanadi.
5. Mention at least three lakes (Wular, Chilika, Sambhar) with their locations when asked about lakes.
6. Use the term 'drainage basin' and 'watershed' correctly to define concepts.
7. Practise locating the Sunderban delta and Majuli island as important geographical landmarks.

Conclusion

The drainage system of India, with its Himalayan and Peninsular rivers, is a lifeline for the country. The perennial Himalayan rivers like the Ganga and the Brahmaputra carry enormous amounts of water and sediment, creating some of the most fertile plains and the largest delta in the world. The Peninsular rivers, including the Godavari, Krishna, Kaveri, and Mahanadi, support agriculture and industry in the south. The west-flowing Narmada and Tapi, flowing through rift valleys, complete the picture. Lakes like Wular, Chilika, and Sambhar add to the diversity of India's water resources. Rivers and lakes are essential for irrigation, drinking water, transport, fishing, and hydroelectric power, making the study of drainage essential for understanding India's economy, environment, and the lives of its people.