Drainage System — Study Notes

1. Introduction

The term "drainage" describes the river system of an area. The drainage system of India consists of the river basins that carry the surface run-off and groundwater of the country. Rivers are not merely water bodies; they are the lifelines of a region, providing water for irrigation, domestic use, industry, transport and power generation, and they shape the landforms through which they flow. The drainage system of India is the result of the geological history and physiography of the subcontinent.

The drainage patterns of India are broadly divided into two groups on the basis of their origin: the Himalayan drainage system (the perennial rivers like the Indus, Ganga and Brahmaputra) and the Peninsular drainage system (the older rivers like the Narmada, Tapi, Godavari, Krishna and Kaveri). These two systems differ in their origin, nature, catchment areas and mode of formation. In this chapter we study the drainage patterns, the major river systems of India, and their characteristics.

2. Drainage Patterns

The pattern of a river system depends on the topography and geology of the region. The main drainage patterns found in India are: 1. Dendritic pattern: A tree-like pattern in which the river and its tributaries branch out irregularly, like the branches of a tree. It develops on homogeneous, gently sloping rocks. Example: the rivers of the Northern plains. 2. Trellis pattern: A pattern in which the tributaries join the main river at right angles, forming a trellis or grid. It develops where hard and soft rocks alternate. Example: the rivers in the Himalayas and the Eastern Ghats. 3. Radial pattern: A pattern in which rivers flow outwards in all directions from a central high point, like the spokes of a wheel. Example: the rivers originating from the Amarkantak hills. 4. Centripetal pattern: A pattern in which rivers flow towards a central depression or lake. Example: rivers draining into lakes.

3. The Himalayan Drainage System

3.1 Characteristics

The Himalayan rivers are perennial (flow throughout the year) because they are fed by rain as well as by the melting snow and glaciers of the Himalayas. They have large catchment areas, are long, and form deep gorges and valleys in the mountains before descending to the plains. These rivers were formed in the recent geological past (the Tertiary period). The three major Himalayan rivers are the Indus, the Ganga and the Brahmaputra.

3.2 The Indus System

The Indus river originates in Tibet near Lake Mansarovar and flows through the Himalayas. It enters India through Ladakh. The Indus flows through a region of gorges in the north-west Himalayas and receives tributaries like the Jhelum, Chenab, Ravi, Beas and Sutlej. The total length of the Indus is about 2,900 km, of which about 700 km lies in India. It flows into the Arabian Sea near Karachi in Pakistan.

3.3 The Ganga System

The Ganga originates as the Bhagirathi from the Gangotri glacier in Uttarakhand. At Devprayag, the Bhagirathi meets the Alaknanda, and the combined river is called the Ganga. The Ganga is about 2,525 km long and drains about one-fourth of the area of India. Its major tributaries include the Yamuna, Ghaghara, Gandak, Kosi (from the north), and the Chambal, Betwa, Son (from the south). The Ganga-Brahmaputra delta is the largest delta in the world.

3.4 The Brahmaputra System

The Brahmaputra originates in Tibet, near the Mansarovar lake, where it is called Tsangpo. It enters India through Arunachal Pradesh, where it is called the Dihang, and is joined by the Dibang and the Lohit. The Brahmaputra flows through Assam as a wide, braided river and turns southwards to enter Bangladesh, where it joins the Ganga and flows into the Bay of Bengal.

4. The Peninsular Drainage System

4.1 Characteristics

The Peninsular rivers are older than the Himalayan rivers. They flow through the ancient rocks of the Peninsular plateau and are mostly non-perennial (seasonal), because they depend mainly on monsoon rainfall. Their catchment areas are smaller, and they form relatively shallower valleys. Most peninsular rivers flow eastwards and drain into the Bay of Bengal, while only a few (Narmada and Tapi) flow westwards into the Arabian Sea.

4.2 West-flowing Rivers

• The Narmada: Originates at Amarkantak in Madhya Pradesh and flows westwards through a rift valley between the Vindhya and Satpura ranges into the Gulf of Khambhat in the Arabian Sea. It is about 1,312 km long and forms a delta? No, it forms an estuary. The Narmada forms waterfalls like Dhuandhar.
• The Tapi (Tapti): Also originates in Madhya Pradesh and flows westwards into the Arabian Sea. It is shorter than the Narmada and forms an estuary.

4.3 East-flowing Rivers

• The Mahanadi: Originates in Chhattisgarh and flows eastwards into the Bay of Bengal. The Hirakud dam is built on it.
• The Godavari: The longest peninsular river, about 1,465 km long. It originates in the Western Ghats in Maharashtra and flows eastwards through Andhra Pradesh into the Bay of Bengal. It forms a large delta.
• The Krishna: Originates near Mahabaleshwar and flows eastwards through Maharashtra, Karnataka and Andhra Pradesh into the Bay of Bengal.
• The Kaveri: Originates in the Western Ghats in Karnataka and flows southwards and eastwards through Tamil Nadu into the Bay of Bengal. It is known for the famous waterfalls of Sivasamudram.

5. Rivers of the Peninsular Plateau and Coastal Plains

Besides the major rivers, the peninsular region has many smaller rivers that are often seasonal, flowing only during the monsoon. The rivers of the Western Ghats, like the Netravati and Bharathapuzha, flow westwards in short courses. The east-flowing rivers, in contrast, are longer because they have to travel across the entire plateau. The deltas of the Mahanadi, Godavari, Krishna and Kaveri form some of the most fertile agricultural regions of India.

Quick Revision Tables

Himalayan vs Peninsular Rivers

Major Rivers of India

Mind Map

Important Diagrams (SVG)

Diagram 1: Himalayan River Systems

Diagram 2: Peninsular River Systems

Common Mistakes

1. Writing that Himalayan rivers are seasonal; they are perennial because they are fed by glaciers and snow, whereas peninsular rivers are mostly seasonal.
2. Confusing the origins of the rivers: the Ganga originates as the Bhagirathi from the Gangotri glacier, not from Gangotri town alone.
3. Writing that the Narmada forms a delta; it forms an estuary because it flows through a rift valley and enters the sea abruptly.
4. Confusing the longest peninsular river; it is the Godavari (1,465 km), not the Narmada or the Krishna.
5. Writing that the Brahmaputra is called the Tsangpo in India; it is called Tsangpo in Tibet and Dihang in Arunachal Pradesh.
6. Confusing the dendritic pattern (irregular branching like a tree) with the trellis pattern (tributaries at right angles).
7. Saying that the Indus flows into the Bay of Bengal; it flows into the Arabian Sea near Karachi.
8. Forgetting that the Godavari is often called the "Dakshin Ganga"; it is the longest river of South India.

Exam Tips

1. Prepare a comparison table of Himalayan and Peninsular rivers (origin, nature, age, valley, length).
2. Learn the origin, length and mouth of at least six major rivers: Ganga, Indus, Brahmaputra, Godavari, Narmada, Kaveri.
3. Draw labelled diagrams of the Himalayan and Peninsular river systems.
4. Remember which rivers flow east (Godavari, Krishna, Kaveri, Mahanadi) and which flow west (Narmada, Tapi).
5. Know the tributaries of the Ganga: Yamuna, Ghaghara, Gandak, Kosi (north); Chambal, Betwa, Son (south).
6. Mention the drainage patterns (dendritic, trellis, radial, centripetal) with one example each.
7. Note that the Ganga-Brahmaputra delta is the largest delta in the world.

Conclusion

The drainage system of India is a reflection of its geological structure and physiography. The young, glacier-fed Himalayan rivers, the Indus, Ganga and Brahmaputra, are perennial and have carved deep valleys and formed the vast Northern plains and the largest delta in the world. The old, rain-fed peninsular rivers are mostly seasonal; the Godavari, Krishna and Kaveri flow eastwards into the Bay of Bengal, while the Narmada and Tapi flow westwards through rift valleys. The drainage patterns of dendritic, trellis, radial and centripetal types add to the diversity of the country's river systems. Rivers are the lifelines of India, providing water for irrigation, domestic use and power, and sustaining the agriculture and economy of the country.

Keywords: Drainage, dendritic, Himalayan rivers, Indus, Ganga, Brahmaputra, Godavari, Narmada, Tapi, peninsular rivers, estuary, delta.