Drainage
Drainage refers to the river systems of an area. This Class 9 Geography chapter describes how India's rivers are divided into Himalayan and Peninsular systems, the major rivers and lakes, and the importance and pollution of rivers.
Learning objectives
- Define drainage and drainage systems.
- Distinguish Himalayan and Peninsular rivers.
- Name India's major rivers and lakes.
- Understand the value and pollution of rivers.
Key concepts
Drainage systems
Drainage means the river system of an area — the network of channels through which water flows. The area drained by a single river and its tributaries is called a drainage basin. Indian rivers are divided into two major groups: the Himalayan rivers and the Peninsular rivers, which differ in their sources and nature.
Himalayan rivers
The Himalayan rivers — the Indus, the Ganga and the Brahmaputra and their tributaries — rise in the snow-covered Himalayas. Because they are fed by both rain and melting snow, they are perennial, flowing throughout the year. They carry large amounts of silt, form fertile plains, and create large meanders and deltas in their lower courses.
Peninsular rivers
The Peninsular rivers flow across the old plateau. Most, like the Godavari, Krishna, Kaveri and Mahanadi, flow eastwards into the Bay of Bengal and form deltas. A few, like the Narmada and Tapi, flow westwards into the Arabian Sea and form estuaries. These rivers depend mainly on rainfall, so their flow varies with the seasons.
Lakes, importance and pollution
India also has many lakes, some freshwater and some salty, which are useful for water, irrigation and tourism. Rivers are vital for drinking water, irrigation, hydroelectricity, navigation and fishing. However, the dumping of sewage and industrial waste has badly polluted many rivers, and efforts such as river-cleaning action plans aim to restore them.
Key definitions
- Drainage
- The river system through which the water of an area flows.
- Drainage basin
- The area drained by a river and its tributaries.
- Perennial river
- A river that flows throughout the year, like the Himalayan rivers.
- Tributary
- A smaller stream or river that joins a larger river.
Solved examples
Q1. Name the three major Himalayan river systems.
Solution: The Indus, the Ganga and the Brahmaputra.
Q2. Which Peninsular rivers flow westwards?
Solution: The Narmada and the Tapi.
Q3. Why are Himalayan rivers perennial?
Solution: Because they are fed by both rain and melting snow.
Common mistakes to avoid
- Confusing Himalayan (perennial) and Peninsular (seasonal) rivers.
- Thinking all Peninsular rivers flow east (Narmada and Tapi flow west).
- Mixing up deltas (east coast) and estuaries (west coast).
- Forgetting that a drainage basin is the area drained by a river system.
Drainage — MCQ Quiz
10 questions with instant feedback. Use number keys 1–4 to answer.
Drainage refers to the ___ of an area.
Practice questions
Short answer
What is a drainage basin?
The area drained by a river and its tributaries.
Name two west-flowing Peninsular rivers.
The Narmada and the Tapi.
Why are Himalayan rivers perennial?
Because they are fed by both rain and melting snow.
Long answer
Distinguish between the Himalayan and Peninsular river systems.
India's rivers fall into two major systems that differ in several ways. The Himalayan rivers — the Indus, Ganga and Brahmaputra with their tributaries — rise in the snowy Himalayas. Because they are fed by both rainfall and melting snow, they are perennial and flow throughout the year. They carry large amounts of silt, form broad fertile plains, and develop large meanders and deltas in their lower courses. The Peninsular rivers, by contrast, flow across the old, hard plateau. Most of them, such as the Godavari, Krishna, Kaveri and Mahanadi, flow eastwards into the Bay of Bengal and form deltas, while a few like the Narmada and Tapi flow westwards into the Arabian Sea and form estuaries. Since they depend mainly on rainfall, their flow varies with the seasons. Thus, the Himalayan rivers are snow-fed and perennial, while the Peninsular rivers are rain-fed and seasonal.
Why are rivers important, and what is being done about river pollution?
Rivers are extremely important to human life and the economy. They provide water for drinking and for irrigating crops, which is vital in an agricultural country like India. They are used to generate hydroelectricity, support navigation and trade, and provide fish and other resources. Riverside areas have therefore long been centres of settlement and civilisation. However, the growing dumping of untreated sewage from towns and harmful waste from industries has badly polluted many Indian rivers, harming both people and aquatic life. To address this, the government has launched river-cleaning programmes and action plans aimed at treating waste, reducing pollution and restoring the health of the rivers, though much effort is still needed to keep them clean.
HOTS (Higher Order Thinking)
Why do Peninsular rivers often have less water in summer than Himalayan rivers?
Because Peninsular rivers depend mainly on rainfall and dry up in the rainless season, while Himalayan rivers are also fed by melting snow and so keep flowing.
Why is river pollution a serious problem for India?
Because rivers supply water for drinking, farming and many uses, and polluting them endangers health, agriculture and aquatic life on which millions depend.
Quick revision
Revision notes
- Drainage = river system; drainage basin = area drained by a river and its tributaries.
- Himalayan rivers (Indus, Ganga, Brahmaputra): snow-fed, perennial, silt-rich, deltas.
- Peninsular rivers: rain-fed/seasonal; most flow east (Godavari, Krishna, Kaveri); Narmada & Tapi flow west.
- Rivers vital for water, irrigation, power; many polluted by sewage and industrial waste.
Key takeaways
- Himalayan rivers are perennial; Peninsular rivers are seasonal.
- Most Peninsular rivers flow east; Narmada and Tapi flow west.
- Rivers are vital but badly polluted.
Frequently asked questions
What are the major Himalayan rivers?
The Indus, the Ganga and the Brahmaputra.
Which Peninsular rivers flow west?
The Narmada and the Tapi.
Why are rivers polluted?
Mainly by untreated sewage and industrial waste.