Water Resources, River Basins, and Conservation

A Today you'll learn

Differentiate perennial Himalayan rivers from seasonal Peninsular rivers.
Trace major river basins of India (Ganga, Brahmaputra, Indus, Godavari, Krishna, Narmada).
Evaluate urgent water conservation strategies: rainwater harvesting, drip irrigation, and river cleanup.

B Let's understand

Water is essential for life, agriculture, industries, and power generation. India's river systems are divided into two major groups: 1) Himalayan Rivers (Indus, Ganga, Brahmaputra): Perennial rivers that flow year-round because they are fed by melting mountain glaciers in summer and monsoon rains in wet months. 2) Peninsular Rivers (Godavari, Krishna, Mahanadi, Kaveri, Narmada, Tapi): Non-perennial, rain-fed rivers whose water levels swell during monsoons and shrink during dry seasons. Most Peninsular rivers flow eastwards into the Bay of Bengal, forming fertile deltas, while Narmada and Tapi flow westwards through rift valleys into the Arabian Sea. Due to growing population, industrial pollution, and groundwater depletion, conserving water through rainwater harvesting, watershed management, and pollution control is a national priority.

C See it step by step

Example 1: Why does the River Ganga flow all year round whereas the River Godavari carries significantly less water in May?

Step 1: The Ganga originates in the high Himalayas from the Gangotri glacier.
Step 2: In hot summer months, melting snow and glaciers replenish river flow constantly (perennial).
Step 3: The Godavari originates in Maharashtra's Western Ghats and relies almost entirely on monsoon rainfall.
Step 4: By May (pre-monsoon summer), dry weather leaves rain-fed Peninsular rivers with much lower discharge.

Example 2: How does rooftop rainwater harvesting replenish groundwater?

Step 1: Rainwater falling on roofs is directed into collection gutters instead of draining away into roads.
Step 2: Water passes through a gravel and sand filtration pit to remove debris.
Step 3: Filtered water is piped into an underground recharge well or recharge pit.
Step 4: Water slowly percolates down to recharge underground aquifers, raising the local water table.

D Your turn

Why are the Himalayan rivers called perennial rivers?

Look back at "Let's understand" above for a clue.

E Ready to practise?

Himalayan rivers (Ganga

Himalayan rivers (Ganga, Indus) are perennial because they are fed by melting glaciers and rain.

Peninsular rivers (Godavari

Peninsular rivers (Godavari, Krishna) are rain-fed and fluctuate with seasonal rainfall.

Key idea 3

Narmada and Tapi are the two major west-flowing rivers that drain into the Arabian Sea.

Key idea 4

Groundwater is stored in underground permeable rock layers called aquifers.

Key idea 5

Rainwater harvesting captures and filters rainfall to recharge groundwater aquifers.

Warm up

1. What is a perennial river? Give one example from India.

2. Which river is known as the "Dakshin Ganga" (Ganga of the South)?

3. Name the two major Peninsular rivers that flow westward into the Arabian Sea.

Practise

4. Where does the River Ganga originate?

5. Why is the Brahmaputra River called "Tsangpo" in Tibet?

6. What is the underground water-holding rock formation called?

Challenge

7. Explain how rooftop rainwater harvesting helps homes during summer water scarcity.

8. State two common causes of river water pollution in India and how they can be prevented.

Download worksheet (PDF)

Question 1: What is a perennial river? Give one example from India.

Answer: A river that flows continuously with water throughout the entire year (e.g., River Ganga or Indus)

Question 2: Which river is known as the "Dakshin Ganga" (Ganga of the South)?

Answer: River Godavari

Question 3: Name the two major Peninsular rivers that flow westward into the Arabian Sea.

Answer: Narmada and Tapi

Question 4: Where does the River Ganga originate?

Answer: Gangotri Glacier (as Bhagirathi river)

Question 5: Why is the Brahmaputra River called "Tsangpo" in Tibet?

Answer: Because "Tsangpo" is the Tibetan language name meaning "the Purifier"

Question 6: What is the underground water-holding rock formation called?

Answer: An aquifer

Question 7: Explain how rooftop rainwater harvesting helps homes during summer water scarcity.

Answer: It stores surplus clean rainwater in tanks or recharges groundwater wells, providing reliable water during dry summer shortages

Question 8: State two common causes of river water pollution in India and how they can be prevented.

Answer: Discharge of untreated industrial chemicals and untreated municipal sewage into rivers; prevent by installing sewage and effluent treatment plants