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Class 10 Water Resources: cheat sheet
CBSE Social Science. Why water is scarce, multi-purpose river projects and their problems, and traditional and rooftop rainwater harvesting.
Key ideas
- Water can be scarce even where it is plentiful, because of over-use, pollution, unequal access and growing towns and industry.
- Only a small part of the Earth’s water is fresh, and much of that is frozen or underground.
- Multi-purpose projects serve irrigation, electricity, flood control and water supply together.
- Large dams can disrupt rivers and sediment, submerge land and forests, displace people and cause water-sharing disputes.
- Traditional harvesting includes guls and kuls in the Western Himalayas, inundation channels in Bengal, khadins and johads in Rajasthan, and tankas under houses.
- Rooftop harvesting stores rain in tanks or lets it soak in to recharge groundwater; Meghalaya uses bamboo drip irrigation.
- The Jal Jeevan Mission aims at piped drinking water for every rural home, and Atal Jal manages groundwater with village help.
Remember
| Projects and rivers | Bhakra-Nangal: Sutlej–Beas; Hirakud: Mahanadi; Sardar Sarovar: Narmada |
| Rooftop water | 1 mm of rain on 1 m² = 1 litre; litres = area × rainfall (mm) × share collected |
| Tankas | underground rain tanks of Bikaner, Phalodi and Barmer |
| Old water works | Bhopal lake: 11th century; Hauz Khas tank, Delhi: time of Allauddin Khilji |
Watch out
- Forgetting that only part of the rain is collected: multiply by the share given, such as 80%.
- Mixing up projects and rivers: Hirakud is on the Mahanadi, Sardar Sarovar on the Narmada.
- Thinking scarcity only means too little rain: over-use and pollution cause it too.
Worked example
A school roof of 130 square metres gets 700 mm of rain a year, and 80% can be collected (1 mm on 1 m² = 1 litre). (a) How many litres? (b) If the school uses 800 litres a day, how many full days will it last? (c) Give two benefits of rooftop harvesting.
Working: 130 × 700 × 80%; ÷ 800
Answer: (a) 72,800 litres (b) 91 days (c) It saves water, recharges groundwater and reduces flooding.
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