Chapter Summary
This section is a concise recap of all of Chapter 3 — Water Resources. Use it for last-minute revision before the Board examination.
Water is a renewable resource, renewed through the hydrological cycle, yet only a small proportion is usable freshwater. Despite abundance, by 2025 nearly two billion people may face absolute water scarcity — caused mainly by over-exploitation, excessive use and unequal access, not just low rainfall.
Causes and Quality — At a Glance
- Causes of scarcity: growing population (more domestic use + more food); irrigated agriculture (largest consumer, over-draws groundwater via wells/tube-wells); industrialisation (heavy use + power); urbanisation (city colonies pumping groundwater).
- Quality and access: even where water is plenty, pollution (domestic, industrial, agricultural) and unequal access cause scarcity — so conservation is needed everywhere.
Multi-Purpose Projects — At a Glance
- Dam = barrier across flowing water creating a reservoir (spillway/weir; timber/embankment/masonry; low/medium/high).
- Multi-purpose project integrates: irrigation, hydel power, water supply, flood control, navigation, fish breeding, recreation. Nehru: 'temples of modern India'.
- Examples: Bhakra-Nangal (Sutlej-Beas; power + irrigation); Hirakud (Mahanadi; conservation + flood control); Sardar Sarovar (Narmada).
- Problems: sedimentation, rockier beds, river fragmentation, dam-triggered floods, loss of silt, induced earthquakes, water-borne diseases, displacement. Narmada Bachao Andolan; Krishna-Godavari inter-state dispute (Koyna diversion).
Rainwater Harvesting — At a Glance
- Traditional: guls/kuls (Western Himalayas); inundation channels (Bengal); khadins (Jaisalmer); johads (Rajasthan); rooftop harvesting into tankas storing palar pani (purest natural water); first spell of rain not collected.
- Modern: Tamil Nadu — first state to make rooftop harvesting compulsory; Shillong (15-25% of household needs); Gendathur, Karnataka ('rich in rainwater'); bamboo drip irrigation, Meghalaya (200-year-old; springs by gravity; 18-20 litres → 20-80 drops/min).
- Decline in western Rajasthan due to the Indira Gandhi Canal.
Quick Revision — Must-Know Facts
- Water renewed by the hydrological cycle; ~2 billion in absolute scarcity by 2025.
- Irrigated agriculture = largest consumer of water.
- Nehru: dams = 'temples of modern India'. Bhakra-Nangal (Sutlej-Beas), Hirakud (Mahanadi), Sardar Sarovar (Narmada).
- Tamil Nadu = first state with compulsory rooftop harvesting. Bamboo drip irrigation = Meghalaya. Tankas / palar pani = Rajasthan.
Quick Revision — Commonly Confused Points
- Quantity scarcity (low rainfall/over-use) vs quality scarcity (pollution) vs access scarcity (unequal sharing).
- Benefit vs problem of dams: irrigation/power/flood-control are benefits; displacement/sedimentation/dam-triggered floods are problems.
- Guls/kuls = Western Himalayas; khadins = Jaisalmer; johads = Rajasthan; tankas = Rajasthan (drinking water); bamboo drip = Meghalaya.
- Narmada Bachao Andolan = displacement; Krishna-Godavari dispute = inter-state water sharing.