Water Resources — NCERT Solutions

Definition:
Water scarcity means the lack of sufficient available freshwater resources to meet the water demands of a region or population.

Main Causes of Water Scarcity:

1. Over-population: Large and growing populations increase demand for water beyond available supply.
2. Over-exploitation: Excessive use of water for agriculture (especially irrigation), industries, and domestic purposes depletes water sources.
3. Unequal distribution: Water may be abundant in one region but scarce in another due to uneven rainfall and poor management.
4. Pollution: Industrial effluents, agricultural chemicals, and untreated sewage pollute freshwater bodies, making water unfit for use.
5. Urbanisation: Rapid urban growth increases water demand and leads to mismanagement of water resources.

Advantages of Multi-purpose River Projects:

1. They provide irrigation to water-scarce areas, boosting agricultural production.
2. They generate hydroelectric power, meeting industrial and domestic energy needs.
3. They help in flood control by regulating river flow.
4. They facilitate inland navigation and water supply for drinking and domestic use.
5. They promote tourism and recreational activities.

Disadvantages of Multi-purpose River Projects:

1. They cause large-scale displacement of local communities, especially tribal and rural populations.
2. They disrupt the river's natural flow and sediment transport, affecting downstream ecosystems.
3. Submergence of forests and biodiversity leads to ecological damage.
4. They cause fragmentation of rivers, harming aquatic life and fish migration.
5. They lead to waterlogging and soil salinity in irrigated areas over time.
6. They create conflicts among states over sharing of river water.

Introduction:
Rajasthan is a semi-arid to arid state with low and erratic rainfall. Historically, people here developed ingenious traditional methods to harvest and store rainwater.

Traditional Methods of Rainwater Harvesting in Rajasthan:

1. Khadins and Johads:

• In the western arid districts of Rajasthan (like Jaisalmer), khadins (also called dhoras) are embankments built across hill slopes to collect rainwater runoff. The collected water is used for agriculture.
• Johads are small earthen check dams that collect and conserve rainwater, allowing it to percolate and recharge groundwater.

2. Kunds (or Kundis):

• These are covered underground tanks (cisterns) built in the courtyard of houses or near fields.
• Rainwater from rooftops or a specially prepared catchment area flows through a pipe into the kund.
• The water stored in kunds is used for drinking purposes throughout the dry season.
• Kunds are found widely in the Thar Desert region.

3. Tanka System:

• A tanka is a cylindrical underground tank traditionally built inside the main house or courtyard.
• Rooftop rainwater is channelled into the tanka through pipes.
• It can store enough water to last a family through the dry summer months.
• The first spell of rain is usually not collected (to wash the roof); subsequent rains fill the tanka.

Significance:
These methods ensured water security in a region with scarce rainfall. They represent the wisdom of local communities in adapting to their environment. However, with the arrival of the Indira Gandhi Canal, these practices have declined in some areas as people shifted to canal water.

Introduction:
Traditional rainwater harvesting methods developed over centuries are now being revived and modernised across India to address growing water scarcity.

Modern Adaptations of Traditional Rainwater Harvesting:

1. Rooftop Rainwater Harvesting (Urban Areas):

• In cities like Chennai, rooftop rainwater harvesting has been made compulsory by law for all buildings.
• Rainwater collected from rooftops is channelled through pipes into underground storage tanks or used to recharge groundwater through bore wells.
• This has significantly raised the groundwater level in many urban areas.

2. Revival of Stepwells (Baoris/Baolis):

• Ancient stepwells are being restored and maintained to collect and store rainwater.
• In Rajasthan and Gujarat, NGOs and government agencies are reviving these structures.

3. Check Dams and Percolation Tanks:

• Modern check dams are built across streams and gullies to slow runoff and allow water to percolate into the ground, recharging aquifers — a modern adaptation of the traditional johad.

4. Bamboo Drip Irrigation (Meghalaya):

• In Meghalaya, the 200-year-old tradition of bamboo drip irrigation channels spring and rainwater through bamboo pipes to irrigate fields. This traditional system is now being studied and adapted for wider use.

5. Guls and Kuls (Himachal Pradesh):

• Traditional guls (diversion channels from glacial streams) are being modernised with better lining and management to supply water to fields.

Conclusion:
These modern adaptations combine traditional ecological knowledge with contemporary engineering to ensure sustainable water conservation, reduce dependence on large dams, and empower local communities to manage their own water resources.