Introduction to Water Resources

Water is one of the most vital natural resources required to sustain life on Earth. About three-fourths of the Earth's surface is covered with water, but only a tiny fraction of it is fresh water that can be put to direct human use. Fresh water is mainly obtained from surface runoff and groundwater, which are continually renewed and recharged through the hydrological cycle. You might wonder why water conservation and management have become critical global discussions when three-fourths of the world is water. The answer lies in the distribution, quality, and management of usable fresh water.

In Chapter 3 of NCERT Class X Geography, titled Water Resources, we explore the paradox of water abundance versus water scarcity, examine the role of multipurpose river projects and dams, address the ecological and social concerns surrounding large dams, and study traditional and modern rainwater harvesting techniques across India.

Water Scarcity and the Need for Water Conservation

When we talk about water scarcity, we often imagine dry, arid deserts like Rajasthan where women walk long distances with earthern pots to fetch water. While geographical variation in seasonal and annual precipitation is a major cause of water scarcity, it is increasingly caused by over-exploitation, excessive use, and unequal access to water among different social groups.

Causes of Water Scarcity in India

  • Growing Population: A larger population requires more water not only for domestic use but also to produce more food. To increase food production, water resources are being over-exploited to expand irrigated areas, especially for dry-season agriculture.
  • Intensive Agriculture: The post-Green Revolution era saw widespread adoption of high-yielding crop varieties that require heavy irrigation. Tube wells and borewells installed by individual farmers have led to a drastic fall in underground water tables across states like Punjab, Haryana, and western Uttar Pradesh.
  • Industrialisation and Urbanisation: Post-independence India witnessed rapid industrialisation. Industries are heavy users of water and require reliable hydroelectric power. Urban centres with dense populations and modern lifestyles have further escalated domestic water demand.
  • Deteriorating Water Quality: Even in areas where water is available in sufficient quantity, it may be polluted by domestic and industrial wastes, chemicals, pesticides, and fertilisers used in agriculture, making it hazardous for human consumption.

Multipurpose River Projects and Integrated Water Resources Management

To store, control, and conserve water, India has historically relied on water harvesting structures such as dams, reservoirs, canals, and embankments. In post-independence India, large dams were hailed as the 'Temples of Modern India' by Jawaharlal Nehru, as they were integrated development projects designed to combine agriculture with rapid industrial growth and urbanisation.

What is a Dam?

A dam is a barrier across flowing water that obstructs, directs, or retards the flow, often creating a reservoir, lake, or impoundment. Dams are classified according to their structure, intended purpose, or height (e.g., timber dams, embankment dams, masonry dams, high dams, medium height dams).

Functions of Multipurpose Projects

Modern multipurpose projects serve several interconnected purposes beyond simple irrigation:

  • Electricity Generation: Hydroelectric power generation provides clean energy for industries and households.
  • Flood Control: Reservoirs store excessive rainfall runoff during monsoons to prevent severe flooding downstream.
  • Water Supply: Transporting potable water to urban and rural areas for domestic and industrial consumption.
  • Inland Navigation and Tourism: Creating navigable waterways and recreational boating hubs.
  • Pisciculture: Developing inland fish breeding grounds within large reservoirs.

Major Multipurpose Projects in India

Some prominent examples discussed in the NCERT textbook include:

  • Bhakra-Nangal Project: Constructed on the Sutlej-Beas river basin, providing irrigation and hydroelectric power to Punjab, Haryana, and Rajasthan.
  • Hirakud Project: Built on the Mahanadi River in Odisha, integrating conservation of water with flood control.
  • Damodar Valley Corporation (DVC): Built on the Damodar River in Jharkhand and West Bengal for flood control and power generation.
  • Sardar Sarovar Dam: Constructed on the Narmada River in Gujarat, designed to meet water needs in drought-prone areas of Gujarat and Rajasthan.

Social and Environmental Concerns Surrounding Large Dams

In recent decades, multipurpose projects and large dams have come under intense scrutiny and opposition from environmentalists, local communities, and civil society groups due to several negative impacts:

  • Regulating Natural River Flow: Dams disrupt the natural flow of rivers, causing poor sediment flow and excessive sedimentation at the bottom of the reservoir. This leads to stream bed erosion and harms aquatic life.
  • Submergence of Vegetation and Soil: Reservoirs submerge vast tracts of existing forests and fertile land, leading to vegetation decomposition over time and releasing greenhouse gases like methane.
  • Displacement of Local Communities: Large dams often require the displacement of thousands of local indigenous communities without adequate rehabilitation, compensation, or livelihood restoration.
  • Inter-State Water Disputes: Sharing river waters has led to disputes between neighboring states, such as the Krishna-Godavari dispute over water diversion by Maharashtra, affecting Andhra Pradesh and Karnataka.
  • Triggering Induced Seismicity and Floods: Heavy water pressure in huge reservoirs can trigger earthquakes. Paradoxically, dams built to control floods have sometimes caused devastating floods when massive amounts of water are released during heavy rainfall.

Rainwater Harvesting: Traditional and Modern Practices

Given the ecological and social drawbacks of large dams, rainwater harvesting is widely recognised as a viable, eco-friendly, and socio-economically sustainable alternative for water management.

Traditional Rainwater Harvesting Methods in India

  • Guls and Kuls: In Western Himalayan regions, people built diversion channels called 'guls' or 'kuls' to collect water from mountain streams for agricultural irrigation.
  • Rooftop Rainwater Harvesting: Common in Rajasthan, where rainwater falling on roofs is collected using pipes and stored in underground tanks called tanka.
  • Khadins and Johads: In agricultural fields of arid regions like Jaisalmer, land was converted into rain-fed storage structures ('khadins' and 'johads') that allowed water to stand and moisten the soil.
  • Bamboo Drip Irrigation System: In Meghalaya, a 200-year-old system uses bamboo pipes to tap stream and spring water, transporting it over long distances to irrigate crops drop by drop.

Modern Rooftop Rainwater Harvesting

In modern urban and rural setups, rooftop rainwater harvesting involves collecting rainwater directly from rooftops using PVC pipes, filtering it through sand and charcoal, and storing it in underground sumps or injecting it into existing wells to recharge groundwater aquifers. Tamil Nadu holds the distinction of being the first state in India to make rooftop rainwater harvesting compulsory for all houses across the state.

Summary & Key Takeaways

Water management requires balancing human demand with ecological sustainability. Relying solely on large dams creates environmental and social friction, making community-based rainwater harvesting an essential component of water security.

  • Hydrological Cycle: Fresh water is a renewable resource continually recycled through evaporation, condensation, and precipitation.
  • Causes of Scarcity: Driven by population growth, commercial agriculture, industrial demand, and chemical pollution.
  • Multipurpose Projects: Offer irrigation, flood control, power, and navigation, but cause community displacement, siltation, and ecological disruption.
  • Rainwater Harvesting: Sustainable practices such as rooftop tankas, khadins, kuls, and bamboo drip systems preserve water efficiently across different topographies.