Water resources Tnpsc Samacheer Notes

1. Introduction and Nature of Water

• Water is one of the most important and indispensable elements on Earth without which life cannot exist.
• All plants and animals require water for survival.
• In addition to drinking, water is required for domestic, agricultural, and industrial purposes, and is essential for carrying out almost all economic activities.
• Water resources are potentially useful to humans.
• Water acts as a natural filter in the soil and purifies it.
• Water is an abiotic and renewable natural resource that supports ecosystems.

2. Status and Global Distribution of Water

• Coverage & Total Quantity:
  • About 71% of the Earth’s surface is covered by water.
  • Total water present on Earth is approximately 326 million cubic miles.
• Salt Water vs. Fresh Water:
  • Salt water (oceans, seas) constitutes about 97.20% (or 97.2%) of total water.
  • Fresh water constitutes only about 2.80% (or 2.8%).
• Breakdown of Fresh Water (2.80%):
  • Surface water: Accounts for 2.20% (or 2.2%) (also broken down as 0.30% of total fresh water in specific diagrams).
  • Groundwater: Accounts for 0.60% (or 0.6%) (or 30.10% of fresh water).
  • Others: Make up 0.90% (or 0.9%).
• Breakdown of Surface Water:
  • Glaciers and icecaps: Represent 2.15% of surface water (or 68.70% of fresh water).
  • Lakes and streams: Comprise 0.01% (with lakes representing 87% and rivers 2% of liquid surface fresh water).
  • Swamps: Comprise 11% of surface fresh water.
  • Other forms: Account for 0.04%.
• Extractable Groundwater:
  • Only about 0.60% of total groundwater can be economically extracted with present drilling technology (noted in older editions as 0.25% of the 0.6% groundwater).

3. Estimated Volume of Water by Source (Shiklomanov, 1993)

• Oceans, Seas, & Bays: 321,000,000 cubic miles (96.54% of total water).
• Ice caps, Glaciers, & Permanent Snow: 5,773,000 cubic miles (1.74% of total water).
• Groundwater: 5,614,000 cubic miles (1.69% of total water).
• Soil Moisture: 3,959 cubic miles (0.001% of total water).
• Ground Ice & Permafrost: 71,970 cubic miles (0.022% of total water).
• Lakes: 42,320 cubic miles (0.013% of total water).
• Atmosphere: 3,095 cubic miles (0.001% of total water).
• Swamp Water: 2,752 cubic miles (0.0008% of total water).
• Rivers: 509 cubic miles (0.0002% of total water).
• Biological Water: 269 cubic miles (0.0001% of total water).

4. Water Resources in India

• Sources of Water: Water in India is available through three primary sources:
  1. Precipitation
  2. Surface water
  3. Groundwater
• Perennial Rivers:
  • Porunai (Thamirabarani): The only perennial river in Tamil Nadu, flowing through Tirunelveli and Thoothukudi districts.
  • Archaeological excavations at Adichanallur and Sivakalai date the Thamirabarani civilization to circa 1155 BC (BCE), making it nearly 3,200 years old.
• Other Historical River Systems:
  • Kosasthalaiyar River: Considered one of the major cradles of human ancestors in the world.
  • Ganga (Ganges) and Brahmaputra: Major river valleys that provided fertile alluvial lowlands, supporting dense populations, agriculture, and early urban centers.
  • Pennar River: Flowing through the Erramala hills in Kadapa district, Andhra Pradesh, it created the spectacular Gandikota Gorge (known as the Grand Canyon of India).
  • Narmada River: Forms a rift valley between the Vindhyas and Satpura ranges and develops an estuary in Gujarat.
  • Kaveri (Cauvery), Vaigai, Noyyal, and Tungabhadra: Served as historic centers of agriculture, deltaic irrigation, and town settlements.
• Per Capita Urban Consumption:
  • Average daily per capita water consumption is 250 liters in Kolkata, 175 liters in Mumbai, and 80 liters in Delhi (compared to 1,200 liters in Los Angeles and 1,100 liters in Chicago).
• Urban Scarcity & Regulation:
  • Acute water scarcity exists in Indian urban centers; cities such as Chennai, Hyderabad, Jaipur, Jodhpur, Nagpur, Shimla, Solan, Surat, Udaipur, and Vadodara permit only 1 to 2 hours of water supply per day.
  • New Delhi regulates water supply to approximately 4 hours per day.
• Marine & River Pollution:
  • Most urban garbage and sewage in India are dumped into rivers or along their banks.
  • Major coastal cities including Mumbai, Kolkata, and Chennai continuously discharge substantial portions of untreated waste into the sea.

5. Water Management and Irrigation History in India

• Prehistoric & Sangam Periods:
  • Irrigation management began during the Iron Age/Megalithic period, with settlements deliberately situated near rivers and tanks.
  • Ancient settlements utilized ring wells and brick-built tanks for water storage (excavated at Arikkamedu and Keezhadi).
  • At Adichanallur, advanced water and sewage management included raised brick structures with 29 courses of bricks and perforated terracotta pipes arranged in 9 courses.
  • King Karikalan Chola effectively utilized water from the River Kaveri, establishing extensive canal systems that peaked during the 10th to 13th centuries.
• Medieval Systems:
  • Agriculture depended heavily on irrigation via rivers, canals, tanks, and wells.
  • In the 14th century, Firuz Shah Tughluq constructed India’s largest known network of canals in the Delhi area.
  • Water extraction utilized lift irrigation and the Persian wheel in North India.
  • Check dams, reservoirs with sluice gates, and Chola canal networks linked Kaveri’s tributaries.
  • Village assemblies (ur, nadu, brahmadeya, and nagaram) were tasked with maintaining local water bodies and irrigation infrastructure.
• Ancient State Policy:
  • Under the Mauryan Empire, the central administration directly initiated and organized irrigation projects while regulating water distribution.

6. The Hydrological (Water) Cycle

• Definition & Characteristics:
  • Hydrology is the science dealing with the occurrence, distribution, movement, and properties of water on Earth.
  • The cycle is a continuous, sun-driven process transporting water from oceans to the atmosphere, from atmosphere to land, and back to oceans.
  • It represents a closed system where the overall volume of water remains constant, though its spatial and temporal distribution varies.
• Three Primary Phases:
  1. Evapotranspiration
  2. Precipitation
  3. Runoff
• Six Core Components:
  1. Evapotranspiration: Total water loss combining surface water evaporation and plant transpiration.
  2. Evaporation: Phase change of liquid water into gas. It begins at 0°C (32°F) and boils at 100°C (212°F). Oceans, seas, lakes, and rivers supply ~90% of atmospheric moisture via evaporation. Evaporation increases with higher temperature, higher wind speed, lower humidity, and larger surface area.
  3. Transpiration: Release of water vapor into the air by plants, contributing ~10% of atmospheric moisture.
  4. Condensation: Vapor cooling into liquid droplets to form clouds when saturated air cools below dew point.
  5. Precipitation: Condensed droplets falling to Earth under gravity, depositing fresh water.
  6. Infiltration, Percolation, & Runoff: Water either moves across the land surface (runoff) or infiltrates through soil horizons and percolates deeper to replenish groundwater.

7. Water as an Energy Resource

• Hydroelectricity (Hydel Power):
  • Generated from the potential energy of water falling from heights to spin turbine blades.
  • Clean, eco-friendly, renewable, and contributes roughly 7% of world electricity.
  • Leading producers globally are China and Canada.
• Tidal Energy:
  • Renewable energy powered by the natural rise and fall of ocean tides via tidal streams, barrages, and tidal lagoons.
  • First tidal power station: La Rance (France); largest tidal power station: Sihwa Lake (South Korea).
  • Tidal Projects in India:
    • India’s first proposed plant is a 3 MW installation at Durgaduani Creek in the Sundarbans delta, West Bengal.
    • Identified potential sites for tidal power generation include the Gulf of Kutch and Gulf of Khambhat (Cambay) in Gujarat, and the Ganges delta in the Sundarbans.
• Geothermal Water:
  • Heated groundwater and steam emerging in volcanic and fault areas create hot springs and geysers.
  • Promising Indian spots identified for geothermal power include Puga Valley in Ladakh and Manikaran in Himachal Pradesh.

8. Global Water Stress and Resource Depletion

• Overpopulation has polluted most freshwater systems, leaving less than 1% of Earth’s fresh water readily accessible for human use.
• Human activities such as over-exploitation, industrial pollution, and water acidification have severely endangered freshwater ecosystems, pushing millions of freshwater fish species toward extinction.
• Water conservation measures outlined include checking pollution, recycling wastewater, constructing check dams and reservoirs, controlling population growth, and using water resources without depletion.