💧 Water Resources Management
Hydrological cycle, groundwater, water quality parameters, watershed management, rainwater harvesting, and waterlogging solutions for ELEC 13.
This lesson builds core elective concepts in BSc Agriculture with practical applications and exam-oriented clarity.
Water Resources Management
Hydrological Cycle and India's Water Budget
The hydrological cycle (water cycle) describes the continuous movement of water through the atmosphere, land surface, and subsurface. Key processes: precipitation → infiltration → runoff → evapotranspiration → percolation → groundwater → discharge → evaporation → condensation → precipitation.
India's water budget:
- Average annual precipitation: ~4,000 BCM (billion cubic metres)
- Total utilisable water resources: 1,123 BCM (surface: 690 BCM + groundwater: 433 BCM)
- Per capita water availability: declining — 5,177 m³ (1951) → ~1,486 m³ (2021) → projected 1,140 m³ by 2050 (water stress threshold: 1,700 m³/capita/year)
Surface Water Resources
India has 12 major river basins (drainage area > 20,000 sq km each):
| River Basin | Length (km) | Major States | Utilizable Potential (BCM) |
|---|---|---|---|
| Ganga-Brahmaputra-Meghna | 2,525 | UP, Bihar, WB, Assam | 250 |
| Indus | 3,180 | J&K, Punjab, HP | 73.3 |
| Godavari | 1,465 | Maharashtra, AP, Telangana | 76.3 |
| Krishna | 1,400 | Maharashtra, Karnataka, AP | 58.0 |
| Mahanadi | 851 | Odisha, Chhattisgarh | 50.0 |
| Narmada | 1,312 | MP, Gujarat | 34.5 |
| Cauvery | 800 | Karnataka, Tamil Nadu | 21.4 |
| Tapti | 724 | MP, Maharashtra, Gujarat | 14.9 |
Other surface water bodies: ~5 million tanks and ponds (traditional water harvesting); major reservoirs (3,600+); wetlands (~15.98 Mha).
Groundwater Resources
Groundwater is water stored in aquifers below the ground surface. It accounts for ~80% of rural drinking water and ~60% of agricultural irrigation in India.
Types of Aquifers
| Type | Description | Example Regions |
|---|---|---|
| Unconfined (Phreatic) aquifer | Water table aquifer; not overlain by impermeable layer; recharged directly from surface | Indo-Gangetic Plain (shallow alluvial) |
| Confined aquifer | Sandwiched between impermeable layers (aquicludes); water under pressure | Deep aquifers in hard rock areas |
| Artesian aquifer | Confined aquifer where pressure causes water to rise above aquifer level; flows without pumping | Parts of Rajasthan, coastal areas |
| Perched aquifer | Small, localised unconfined aquifer above main water table; separated by local impermeable layer | Hilly areas, laterite plateaus |
India's Groundwater Scenario (CGWB Data)
- Total annual groundwater recharge: 433 BCM
- Net annual groundwater availability: 398 BCM
- Annual groundwater draft (extraction): ~245 BCM
- Groundwater assessment units: 6,965 (blocks/mandals/talukas)
- Over-exploited: 1,592 units (22.8%)
- Critical: 253 units (3.6%)
- Semi-critical: 681 units (9.8%)
- Most stressed states: Punjab (79% blocks over-exploited), Rajasthan, Haryana, Delhi
Hard rock aquifers (Deccan Plateau, peninsular India) have low storage and slow recharge — highly vulnerable to depletion.
Water Quality Parameters
Water quality is assessed through physical, chemical, and biological parameters. IS 10500:2012 sets Indian drinking water standards.
Physical Parameters
| Parameter | Significance | Acceptable Limit (IS 10500) |
|---|---|---|
| Turbidity | Suspended particles; affects aesthetics and disinfection efficiency | 1 NTU (desirable), 5 NTU (permissible) |
| Colour | Natural organic matter, algae, industrial pollutants | 5 Hazen units (desirable), 15 (permissible) |
| Temperature | Affects dissolved oxygen, chemical reactions | — |
| Odour and Taste | Dissolved gases (H₂S), organics | Unobjectionable |
| Total Suspended Solids (TSS) | Undissolved particles | — |
Chemical Parameters
| Parameter | Significance | Limit (IS 10500) |
|---|---|---|
| pH | Acidity/alkalinity; affects corrosion and disinfection | 6.5–8.5 |
| Total Dissolved Solids (TDS) | Salinity; taste; affects crops | 500 mg/L (desirable), 2000 (permissible) |
| Hardness | Ca²⁺, Mg²⁺; scale formation; soap consumption | 200 mg/L (des.), 600 (perm.) |
| BOD (Biochemical Oxygen Demand) | Organic pollution load; O₂ needed to oxidize organics biologically | < 3 mg/L for drinking |
| COD (Chemical Oxygen Demand) | Total organic + inorganic oxidizable matter; broader than BOD | — |
| DO (Dissolved Oxygen) | Essential for aquatic life; low DO = pollution | > 6 mg/L for healthy aquatic life |
| Nitrates | Agricultural runoff (fertilizers); causes methemoglobinemia (blue baby) | 45 mg/L |
| Fluorides | Geogenic; causes fluorosis (dental, skeletal) | 1.0 mg/L (des.), 1.5 (perm.) |
| Arsenic | Geogenic contamination; carcinogenic | 0.01 mg/L |
| Electrical Conductivity (EC) | Total ion concentration; irrigation water quality | < 0.75 dS/m (safe for most crops) |
Biological Parameters
- Total Coliforms: Indicator of fecal contamination; should be absent in drinking water
- E. coli / Fecal coliforms: Specific fecal indicator; must be zero per 100 mL
Watershed Management
A watershed (catchment area) is the land area that drains to a common point (stream, river, lake). Watersheds are the basic hydrological unit for integrated natural resource management.
Watershed Delineation
- Based on topography using contour maps, DEM (Digital Elevation Model), satellite imagery
- Hierarchy: micro-watershed (< 500 ha) → sub-watershed → watershed → sub-basin → basin
Objectives of Watershed Management
- Control soil erosion and sedimentation
- Improve water availability — increase infiltration, reduce runoff
- Increase land productivity
- Improve livelihoods of watershed communities
- Recharge groundwater
- Reduce flood peaks and drought impact
Major Watershed Development Programmes in India
- IWMP (Integrated Watershed Management Programme): Merged into PMKSY-WDC (Pradhan Mantri Krishi Sinchayee Yojana – Watershed Development Component) in 2015. Covers ~26 lakh ha/year.
- Hariyali: 2003 watershed programme through Gram Panchayats
- NWDPRA: National Watershed Development Project for Rainfed Areas (ICAR-implemented)
Rainwater Harvesting
Rainwater harvesting (RWH) is the collection and storage of rainwater for productive use before it becomes runoff.
Techniques
| Technique | Description | Best For |
|---|---|---|
| Rooftop RWH | Collect rain from rooftop → storage tank | Urban areas, drinking water |
| Surface runoff harvesting | Farm ponds, check dams to collect field runoff | Agriculture, recharge |
| Percolation tanks (ponds) | Shallow earthen structures; allow seepage to recharge groundwater | Hard rock areas |
| Check dams | Small masonry/earthen structures across streams; slow flow, trap silt, recharge | Small streams |
| Johad (traditional) | Village ponds — traditional system of Rajasthan; revived by Tarun Bharat Sangh | Rural Rajasthan |
| Kund / Tanka | Underground cisterns; traditional RWH in Thar Desert | Drinking water in desert |
| Contour trenches | Trenches along contours on degraded slopes | Afforestation areas |
Groundwater Recharge: Artificial Methods
- Injection wells / recharge wells: Direct injection of treated water into aquifer
- Spreading basins / percolation ponds: Divert surface water to spread over permeable area
- Induced recharge: Pumping from river bank wells induces recharge from adjacent river
- Recharge shafts: Vertical shafts to bypass impermeable layers and reach deeper aquifer
- Roof-top recharge: Rooftop collection diverted to borewell / pit for recharge
Waterlogging
Waterlogging is the condition where soil pores are saturated with water, depriving roots of oxygen.
Causes:
- Excessive irrigation without adequate drainage
- Seepage from canals and reservoirs
- High rainfall combined with flat topography and impermeable subsoil
- Rise in water table due to over-irrigation
Effects on crops: Reduced O₂, anaerobic conditions, root rot, nutrient deficiencies (especially iron/manganese toxicity in rice).
Drainage solutions:
- Surface drainage: Field levelling, land grading, open drains/ditches — remove excess surface water
- Subsurface drainage: Perforated pipes (tile drains) or mole drains buried 60–120 cm deep — lower water table
- Mole drainage: Bullet-shaped mole creates unlined channel; suitable for clay soils; cheaper than tile drainage
- Pumped drainage: Electrical/diesel pumps to lower water table in flat areas (common in Punjab/Haryana)
Water Use Efficiency in Agriculture
Agriculture uses ~85% of India's freshwater. Improving efficiency is critical.
- Micro-irrigation: Drip (trickle) and sprinkler systems save 30–50% water vs. flood irrigation
- Irrigation scheduling: Irrigate based on crop water requirement (ET-based scheduling), soil moisture sensors
- Alternate furrow irrigation: Irrigate every other furrow — saves 30–40% water for maize, sugarcane
- System of Rice Intensification (SRI): Saves 25–50% water vs. conventional paddy
Inter-Basin Water Transfer
The National Water Grid concept proposes linking surplus river basins to deficit basins. National River Linking Project (NRLP) has two components:
- Himalayan component: 14 links — Ganga-Brahmaputra tributaries to western rivers
- Peninsular component: 16 links — Mahanadi-Godavari-Krishna-Cauvery linking
Challenges: ecological impacts, interstate disputes, displacement, very high cost (~₹11 lakh crore).
Summary Cheat Sheet
| Topic | Key takeaway |
|---|---|
| Main focus | Hydrological cycle, groundwater, water quality parameters, watershed management, rainwater harvesting, and waterlogging solutions for ELEC 13. |
| Section context | Revise this lesson with the rest of Land and Water Resources for stronger conceptual continuity. |
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