1. Surface water and groundwater
- Surface water: rivers, lakes, ponds, tanks, reservoirs; fed by rain and (in the north) snowmelt.
- Groundwater: water that has soaked into the ground and fills pores and cracks below the water table, in aquifers; reached by wells and tube wells; recharged by rain and seepage from rivers and canals.
- Northern plains: perennial snow-fed rivers; porous alluvium with plentiful, shallow groundwater.
- Peninsula: seasonal rain-fed rivers; hard crystalline rock with limited groundwater; tanks.
| Surface water | Groundwater |
|---|---|
| Rivers, lakes, tanks | Below the water table |
| Seen on the surface | Reached by wells |
| Loses water by evaporation | Little evaporation |
Key terms
- Water table
The upper level of the saturated zone below the ground, under which rocks are full of water.
- Aquifer
A layer of porous rock or sediment that holds and yields groundwater.
2. Need for water conservation
- Rain is seasonal (three to four monsoon months) and uneven across regions.
- Rising demand: population, irrigation, industry, cities.
- Over-use of groundwater: water tables falling in parts of Punjab, Haryana, western Uttar Pradesh, Rajasthan and Tamil Nadu.
- Pollution of rivers and lakes by sewage, industrial waste and farm chemicals.
- Recurring droughts when the monsoon fails.
- Ways to conserve: rainwater harvesting, efficient irrigation (drip, sprinkler), less thirsty crops, recycling waste water, fixing leaks, protecting lakes and rivers from pollution.
| Cause of scarcity | Remedy |
|---|---|
| Over-pumping | Recharge pits, drip irrigation |
| Pollution | Treat sewage and waste |
| Seasonal rain | Store and harvest rain |
Key terms
- Water conservation
Using water carefully and protecting its sources so that enough clean water remains for the future.
3. Rainwater harvesting
- Meaning: collecting and storing rain where it falls, for use or to recharge groundwater.
- Rooftop harvesting: roof → gutter → down pipe → first-flush device → filter (sand, gravel) → storage tank → overflow to a recharge pit or well → aquifer.
- Other methods: recharge pits and trenches, check dams, percolation tanks, farm ponds, reviving village tanks.
- Importance: raises the water table; water in the dry season; less street flooding in cities; less soil erosion; better groundwater quality (dilutes fluoride and salts); cheap; people's participation.
- Harvest (litres) = roof area (m²) × rainfall (mm) × runoff coefficient.
| Step | Part |
|---|---|
| Collect | Roof, gutter, down pipe |
| Clean | First-flush, filter |
| Store | Tank |
| Recharge | Pit or old well |
Key terms
- Rainwater harvesting
Collecting and storing rainwater for use or for recharging groundwater.
- Recharge pit
A pit filled with gravel and sand through which harvested water soaks down to the groundwater.
- Runoff coefficient
The fraction of rain falling on a surface that can actually be collected.
4. Irrigation: need, wells and tube wells
- Need: seasonal, uncertain and uneven rain; dry rabi season; thirsty crops (rice, sugarcane); multiple cropping; high-yielding seeds; porous soils.
- Wells: dug to the water table; water lifted by hand, Persian wheel or pump; cheap, owned by farmers; small areas.
- Tube wells: deep bores with electric or diesel pumps; large supplies.
- Wells and tube wells are the leading source of irrigation (as of the early 2020s): Punjab, Haryana, Uttar Pradesh, Bihar, Gujarat.
- Why tube wells in the northern plains: soft alluvium easy to bore; plentiful recharged groundwater; electricity; flat land; high demand.
| Feature | Well | Tube well |
|---|---|---|
| Depth | Shallow | Deep |
| Lifting | Hand, animal, small pump | Electric or diesel pump |
| Area watered | Small | Larger |
Key terms
- Irrigation
The artificial supply of water to crops.
- Tube well
A deep, narrow bore into an aquifer from which water is lifted by a power-driven pump.
5. Tank irrigation
- Tank: natural or man-made depression (often an earth embankment across a stream) that stores rainwater.
- Where: Tamil Nadu, Karnataka, Telangana, Andhra Pradesh.
- Why in the peninsula: hard impervious rock (little groundwater); seasonal rain-fed rivers; undulating land with natural hollows; rain concentrated in a short season; small scattered fields.
- Drawbacks: dry up in droughts; silting; evaporation loss; occupy fertile land; small command area.
| Advantage | Drawback |
|---|---|
| Cheap, local | Dries up in droughts |
| Stores monsoon rain | Silting, evaporation |
Key terms
- Tank
A small reservoir, natural or made by an embankment, that stores rainwater for irrigation.
6. Canals and modern irrigation
- Inundation canals: from a river without a barrage; water only in floods (rainy season); unreliable.
- Perennial canals: from a barrage, weir or dam; water all year; northern plains (Punjab, Haryana, Uttar Pradesh) and southern deltas.
- Examples: Indira Gandhi Canal, Upper Ganga Canal, Western Yamuna Canal, Sirhind Canal.
- Disadvantages: waterlogging; salinity and alkalinity (reh, kallar); mosquitoes and malaria; seepage and evaporation losses; costly; only on flat land; tail-end farms short of water.
- Drip irrigation: water drop by drop at the roots through pipes and emitters; least waste; orchards, sugarcane, vegetables in dry areas.
- Sprinkler irrigation: water sprayed like rain; uneven land, sandy soils; wheat, pulses, vegetables, tea.
| Head | Perennial | Inundation |
|---|---|---|
| Headworks | Barrage, weir or dam | None |
| Flow | All year | Only in floods |
| Reliability | High | Low |
Key terms
- Perennial canal
A canal taken from a river at a barrage or dam, which flows throughout the year.
- Inundation canal
A canal taken from a river without a barrage, which carries water only when the river is in flood.
- Drip irrigation
Supplying water drop by drop directly to the root zone of plants through pipes and emitters.
Exam tips
Common mistakes
- Calling water in a reservoir "groundwater".
- Saying inundation canals flow all year.
- Placing tank irrigation in Punjab instead of the southern plateau.
- Leaving out the runoff coefficient in harvest calculations.
How marks are usually awarded
- Reasons (1 mark each): the geographical factor and how it acts, with a named region.
- Canal comparison: headworks, period of flow, reliability.
- Harvest sums: rule, substitution, answer with unit.