Farm Rainwater Harvesting

India receives 1,170mm of average annual rainfall — enough to meet most agricultural water needs if captured and used efficiently. Yet 60%+ of this rainfall runs off uncaptured. Rainwater harvesting closes this gap.

The Runoff Calculation

Understanding how much water falls on your farm:

Rainfall volume = Area (m²) × Rainfall depth (m)

Example: 1 hectare (10,000 m²) receiving 800mm (0.8m) annual rainfall
= 10,000 × 0.8 = 8,000 cubic metres = 80 lakh litres per year

Even capturing 25% = 20 lakh litres — significant irrigation supplement

1. Farm Ponds (Most Common)

The most impactful single water harvesting structure for Indian small farms.

Sizing:

For 1 hectare of crops: 20m × 20m × 3m deep pond (1,200 cubic metres capacity)
Lined with plastic or clay to reduce seepage
Located at lowest point of farm to collect runoff

Government support:

PMKSY (Pradhan Mantri Krishi Sinchayee Yojana): Farm pond subsidy ₹75,000–1,50,000
MGNREGS: Labor costs covered for pond construction
Many state schemes with 50–90% subsidy

Use: Store monsoon runoff; use for dry-season irrigation via drip or sprinkler.

Integrated fish farming: Stock farm pond with carp (Rohu, Catla) for additional income. Fish eat algae and organic matter; their waste fertilizes irrigation water. Excellent income diversification.

2. Earthen Bunding (Contour Bunds)

For sloped or undulating land:

Earthen ridges built along contour lines perpendicular to slope
Slow runoff; force water to spread and infiltrate
Space: Every 10–20m vertical drop depending on slope
Height: 30–50 cm
Constructed by hand or with tractor blade

Cost: ₹15,000–25,000/hectare with MGNREGS labor subsidy.

3. Swales

A swale is a water-harvesting trench dug along contour lines — on the contour means water stays level and spreads evenly.

How to make a swale:

Mark the contour line using an A-frame level or bunyip level
Dig a trench 30–60 cm wide × 30–60 cm deep along the line
Pile excavated soil as a berm on the downhill side
Plant trees/crops on the berm (gets moisture from below as water percolates)

Benefit: Dramatically increases groundwater recharge; prevents gully erosion; creates moist growing zone for trees.

4. Check Dams and Nala Bunding

For streams (nalas) crossing the farm:

Small earthen or rock-filled check dams slow water flow
Water backs up → infiltrates → recharges groundwater
Multiple small dams more effective than one large
Government subsidy available under watershed programs

Ancient Indian Water Harvesting

India's ancestors were brilliant rainwater harvesting engineers:

System	Region	Principle
Kund	Rajasthan	Underground cisterns catching every drop of roof/courtyard water
Baoli (Stepwell)	Gujarat, Rajasthan	Deep access to groundwater; maintained groundwater table
Johad	Haryana	Village earthen ponds; community maintained
Katta	Karnataka	Small check dams across streams
Phad	Maharashtra	Sophisticated canal distribution from river storage
Tank irrigation	South India	1,00,000+ traditional tanks; most now silted and neglected

Next: Ancient Indian Irrigation — Vrikshayurveda and Cow-Based Farming

Farm Rainwater Harvesting: Ponds, Farm Ponds, and Bunding Systems