Classification of Irrigation Methods

Broad classification 

1. Surface (Gravity) irrigation — water applied on soil surface and moved by gravity (most common worldwide).
2. Subsurface (Subirrigation) — water supplied below the surface (underground channels, perforated pipes, subirrigation).
3. Pressurized / Micro irrigation — water supplied under pressure: sprinkler, rain-gun, drip (trickle).

1. Surface (gravity) irrigation

• Definition: Water applied to the field surface and distributed by overland flow, controlled by small bunds/checks/levies.
• Advantages: simple, low capital cost, easy to maintain, little technical skill required.
• Prerequisites for good performance: uniform soils, well-prepared and levelled field surface, adequate water supply and controlled delivery.
• Main types / classification:
  • Border strip (graded / level)
  • Check basin (beds & channels)
  • Basin (paddy & ponding)
  • Ring basin (orchards)
  • Furrow (straight / contour)
  • Corrugation (small furrows for pastures, steep slopes)

a) Border strip method

• Description: Field divided into long parallel strips by low earthen bunds; water introduced at upstream end and allowed to advance as a thin sheet. Ends may be closed or open depending on length and runoff control.
• Suitability: soils with moderate infiltration (not extremely coarse or extremely clayey); gentle slopes (0–0.5%); can be adapted up to ~4% for very dense close-spaced crops if erosion risk is controlled. Ideal for closely spaced cereals, fodder, pulses, wheat, barley, berseem.
• Typical dimensions & guidelines: strip width commonly 3–15 m (depends on stream size and equipment); length and safe slope depend on soil texture (clay soils allow longer strips than sandy soils). Graded borders (longitudinal slope 0.1–0.5%) or level borders (near-zero slope) are used.
• Merits: better uniformity than uncontrolled flooding; relatively high application efficiency (≈75–85% with good leveling/management).
• Demerits / precautions: needs good leveling and uniform soil; poor in very sandy or very heavy clay soils; may require end-closures for long strips.

b) Check basin method (beds & channels)

• Description: Field is divided into small basins (plots) surrounded by bunds; water is impounded within each basin for the required infiltration period. Common and simple; often used for flat fields.
• Suitability: best for fine textured soils (clayey, clay-loam) where infiltration is slow and uniform — gives good distribution and leaching ability; suitable for cereals, millets, pulses, oilseeds.
• Merits: can achieve very high application efficiency (often > 85–90% in fine soils); good for leaching salts because water can be ponded; easy to control applied depth.
• Demerits / precautions: requires good levelling and uniform soil within basin; not suitable for coarse textured soils with high infiltration; bunds must be well made to resist ponding; avoid long stagnation in very low infiltration soils (risk of anaerobiosis); basin area must be planned relative to inflow rate, slope and soil (smaller basins for sandy soils / small stream sizes; larger basins for clay soils / large streams).
• Design note: basin area limits depend strongly on soil texture and stream (inflow) to basin; consult local design tables (basin sizes range from a few 10s of m² for small stream and sandy soils to several 1000s m² for large streams and clay soils).

c) Basin method (paddy / submergence)

• Description: Basin fully bounded on all sides and water is ponded to desired depth — typical for lowland rice and bunded rainfed rice.
• Suitability & guidelines: requires thorough leveling; efficient ponding possible for rice; optimum field size for efficient water management in rice often recommended in the order of 25–0.40 ha per management unit where mechanized leveling and separate inlet/drainage are available.
• Merits: excellent for paddy, salt leaching; precise control of depth.
• Demerits: needs very good leveling; risk of long stagnation in heavy soils; requires strong bunds.

d) Ring basin (orchard rings)

• Description: Circular (ring) basins formed around individual trees; water delivered to rings only so inter-row spaces remain dry. Rings connected to feed channels.
• Suitability: wide-spaced fruit trees, plantation crops.
• Merits: saves water compared with flooding whole orchard; reduces weed growth in interspaces; concentrates moisture in root zone.
• Demerits: requires construction of rings/mini bunds; management of rings and cleaning of feeder channels needed.

e) Furrow irrigation

• Description: Small channels (furrows) running between crop rows; water flows down furrows and infiltrates to wet the root zone; often used with alternate ridges (ridge and furrow). Very common for row crops — maize, cotton, sugarcane, potato, onion, vegetables.
• Types: straight (longitudinal) furrow for nearly flat fields; contour or graded furrow for sloping land (furrows given gentle slope to control velocity).

Typical dimensions / practical ranges:

• Furrow spacing (ridge centre to centre): commonly 60–120 cm (crop dependent).
• Furrow depth: often around ~10–15 cm (12.5 cm commonly cited) — depends on flow and soil.
• Furrow stream (inflow): typically 0.5–2.5 L/s per furrow (depends on furrow length, soil conductivity and crop).
• Minimum slope: ~0.05% recommended to ensure surface drainage; maximum safe slope for straight furrow is often limited (~0.75%); contour furrows can be used on steeper slopes (up to ~5% or more) with erosion control.
• Design considerations: furrow spacing, furrow length, slope (grade), stream size and allowable advance time must be matched to soil infiltration characteristics and crop root depth. In sandy soils furrow lengths must be shorter because infiltration is rapid and lateral wetting is limited. In heavy clay longer furrows are possible.
• Merits: more efficient than broad flooding; less water used, better suited for row crops and mechanized cultivation.
• Demerits / precautions: needs proper land shaping and erosion control on slopes; risk of rill formation/erosion if stream too large or slope too steep; salt accumulation possible on ridges; initial labor or machinery needed to form furrows.

f) Corrugation irrigation

• Description: Many small close-spaced V or U shaped channels (corrugations) 6–10 cm deep and 40–75 cm apart used for close-growing crops, pastures and steep slopes. Water runs in corrugations down slope.
• Suitability: close-growing cereals, pasture on sloppy land. Not suitable for saline soils or saline water.
• Merits: easy to create (simple tools), suitable on slopes where other surface methods fail.
• Demerits / precautions: limited application depth; corrugation length must be short on steep or light soils to avoid erosion or breaching.

g) Furrow irrigation

When designing furrow irrigation consider these sequentially:

• Soil infiltration characteristics (hydraulic conductivity) — determine lateral spread & required spacing/advance time.
• Crop root depth and wetted area needed — determines spacing and emitter/stream size.
• Furrow spacing — normally matches row spacing and machine operations (60–120 cm common).
• Furrow length — choose the longest length that gives uniform wetting without erosion and acceptable advance time; sandy soils → shorter furrows; clay soils → longer furrows.
• Furrow slope (grade) — controls flow velocity; too steep → erosion; too flat → poor advance. Minimum slope ~0.05% for drainage; straight furrows often ≤0.75% gradient; contour furrows used on steeper ground.
• Furrow stream (Q) — select inflow so that water reaches end of furrow within allowable advance time and flow velocity remains below non-erosive limits. Typical stream 0.5–2.5 L/s per furrow.
• Non-erosive velocity — ensure flow velocity (function of Q and furrow cross-section) is below soil erosion threshold (depends on soil and practice). Designers use empirical relations or charts in manuals to find maximum non-erosive Q for a given slope and furrow geometry. If in doubt, use conservative flows and shorter furrows.
• Operation tips: open flow at head, allow advance for design time, then close; avoid creating high velocities; check lateral wetting after irrigation and adjust intervals.

When to choose which surface method?

• Flat clayey fields, need for leaching (saline soils), paddy rice → Basin / Check basin.
• Closely spaced cereals/forage on moderate soils → Border strips.
• Row crops (maize, sugarcane, cotton, potato) → Furrow irrigation (better suited to mechanization).
• Orchards / isolated trees → Ring basin.
• Steep plots or close-growing crops on slope → Corrugations / contour furrow with erosion control.