Border Strip Irrigation
Part of Irrigation
Border strip irrigation divides a field into long, narrow, level strips separated by low earthen borders. Water flows down each strip in a controlled sheet, soaking the soil evenly as it advances. It is one of the oldest and most reliable surface irrigation methods, requiring no pumps or pipes — only a reliable water source, basic earthmoving tools, and careful land preparation. For a rebuilding community with access to a stream or canal, border strips offer a scalable, low-maintenance way to irrigate pasture, grain crops, and fodder fields.
What Border Strip Irrigation Is
A border strip is a rectangular section of field, typically 3–12 meters wide and 30–300 meters long, enclosed on its two long sides by low earthen ridges called borders or bunds. Water enters at the upper end of the strip and flows as a thin sheet down the slope toward the lower end. When managed correctly, the advancing water front wets the soil uniformly before excess water either drains off the lower end or soaks in completely.
The method works best on land with a gentle, uniform slope (0.2–2%) in the direction of flow and relatively flat cross-slope (less than 0.1%). Heavy clay to loam soils with moderate infiltration rates are ideal. Sandy soils lose water too fast; very flat land requires more precision earthwork.
Planning and Layout
Slope Assessment
Before laying out strips, measure the slope of your field. A simple slope board (a straight plank with a spirit level and a known leg height) can measure grade over short distances.
| Slope Range | Suitability | Notes |
|---|---|---|
| 0–0.1% | Poor | Water stagnates; needs laser leveling |
| 0.1–0.5% | Good | Gentle flow; suitable for most soils |
| 0.5–1.5% | Excellent | Ideal range for most crops |
| 1.5–3% | Acceptable | Higher erosion risk; shorten strip length |
| Above 3% | Poor | Erosion likely; use terracing instead |
Strip Dimensions
Strip width and length depend on soil type, slope, and available water flow rate.
| Soil Type | Strip Width | Max Strip Length |
|---|---|---|
| Sandy loam | 3–6 m | 60–100 m |
| Loam | 6–9 m | 100–200 m |
| Clay loam | 9–12 m | 150–300 m |
| Heavy clay | 9–15 m | 200–400 m |
Wider strips require higher inflow rates to achieve uniform wetting across the strip width. If your water source delivers modest flow, use narrower strips.
Setting Out the Borders
- Run a baseline along one edge of the field parallel to the intended flow direction.
- Use a level (or water-filled hose as a spirit level) to check that the baseline runs neither uphill nor downhill across the field — the cross-slope must be near zero.
- Mark strip widths at right angles to the flow direction using stakes and string.
- Run border lines from top to bottom of the field along each stake line.
Correcting Cross-Slope
If the ground slopes sideways across a strip, water will pool against the lower border and leave the upper side dry. Correct this with a few hours of hand leveling before building borders. Even a 5 cm height difference across a 6 m strip causes uneven wetting.
Constructing the Borders
Borders are low earthen ridges, typically 15–30 cm high and 30–50 cm wide at the base. Construction materials come entirely from the soil alongside each border line.
Construction Steps
- Plow or spade a shallow furrow along each border line.
- Throw the loosened soil toward the center of the border, building a low mound.
- Compact the mound by treading or tamping with a flat board — loose borders erode quickly.
- Check height and alignment with a straightedge or string line stretched between stakes.
- Allow a 10–15 cm freeboard (border height above expected water level) to prevent overtopping.
Borders should be firm enough to withstand moving water for the duration of an irrigation set (the time water is running down the strip, typically 1–6 hours).
Head Ditch
At the upper end of all strips, cut a shallow supply ditch perpendicular to the strip direction. Water flows from the main canal into this head ditch and is then released into each strip through a cut or removable plug in the border.
Plug the release point with a tuft of straw wrapped in burlap, or a cut sod block. To irrigate a strip, remove the plug; to stop, replace it.
Managing Water Distribution
Inflow Rate
The inflow rate into each strip must be high enough to advance the water front to the far end of the strip before the soil soaks up too much, but not so high that erosion occurs.
A rough guide: inflow should allow the water front to reach the far end of the strip in about one-quarter to one-third of the total irrigation time. If it takes too long to reach the end, the upper part of the strip is over-irrigated and the lower part under-irrigated.
| Strip Length | Approximate Target Inflow (per meter of width) |
|---|---|
| 50 m | 0.5–1.0 L/s per meter |
| 100 m | 1.0–2.0 L/s per meter |
| 200 m | 2.0–4.0 L/s per meter |
These are starting estimates; adjust based on observed water advance and soil conditions.
Irrigation Scheduling
Irrigate when the topsoil is dry to a depth of 5–10 cm, but before crops show wilting stress. In practice, for grain crops, this is every 7–14 days in dry conditions, or as directed by rain.
Run water until the front just reaches or slightly passes the lower end of the strip, then cut off inflow. The advancing water will continue soaking in (the “opportunity time”) for an additional period.
Avoid Over-Irrigation
Letting water run too long past the lower end wastes water and can waterlog the root zone. Watch the lower border for seepage or ponding and cut off inflow before this occurs.
Suitable Crops
Border strip irrigation is well-suited to:
| Crop Type | Suitability | Notes |
|---|---|---|
| Small grains (wheat, barley, rice) | Excellent | Tolerates brief flooding |
| Pasture and hay grasses | Excellent | Robust; tolerates variation |
| Forage legumes (alfalfa, clover) | Good | Needs well-drained soil |
| Maize (corn) | Good | Avoid prolonged ponding |
| Root vegetables (potatoes, beets) | Moderate | Sensitive to waterlogging |
| Row vegetables | Poor | Uneven wetting damages plants |
For sensitive vegetables and transplants, drip or furrow irrigation is more appropriate.
Maintenance
- Inspect borders after each irrigation. Repair any breaks or low spots immediately before the next irrigation event.
- Clear the head ditch of sediment and debris at the start of each season.
- Re-level strips if borders are repeatedly overtopped on one side. Settling soil shifts grade over time.
- Reseed or sod borders if erosion begins. Grass-covered borders resist erosion far better than bare earth.
A well-maintained border strip system can last for decades with minimal inputs beyond seasonal inspection.
Efficiency and Improvements
Unimproved border strip irrigation achieves 50–65% efficiency — roughly half the applied water actually reaches crop roots. Simple improvements can raise this to 70–80%:
- Pre-irrigate before planting to wet subsoil and reduce infiltration rate during crop irrigations.
- Shorten strip length if uniformity is poor — shorter strips are easier to manage with limited flow.
- Irrigate at night when evaporation losses are low.
- Use alternate strip irrigation — irrigate every other strip, letting the soil rest between sets.
Community-Scale Impact
A single gravity-fed canal supplying 10 L/s can irrigate 1–3 hectares of border strips per day with one or two workers managing plugs. For a small settlement, this can sustain the grain and fodder needs of 20–40 people.
Border Strip Irrigation Summary
Border strips are a proven, low-technology surface irrigation method suited to grain crops, pasture, and fodder on gently sloping land. Strips are laid out parallel to slope direction, separated by compacted earthen borders, and irrigated from a head ditch by removing simple plugs. Strip width ranges from 3–15 m and length from 60–400 m depending on soil type and slope. Proper inflow management — allowing the water front to advance at the correct speed — is the key skill. With simple maintenance, a border strip system provides reliable irrigation for decades using only hand tools and earthwork.