Border Irrigation Calculator

About the Border Irrigation Calculator

Border irrigation applies water to long, narrow strips of land bounded by low ridges (borders). Water is released at the upstream end and flows as a thin sheet across the strip, infiltrating as it advances. The strip width, length, and application depth determine the total volume, while the inflow rate must be matched to advance the water front at a pace that achieves the target depth.

Border strips are simpler to manage than individual furrows and work well for close-grown crops like alfalfa, wheat, and pasture. They require well-leveled fields with a gradual slope (0.1–0.5%) in the flow direction. Strip widths range from 20 to 100 feet and lengths from 300 to 1,500 feet.

This calculator computes the volume of water needed and the inflow rate required to irrigate a border strip efficiently. Use it to check strip size and inflow assumptions before setting turnout size, irrigation duration, or water orders.

When This Page Helps

Border irrigation is cost-effective for crops that cover the entire soil surface. This page helps you estimate whether a planned strip and inflow rate are likely to spread water evenly without excessive runoff at the tail end.

How to Use the Inputs

1. Enter the border strip width in feet.
2. Enter the border strip length in feet.
3. Enter the target application depth in inches.
4. Enter the desired advance time in minutes.
5. Review the total volume and required inflow rate.
6. Adjust dimensions or timing if the inflow rate exceeds your supply.

Example Calculation

Tips & Best Practices

• Field slope should be 0.1–0.5% for efficient border irrigation.
• Laser-level fields to minimize cross-slope variations.
• Border ridges should be 6–8 inches high and well compacted.
• Cut off inflow when water reaches about 80% of strip length.
• Wider strips need higher inflow rates for uniform advance.
• Measure actual advance rate periodically to verify design assumptions.

Border Irrigation Design

Designing a border strip system involves selecting strip width, length, and slope to match the available water supply and soil intake characteristics. NRCS design manuals provide tables and equations relating these variables for different soil types.

Cutoff Ratio

The cutoff ratio is the fraction of the strip length water has advanced when inflow is stopped. For efficient irrigation, the cutoff ratio should be 0.80–0.90. Water momentum and continued tail-water recession carry the front to the end of the strip after cutoff.

Comparing Surface Methods

Border irrigation is more uniform than wild flooding but less precise than graded furrows. It requires less labor than furrow irrigation because fewer individual streams need management. For flat, well-leveled fields growing broadcast crops, borders are often the most practical surface irrigation method.

Frequently Asked Questions

• What crops are suited for border irrigation?

  Close-grown crops like alfalfa, pasture grasses, small grains (wheat, barley), and orchards on flat ground work well with border irrigation. Row crops are generally better served by furrow or drip systems.

• How wide should the border strips be?

  Strip width depends on available flow: 20–40 ft for small supplies, 40–80 ft for moderate supplies, and up to 100 ft for large canal deliveries. Wider strips need higher inflow rates.

• What is the maximum recommended length?

  Strip length depends on soil intake rate and slope. Typical lengths are 300–600 ft for fast-intake sandy soils, 600–1,000 ft for medium soils, and up to 1,500 ft for slow-intake clay soils.

• Why is cross-slope leveling important?

  Cross-slope variations cause water to concentrate on the low side, leaving the high side dry. Laser-leveling to within ±0.05 ft ensures uniform lateral distribution across the strip.

• How does border irrigation compare to pivot?

  Border irrigation has lower capital cost but higher labor cost and lower efficiency (50–70% vs 80–90%). Pivots automate the process, saving labor on large fields.

• Can I automate border irrigation?

  Partially. Automated check gates and timers can start and stop inflow, but the water advance and distribution rely on gravity and field preparation.