Sprinkler Irrigation Design, Installation and Operation
What the exam tests
This domain tests sprinkler spacing, precipitation rate, uniformity, pressure requirements and wind effects in solid-set and portable sprinkler systems.
Core rules and concepts
- Sprinklers must overlap. A common design guide is spacing at about 50–60% of the wetted diameter, depending on wind and manufacturer data.
- Precipitation rate PR (mm/h) = sprinkler discharge (L/h) ÷ area served per sprinkler (m²). The area is the sprinkler spacing multiplied by the lateral spacing.
- Application rate should not exceed the soil infiltration rate, or runoff and uneven distribution occur.
- Uniformity depends on pressure, nozzle size, spacing, wind and pipe friction. Wind distorts the pattern and requires closer spacing or smaller droplets.
- Laterals and mains must be sized for friction loss so that pressure at the farthest sprinkler remains adequate.
- Operating checks include nozzle wear, blocked nozzles, leaks, pressure at the end of laterals and timer or valve settings.
Worked example
A sprinkler discharges 1,200 L/h. Sprinklers are spaced 12 m apart on laterals, and laterals are 18 m apart. Area per sprinkler = 12 × 18 = 216 m². PR = 1,200 ÷ 216 = 5.56 mm/h. If the soil infiltration rate is 8 mm/h, the application rate is acceptable. If it is 4 mm/h, the system will pond and runoff unless runtimes are split or sprinklers are changed.
Traps that cost marks
- Using wetted diameter as spacing instead of a fraction of it.
- Forgetting to multiply lateral spacing by sprinkler spacing.
- Ignoring wind when checking uniformity.
- Comparing precipitation rate with crop water use instead of soil infiltration rate.
- Assuming nozzle flow is correct without checking pressure.