Drip and Sprinkler System Design, Layout and Components
What the exam tests here
Turning a crop plan into a working layout: how many laterals, how long, how many sections, what pipe sizes, and what pressure the head unit must deliver.
Core rules
- Design on peak ET and peak Kc. Daily volume (m³) = area (ha) × gross depth (mm) × 10.
- Section the field so the pump runs 4–8 hours a day at peak. Number of sections = total emitter flow ÷ pump capacity.
- Keep velocity below about 1.5 m/s in laterals and submains to control friction loss.
- Pressure variation along a lateral should not exceed 20% of the inlet pressure.
- Emission uniformity EU = 100 × (1 − 1.27 CV ÷ √n); a well-designed drip system reaches about 90% or better.
- Sprinkler precipitation rate (mm/h) = nozzle flow (l/h) × 1000 ÷ (spacing along × spacing across, m²). It must stay below the soil infiltration rate.
- Fit air-release valves at high points, flush valves at lateral ends, and a non-return valve plus pressure gauge at the head.
Worked example
1 ha tomato, rows 1.2 m, laterals 100 m long, emitters 3 lph at 0.5 m. Laterals needed = 10,000 ÷ 1.2 = 8,333 m. Emitters = 8,333 ÷ 0.5 = 16,666. Full flow = 16,666 × 3 = 50 m³/h. With a 12.5 m³/h pump, run 4 sections. Peak requirement is 60 m³/day, so pumping time = 60 ÷ 12.5 = 4.8 hours.
Traps that cost marks
- Designing lateral length from a catalogue maximum without checking inlet pressure.
- Ignoring the 20% pressure-variation rule.
- Using plant spacing instead of row spacing when counting laterals.
- Ignoring wind for sprinkler spacing; use 50–60% of wetted diameter and closer in windy conditions.
Quick recall
Volume = area × depth × 10; sections = total flow ÷ pump flow.