Drip Irrigation Design, Installation and Operation
What the exam tests
This domain tests hydraulic design, emission uniformity, pressure management, installation sequence and routine operation of drip systems.
Core rules and concepts
- Emission uniformity (EU) compares the average of the lowest-quarter emitter flows with the average of all measured emitter flows: EU = (low-quarter average ÷ overall average) × 100.
- A high EU requires matched emitters, adequate pressure and good filtration. Manufacturer coefficient of variation (CV) affects uniformity.
- Pressure variation along laterals should be kept small; excessive lateral length or too many emitters causes poor end-of-line flow.
- Installation sequence: head unit, main and submain, flush the lines, install laterals, install emitters, pressure test, then flush again before operation.
- Operating rules include regular flushing, filter cleaning, pressure checks and chlorination or acid treatment when clogging risk is high.
- Flushing should achieve a velocity high enough to move sediment; a common target is about 0.3–0.5 m/s at the lateral end.
Worked example
A field test measures emitter flows. The overall average is 4.0 L/h; the average of the lowest quarter is 3.4 L/h. EU = (3.4 ÷ 4.0) × 100 = 85%. If the design target is 90%, the system is below target. Before changing emitters, check head pressure, filter condition, partially closed valves, lateral length and clogging. The reasoning is that low EU is a symptom, not necessarily an emitter defect.
Traps that cost marks
- Using the average emitter flow instead of the low-quarter average for EU.
- Replacing emitters without flushing the lateral first.
- Ignoring pressure differences caused by elevation.
- Installing emitters before the first flush.
- Mixing incompatible fertilizers in the tank and causing precipitation.