Irrigation & Water Management
Irrigation & Water Management
This domain tests irrigation design, scheduling, backflow protection, and winterization in a cold climate. Marks are lost by ignoring pressure, precipitation rate, or freeze damage.
Design and hydraulics
- Group heads into hydrozones by plant water need, sun, soil, and slope.
- Match precipitation rates on a zone; use head-to-head spacing for uniform coverage.
- Check static and dynamic pressure, flow, and pipe sizing before specifying nozzles.
- Use drip for beds and smart controllers with rain or soil-moisture sensors.
Backflow and code
- Irrigation systems need an approved backflow assembly, such as an RPZ or PVB, installed per code.
- Test backflow assemblies annually and keep records.
- Never allow chemigation without proper backflow protection.
Scheduling
- Apply about 1 in. per week, including rainfall; adjust for season and soil.
- On clay, use cycle-and-soak: split runtime into two or more cycles.
- Water early morning to reduce evaporation and disease.
Winterization
- Blow out with compressed air at appropriate pressure and flow; excessive pressure damages components.
- Drain lines, protect the backflow assembly, and shut down the controller.
Worked example
A zone has six heads at 2 gpm each = 12 gpm. The precipitation rate is 1.5 in./hr. To apply 1 in., runtime = 1 ÷ 1.5 × 60 = 40 minutes. On clay, split it into two 20-minute cycles with a soak interval. Confirm the water source can supply 12 gpm at dynamic pressure.
Traps that cost marks
- Mixing nozzles with different precipitation rates.
- Ignoring pressure loss and pipe size.
- Omitting backflow protection or annual testing.
- Blowing out at excessive pressure.
- Watering daily and shallowly instead of cycling and soaking.