Water Source, Water Quality and Environmental Considerations
What the exam tests
This domain tests source yield, water-quality parameters, clogging and soil hazards, and environmental safeguards in micro-irrigation.
Core rules and concepts
- The source must supply peak demand, not just average demand. Check well yield, canal supply hours and storage capacity.
- Key quality parameters include EC, TDS, pH, SAR, chloride, boron, iron, manganese, hardness and suspended solids.
- High EC increases salinity stress; high SAR increases sodicity risk and can reduce infiltration. Iron and manganese oxidise and clog emitters.
- Water testing before design is essential. Treatment may include settling, media filtration, screen filtration, aeration or acidification.
- Environmental safeguards include avoiding over-extraction, preventing fertilizer or chemical backflow, managing runoff and disposing of filter backwash safely.
- Leaching fraction may be needed where salts accumulate, especially under drip where wetting is localised.
Worked example
A water test reports EC 2.0 dS/m, SAR 12 and pH 8.2. The EC indicates moderate salinity, while SAR around 12 indicates a sodicity hazard for many soils. The high pH also raises the risk of carbonate scaling in drippers. A suitable response is to select a tolerant crop, apply gypsum where soil tests support it, use a leaching fraction, monitor emitter flow and consider acid treatment for scaling. The reasoning is that salinity, sodicity and scaling are different problems and need different responses.
Traps that cost marks
- Using EC as a substitute for SAR.
- Ignoring iron and manganese because the water looks clear.
- Designing for average source yield instead of peak demand.
- Assuming high pH is harmless without checking scaling risk.
- Discharging backwash or fertilizer solution into a drain or field without control.