In an irrigation design, pressure losses due to head are accounted for by subtracting them from which value to determine if there is adequate pressure to raise water to the required height?

• A. Static Pressure
• B. Available Pressure
• C. Dynamic Pressure
• D. Incoming Pressure

Answer: (B)

The key idea is using the pressure you have available to do the work of moving water. In an irrigation system, water loses pressure as it climbs to higher elevations and as it flows through pipes (friction losses and any elevation gain). To know if you can lift water to the required height, start with the available pressure at the source and subtract all head losses along the path. What remains is the pressure available to overcome the elevation head. If that leftover pressure is at least equal to the height you need to raise the water (the required head), then there is adequate pressure.

Static pressure, by contrast, is simply the pressure from elevation at rest and doesn’t account for losses along the system. Dynamic pressure relates to the velocity of the flow, not the usable pressure to lift water. Incoming pressure is the source pressure before losses, but the calculation for adequate lift uses the available pressure after subtracting head losses.