To assess the performance of your centre pivot irrigation system to determine how evenly the water is being distributed over your irrigation area, it is necessary to:
- Measure the pressure and flow at various points in the system;
- Measure the operating speed at the far end; and
- Measure the output of the sprays using catchcans.
To measure pressure requires some equipment such as an accurate pressure gauge with an appropriate scale so it works mid range (0-600kpa), a pitot tube or PVC tee and fittings such as reducing bushes or a Schrader valve.
Measure your pivots speed by staking out a measured distance around the outer wheel track and record the time for the end drive unit to travel between the stakes.
Measuring spray output
To measure sprinkler coverage requires items such as catchcans, 30m tape measure, stop watch, manufacturers nozzle specifications, a measuring cylinder or jug, calculator, pen and record sheets.
The pivot must be moving at its normal speed for the test to be accurate.
Place catchcans at equal spacing’s (5m to 10m) to cover the whole wetted length of the pivot.
Measure the width of the wetting pattern near the end drive unit and record.
After the system has passed all catchcans, measure the volumes in the catch cans and record these on the catchcan record sheet.
Measure and record the pressure and flow at outlets near the start and end of your pivot and also at other positions on towers along the pivot.
Bringing it all together
Once all the information is gathered, it is then time to work out all the results.
The New South Wales Department of Primary Industries has a catchcan calculator and a guide to evaluating a centre pivot irrigation system that you can use to assist with the calculations.