Centre pivot design — also called center pivot design — combines geometry, water demand, hydraulics and machine operation. Start with the area that will actually be irrigated and the hours available to supply it. Radius alone does not select the pump, nozzles or drive package.
Define the site and operating case
Record the irrigated radius, full-circle or sector operation, crop requirement, soil intake, elevation profile and available water supply. Separate the machine length from any additional wetted radius or end-gun area. Note the hours available after allowing for maintenance and other interruptions.
Agriculture Victoria's centre-pivot planning guidance identifies system capacity, crop requirement, application efficiency and operating hours as connected design inputs. It also highlights the risk of application rates exceeding soil infiltration near the outer end.
Worked example: a 300 m irrigated radius
Assume a hypothetical full circle with a 300 m irrigated radius, no end gun, no excluded area, a net irrigation requirement of 6 mm/day, assumed application efficiency of 85%, and 20 operating hours per day. No effective rainfall or other water contribution is credited. The efficiency is an assumption, not a guaranteed system performance.
| Step | Calculation | Result |
|---|---|---|
| Irrigated area | π × 300² / 10,000 | 28.27 ha |
| Gross daily depth | 6 / 0.85 | 7.06 mm/day |
| Daily water volume | 28.2743 × 7.05882 × 10 | 1,995.84 m³/day |
| Supply flow | 1,995.8353 / 20 | 99.79 m³/h |
| Supply flow in litres per second | 99.7918 / 3.6 | 27.72 L/s |
One millimetre over one hectare is 10 m³. Keep unrounded values through the calculation. A smaller operating window requires a larger flow for the same daily volume; using a larger pump does not remove sprinkler, pressure, soil or supply constraints.
Why the outer spans need more flow
A sprinkler further from the pivot centre covers a larger ring of land. For uniform gross depth and a common revolution time, a ring from radius r1 to r2 receives the fraction (r2² − r1²) / R² of the total flow. This is an area allocation, not a nozzle-selection formula.
| Radial band | Area share | Allocated flow |
|---|---|---|
| 0–100 m | 1/9 | 3.08 L/s |
| 100–200 m | 3/9 | 9.24 L/s |
| 200–300 m | 5/9 | 15.40 L/s |
A real sprinkler package divides the area among individual outlets, with boundary and overlap treatment. Use current manufacturer charts to select nozzles at the available pressure, and check regulator requirements, wetted diameter, spacing and distribution. The geometric allocation above does not account for wind, runoff or non-uniform application.
Time to apply a selected depth
At the calculated flow, applying 10 mm gross depth across the full circle needs 28.2743 × 10 × 10 = 2,827.43 m³. Continuous pumping time is 2,827.4339 / 99.7918 = 28.33 hours.
The example requires about 28 hours 20 minutes of pumping to apply 10 mm gross depth over a full revolution at constant flow. With only 20 operating hours per day, that revolution spans more than one day.
This water-volume relationship is not a percent-timer setting. The timer also needs the machine's measured or specified full-speed revolution time and the control method. Instantaneous sprinkler application rate is a different quantity and must be checked against soil intake and surface storage.
Complete the hydraulic and machine design
- Pump duty: combine source lift, mainline and span-pipe losses, elevation changes, equipment losses and the required outlet pressure. Check the critical operating position.
- Sprinklers and regulators: use the actual outlet schedule, nozzle charts and regulator requirements. Include the end gun and booster separately if fitted.
- Machine: verify span lengths, tower locations, overhang, terrain limits, wheel/drive configuration and alignment requirements with the supplier.
- Site operation: check wheel tracks, field obstructions, soil intake, supply availability, electrical requirements and the maintenance window.
The Irrigating Agriculture design overview discusses the interaction between pipe selection, operating pressure, sprinkler packages, end guns and pump matching. These checks remain necessary after calculating a target flow.
Centre pivot design questions
Are centre pivot and center pivot different systems?
No. They are Australian/British and American spellings of the same irrigation-system term.
Does a 300 m machine always irrigate 28.27 ha?
Only a full circle with an effective irrigated radius of 300 m has that geometric area. Sector operation, exclusions, end-gun coverage and the actual wetted boundary change the irrigated area.
Can I choose a nozzle from the ring-flow table?
No. The table allocates total flow to broad rings. Individual nozzle selection requires outlet spacing, pressure, sprinkler and regulator data, and a distribution assessment.
Use Tenselo for the connected calculations
Explore the centre pivot design calculator, sprinkler package calculator and advanced irrigation design tools. Connect the design to the pump sizing and pipe hydraulics guides.