A self-cleaning automated irrigation system

NIWA has been working on installing and operating a novel self-cleaning irrigation system intake at Totara Valley, near Timaru.

Screening debris out of the water

Water for the scheme is sourced from the Opuha Dam and taken from the Opihi River. A self-cleaning perforated screen is a novel element. The screen was developed and installed by Andar Holdings of Timaru. The screen filters Didymo and other debris from the intake water, preventing it from entering the irrigation system and potentially blocking pumps and spray nozzles.

A NIWA Gate Control Module (GCM) ‘tells’ the screen when it needs cleaning. Sensors measure the difference between the water level in the storage pond and the level in the intake, indicating that the screen is blocked and water is no longer flowing freely through it. The GCM turns on a conveyor which moves the debris out of the water and deposits it behind the screen. Hard-wearing nylon brushes then automatically clean the screen.

Other technology in the Totara Valley system

The system features a Neon Metering Module (NMM), which measures and records the water level at the single downstream outflow point and converts this to flow rate. The NMM then compares the measured flow rate with a user-programmable target flow, and incrementally opens or closes the motorised gate to let more or less water through, maintaining the flow rate close to its target.

The flow data are continuously recorded on the NMM and regularly pushed to the system server from where managers can view historical and real-time data via the internet. Alarm values can be set for all data, and text alarms sent to nominated users using SMS messaging.

All this means that the system’s managers can regularly and remotely ensure that the irrigation system is working properly and complies with consent requirements.

Communications challenge

Communications between the NMM and the server use the GPRS cellular network. The Totara Valley site is remote, and surrounded by hills on three sides. Because the GPRS network has distance limitations, we needed to communicate via the closer but hidden Fairlie comms tower, while avoiding interference from the Timaru tower that provided a clear but too-distant signal directly down the valley.

A 10-metre mast, corner reflector antenna, and mast-top signal booster eventually gave us reliable communications, enabling us to select the Fairlie tower and exclude the stronger Timaru signal.

A team effort!

Like many of our irrigation projects, this was a collaborative project.

  • Andar Holdings (Timaru) manufactured and installed the gate and screen structures.
  • NIWA Instrument Systems was subcontracted by Andar to provide the gate control, level monitoring, flow regulation instrumentation, and data communications system.
  • Environmental Consultancy Services (Timaru) carry out the day-to-day resource compliance monitoring for the owners.

Read more about NIWA's irrigation projects:

A decade of irrigation automation
Integrated irrigation eases the work for landowners

Contact

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Principal Technician - Instrument Systems
The control module with the Gate Controller Module at the top and the Neon Metering Module in the middle. (Photo: Lindsay Anderson, Environmental Consultancy Services Ltd.)
A self-cleaning irrigation screen. [NIWA]
Research subject: HydrologyInstrumentation