A decade of irrigation automation
NIWA’s Instrument Systems team has just commissioned three new state-of-the-art water monitoring and control stations on the Waimakariri Irrigation Scheme, one of the largest schemes in the South Island. The scheme has consent to abstract up to 12 cubic metres of water per second from the Waimakariri River. NIWA now has installed 14 control stations on the scheme.
Over the past decade, NIWA has played a major role in providing and managing automatic water-flow monitoring and control systems on the Waimakariri Scheme. We design, build, install and support the instruments, and then manage the data transfer from the instruments back to the Scheme’s managers, Waimakariri Irrigation Ltd.
How does the control system work?
A raceman sets a target flow rate into the system to supply the demand for irrigation water. This can be carried out on site, or remotely, via cell phone text message or a laptop with a cellular connection. The flow control system compares the actual water flow rate in the race with the target. If the actual flow rate drops below the target, the data logger commands the gate to open a little more, to let more water through, to bring the actual flow rate back up toward the target. If the flow rate is higher than the target, the data logger commands the gate to close a bit, to reduce the flow.
How does the controller know what the actual flow rate is?
A datalogger reads the water-level from a water-level encoder in a stilling well and converts this into a flow rate by applying a mathematical formula. This formula is specific to the shape of the race and is determined by gaugings carried out by NIWA hydrologists.
Adjusting flow rate targets
Flow rate and other data are regularly transferred from the data logger to the NIWA Flosys server. The client can access all station data, both historical and in near real-time, from the server at any time. Flow rates can be monitored remotely and target changes sent to the control stations by text message or from a remote desktop or laptop PC
Providing system support
NIWA provides ongoing maintenance and operational support for all the monitoring and automatic flow-control equipment at each of the 14 stations.
We also collect and manage the various hydrological data, which we archive in a secure database. They can be easily accessed for management and resource consent compliance purposes.
Keeping an eye on changing conditions
The shape of water races can change with time and, if this happens, the water level-to-flow relationship must be revised. We regularly gauge water races to check for changes, and, when required, upload any changes to site controllers. This ensures that the controlled flow is kept accurate – critical in high-output schemes such as this, where small changes in relationships can mean a big difference in the amount of water extracted in a given time.
Near real time flow information is displayed on the WIL website.
Our sixth major automated irrigation scheme
NIWA has now installed systems at six large South Island irrigation schemes:
- Morven Glenavy Irrigation (15 cumecs, 6 gate control stations)
- Waimakariri Irrigation (12 cumecs, 14 gate control stations)
- Benmore Irrigation (4 cumecs, 3 gate control stations)
- Glenroy Irrigation (3.5 cumecs, 1 gate control station)
- Spencer-Bower farm (3 cumecs, monitoring only, control later)
- Kakahu Irrigation (1.4 cumecs, 2 gate control stations and 1 monitoring station).