Irrigation low-cost ways of improving the efficiency of water use

July 2007
Historically, water management has been in the hands of catchment boards and regional councils but now the irrigators and the water users are taking more responsibility. They have formed Irrigation New Zealand that, amongst other things, is working to develop better water management systems and help regulators with collecting required information on water supply and use.

Many of the physical structures, like gates and channels, have been in existence for some time. What is new is the development of remote monitoring and control through electronics, hydraulics, and some simple control measures like creating ponds.

NIWA has developed the electronics over the years for a variety of purposes, and helped with the adaptation of the technology to irrigation. Local companies in many areas have supplied hydraulics, and individual irrigation schemes have put in place appropriate combinations of low and high technologies to enhance control of water and hence the efficiency with which it is used.

Dennis Jamieson, a NIWA engineer based in Christchurch, says that over recent years NIWA has been in touch with the various irrigation schemes in Canterbury where the people running schemes are looking at ways of improving their water use, sharing the water more effectively, and generally getting better control over what they are doing.

The approaches to us were about automating the equipment for canal gates. The problem was how to get the right amount out of the main canal flowing through so it can be most effectively used by farmers, says Dennis.

Our approach was to adapt devices that have been used for a long time for measuring flows in lakes and rivers around New Zealand. They tend to be low in power use, reliable in remote situations, and have data logging capabilities, so they can make information available to the scheme operators both in the short and long term so that they can keep making improvements.

The first step was to demystify the control gates and systems: the technology is available locally particularly the hydraulics to control gates, the electronic equipment is well proven and it can be customised.

The next step is to get a number of these control gates and sites talking to each other and it isn't that difficult, the Waimakiriri scheme has a website, the others are in a transitional phase between manual control, with people running around altering control gates, and remote control using a higher level of automation.

NIWA installed a number of gates around Canterbury and Dennis says they observed that the water users are making very effective use of the control systems, combining them with other low-cost methods such as building storage ponds within the canal systems. The measures adopted are appropriate to current levels of profitability, but he sees that in higher-profit situations more pipe systems and higher cost systems could be justified. The, he says, is that the users decide on what is appropriate for them and call on NIWA and consultants for help.

They are the ones that are familiar with farm operations they are subject to resource consent restrictions and so they are able to put that mix together, get some extra technology options and come up with solutions that would not otherwise be thought of, he says.

Monitoring devices on control gates essentially monitor how much water goes through, and when.

Dennis: We use our experience from working in channels to find places where flow can be measured, and that might involve putting in a very simple concrete structure to provide a controlled cross-section and then putting in a very low-cost level sensor and logger. Information from that it is fed back to the control gate which regulates itself to provide the required flow downstream. Built into it is the data logger that collects information on what is going on.

Other developments and improvements include the actual control gate itself, many of which are quite old and based on proven design. The control systems are provided by hydraulics companies that are based in a lot of smaller towns in Canterbury. The result is a combination of local innovation with proven technology that by chance has come out of an area of science where it has been applied for a long time, and the net result is low-cost but effective.

Managing for interruptions to supply: Irrigation systems can be subject to unexpected interruptions due to, say, damage to the intake or there failure of an on-farm system that leaves some extra water continuing on down the canal. The system has to be able to deal with short-term loss of supply at the intake or with any extra water coming through. In many cases it is not possible to bypass that water into nearby rivers, so it needs to be stored to give the scheme operators time to adjust and find other places for the water to go.

Also during the season grass may grow in canals or sediment move around in them so the hydraulic properties of the canals change slightly over time and, rather than spend a lot of time modeling them and continuously taking measurements, putting some ponds in the system allows those changes to be managed around without too much effort.

Increased collaboration needed in future: Greater pressure on water supplies is going to mean closer collaboration between individual irrigators and between irrigation schemes within council areas, sharing information and helping to allocate and use water supplies as agreed, particularly during times of shortage.