*2.1. Irrigation Water Distribution Systems*

Irrigation has been practiced for many decades in Australia, especially in the Murray Darling Basin (MDB) (Figure 1), which consumes about two-thirds of the water abstracted for irrigation of crops and pasture [2]. The bulk of the water in the basin is delivered to irrigators by private and farmer-owned companies. Murray Irrigation in the MDB, which supplies water to 2300 farms with a total area of 748,000 ha is the largest in the country. Other large companies include Murrumbidgee Irrigation and Coleambally Irrigation Co-Operative Limited, which supply water to the Murrumbidgee Irrigation Area and the Coleambally Irrigation District, respectively.

In the last few years, irrigation water in the MDB has been largely conveyed via open channels. In addition, a significant portion of the infrastructure supporting irrigation, with some built in the early years of the last century, have started to age and become inefficient. From the WUE perspective, irrigation water conveyed via open channels is of interest because of the associated losses. Hence, the Federal and State and Territory Governments developed the Murray Darling Basin Plan and embarked on a program of modernising and automating this critical infrastructure, as discussed below.

Seepage losses, particularly in earthen open channels, may consume up to approximately 14% of the total water supplied to an irrigation scheme. Evaporation losses, especially in large open channels, may also be considerable [7], especially in arid parts of Australia. Therefore, one of the priorities of the modernisation plan of the MDB was to reduce these losses using a variety of methods including lining the canals with clay or rubber, repair of earthen and concrete channels, installation of gravity pipelines in place of open channels, and upgrade of on-farm irrigation infrastructure (discussed in greater detail in the next subsection). One example of such a project undertaken in the MDB from 2011

to 2015 is the Trangie-Nevertire Irrigation Scheme, which returned about 40% of the original water entitlements, significantly reduced water losses, and improved the water delivery efficiency from about 65% to 93% [8].

**Figure 1.** The Murray Darling Basin, which consumes about 70% of the water abstracted for irrigation in Australia.

A critical step towards improving the WUE is the ability to accurately measure the amount of water supplied to irrigators. This is in line with the saying that goes: "You cannot manage what you cannot measure." However, previous research undertaken in Australia showed that inaccurate flow measurement techniques, for instance using the Dethridge wheels, led to the supply of irrigation water in excess of entitlement volumes. A study by Goulburn Water [9] showed that large Dethridge wheels operated with inaccuracies of between −18% to +3%. Hence, regulatory requirements were put in place to ensure that irrigation water meters operate at an acceptable level of performance [10]. The requirements include pattern approval by the National Measurement Institute (NMI) and the ability of the meters to perform within maximum limits of error of ±5% in field conditions. The irrigation modernisation program involved the replacement of Dethridge wheels with water meters that were compliant with these regulations.

The above examples, therefore, demonstrate the opportunities for improving the WUE before the water is delivered to the farm and provide an indication of the magnitude of savings that have occurred in specific projects. There are still many irrigation enterprises that rely on open and unlined channels for their water supply, although statistics on their proportion are not immediately available. Some of the strategies used to modernise and automate flow of water in irrigation canals are also used on-farm to control the flow of water to different portions of the field. These include automatic regulators or gates and telemetry systems. These are discussed in the next subsection.
