2.3.7.1 - How much water can I potentially save?

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Potential water saving = current irrigation use – irrigation requirement.

You may be able to save water if your current irrigation use is greater than your irrigation requirement. The larger the difference, the greater the potential saving.

This can be illustrated by the following case studies. Note that the irrigation water use figures differ slightly from Table 2.3, because the rainfall at the case study varied from that recorded at the centres shown in Table 2.3.

Table 2.6 - Case study - potential water savings - (Nathalia)

Year	Irrigation water use ML/ha	Irrigation requirement ML/ha	Potential water saving ML/ha
1	8.2	6.6	1.6
2	11.7	8.6	3.1
3	9.1	7.4	1.7
4	10.8	9.7	1.1
5	10.8	8.5	2.3

The data in the table above suggest that too much water has been applied on this farm. The excess water has either run off the farm and/or has been lost to the watertable under the farm. In the latter case this may have caused pasture losses through waterlogging and would have contributed to potential salinity problems caused by a rising watertable.

There is potential to save some 2 ML/ha on this farm.

Table 2.7 - Case study - limited water savings - (Katamatite)

Year	Irrigation water use ML/ha	Irrigation requirement ML/ha	Potential water saving ML/ha
2004/05	8.8	8.0	0.8
2005/06	9.8	8.9	0.9

This indicates that there is limited potential to save water on this farm. However, there is considerable uncertainty in estimates of both applied irrigation volumes and the irrigation requirement. It is recommended that you discuss your farm scenario with a DPI irrigation extension officer or a specialist private consultant.

If you are applying less water than the irrigation water requirement, your pasture will occasionally/often be stressed, and not growing to its potential.

Summary

Irrigation systems will never be 100% efficient (efficiency being the proportion of the applied water used by the crop/pasture). Consequently you cannot expect to exactly match your water use to the irrigation requirement. A really well designed and managed border-check irrigation system may achieve 95% efficiency. That is, approximately 0.5 ML/ha of water is applied in excess of the 8 to 9 ML/ha irrigation requirement over a season. However, in practice it is more realistic to aim for an excess of no more than 1.0 ML/ha, or 90% efficiency/

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