2.3.4 - How much water do I use for irrigation?
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Irrigation water can come from a number of sources i.e. channel supply, groundwater, drains, and streams. To calculate how much water you apply to the area of perennial pasture on your farm all these sources have to be considered (Table 2.4). Water that is recycled from your farm’s drainage reuse system should not be included in your water budget. But if runoff from your pasture area is used to irrigate a crop elsewhere outside the area, then an allowance for this would need to be made. If your runoff is not used for irrigation, it should be included as water use. This is an obvious area for improvement.
Table 2.4. Annual water budget for irrigated area (example)
Water source ML | |
| Channel supply water (ML) | 200 |
| Bore water (ML) | 100 |
| Drainage diversion (ML) | 50 |
| Stream diversion (ML) | 10 |
| Runoff used elsewhere (deduct) (ML) | -20 |
| Total (ML) | 340 |
The total volume of applied irrigation water in Table 2.4 needs to be divided by the irrigated area to calculate the irrigation intensity in the area.
i.e. Irrigated area = 30 ha
Irrigation intensity 340/30 = 11.3 ML/ha
It is important to note that it is difficult to get accurate measurements of applied irrigation water and (even more so) runoff. Many water meters are often only accurate to within about +5%.
If you don't have a record of your water use, your Rural Water Authority should have a record.
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