Weekly Irrigation Requirements – Macalister Irrigation District (Gippsland)

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MID ETo Update
10-16 September 2020



    • Flood irrigation interval for the last week was 14 days
    • Spray irrigation amount was 18 mm of irrigation water for the last week
    • The predicted weekly pasture water use:
      • Bairnsdale is 24 mm, MID 24 mm, Orbost 26 mm and Yarram 20 mm
    • Glenmaggie is at 90.4%

    * These figures are approximate and do not take into account rainfall on farm*


The Odd Spot

Incentives deadline approaching
The deadline for completion of all open irrigation incentive projects is the 30th of September. Please give us a call on 5147 0800 if you need to talk about timelines.

Time to Irrigate
As soils are drying out now is the time to be irrigating if you haven’t irrigated already. It has been at least three weeks since a decent rainfall event. Over the past three weeks we have had an average of 59 mm of evapotranspiration in the MID.

The below graph illustrates the significant loss of moisture from the soil profile over the last three weeks, and the response to a flood irrigation event.


ETo – Last Week Totals

Location ETo (mm) Effective Rain * mm (R) Dairy pasture coefficient Required Irrigation mm (ETo – R)
Boisdale 18 0 1 18
Cowwarr 17 0 1 17
East Sale 18 0 1 18
Nambrok 20 0 1 20
Tinamba 16 0 1 16


Location ETo (mm) Effective Rain * mm (R) Dairy pasture coefficient Required Irrigation mm (ETo – R)
Bairnsdale 18 0 1 18
Latrobe Valley Airport 17 2 1 15
Orbost 16 3.4 1 12.6
Yarram 16 7.8 1 8.2


Tip:  To convert mm to megalitres/ha, divide by 100.  Eg. 50mm = 0.5ML /ha.
* Effective rainfall = daily rainfall minus 2mm.
ETₒ   and the “crop coefficient” (conversion factor) of 1.0 applies to a healthy productive pasture 12 cm high.
** This data is not included when doing any of the below calculations
MID average daily pasture water use over the last week was 2.5 mm/day.

The approximate MID flood irrigation interval based on last week’s daily pasture water use rate was 14 days. (This figure assumes that 30 mm of readily available water is held in the pasture root zone divided by the 2.5 mm/day = 12 days and then add an extra two days to account for waterlogging). This does not take into account any rain your farm may have got during the week which will extend the interval.

Spray irrigators in the MID needed to have applied on average 18 mm of irrigation water for the week to meet pasture water use (2.5 x 7). This irrigation figure does not take into account any rainfall on your farm, which must be subtracted from the required irrigation figure, and assumes that the spray irrigation system is applying water at 100% uniformity. This figure may be greater depending on the specific spray irrigation system uniformity.


For Thursday 17 September to Wednesday 23 September


Location Predicted weekly pasture water use (mm/ha) Predicted Weekly Pasture water use (ML/ha) Predicted daily pasture water use (mm/day)
Bairnsdale 24 0.24 3.4
MID 24 0.24 3.4
Orbost 26 0.26 3.7
Yarram 20 0.2 2.9


This ETo update is also available as an email. Contact james.paulet@agriculture.vic.gov.au

The intention of this service is not for the information to be used in isolation when making decisions about irrigation
This publication is provided solely for information purposes and no representation or warranty is made as to its quality, accuracy, completeness, suitability or fitness for any particular purpose. You should make your own inquiries as to its appropriateness and suitability for your particular circumstances. The State of Victoria as represented by its Department of Jobs, Precincts and Regions accepts no duty of care and disclaims all liability in relation to use of this publication.
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