Weekly Irrigation Requirements – Northern Victoria



*Weekly Irrigation requirements will recommence at the beginning of the next irrigation season

Thursday 13 May 2021

Weekly Irrigation Requirement$ Summary – Driving Water Productivity

This update provides ‘reference evapotranspiration’ (ETo) information to assist with improved irrigation scheduling for top yields and high water productivity.

This is the last Weekly Irrigation Requirement$ Summary for the 2020-21 season.  Many thanks to you, the reader – we hope these updates have been useful.  And may the lakes keep filling!

This interactive irrigation scheduling tool uses the same data in the ET tables below.



  • The ‘water requirement’ for our reference crop of pasture (ETo) over the past 7 days was 12mm (0.12ML/ha), which is 4mm less than the previous week (16mm) and 1mm more than the long-term May average (11mm), at Kyabram. See the tables and graphs below
  • For most locations, cumulative ETo is forecast to be about the same over the next 7 days.  See the tables and graphs below
  • Unfortunately, no significant rain is forecast over the next 7 days at this stage.  See the tables and graphs below



  • The total ‘water requirement’ for our reference crop of pasture over the 2020-21 season (1 July 2020 to 12 May 2021) for our reference crop of pasture (ETo) was 1,235mm (12.3 ML/ha), at Kyabram
  • Over this period 295mm of rainfall was recorded at Kyabram, indicating 940mm (9.4 ML/ha) of irrigation was required on good pasture. ie. 1,235mm – 295mm = 940mm
  • Irrigation requirements for 2020-21 and the previous four years are summarised in the table below



Menindee Lakes

  • WaterNSW have increased their estimate that 800 to 1,000GL of inflow may reach the Menindee Lakes as a result of flow in the Darling River
  • Menindee Lakes storage is currently at 755GL, meaning that the 640GL threshold has been reached and the water held in storage is shared evenly between the Victorian and NSW Murray, until the Lake volume falls below 480GL
  • In mid-October 2016, Menindee storages passed 640GL triggering the water share agreement until mid-December 2017.  In this time, 468GL was released for entitlement holders, 225GL was released for the environment and 800GL was lost to evaporation and seepage


Climate outlook released today

  • The BoM climate outlook is for wetter than average conditions for July to August, but drier for the next fortnight.


Seasonal streamflow forecast – released today

  • The BoM seasonal streamflow forecast for May to July for:
    – Hume Dam, is for ‘average to just below average’ inflows
    – Lake Dartmouth, is for ‘average to below average’ inflows
    – Lake Eildon, is for ‘average to just below average’ inflows



  • Monash University and the BoM are currently conducting a study on providing early warning information for droughts in localised areas in the Murray Darling Basin, and would like to talk to farmers about it
  • If you are a farmer and are willing to share 15 minutes of your time to chat about your experiences and needs, please respond to robert.oconnor@agriculture.vic.gov.au



  • The soil temperature measured by a capacitance probe at 9am today (Thursday 13 May) under ‘surface irrigated pasture’ at 10cm depth at Lancaster was 11oC, 1oC less than last week (6 May)
  • This time last year (13 May 2020), the soil temperature at the same site was 10oC



 Weekly Totals Thurs 6 May to Wed 12 May 2021

Location ETo+





ETo – R

(mm irrigation required) 

Dairy x pasture crop coefficient Average^ ETo
 (mm /DAY)
Required@ Surface Irrigation Interval (days) Spray> irrigators needed to apply (mm)
Deniliquin* 18 2 16 1 2.6 17 16
Kyabram* 12 0 12 1 1.7 26 12
Tatura*   12 3 9 1 1.7 25 9
Kerang# 14 3 11 1 2.0 21 11
Echuca# 14 2 12 1 2.0 21 12
Yarrawalla# 13 4 9 1 1.9 22 9
Numurkah# 14 5 9 1 2.0 21 9
Launceston Tas* 11 7 4 1 1.6 27 4

Tip:  To convert mm to megalitres /ha, divide by 100.  Eg. 50mm = 0.5ML /ha

Important:  The “required surface irrigation interval” shown in these tables is calculated only using cumulative ETo and needs to be considered in conjunction with rainfall on your farm.  For example, this time of the year (May) for each 1.6mm of effective rain on your property, typically an extra day can be added to the “required surface irrigation interval” for pasture.



Weekly Totals Thurs 13 May to Wed 9 May 2021

Location ETo





ETo – R

(mm irrigation required)

Average ETo
(mm /DAY)
Required Surface Irrigation Interval (Days) > Spray irrigators will need to apply (mm)
Deniliquin 15 0 15 2.2 20 15
Kyabram 12 0 12 1.6 26 12
Tatura 11 0 11 1.6 27 11
Kerang 15 0 15 2.1 21 15
Echuca 13 0 13 1.9 23 13
Yarrawalla 13 0 13 1.9 23 13
Numurkah 13 0 13 1.8 24 13


DAILY ETo and rainfall – last week & next week



SWAN SYSTEM 7-DAY FORECAST for Koroop – near Kerang.  (Free daily email service for practically any location.)



The intention of this service is not for this information to be used in isolation when making decisions about irrigation timing.  ETo data provides another handy tool in your irrigation ‘tool box’ and needs to be used in conjunction with other preferred scheduling methods and updated weather information.


You can also follow on Twitter and Facebook.


For more detail about using evapotranspiration data refer to this Agriculture Victoria fact sheet “What is evapotranspiration and how do I use it to schedule irrigations or this scientific booklet.

 Here’s a top offer!  If you would like 7-day forecast ETo (and rainfall, temperature and wind) for any selected location/s emailed to you daily for free, please click here.

irriSAT is an Australian web based irrigation scheduling tool that uses satellite ‘vision’ to tailor irrigation scheduling for your paddocks and crops.


+ Reference evapotranspiration (“ETo”).  Refers to the evapotranspiration from an actively growing, well-watered, grass stand 120mm in height.

* ETo and rainfall data sourced from the  Bureau of Meteorology

# ETo and rainfall data sourced from the Queensland government’s SILO web site based on climate data provided by the Bureau of Meteorology.  This is “triangulated” data – based on calculations and measurements from the closest weather stations which are not on-site.  Comment: SILO ETo data generally appears to be slightly lower than BOM ETo data.

~Rainfall R.”  Where a rainfall event is less than 2mm it is usually not ‘effective’ and unlikely to be listed.  Any rain in excess of that which fills the soil profile (or reduces ‘cumulative ETo-R’ back below the estimated RAW) also needs to be disregarded.  Because rainfall can vary over short distances, irrigators are encouraged to collect and use their own rainfall figures for their farm.

x  “Dairy pasture crop coefficient.”  For crops other than pasture refer to this Tech Note for discussion of an appropriate crop coefficient “What is evapotranspiration and how do I use it to schedule irrigations?”

^ The “Average (daily) ETo” is simply calculated by dividing the total weekly cumulative ETo by 7 days.
@ To calculate the “Required surface irrigation interval” it is assumed there is 40mm of ‘readily available water’ in the pasture root zone.  eg.  Required surface irrigation interval = 40mm  ÷  average (daily) ETo, plus 2 days to allow for excess water to drain away following a surface irrigation event.  (Where SILO ETo data is used – Kerang, Echuca, Yarrawalla and Numurkah, 1day is added rather than 2 days because SILO ETo figures are appearing to be slightly lower than BOM ETo figures.)
> Spray irrigators need/ed to apply.”  This figure is based only on evapotranspiration minus rainfall (“ETo – R”) and assumes a good spray uniformity and, application efficiency.  If a spray irrigation system has compromised spray uniformity or application efficiency, then more water will need to be applied to best meet plant needs.   Typically, with pressurised irrigation systems, irrigations will be applied more regularly than once per week in summer to optimise plant growth.

¥Next weeks forecast reference evapotranspiration – pasture irrigation requirement.”  These figures are sourced from the BOM.  This is a ‘fee for service’ arrangement and these specific forecast ETo figures are not publicly available.  If you would like 7-day forecast ETo (and rainfall, temperature and wind) for any selected location/s emailed to you daily, click here.


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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