Weekly Irrigation Requirements – Northern Victoria





Friday 20 April 2018

Weekly Irrigation Requirement$ Summary – Driving Water Productivity

This update provides ‘reference evapotranspiration’ (ETo) data to assist with improved irrigation scheduling for top growth rates and yields.

This interactive Irrigation Scheduling Tool helps you determine the most productive timing for the next irrigation for your unique circumstances.

Irrigation commentary

Recent water requirements

  • ETo over the past 7 days returned to more typical autumn values after the heat-wave experienced a fortnight ago
  • Wednesday 11 April was the hottest day on record for a large part of northern Vic and southern NSW

Rainfall in the hills last weekend

  • Mount Bulla received the highest Victorian rainfall total last week of 153mm
  • Most of the catchment area in the hills for Lakes Hume, Dartmouth and Eildon received between 15mm to 50mm
  • Unfortunately the rain fell on dry catchments and limited streamflow responses were observed in the upper Murray
  • Flow in the upper Mitta Mitta at Hinnomunjie Bridge peaked at 550ML/day following the rain and is now 360ML/day
  • For more details go to https://www.mdba.gov.au/river-information/weekly-reports

Review of Effectiveness of Victoria’s Water Markets

The above DELWP report was released yesterday and outlines:

  • That the water market in northern Victoria is largely working effectively, but needs to continue to develop to match changing demand and sophistication in the market
  • Water market information and communications will be improved in future to help water users better understand the market and how it works
  • The water market will be monitored and settings will be changed when necessary to support the needs of water users
  • Market transparency will be increased to maintain confidence in already robust compliance and enforcement systems
  • It is important that work continues to improve the attractiveness of irrigation districts for investment
  • To view the report go to http://waterregister.vic.gov.au/

Soil temp

  • The soil temperature (as measured by a capacitance probe) at 9am this morning under irrigated pasture at Lancaster at 10cm depth was 14oC, 2oC cooler than last week
  • The soil temperature (as measured by a capacitance probe) at 9am this morning under dried-off perennial pasture at Yarrawalla at 10cm depth was 14oC, 3oC cooler than last week. This time last year the soil temperature at Yarrawalla was 14oC

Last Week’s Reference Evapotranspiration – Pasture Irrigation Requirement$

Weekly Totals –  Fri 13 April to Thu 19 April, 2018

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* 27 0 27 1 3.8 13 27
Kyabram* 18 7 11 1 2.6 18 11
Tatura* 20 7 13 1 2.9 16 13
Kerang# 19 2 17 1 2.7 16 17
Echuca# 17 8 9 1 2.5 17 9
Yarrawalla# 18 8 10 1 2.6 17 10
Numurkah# 18 4 14 1 2.5 17 14

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

The “required surface irrigation interval” shown in these tables is based only on cumulative ETo and needs to be considered in conjunction with rainfall on your farm.  For example, this time of the year (April) for each 3mm of effective rain that falls on your property, typically an extra day needs to be added to the “required surface irrigation interval.”

ETo during April at Kyabram over the previous 7 years has averaged 19mm /week or 2.7mm /day (BoM ETo).  Average ETo for the previous month of March  (for the previous 7 years) is 32mm /week or 4.5mm /day.

Next Weeks Forecast Reference Evapotranspiration – Pasture Irrigation Requirement$¥

Weekly Totals –  Fri 20 April to Thu 26 April, 2018

Location ETo





ETo – R

(mm irrigation required)

Average ETo
(mm /DAY)
Required Surface Irrigation Interval (Days) > Spray irrigators will need to apply  (mm)
Deniliquin 25 0 25 3.6 13 25
Kyabram 22 0 22 3.1 15 22
Tatura 21 0 21 2.9 16 21
Kerang 25 0 25 3.6 13 25
Echuca 23 0 23 3.3 14 23
Yarrawalla 24 0 24 3.4 14 24
Numurkah 22 3 19 3.2 15 19

 Daily ETo & rainfall – last week & next week




You can follow on Twitter and Facebook or to receive this weekly update as an email, contact robert.oconnor@ecodev.vic.gov.au


* ETo and rainfall data sourced from Bureau of Meteorology http://www.bom.gov.au/watl/eto/

# 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. http://www.longpaddock.qld.gov.au/silo/index.html

+ Reference evapotranspiration (“ETo”).  Refer to the ‘Important Background Information’ section above.

~Rainfall R.”  Where a rainfall event is less than 2mm it is unlikely to be listed.  In practice it is not always be the case that all rain contributes to plant available moisture reserves and is available for plant growth.  Any rain in excess of that which fills the soil profile (or reduces ‘cumulative ETo-R’ back below the estimated RAW) 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.”  Refer to the section above “Crops Other Than Pasture”, for more information.

^ 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.  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.)  The “required surface irrigation interval” is based only on cumulative ETo and needs to be considered in conjunction with past and forecast rainfall for your farm.
> 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.  Unfortunately this is a ‘fee for service’ arrangement and the forecast ETo figures are not publically available.


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