Thursday 15 April 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.

The interactive irrigation scheduling tool helps you determine the most productive timing for the next surface irrigation for your unique circumstances.  It uses the same ETo information in the tables below.

 

WEEKLY IRRIGATION REQUIREMENT$ SUMMARY – READER SURVEY – Please complete

• We plan to make some improvements to the Weekly Irrigation Requirement$ Service over coming months
• To ensure these improvements are what you require, it would be great to have your feedback
• If you could possibly find 2 minutes to complete this short Weekly Irrigation Requirement$ reader survey, it would be greatly appreciated. (Thanks!)

 

WEEKLY IRRIGATION REQUIREMENTS

• The ‘water requirement’ for our reference crop of pasture (ETo) over the past 7 days was 20mm (0.20ML/ha), which is 5mm less than the previous week (25mm) and 1mm more than the long-term April average (19mm), at Kyabram. See the tables and graphs below
• Cumulative ETo is forecast to be similar over the next 7 days, at Kyabram.  See the tables and graphs below

 

UPCOMING IRRIGATION WATER AVAILABILITY

 Current water availability

Vic Murray system

• On the Vic Murray system (according to the NVRM web site), there is currently 607 GL of private water available in allocation accounts
• Current total water availability (private, environment and water-corp water) on the Vic Murray is 980 GL.  At the same time last year, this volume was 731 GL

Goulburn system

• On the Goulburn (according to the NVRM web site), there is currently 566 GL of private water available in allocation accounts
• Current total water availability (Private, Environment and Water Corp water) on the Goulburn is 975 GL.  At the same time last year, this volume was 593 GL
• Currently, for the combined Vic Murray and Goulburn total water availability, there is currently about an extra 630 GL available compared to the same time last year

MDBA active storage

• Currently there is 3,900 GL (46%) of MDBA active storage (Dartmouth, Hume, Victoria plus Menindee Lakes) compared to 2,250 GL (27%) at the same time last year

 

NSW & SA allocation outlooks – released today

NSW Murray

• For mean (50%) and dry (75%) inflow scenarios, forecast General Security allocations for the NSW Murray are 23% and 12% respectively on 1 Nov 2021
• The good news is, end-of-year carryover is estimated to be 650 GL (39% of General Security).  For comparison, 350 GL (21%) was carried over on the NSW Murray system into this irrigation season (2020-21)

NSW Murrumbidgee

• With mean (50%) and dry (75%) inflow scenarios, forecast General Security allocations for the Murrumbidgee are 65% and 45% respectively on 1 Nov 2021
• End-of-year carryover is estimated to be close to the maximum allowable limit of 30% of GS entitlement, or 565 GL.  For comparison, 348 GL (18%) was carried over on the NSW Murrumbidgee system into this irrigation season (2020-21)

SA Murray

• Under every inflow scenario other than the worst-case and extreme dry, the opening allocation on 1 July 2021 is likely to be 100% on the SA Murray

• Carryover will not be permitted into 2021-22, because the projected minimum opening allocation is greater than 50%

Menindee Lakes

• The Menindee Lakes system has started to receive inflows from the Barwon-Darling system
• Menindee Lakes currently holds about 330 GL (19% full) and forecasting estimates show that inflows in excess of 400 GL in total are possible
• The Menindee resource becomes shared with other States when the system next holds more than 640 GL, until it falls to 480 GL

 

Streamflow forecasts

• The current BoM streamflow forecast for April to June for
  – Hume Dam is for average inflows
  – Lake Dartmouth is for above average inflows
  – Lake Eildon is for above average inflows

 

Catchment condition

• Rootzone soil moisture (0-1m) in the
  – upper-Murray catchment is currently average to above-average compared to long-term values through the year
  – upper Goulburn catchment is currently average compared to long-term values through the year

 

GOULBURN TO MURRAY WATER TRADE REVIEW

• A recording of the AgVic “Goulburn to Murray Water Trade and Murray Delivery Risk” webinar (and a summary of the key messages delivered) can be viewed by clicking on the hyperlink
• Visit the Engage Victoria website to make a submission or to participate in a public consultation session

 

UPCOMING EVENTS

Understanding your electricity bill and supply

• The new AgVic energy webinar series will ‘kick off’ with the focus topic of “Understanding your electricity bill and supply” at noon, Wednesday 21 April

 

ACCC Murray-Darling Basin water markets inquiry

• A summary of the ACCC MDB water markets inquiry findings and recommendations will be presented in a webinar conducted by the NSW Department of Planning, Industry and Environment at 2pm Friday 23 April

 

SOIL TEMPERATURE

• The soil temperature measured by a capacitance probe at 9am today (Thursday 15 April) under ‘surface irrigated pasture’ at 10cm depth at Lancaster was 13oC, 4oC cooler than last week (8 April)
• This time last year (15 April 2020), the soil temperature at the same site was also 13oC

 

LAST WEEK’S REFERENCE EVAPOTRANSPIRATION (ETo)⁺ – Pasture Irrigation Requirement$

 Weekly Totals – Thurs 8 Apr to Wed 14 Apr 2021      

Location	ETo+ (mm)	Rainfall~ R (mm)	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*	30	0	30	1	4.2	11	30
Kyabram*	20	0	20	1	2.9	16	20
Tatura*	23	0	23	1	3.3	14	23
Kerang#	20	0	20	1	2.9	15	20
Echuca#	18	0	18	1	2.6	16	18
Yarrawalla#	19	0	19	1	2.7	16	19
Numurkah#	18	0	18	1	2.6	16	18
Mildura*	29	0	29	1	4.1	12	29

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 (April) for each 2.7mm of effective rain on your property, typically an extra day can be added to the “required surface irrigation interval” for pasture.

 

NEXT WEEK’S FORECAST REFERENCE EVAPOTRANSPIRATION (ETo) – Pasture Irrigation Requirement$^¥

Weekly Totals – Thurs 15 Apr to Wed 21 Apr 2021

Location	ETo (mm)	Rainfall R (mm)	ETo – R (mm irrigation required)	Average ETo (mm /DAY)	Required Surface Irrigation Interval (Days)	> Spray irrigators will need to apply (mm)
Deniliquin	26	0	26	3.7	13	26
Kyabram	21	2	19	3.0	15	19
Tatura	20	3	17	2.9	16	17
Kerang	25	2	23	3.6	13	23
Echuca	24	2	22	3.4	14	22
Yarrawalla	24	2	22	3.4	14	22
Numurkah	23	3	20	3.3	14	20

 

DAILY ETo and rainfall – last week & next week

  

 

 SWAN SYSTEM 7-DAY FORECAST for Pental Island – near Lake Boga.  (Free daily email service for practically any location.)

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You can follow on Twitter and Facebook or to receive this weekly post as a weekly email contact  robert.oconnor@agriculture.vic.gov.au

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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.

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.

 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.

If you have any questions, comments or feedback related to this service please don’t hesitate to contact me, robert.oconnor@agriculture.vic.gov.au

If you would like to receive this information as a weekly email, please request to robert.oconnor@agriculture.vic.gov.au

AgVic also provides weekly ET email updates for North East Victoria (contact dennis.watson@agriculture.vic.gov.au), the Mallee (maxine.schache@agriculture.vic.gov.au) and the Macalister District (alexis.c.killoran@agriculture.vic.gov.au).  Alternatively, irriSAT (Ctrl click) is an Australian web based irrigation scheduling tool that uses satellite ‘vision’ to tailor irrigation scheduling for your paddocks and crops.

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⁺ 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.

 

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