This project is supported by Perth Region
NRM, through funding from the Australian
Government’s Caring for our Country.
Irrinote Factsheet 5
WATER BUDGET AND SCHEDULING
1mm = 1L
1m2
Question: What does it mean?
Answer: 1 litre of water applied evenly to 1 m2, is equivalent to
1mm of irrigation.
Note: 1 mm of water applied to the surface of a soil will soak in more than 1mm. Deeper in
sandy soils, shallower in heavy soils.
Question: How do I use this formula?
Answer: If you have a meter on your bore/pump, you can work out
the millimetres (mm) of irrigation applied, by dividing the volume (L)
by the irrigated area in square metres (m2).
For example, if your meter measures volume in kilolitres (kL) or cubic metres
(m3), and your pump delivers 45 kL (or 45 m3) over a wetted area of 1.4 ha, the
depth of irrigation applied (in mm) will be: 45,000 ÷ 14,000 m2 = 3.2 mm.
*This example assumes water is applied over the entire field area (eg. overlapping solid set). For
drip, non-overlapping sprinklers, and under-tree jets/spinners, the wetted area will be much
smaller and will need to be adjusted accordingly.
We can also rearrange the above formula to estimate:
a) Volume of water required to apply a given depth of irrigation over a
known area
Volume (L) = Area (m2) x Depth (mm)
b) Area of crop that can be grown using a defined volume of water and
known irrigation depth
Area (m2) = Volume (L)
Depth (mm)
Perth Region NRM Inc.
Perth Region
NRM
80 Great Northern Highway (Corner Bishop Road)
MIDDLE SWAN WA 6056
Tel: (08) 9374 3333 Fax: (08) 9374 0685
Email: enquiries@perthregionnrm.com
www.perthregionnrm.com