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