# Converting Readily Available Water to litres for drip irrigation

Page last updated: Friday, 28 August 2020 - 2:36pm

Please note: This content may be out of date and is currently under review.

## Calculating irrigation time

Irrigation time can be determined from the volume of water that can be held in the root zone wetted area and the discharge rate of the drippers.

Irrigation time (hours) = Volume RAW (L) ÷ dripper discharge rate (L/hr)

### Examples

Example 1

Overlapping drippers with a RAW of 63 litres per tree, 2L/hr drippers spaced 0.5m apart. Each tree has access to the full 3m wetted length between trees.

• 3m wetted length ÷ 0.5m dripper spacing = 6 drippers per tree
• 6 drippers per tree x 2L/hr drippers = 12L/hr/tree
• 63L/RAW/tree ÷ 12L/hr/tree = 5.25 hours irrigation time.

Example 2

Non-overlapping drippers with a RAW of 1.8 litres per dripper and 8L/hr drippers.

• 1.8L/RAW/dripper ÷ 8L/hr =0.225 hours = 13.5 minutes

(Multiply time in hours by 60 to determine the number of minutes.)

Using RAW to determine irrigation time will give the maximum time you need to irrigate to refill the Readily Available Water. If your soil dries out beyond the moisture content that is considered readily available to your crop, irrigate for a longer period of time.

### Measuring dripper discharge

Although manufacturers specify the expected output of drippers, check actual output rates as your system may be operating at a different pressure or be affected by blockages and wear. Check discharge by digging a hole under the dripper and use a container to measure the volume of water emitted over a known period. Randomly check drippers across the irrigation system, including drippers close to and furthest from the mainline.

#### Acknowledgement

This material was adapted from a similar publication produced by the Queensland Fruit and Vegetable Growers Water for Profit project.

It replaces Farmnote 542 'Converting Readily Available Water to litres for drip irrigation' by Helen Newman.