At the block
Micro sprinklers and drip systems
At each block, measurements are taken so that the distribution uniformity (DU) of the micro sprinklers or drippers can be calculated. This is done by taking pressure and flow measurements at 16 points around the block. A high DU means the system is applying water evenly, and that any soil moisture monitoring gear installed is providing a representative indication of soil moisture status.
The flow rate of the drip emitters or micro sprinklers is recorded by measuring the output from an emitter over a set period of time so that the flow can be calculated in litres per hour (L/h).
Pressure is measured by inserting pressure point adapters into the poly line or dripline at the selected points around the block. A pressure gauge with a needle attachment is inserted into these adapters to take the readings. The adapters are left in the line for the grower to use for later pressure tests.
This data can then be used to calculate the total water flow to the block. The number of laterals running to any other blocks (and the total number of emitters and output) at the time of the test needs to be recorded in order to account for the total water flow for the particular irrigation shift.
Solid set systems
A grid of catch-cans is set up and the volume of water collected over a set period of time is measured to assess the distribution uniformity of a solid set system, like those used for vegetable crops. This grid collects the output from four sprinklers located on two adjacent lateral lines. Pressure and flow measurements are recorded while the system is running, at six locations around the block using a pressure gauge with an appropriate fitting and timing the flow into a 20L container. Two of these measurements should be at the closest and most distant point from the sub-main.
The measurement points and the catch-can grid location are plotted with GPS device. The total number of sprinklers operating is counted, including those which may be running in other blocks at the time of the test. The sprinkler type and spacing is also recorded.
Centre pivot systems
With centre pivot irrigation systems, like those used by dairy farmers and some vegetable growers, the assessment is essentially the same with pressure and flow being measured at the pivot point and pressure recorded at the end of the pivot.
Catch-cans are placed along the length of the pivot and the volume of water collected in each can is recorded after the pivot has passed over them.
The speed of the pivot is recorded by the time it takes the outer wheel to travel between two marked points (usually 10m). The flow at the pivot point is recorded using an ultrasonic flow meter or information from the controller. A properly set up pivot will have a pressure gauge at the pivot point and on the end of the last span.