Irrigation Water Management

There are two key aspects to getting the best out of a well-designed irrigation system – effective maintenance and good management.  The combination of these can maximise the on-farm benefits of irrigation, while minimising environmental impacts.  

To help implement this on farm, you can use the HBRC Irrigation Good Management Practices Guidance Document.  This outlines a range of GMP’s for a variety of irrigation and farming systems.  Tailoring this check list and identifying positive actions for your property can also be a good addition to your overall farm planning.

For more information on irrigation good management practices check out the Irrigation NZ website

The purpose of an irrigation evaluation is to check if water is being applied evenly and flag if there is an issue. If poor performance is identified and the reason is not obvious, it lets you know that further investigation is required. 

Why do an irrigation performance evaluation?

There are many reasons to do an irrigation performance evaluation. For a newly installed irrigation system, it’s a way to check that you got what you paid for. This can be part of the irrigation system commissioning test. For an older system, it’s about checking if the irrigation is still operating the way it was designed to. If it’s not working the way it should and you know about it, that’s the first step to getting it fixed.

Like anything mechanical, things break and deteriorate over time. It is very difficult to determine how well a system is working just by looking at it. A performance evaluation gives some guidance about how a system is applying water. 

What is an irrigation performance evaluation?

An irrigation performance evaluation is a way of checking how evenly an irrigation system applies water to the soil (EU: Emitter Uniformity, or DU: Distribution Uniformity). If a system applies water unevenly, then areas of a crop will be over or under irrigated. This can result in:

• inconsistent crop production
• overwatering, potentially wasting water and nutrient to drainage
• underwatering, potentially reducing crop yield
• unnecessary energy use.

A performance evaluation also checks how many millimeters (mm depth) of water is being applied in comparison to what it should be applying.  Depending on whether soil moisture monitoring is being used or not, this can mean over or under irrigation is occurring throughout the block. 

Large spray irrigation systems

For large spray irrigation systems like pivots, linear, or traveling irrigators (guns) we use a ‘bucket test’ to find out the Distribution Uniformity (DU).  Buckets are positioned for the irrigator to go over the top, filling the buckets. The water collected is measured, recorded and processed to calculate the Distribution Uniformity coefficient (DU) and application depth (mm).  

What do the results mean?

The uniformity result is a coefficient between 0-1.  The closer the result is to 1, the more evenly water is being applied, and the better the result. The following table shows how to interpret the result.

How to interpret Bucket Test App Distribution Uniformity results for large spray irrigators:

Drip and micro sprinkler systems

For drip and micro sprinkler systems, which are usually in a grid type pattern, we check for Emitter Uniformity (EU). That is, we collect the flow from 12 individual emitters, in each of three different blocks: The block closest to the pump, the furthest from the pump, and one in the middle. 

Why these blocks? The closest to the pump is usually considered the ‘cleanest block’ where debris in the water is usually flushed away, whereas the furthest block is normally where dirt and grit builds up, affecting the system performance. The third block is a mid-point between the two. The water collected is measured, recorded and processed to calculate the Emitter Uniformity coefficient (EU) and application depth (mm). 

The uniformity result is a coefficient between 0-1.  The closer the result is to 1, the more evenly water is being applied, and the better the result. The following table shows how to interpret the uniformity result.

How to interpret Emitter Uniformity (EU) results for drip and micro irrigation systems:

There are two main levels for checking how well an irrigation system applies water:

• A basic assessment called an Irrigation Calibration (bucket test), or
• A more in-depth assessment called a Full Irrigation Performance Evaluation 

The difference between these options is explained below.

Irrigation Calibration

This is sometimes called a basic bucket test.  The software or App for an irrigation system calibration can be accessed and done by anyone but the assessment is usually done by the irrigator owner or manager, or someone appointed by them.  This type of testing is a simplified version of a full evaluation and is usually enough to answer the question ‘is my system doing what it should or is there a problem that needs fixing?’  if a problem is highlighted, then it might be time to bring in the experts to get to the bottom of it.

Where can I find the information to check my own irrigation system?

For large spray irrigation systems including pivots, linear, and travelling irrigators, check out the CHECK-IT BUCKET TEST APP How to Guide from Irrigation NZ.

For drip and micro irrigation systems, the Irrig8lite software is available for download. Please note, this is old software and may be difficult to download for some networks. Contact Monique Benson at monique@hbrc.govt.nz if you are unable to access this and would like to check your irrigation system. 

Full Irrigation Performance Evaluation 

A full irrigation system performance evaluation can be done by an Irrigation NZ certified Irrigation Performance Evaluator. This type of assessment gathers more data than a basic bucket test. This means that if issues are identified with water application, the evaluator is in a better position to pinpoint the cause of the issue or narrow down what needs further investigation. 

Find a full list of Certified Performance Evaluators at Irrigation NZ.

In many cases irrigation performance can be improved by regular maintenance e.g. unblocking sprinklers, cleaning filters, flushing lines, repairing leaks etc.  It is best to sort the obvious issues first if they are within your capabilities.

Some issues can be more complex to resolve such as excessive pressure loss or inadequate flow for example. If you come across a tricky one, contact your preferred irrigation service provider for advice.

The short answer is a well performing irrigation system means water application can be targeted and controlled more accurately than a poor performing system. This can result in water savings in many situations.

The goal with irrigation is to supply the right amount of water to 7/8th of the crop. The remainder of the crop will be either slightly over or under irrigated.  The more uneven the application of water, the harder it is to reach the goal of getting it right for 7/8th of the crop. More of the crop will be over or under irrigated with a poor performing system.

An case study on two orchards was commissioned by HBRC in 2020 to see how irrigation system maintenance affected irrigation performance and water use. An irrigation performance evaluation was done before and after maintenance to see if any water savings could be achieved.

See the table below for some of the results. One block had issues with the maintenance and faulty equipment that actually made it perform worse. However, the remaining blocks saw a moderate to significant improvement in Emitter Uniformity (EU). It was found that for all the blocks assessed, the instantaneous flow rate changed after maintenance (increase or decrease). This flow rate difference did not necessarily indicate whether water savings would be possible. 

When taken a step further to see how much water would be needed to irrigate 10mm for 7/8th of the crop, it showed that the system with a decline in uniformity resulted in an 8% increase in water use. The blocks that had an improvement in uniformity regardless of changes in instantaneous flow rate (increase or decrease) required less irrigation time, which resulted in water savings (5% and 46%).

This shows that improving irrigation performance can result in water savings in some instances. These water savings are more related to being able to reduce irrigation duration while adequately irrigating 7/8th of the crop, as opposed to changes in instantaneous flow rate. The greatest water savings were seen in blocks with the greatest improvement in Emitter Uniformity.

The results are presented for illustrative purposes only. They are applicable to the blocks and issues presented in this particular assessment and results will vary for different conditions.   

The overarching requirement for efficient water use is in the National Policy Statement for Freshwater Management 2020, specifically ‘Policy 11: Freshwater is allocated and used efficiently, all existing over-allocation is phased out, and future over-allocation is avoided’. 

The requirement to use water more efficiently in Hawke’s Bay is being strengthened through regional plans and water take consents. The proposed TANK plan change for the Heretaunga area of Hawke’s Bay will require consents to reflect ‘actual and reasonable’ water use and there are specific requirements for efficient water use. 

The Tukituki Plan requires good management practices to be implemented. This includes “Irrigation management: To operate irrigation systems that are capable of applying water efficiently and management that ensures actual use of water is monitored and is efficient (including deficit irrigation and consideration of the use of precision irrigation).”

In some areas, water take consents have conditions about checking the performance of irrigation systems and requiring soil moisture monitoring. If you have a water take consent, check what conditions you are required to meet.