4 Pre-Season Checks
4.1 WELLS AND PUMPS
The most common question asked about wells and pumps is whether or not they should be tested.
For irrigation systems with high system capacities, a small loss of pumping performance may not be an issue. For systems with limited system capacities, a drop in performance may be very serious indeed, because it could result in significant water shortages and yield losses.
If your pump and well was properly tested at the time of installation, and you have data to show that the current performance is close to specification, then the answer is probably no, you don’t need to test it. Properly installed pumps that are pumping clean water can run for many years without problems.
If your system has dropped in performance, for example by failing to run the irrigation system at the correct pressures, then a pump and well test is recommended.
All wells and pumps deteriorate over time. The rate of deterioration depends on the age of the well and pump, water quality, screen type, and operating conditions. The loss of performance is usually a gradual process, and unless hard data through testing was provided at the time of installation, it can be difficult to know whether the performance has changed. It is also difficult to know which factors are contributing to loss of performance where this has occurred. Possible reasons are water level changes or aquifer depletion, pump wear, screen blockages, casing failure, or contamination.
Pump repairs can be kept to a minimum if these repairs are carried out while problems are small. Major failures, particularly with submersible pumps, can be expensive to correct.
Irrigation systems with water meters installed are relatively easy to test, and most irrigation or well drilling companies can do this. If a water meter is not currently installed, a test is still relatively easy, but a meter will need to be temporarily connected to the system, such as at the closest hydrant.
4.2 TRAVELLING IRRIGATORS
The Owners Manual, if provided for your irrigator, will give you guidance on what should be attended to before the irrigation system begins. Attention is usually given to lubrication, bearings, seals, tyre pressures, drag hoses, wire ropes, and structural aspects of the machine.
Pressure gauges, particularly those that have been subjected to large pressure variations, are often not accurate. A second gauge should be kept to test and compare the readings.
Pipes and hoses should be checked for foreign matter. Rabbits and birds often cause blockages, and foreign objects could cause serious damage to the drive units of travelling irrigators if allowed to pass through the system.
Leaks in pipes (particularly pipes on the ground surface) should be identified and repaired.
Sprinklers, nozzles and/or jets should be examined and repaired or replaced if necessary.
The system should be run to check sprinkler operation, application depths and travel speeds. Adjustment to lane spacings should be made if necessary.
4.3 HORTICULTURAL SYSTEMS
One of the biggest problems with horticultural systems is damage to lateral pipes and sprinklers, jets or drippers during harvesting and follow-on work. These must be repaired before the irrigation season begins.
If there is any likelihood of foreign matter in pipes, the system should be properly flushed out before any pressurisation of the system occurs.
Operation of solenoid valves and controllers should be checked and repaired if necessary.
4.4 SURFACE IRRIGATION (BORDERDYKE)
Borderdyke irrigation systems also need maintenance.
In particular, attention should be given to the condition of headraces to ensure that the full flow is able to reach all parts of the system without overflowing. Gates should be checked for damage, and to ensure they seal correctly.
Sills should be checked to ensure they are clear of debris, are level and at the correct height. Borders, if severely damaged, may require reforming.
Headraces should be fenced, and periodically grazed with sheep (not cattle) to keep them clean.
4.5 WASTEWATER IRRIGATION SYSTEMS
Animal wastewater is abrasive and corrosive. The importance of preventive maintenance cannot be over-emphasised. Moving parts (pumps, hose couplings, irrigators and sprinklers) should be kept clean and well lubricated.
Regularly
- Make sure that the spray application system is not spraying wastewater into the water troughs.
- Waterways should be checked regularly to ensure that wastewater is not moving into the water.
- Clean and clear any wastewater stone trap and gratings.
- Check that the float switches are clear and working.
- Grease the applicator.
- Check that the sprinklers are not blocked or damaged.
- Flush clean water through the delivery pipeline and sprinklers to keep them from blocking. If the equipment is idle for more than one week flush it with clean water prior to close down. This will prevent the wastewater solidifying and blocking the system.
Six Monthly to Annually
- Strip down the pump for oiling and cleaning.
- Check the pump seals as these are the components most susceptible to wear.
- General maintenance of the storage facility such as removal of sludge and spraying of any weeds growing on storage ponds.
4.6 CARRYING OUT FLOW CHECKS
As stated earlier, knowing how much water has been used is vital for effective irrigation management, and some form of water metering is necessary to use the performance indicators.
Measuring flow rates or volumes allows you to set baseline indicator values and to carry out an ongoing check of the capacity of your system. In particular, you can use water meters to:
- Check that the system is drawing the amount of water you expect;
- Compare performance with the design specifications;
- Check daily variations in quantity or flow rate over the system due to changes in pressure;
- Determine limitations in irrigator positions;
- Determine unacceptable pressure variations due to pipeline sizes, wrong pump duty, or elevation effects;
- Compare performances with resource consent conditions; and
- Monitor the amount of non-irrigation time or downtime in a cycle.
In the longer term, flow or volume measurements allow you to:
- Determine how system performance has changed over time;
- Help pinpoint reasons for changes. Possibilities include pump wear, water supply degeneration, well levels dropping, screen blockages, channel deterioration and diversion problems.
Without making these measurements, you may not be aware that a problem exists.
The accuracy of measurement needs to be considered. An accuracy of 5 percent should be attainable for water meters operating in pressurised systems, while an accuracy of 10 percent is probably more realistic for surface water systems.
Where irrigation systems are applying water at more than one location of the farm at the same time, e.g. for multiple irrigator systems, a water meter on each irrigator is recommended for optimum management.
Contact for Enquiries
MAF Information Services
Pastoral House
25 The Terrace
PO Box 2526
Wellington, NEW ZEALAND
Fax: +64 4 894 0721
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