IRRIGATION SYSTEM ASSESSMENTS The Department of Primary Industries and Regional Development (DPIRD) recently engaged Irrigation Australia to manage a project to conduct free system assessments of horticultural irrigation systems in the Carabooda, Nowergup and Wanneroo districts north of Perth, WA. A total of 22 system assessments were conducted by Willmott Irrigation on behalf of Irrigation Australia. Of the systems tested, 10 used drip irrigation, while 11 used overhead sprinklers and one system used under-tree mini sprinklers. Each assessment consisted of gathering key information and performing tests on a grower’s irrigation system. The assessed system components could be broadly divided into one of two categories; the pumping system, and the delivery system. Pumping system The pump is a major component of any irrigation system. A pump that runs efficiently reduces costs to the grower by using less energy and requiring less maintenance. Any pumping system operating at less than 50% efficiency is considered poor and should be investigated. Delivery system The best way to test the efficiency of a delivery system is to assess the application uniformity, which describes how evenly an irrigation system applies water over the area being irrigated. Application uniformity was measured using the distribution uniformity (DU) method where a higher percentage indicates greater evenness between the depths of water applied across the field. The minimum industry standard for DU of drip irrigation systems is 85%, while the minimum standard for overhead systems is 75%.
Other tests included pressure variation along mainlines and laterals, pressure differential across filters (if applicable), and flow variation between emitters. Results Assessment results were provided to growers in a ‘traffic light’ format that rated the performance of major system components as; Good, Acceptable, or Poor. These ratings indicate whether the performance exceeded, met, or undershot the industry minimum standard. · Drip systems had an average pump efficiency of 61%, resulting in ratings of either ‘Acceptable’ or ‘Good’. · Overhead systems had an average pump efficiency of 55%, which is within the normal operating range. However three individual overhead systems had pump efficiencies below 50% resulting in a rating of ‘Poor’. · Drip systems had an average uniformity score of 91%, which exceeds the minimum industry standard of 85%. This resulted in all the drip systems receiving a uniformity rating of either ‘Acceptable’ or ‘Good’. · Overhead systems had an average uniformity score of 70%, which is below the minimum industry standard of 75%. This resulted in more than half the overhead systems receiving a uniformity rating of ‘Poor’. Unlike drip systems, uniformity tests on overhead systems are highly impacted by wind conditions. This makes one-off tests somewhat unreliable because a system may score significantly higher or lower depending on the wind speed
Above: Example of a results section of a drip system report
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The Overflow - Summer 2020
