Design and management guidelines for contour basin irrigation layouts in southeast Australia

Contour basin irrigation layouts are used in Australia for sequential cultivation of rice and other crops on soils with low infiltration rates. Multiple interconnected basins through gates installed in the check banks and backflow at the inlet end are unique features of contour basin layouts used in southeast Australia. Design and management guidelines were developed using a twodimensional computer simulation model (COBASIM) for contour basin layouts. The computer model was used to simulate and analyse the performance of single- and multiple-basin layouts in response to key design variables including aspect ratio, inflow rates, microtopography, vertical interval between basins and number of interconnecting drainage outlets. The main aim of this study was to provide designers and practitioners with an overall view of the likely impact trends arising from variations in key design factors and to improve design practices. Irrigation performance was measured by the time of advance needed to cover the entire basin area, application efficiency, water requirement efficiency and distribution uniformity. The study revealed that the aspect ratio and local microtopography have a significant impact on the performance in these layouts. A mild slope in the advance direction can improve performance when a small depth of irrigation is required, while there are no significant benefits from increasing the elevation difference between adjacent basins.