Inflow rate and border irrigation performance

Modernisation of regional water delivery infrastructure can provide irrigators using border irrigation systems with the option to apply water to border irrigation bays at much higher inflow rates. Substantial improvements in irrigation performance have been claimed by proponents of higher bay inflow rates, leading to large investments in farm infrastructure. In this work, measurements made on bays irrigated at different inflow rates on a range of soil types, crops and irrigation deficits did not demonstrate substantial differences in irrigation performance. Assessments made using a surface irrigation model fitted to the measured irrigations also showed limited differences in feasible irrigation performance related to inflow rates. Extrapolating irrigation performance over feasible inflow rates and durations revealed that equivalent performance could be achieved with inflow rates ranging from 2 to 7 L s−1 m−1 provided that appropriate inflow durations were adopted. An analysis involving modest variations of ±5% in inflow rate and ±5 mm in the estimate of irrigation requirement produced substantial uncertainties in irrigation performance, suggesting that attempts by irrigators to consistently achieve more precise irrigation performance targets may not be feasible. Improved understanding of the role of uncertainty in border irrigation systems, models and measures of irrigation performance would provide a useful basis for improving border irrigations.