Irrigation performance under alternative field designs in a spate irrigation system with large field dimensions

Abstract The sustainability of spate-irrigated agriculture in a semi-arid climate depends on efficient use of irrigation water. Thus, efficient capture and storage of soil moisture in the field are crucial for sustained productivity. The main objective of this study is to examine the performance of improved field design strategies to manage variable irrigation water supply and application time in the Gash agricultural scheme (GAS) in eastern Sudan where open-end border irrigation is practiced to irrigate large fields with variable sizes that range from 250 to 1250 ha. Irrigation performance was examined using the WinSRFR model for a large-sized field (8400 m × 500 m), continuously irrigated for 25 days but also under alternative designs and irrigation times. The performance was evaluated using efficiency, adequacy and uniformity criteria. The results demonstrate that the current irrigation practices are quite inefficient but could be substantially improved by adopting alternative design and operational strategies. A vertical division of the field (8400 m × 250 m) under the average inflow condition could result in a substantial increase in application efficiency (from less than 50% to over 70%), distribution uniformity (from 0.34 to 0.87), and irrigation adequacy (from 0.68 to 1). Additionally, the fields could be irrigated in considerably less time when an alternate irrigation schedule between two equally divided fields is followed, which indicated time savings of 40 % under a high inflow rate scenario (occurring during a large flood season), and a 20% reduction in time under an average inflow rate scenario (occurring during a medium flood season). Therefore, this modelling study has demonstrated a great potential to significantly improve irrigation performance by applying alternative field designs and operation strategies in the GAS. The modelling outcomes confirmed that the farmers’ indigenous experiment, though without a scientific study, on the vertical division of a large-sized field is indeed successful in improving irrigation performance, and could be adopted in other similar conditions.