Optimal reservoir capacity for centre pivot irrigation water supply: Maize cultivation in Spain

Abstract

Centre pivots are one of the most widespread irrigation systems in the world. The aim was to develop a tool to optimise the design and management of the water distribution and centre pivot systems seeking to minimise water application cost per unit area (CT), including investment (Ca), operation (Ce), and maintenance costs. With this aim, two options were considered: to feed the centre pivot 1) directly from an aquifer or 2) using a regulation reservoir. A software tool DEPIRE (design of centre pivot with regulating reservoir), was developed and implemented in MATLAB 2012b (The MathWorks Inc., Natick, MA, USA). It determines optimal flows, pipe diameters, pumps power and the volume of the regulation reservoir for any crop water requirement, different electricity rates and water availability in the tube well. With this tool, the effect of the irrigated area (S), dynamic water level (DWL) in the aquifer and the pumping flow rate on the CT was evaluated for a maize crop in Spain. The study area representing the minor CT was 70 ha for direct pumping from the borehole and 100 ha when using an intermediate reservoir. Incorporating a regulation reservoir generates lower CT than direct feed from the borehole for S > 100 ha for any DWL. CT increased linearly with the DWL due to a significant increase in Ce which primarily affects the cost of water extraction from the aquifer, with a smaller effect on the application cost of the irrigation system.