Optimal pumping scheduling model considering reservoir evaporation

Reservoir evaporation losses can be high in semiarid areas with high evaporative demand. The volume of water evaporated from a reservoir is a function of the free water surface area. In agricultural reservoirs this water surface varies depending on the volume of water stored. As reservoirs are usually relatively full of water over long periods of time, evaporation water losses are consequently high. Evaporation water savings could be achieved if a pumping policy that considered evaporation losses were developed. However, optimal pumping scheduling models proposed up to now do not take these losses into account. This paper presents a new optimal pumping scheduling model that integrates the evaporation losses from the reservoirs into the optimisation algorithm and provides the optimal pumping policy that minimises both pumping and water costs. The developed model was tested using a real irrigation water distribution system located in southeast Spain to serve as a case study. When evaporation losses were considered, water and energy savings were achieved in comparison to the optimal solution found when evaporation is not considered in the optimisation process.A sensitivity analysis of the optimal solutions to the price of water was then performed. For increasing water prices, the optimal solutions provided by the model tend to delay the pumping decisions with the aim of diminishing the evaporation losses. Although this implies a slight increase in the energy cost, it is compensated with the higher reduction in the water cost.