Multi-objective optimal design of interbasin water transfers: The Tagus-Segura aqueduct (Spain)

Study region: The Tagus-Segura aqueduct (TSA) is a large and strategic water transfer scheme in Spain that connects Entrepen similar to as and Buendia reservoirs in the Tagus river headwaters to the Segura river basin, a highly stressed Mediterranean area.Study focus: The operating rules of the TSA underwent several modifications over the years, and the debate about which are the optimal parameters to meet the interests of the parties involved is still open. We employed Evolutionary Multi-Objective Direct Policy Search to jointly optimize the re-operation of the headwaters dams and the water transfer policy with respect to four conflictingobjectives: Tagus and Segura water demands, hydropower production and socioeconomic benefit of the population living on the shores of the headwaters reservoirs. We tested the optimization under the baseline and the 2027 scenario, which foresees an increased environmental flow (EF) in the Tagus river. New hydrological insights for the region: The proposed operating rule presents optimized control parameters, a higher degree of freedom and a transferred volume that cyclically varies according to the hydrological stage of the year. In the 2027 scenario, despite the increased EF, the deficit in the aqueduct shows a limited increase compared to the historical solution (+10%), while the storage deficit is strongly reduced (-73%). This benefits the population living on the reservoirs shores and also ensures more stability to the aqueduct functioning.