Anthropogenic pressures driving the salinity intrusion in the Guadalquivir Estuary: Insights from 1D Numerical Simulations

Abstract. The study presents a dynamic analysis of the present day behavior of saline intrusion in the Guadalquivir estuary and evaluates the impact of anthropogenic pressures on the dynamics of the salt wedge. A one-dimensional (1D) hydrodynamic model with a transport and dispersion module is used to study the effects of human pressure involved in the salinity concentration along the estuary. The observations, which correspond to continuous measurements taken during different oceanographic campaigns from 2021 to 2023, show an excessive penetration of the salt wedge in the estuary (with salinities of 5 psu at km 60) as compared to the idealized situation when anthropogenic water withdrawals are absent. This highlights the need to include a water withdrawal term in the simulations to accurately reproduce the real behavior of the system. Thus, reflecting the magnitude of the anthropogenic pressures. The model successfully reproduces the observations when this forcing factor is included. Under constant low flow conditions, experiments show that increasing water withdrawals leads to an increase in upstream saline intrusion. Similarly, under constant water withdrawal conditions, a decrease in saline intrusion is observed when freshwater flows exceed 40 m³/s. Variations in anthropogenic pressures, such as water withdrawals for agriculture or industry and reductions in freshwater flow, play a fundamental role in the evolution of saline intrusion. Under the current circumstances, the Guadalquivir estuary requires an urgent regulation of these uses in order to avoid further damage on the aquatic ecosystems.