Abstract:

Coastal aquifers are strategic water resources, especially in arid regions and during droughts, but their resilience is increasingly threatened by the combined effects of human activity and environmental stressors. In urban settings, they play a key role in water supply and require accurate modeling of seawater intrusion to guide management and mitigation measures such as injection barriers. Human interventions land-use change, river modification, tunneling, port construction, and groundwater pumping have cumulative and often irreversible effects on aquifer systems. Each alteration modifies hydraulic gradients, recharge patterns, and subsurface connectivity, all of which strongly influence the dynamics of the freshwater–saltwater interface. In seawater intrusion modeling, neglecting this historical complexity leads to an incomplete or misleading representation of the intrusion front’s extent and evolution. Because the position and intensity of salinization plume are controlled by the superposition of multiple past and present perturbations, reconstructing the full anthropogenic history becomes essential to simulate both the current state and the system’s response to future stressors, such as droughts or rising sea levels. The Baix Llobregat aquifers, near Barcelona, exemplify this challenge. Past models reproduced piezometric trends but failed to capture seawater intrusion. A refined conceptual model that integrates anthropogenic and structural complexity now successfully reproduces the intrusion phenomenon, providing better insight into why it worsens after successive droughts and why some groundwater indicators have lost their diagnostic value.