Optimizing Tidal Methods for Determination of Hydrogeological Parameters: Lessons from the Neretva Valley

Seawater intrusion (SWI) poses a significant threat to groundwater preservation in coastal aquifers. Understanding the mechanisms driving SWI and determining key hydrogeological parameters are essential for developing effective preservation and mitigation strategies. Tidal Methods provide a validated technique for determining these parameters when variations in sea level and aquifer piezometric head are available.

Despite the widespread application of Tidal Methods and the availability of various solutions based on aquifer conceptual models, significant gaps remain. Key challenges include reliably extracting tidal oscillations from raw monitoring signals and determining the optimal duration of data series for analysis.

This study examines the Neretva Valley in southeastern Croatia, a significant agricultural area near the Adriatic Sea, as a case study for the application of Tidal Methods. A monitoring system has been set up to capture the transient dynamics of SWI in situ.

This research expands upon prior studies in the Neretva Valley by examining tidal oscillations during dry and rainy periods—characterized by substantial precipitation and discharge—and investigating the influence of time series duration on the determination of hydrogeological parameters.

Key findings indicate that the diffusivity values of the deep restricted aquifer exhibit considerable variation between dry and rainy periods when determined using same methodology. The duration of the investigated time series strongly impacts the accuracy of hydrogeological parameter determinations. The hydrogeological values acquired during dry periods via Tidal Methods nearly correspond with those determined with geophysical investigation. These findings enhance comprehension of SWI processes and offer significant insights to improve Tidal Method applications in aquifer management.