Influence of Meteo-Marine Forcings on Groundwater Level Fluctuations of a Coastal Multi Layer Aquifer
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A multi-layered aquifer beneath the Roussillon plain (Perpignan, France) consists of alluvial formations from the Quaternary, overlaid by Pliocene sands and clays. This aquifer spans 800 km² and reaches up to 300 meters deep on land, extending several dozen kilometers under the Mediterranean Sea. It holds a freshwater resource, which may mix with seawater depending on its distance from the coast. To monitor the groundwater's piezometric and physicochemical behavior (conductivity, temperature), a hydro-geophysical observatory (Dem'Mer) has been set up along the coastline. The observatory has collected time series data over several years, which were analyzed using spectral analysis to study the impact of meteorological and marine factors on groundwater flow, from seasonal to daily variations. Additionally, cross-correlation and coherence analyses were used to explore how different signals are organized over time. The study provides evidence of how storm waves at the sea bottom, water levels at the shoreline, and tides influence piezometric fluctuations in the aquifer near the coast. These findings offer valuable constraints for ongoing aquifer modeling efforts.