Groundwater recharge zone mapping in a coastal mediterranean aquifer applying fuzzy and analytical hierarchy process and frequency ratio: A case study of northeast Tunisia

Abstract

Global water stress, driven by demographic growth, climate change, industrialization, and agricultural development, is exacerbated by excessive groundwater extraction, depleting aquifer storage. Groundwater recharge is crucial for ensuring water sustainability and preserving coastal water resources. This study assess aquifer suitability zones of the Aoussja Ghar El Melh coastal region in Tunisia using geographic information techniques (GIS), and three numerical methods: Fuzzy Logic, Analytical Hierarchical Process (AHP) and Frequency ratio (FR) method. The aim is to delineate significant groundwater recharge areas. The findings reveal three distinct recharge capacity classes. Fuzzy Logic indicated that a approximately 72 % of the study area, characterized by lithological features like sandstone alluvium and sandy marly soils in central plains, is suitable for groundwater potential zones (GWPZ). In contrast, the AHP indicates about 79% of the area, while FR model indicates 48%. These variations are influenced by the region's lithological and hydrogeological characteristics. Validation against 22 well locations show AHP as the most accurate (AUC = 91%), followed by Fuzzy Logic (AUC = 86 %) and the FR model (AUC = 70%). The application of the Fersi equation shows a strong correlation and spatial distribution similar to the AHP approach. This study concludes that while the Fuzzy Logic and FR models are valid for identifying GWPZ, they are less effective than AHP method, which provides refined recommendations for selecting recharge sites. Environment risks such as groundwater contamination and salinization in agricultural areas highlight the need for land resources management. The final map serves as a guideline for planning aquifer recharge projects and emphasizes the necessity of regulations and pumping limits to prevent overexploitation and saltwater intrusion. This preliminary assessment underscores the importance of implementing protective measures and recharge programs.