Application of an integrated GIS-AHP water quality index to evaluate the groundwater suitability for irrigation in a coastal aquifer in northeastern Algeria

Groundwater in coastal regions worldwide is an essential resource for irrigation, but its quality is increasingly compromised by natural salinization and human activities. In the Collo Plain (northeastern Algeria), existing studies are scattered and lack a comprehensive spatial assessment framework. This study is the first to integrate hydrochemical analysis, Geographic Information Systems (GIS), remote sensing, and the Analytical Hierarchy Process (AHP) to compute a weighted Irrigation Water Quality Index (IWQI) and evaluate groundwater suitability for irrigation. Thirty groundwater samples were analyzed for major physicochemical parameters, and geostatistical interpolation mapped the spatial distribution of irrigation water quality. Groundwater pH ranged from 6.90 to 7.90, while electrical conductivity varied between 1356 and 3388 μS/cm. IWQI values ranged from 35.5 to 87.9, with a mean of 56.8 ± 14.7. Approximately 30% of the Collo Plain exhibited good irrigation water quality, 56.7% was classified as poor, and 13.3% as very poor. The northeastern sector, particularly near Ouled Mazzouz, showed the greatest degradation, driven by paleomarine transgressions, geogenic factors, agricultural practices, and untreated domestic effluents. This study advances irrigation water quality assessment by demonstrating the robustness of a GIS–AHP–IWQI framework. The resulting maps provide practical decision-support tools for farmers and water managers, enabling improved irrigation planning, targeted monitoring, and sustainable groundwater management in coastal agricultural plains.