Application of the analytic hierarchy process to weight the criteria used to determine the Water Quality Index of groundwater in the northeastern basin of the Sidi Bouzid region, Central Tunisia

The Sidi Bouzid and El Hjal Wadi basins together comprise one of the most important agricultural regions in Central Tunisia. Exploitation of the groundwater in this region is increasing exponentially. In this work, hydrochemical characteristics and the analytic hierarchy process (AHP) were used to assess the suitability of the groundwater in the aquifer for use in irrigation. Concentrations of total dissolved solids in the groundwater ranged from 1500 to 5000 mg/L. The most abundant chemical species in the water were SO42− and Cl−, with mean concentrations of 1010 mg/L and 641 mg/L, respectively. The high levels of these species can be explained by sulfate mineral dissolution and the leaching of evaporitic formations into the groundwater flow. Quality criteria weighting using the AHP was employed to generate a map of groundwater suitability for irrigation. This method categorized water samples as either excellent, good, or permissible for irrigation based on the Water Quality Index (WQI). Most of the water samples (76.5%) in the study area were found to contain water that would be good for irrigation, although the groundwater quality deteriorated towards the areas with low elevation.