Multicriteria-analysis of deep groundwater quality using WQI and fuzzy logic tool in GIS: A case study of Kebilli region, SW Tunisia

Abstract

The suitability of groundwater for drinking and irrigation purposes is potentially disturbed by a variety of factors, including climate change, salinization and risky agricultural practices. The region of Kebilli (Southwestern Tunisia) is marked by an arid climatic condition with a Saharan tendency. However, the spatial partition of the stress factors was not addressed so far in spite of the increasing demand for groundwater to the agricultural and domestic activities which supports the social and economic pressure. Therefore, Water Quality Index (WQI) and Fuzzy Logic models were applied to evaluate the groundwater quality in the Kebilli region for both drinking and irrigation purposes using the geographic information system (GIS) environment to analyze the spatial partition of various factors. According to the analytical results, the calculated values of WQI are between 83.421 and 436.858 for drinking and range from 50 to 77 for irrigation purposes. The prepared Fuzzy spatial maps show that the “desirable” and “acceptable” classes of groundwater quality samples are situated in the center of the studied region, while the “undesirable” quality of groundwater is observed mainly at the Southeastern sectors due to the domestic and agricultural activities besides the over-exploitation of the aquifer. In addition, the Fuzzy membership levels generated into a GIS-based maps give a high correlation of 0.88 and 0.79 with assessed values of WQI for both drinking and irrigation purposes respectively. Grouping analyses also confirm the resulted maps, in turn, the anthropogenic effects coincides globally with the unsuitable areas for both drinking and irrigation purposes. Consequently the perturbations in the fragile environment of the oasis ecosystem are closely related to the deterioration of the groundwater quality and the intensive use of fertilizers and pesticides for agricultural needs in the Kebilli region. The research results may improve the understanding of the groundwater sustainability and as support decision makers for planning the water management and its protection.