The seawater intrusion assessment in coastal aquifers using GALDIT method and groundwater quality index: the Djeffara of Medenine coastal aquifer (Southeastern Tunisia)

Abstract

The Djeffara of Medenine coastal aquifer (Southeastern Tunisia) is threatened by the seawater intrusion (SWI). This region is characterized by a notable increase in population and spreading of agricultural activities (increasing of groundwater pumping), which makes it under tremendous stress of SWI. So, the groundwater quality degradation is caused by both anthropogenic activities (pumping) and natural hazards (sea level rise (SLR) and storm surge). Hence, assessing the groundwater vulnerability to SWI is highly crucial to protect this resource. The assessment of SWI represents the principal aim of this study. To achieve this objective, firstly, a parametric method of vulnerability assessment “GALDIT” was applied. It considers six parameters which interfere with each other and determine the SWI effects. Obtained results show three degrees of vulnerability (low, moderate, and high). Most of the coastal broadline represents high classes. In addition to the hydrogeological parameters, these results are closely related to the piezometric level (− 10 to 15 m) and the distance from the shore (< 500 m) parameters. Secondly, a groundwater quality index for seawater intrusion (GQISWI) was developed in order to identify the groundwater type. This method shows that the Djeffara of Medenine groundwaters is classified as mixed water. The validation procedure of these two applied models was performed based on water electrical conductivity (EC). It shows a significant correlation coefficient. Obtained maps may be used as a scientific basis allowing the water management and protection in coastal aquifers threatened by saline waters.