Mapping of the groundwater vulnerability to saline intrusion using the modified GALDIT model (Case: the Ain Temouchent coastal aquifer, (North-Western Algeria))

Abstract

Maps of the vulnerability of groundwater to seawater intrusion were developed for the multi-layered coastal aquifer of Ouled Taoui—Ouled Boujemaa in Algeria. Groundwater in this area is threatened by the risk of salinization due to excessive groundwater use. To protect this aquifer, mapping the vulnerability to potential saline intrusion was carried out using a modified GALDIT index mapping model that takes into account six parameters, namely: (G) groundwater occurrence, (A) aquifer hydraulic conductivity or network development and persistence index (IDPR), (L) depth to groundwater level above sea, (D) distance from shore, (I) impact on the existing status of seawater intrusion in the area, and (T) It’s the thickness of the aquifer. A system for rating, weighting and classifying the GALDIT model according to the relative importance of these parameters was developed under a GIS environment. The compilation results illustrate that the underlying confined aquifer with clay levels characterizing a low hydraulic potential. It will be more vulnerable during excessive pumping and in the presence of karst conducts, which produces an impact of salinity decay as soon as one moves away from the shore. The assessment indicated that the vulnerability of the uppermost unconfined aquifer was particularly sensitive to changes in the weights of parameters (A), (L) and (D). Areas with a “high” vulnerability to seawater intrusion are located especially in the coastal fringe. The results of the vulnerability assessment were validated based on: the density and distribution of existing groundwater production wells, the land cover map, and the hydrochemical quality of groundwater. Finally, the identification of areas of “high” vulnerability to saline intrusion will serve as a tool for the management, control, and protection of coastal groundwater resources.