Appraising seawater intrusion in the Moroccan Ghiss-Nekor coastal aquifer: Hydrochemical analysis coupled with GIS-based overlay approach

Abstract

Seawater intrusion (SWI) into coastal aquifers poses a significant environmental problem, and identifying an effective method to assess its extent is challenging. This study introduces a method for accurately delineating the extent of SWI in the Ghiss-Nekor aquifer, using a dual approach of hydrogeochemical analyses and geospatial technologies. We used several geochemical markers, including four ionic ratios (Cl-/HCO3-, SO42-/Cl-, Na+/Cl-, and Mg2+/[Mg2++Ca2+]) along with two SWI indices (GQIswi and SMI). These markers were interpolated and subsequently overlaid using GIS-based overlay analysis, enabling us to generate an accurate map pinpointing areas affected by SWI. The study reveals that SWI affects roughly 20 % of the investigated region, with 70 % of these cases found within 2 kilometers of the coastline. The detection of saline water as far as 5 kilometers inland, as explained by the aquifer’s geological model, points to SWI emanating from the Souani area, infiltrating through coarse sand and gravel located above the impermeable deep clay-marly strata. These outcomes validate our hydrogeochemical method and offer essential data about SWI’s scope. Such insights are indispensable for policymakers in the Al Hoceima area to forge effective groundwater management strategies in response to climate change-induced challenges like diminishing water resources from reduced rainfall.