Impact assessment of seawater intrusion on shallow coastal groundwater in eastern Saudi Arabia using a multidisciplinary approach

Seawater intrusion is considered the main threat to fresh groundwater resources in coastal regions, especially in arid areas such as Saudi Arabia. For decades, the coastal community in the eastern province of Saudi Arabia has depended on groundwater for domestic and agricultural uses. The current study objective is to assess the degree of seawater intrusion and its impact on the shallow groundwater in the eastern coastal region of Saudi Arabia. We integrated three techniques, including hydrogeology, hydrochemistry, and electrical resistivity. A hydrogeological and electrical resistivity field survey was conducted, coupled with in situ measurement of the shallow groundwater's hydrochemical properties (pH, ORP, DO, EC, temperature, and turbidity). This was followed by collecting 24 water samples for the laboratory analysis of hydrochemical properties (major cation and anion). Geospatial maps of salinity (electrical conductivity (EC)) and chloride were established to trace their concentrations from the sea landward. The hydrochemical spatial maps were correlated with the geoelectrical measurements to delineate the lateral and vertical extent of seawater intrusion in the studied shallow coastal aquifer. The hydrochemical results show that chloride and sodium are the dominant ions, indicating seawater intrusion is the source of elevated salinity. The salinity (EC) and chloride concentrations of the tested GW range from 6452 μS/cm to 44420 μS/cm, and 1041 mg/L to 8523 mg/L, respectively. The study results indicate that the shallow groundwater has been contaminated with seawater up to around 4 km landward, with a maximum depth of 30 m. The main conclusion of the current study is that decades of overexploitation of groundwater aquifers in the studied region have resulted in salinity contamination of shallow groundwater by seawater intrusion to levels of saline and brackish water. The result of this study may help the decision-maker implement a proper management measure to safeguard groundwater resources for coastal communities and develop a plan to remediate the shallow groundwater aquifer through desalination and reinjection for the environment and ecosystem benefits.