Spatial Variation of Groundwater Salinity and Risk Assessment of Saltwater Intrusion in Malekan Aquifer

As the most valuable natural resources, protection and management of groundwater is vital. One of the best ways to protect groundwater resources is identifying the aquifer vulnerable areas and monitoring groundwater quality spatial variations. The spatial variation of the groundwater salinity, has been evaluated in Malekan aquifer, introducing a new method, named GWQISI which has been digitally integrated of TDS, Cl-/sum Anion, Cl-/ (HCO3- + CO32-), Na+/ (Na+ + Cl-) and Ca2+/ (HCO3- + SO42-) ratios. Also, this paper presents the vulnerability mapping of the coastal aquifer system using new multi-criteria decision model as IDLRT. Five thematic layers have been created to adopt the most indicative criteria for investigating the groundwater degradation trends from saltwater intrusion. One of these layers showed the magnitude of existing status of saltwater intrusion. The other chosen layers are Recharge (R), Level of groundwater above the mean sea level (L), Distance from the shore (D) and the aquifer saturated Thickness (T). The results of sensitivity analysis, using both the map removal and single parameter methods, indicate that the Recharge (R) has the most significant impact on the vulnerability index. The groundwater vulnerability map indicates Based on the IDLRT results, about 22.15, 49.45 and 28.4 % of Malekan aquifer have very low, low and moderate vulnerability, respectively. Based on the GWQISI results, about 1.75, 4.25 and 62.4 km2 of Malekan aquifer are extermly, highly and moderately influenced by salinity, respectively. The results reveal that the northwest part is the most affected zone by salinity.