Vulnerability Assessment of saltwater intrusion using simplified GAPDIT method: a case study of Azarshahr Plain Aquifer, East Azerbaijan, Iran

Abstract

The index-based method (GALDIT) has been established over the years for assessing the vulnerability of aquifers for saline water intrusion based on six parameters, i.e., groundwater occurrence, aquifer hydraulic conductivity, level of water table above the sea, distance from shore, impact of existing amplitude of saline water intrusion, and thickness of the aquifer. This method incorporates weight and the importance rating of factors to assess the vulnerable zones to saltwater. The objective of the present investigation is to simplify the GALDIT method as a procedure in vulnerability assessment of saltwater intrusion by substituting for the level of the water table above the sea with the more effective groundwater pumping rate in order to effectively represent the groundwater condition. Hence, the method is named as the GAPDIT method (“L” being replaced by “P”). The developed model was applied to a coastal aquifer in the hyper-saline lake vicinity of Urmia, Iran. The Analytic Hierarchy Process (AHP) was employed to enhance the prediction of vulnerability distribution. Thus, for every factor, a separate interpolated layer was plotted by empirical Bayesian kriging (EBK) method, and then, a final vulnerability map was derived overlaying the individual layers and their special weight application. The outcome revealed that the substituted pumping rate was justified in cases that water table data are not available and resultant maps showed reasonable correlation between the GALDIT and GAPDIT methods. Also, the derived maps revealed that the highest vulnerability exists in the northwest of the study area.