Application of Aquifer Surface Recharge in the Modification of GALDIT Method to Assess the Risk of Seawater Intrusion in Qom Aquifer

A realistic understanding of aquifer vulnerability to seawater intrusion is one of the important prerequisites for coastal aquifer management. The GALDIT method is a proper tool that, despite considering the qualitative, hydrogeological, and geological characteristics of the aquifer, has not considered the role of aquifer surface recharge. The Qom-Kahak study area is a part of the salt lake catchment, which is located in the arid and desert part of central Iran. Due to the shortage of surface and groundwater resources in the region, some of the drinking and industrial needs of Qom city are met from water outside the study area. This study, by adding the aquifer surface recharge parameter introduces the GALDITR model to evaluate the Qom aquifer vulnerability to saltwater intrusion from the Salt Lake. Then, the analytical hierarchy process method is used to review the weight of GALDITR model parameters according to the characteristics of the studied aquifer. Based on the obtained results, the high rank of the aquifer surface recharge parameter in a large part of the aquifer led to an increase in the area of moderate vulnerability of the GALDITR model compared to the GALDIT method. In the GALDITR-AHP model, the parameters of distance from the shore, groundwater level above the lake, and the impact of seawater intrusion gained more weight than other parameters, respectively. With increasing the low vulnerability area in the GALDITR-AHP model, the aquifer vulnerability near Qom city decreased. The vulnerability index of GALDITR-AHP, GALDITR, and GALDIT models showed the highest correlation with chloride ion values at observation points, respectively. The results showed that areas with high and moderate vulnerability in the eastern part of Qom aquifer covering about 14 % of the total aquifer area are more prepared for seawater intrusion and can be considered as the expansion of seawater wedge for monitoring and optimal management of coastal aquifer.