Modification of GALDIT model by using Entropy method for Gharesoo-Gorgan Rood coastal aquifer vulnerability assessment

It is highly important to identify vulnerable areas and protect groundwater resources in the Gharesoo-GorganRood coastal aquifer due to the overexploitation of groundwater resources in this area. Therefore, in this study, the GALDIT model and Entropy method in GIS environment was used to evaluation the vulnerability of coastal aquifer. The parameters of the type of aquifer, the aquifer hydraulic conductivity, the height of groundwater above the sea level, distance from shoreline, the qualitative impact of seawater intrusion, and thickness of aquifer were used in the GALDIT model, which influence the assessment of coastal aquifer vulnerability. The maps were arranged in the form of six information layers using ArcGIS software. To more accurately assess the vulnerability, the weights of GALDIT parameters were modified using the entropy method, and GALDIT-Entropy vulnerability map was obtained. The correlation coefficient between the TDS parameter and vulnerability indices in the study area was used to obtain the optimal model. The correlation coefficient between GALDIT-Entropy model and TDS parameter was obtained 0.51, while the amount of this was 0.43 for GALDIT model. According to GALDIT-Entropy model, the northwest, southwest and west areas of aquifer have higher vulnerability to seawater intrusion. The map of this model is classified into four vulnerability classes of low, moderate, high, and very high which compose 14, 33, 30, and 23% of the study area, respectively. The GALDIT-Entropy model reduced the errors from expert opinions in the initial GALDIT. The proposed method can be used to assess vulnerability with the same hydrogeological conditions.