Evaluation of Aquifer Vulnerability Assessment Methods for Alluvial and Coastal Aquifers, Case Study in Astaneh-Koochesfahan Aquifer, Guilan, Iran

One way to balance the environment is to study and manage aquifer vulnerabilities. In order to decide and manage the aquifer, the need for planning to identify vulnerable areas is very important. Several methods and indicators to assess the vulnerability of the aquifer are presented in each of these indicators is based on a set of factors used. In this study, 5 vulnerability indicators have been used in the coastal region to investigate and compare these methods. The characteristics of DRASTIC, SINTACS, SI, GALDIT and GODS were investigated to assess the sensitivity of the aquifer inherently. The results of these 5 indicators were different according to the nature of each of them and in order to increase the accuracy of the results and practical use of these results in coastal areas, weight and rankings were performed using hierarchical and entropy analysis method. For this purpose, the correlation between the vulnerability index concentrations of TDS, nitrate and chloride and weights of each indicator was calibrated. Sensitivity analysis of various parameters in vulnerability indicators showed that GALDIT index reflects this sensitivity in the results, considering the effect of sea salt water progress. Depth parameter to static level in other indicators and distance parameter from the sea is a sensitive and important criterion in GALDIT index and after model calibration, it was found that 30% of aquifers are exposed to the saline fronts of sea water infiltration.