Qualitative Assessment of the Coastal Plain of Urmia using the Modified GALDIT Vulnerability Method

Sea water intrusion is a major environmental threat to groundwater resources in coastal areas, where groundwater is the main source of water supply in demotic agriculture sections, etc. Due to the over-exploitation of this source, we are witnessing increased pollution in coastal aquifers. In this study, the GALDIT method was used to assess the water vulnerability in the Urmia plain. Then, to improve the model accuracy, the two parameters i (hydraulic gradient) and P (pumping rate), were added to GALDIT. The results of the correlation coefficient between the GALDIT and GALDIT-iP indices with the parameter of EC showed that the correlation coefficient was increased from 0.42 to 0.66, which showed a significant improvement for the modified model. Therefore, the GALDIT map presents a more accurate vulnerability. The results also showed that the vulnerability index is high in the eastern and central parts of the plain and the areas near the coast of the plain, and also the index is low in the western parts and the areas distant from the coast. Also, the sensitivity analysis for removing the model parameters showed that the change of the vulnerability index by removing the status of Impact of seawater intrusion (I) in GALDIT and the hydraulic gradient (i) in GALDIT-iP is more than other parameters. Then, based on the single-parameter sensitivity analysis, the aquifer type (G) and thickness (T) are the most effective parameters in both methods, and in addition, the hydraulic gradient and pumping rate are effective parameters in evaluating the GALDIT-iP index. Overall, the results of the study showed that by using the modified GALDIT method, the percentage of areas swept by the high and very high vulnerability indices increased, while the areas with very low to medium vulnerability indices decreased.