Investigation of Hydrogeological Drought and Groundwater Quality Changes Using GRI and GQI in Semnan and Damghan Plains, Iran

Aims: In this study, the hydrogeological drought and groundwater quality changes are investigated over time in Semnan and Damghan plains. Materials Methods: The groundwater level and groundwater quality changes in of these plains have been evaluated using monthly piezometric wells data for April as the groundwater-recharging month and October as the groundwater-discharging month, and six groundwater quality factors including pH, Chloride (Cl-), Total Dissolved Solids (TDS), Electrical Conductivity (EC), Calcium (Ca2+) and Magnesium (Mg2+) were considered to determine groundwater quality changes. Groundwater Resource Index (GRI) and Groundwater Quality Index (GQI) were used to determine hydrogeological drought and changes in its quality, respectively, in studied plains from 2004 to 2018. Findings: The results illustrated that trends of groundwater level and GRI are decreasing, and there is no steady trend for these indices over the studied period and GRI value is higher in city surrounding regions in both plains. According to the results of GQI, EC and TDS factors have the highest effect on the groundwater quality, respectively, compared to other factors. GQI value is higher in central and northern parts than other parts in Semnan plain, while in Damghan plain, GQI value in central and western parts is higher than eastern parts. Conclusion: The correlation between GRI and GQI showed positive results in both plains, with 0.542 in Semnan and 0.672 in Damghan, reflecting that groundwater quality changes with groundwater level changes.