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

This study has been done to investigate the hydrogeological drought and groundwater quality changes over the time in Semnan and Damghan plains.

In this research, the groundwater level and groundwater quality changes in of these plains has been evaluated using monthly piezometric wells data for April as groundwater-recharging month and October as 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.

The results illustrated that the 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 totally higher in city surrounding regions in both plains. According to 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 compared to other parts in Semnan plain, while in Damghan plain, GQI value in central and western parts is higher than eastern parts.

The correlation between GRI and GQI showed positive results in both plain with 0.542 in Semnan and 0.672 in Damghan, which reflects that the groundwater quality changes with groundwater level changes.