Simulation of seawater intrusion in coastal aquifers: a case study on the Amol–Ghaemshahr coastal aquifer system, Northern Iran

The study presents simulations of seawater intrusion (SWI) in the coastal aquifers of Amol–Ghaemshahr, Northern Iran in response to oscillations of sea level and groundwater extraction and incorporates the assessment of the impacts of future changes in sea level and withdrawals from the aquifers on groundwater salinization. A numerical model of variable-density groundwater flow and solute transport was developed to investigate the extent of SWI. The SEAWAT 4 was used to solve the variable-density groundwater flow and solute transport governing equations. Calibration of the model was carried out in three steps involving the dynamic steady-state and the transient mode of flow models as well as transient mode of solute transport model. Calibrated model run for the year 2010–2011 corroborated well with the field data wherein the seawater intrusion has taken place intermittently along the coastline in the eastern part and 9.7% of the land along the coastline (i.e., 6.96 km) was encroached by seawater. Predictions on the SWI for the year 2030 were made with all hydrogeological conditions assumed to remain the same as those in 2010–2011 by simulating the movement of the interface resulting from the changes in sea-level and groundwater withdrawals. The results show that Amol–Ghaemshahr aquifer is sensitive to groundwater withdrawal and sea-level rise. The studies established that various combinations of groundwater extraction and sea-level oscillations are predominant driver of SWI in the study area.