Investigation of the saltwater intrusion potential into groundwater resources using numerical modeling (case study: Urmia coastal aquifer)

In this study, we have tried to investigate the interaction between groundwater resources of the Urmia domain and Urmia Lake through numerical modeling. The conceptual model of the Urmia aquifer has been prepared using available information and results of geophysical studies. Modeling of flow and soluble transport in the coastal part of Urmia aquifer has been done using the GMS software package. In this case, groundwater flow is first modeled using the MODFLOW module and then the solute transport (in this study, chloride concentration) is performed using the MT3DMS code. After modeling the flow and soluble transport, the outputs are used in the SEAWAT code. The calibration of aquifer hydraulic parameters was performed using the PEST code and manual method. In running the model in unsteady state and using calibrated parameters, the values of ME, MAE and RMSE of the model reached 0.11, 1.14 and 1.41, respectively. The results of flow modeling, solute transport, and mixing of saline and freshwater in the Urmia aquifer show that in the present situation, the relationship between the Urmia aquifer and Urmia Lake is as low as possible and the salinity of the aquifer is very low. Besides, the analysis of the water resources behavior in the coastal parts of this aquifer in two scenarios, including the 50% reduction in discharge of four main rivers and the 50% increase in groundwater extraction, shows that no significant change was made in the results of this model. Since solute transport is a function of flow dynamics in the region, a one-way flow of groundwater towards Urmia Lake, low permeability sediments (due to particle size and formation of salt layers) prevents the invasion of the Urmia Lake saltwater into the aquifer environment.