Simulation of saline and fresh water interference in saturated and unsaturated zones using physical and Hydrus-2D model

One of the threating factors to fresh water resources is the advancement of saline water and intrusion into the groundwater aquifer. This problem occurs in coastal zones and desert margins which causes reduction in the quality of fresh water. Evaporation from the soil surface and the water table depth are factors affecting the salinity and salt distribution in the saturated and unsaturated zones. In this study, by constructing a physical model with dimensions of 4×1×1 m, the proposed situation of saline and fresh aquifer levels was studied in four different hydraulic gradients. During the experiment, moisture and salinity data were collected from the physical model and then the salinity distribution in the physical model was numerically simulated using Hydrus-2D software. The results showed that Hydrus-2D model simulates moisture and salinity distribution well. The Maximum Normalized Root Mean Square Error (NRMSE) for simulation of moisture and salinity were 9.28 and 21.69 percent. The results showed that the pattern of salinity progression and regression were different. In conditions where the fresh water level is higher, it prevents the advance of saline water in saturated zone, and in unsaturated zone it does not have a significant effect on controlling salinity due to evaporation from the soil surface. In the saturated zone, when the saline and fresh water levels were equal, three units salinity increase in saline zone and when the saline water level was higher, 6.5 units salinity increase was observed in the middle of the two saline and fresh water reservoirs.