Experimental study of shallow saline water and freshwater interference on distribution of salinity in the saturated and unsaturated zone using physical model

The phenomenon of mixing saline and fresh water in aquifers near the sea coasts and the margin of salt marshland, limits the application of high-quality groundwater resources. On the other hand, by increasing concentration of saline water in aquifer due to evaporation from the soil surface and also decreasing pressure head in freshwater aquifers as a result of groundwater over exploitation, lead the mixing front advances toward the freshwater aquifer. In this study, by making a physical model, mixing area and salt distribution in both saturated and non-saturated zone of porous media has been studied. Four different hydraulic scenarios have been performed, including equal water table of fresh and saline water, higher freshwater level and two higher saline levels (10 and 15 centimetres). The concentration of saline water and freshwater were 20 and 0.98 dS/m, respectively. The physical model size was 4×1×1 meter. The results showed that the water table shape is an important factor for distribution and scattering of salinity in both saturated and non-saturated areas. By decreasing the water level in the freshwater reservoir by 10 and 15 centimetres, the boundary between the fresh and saline zone below the water table progressed 55 and 96 cm respectively, and by increasing the water level in the freshwater reservoir by 5 cm, the same zone has had a recession to 28 cm.