Abstarct: Aquifers are the main source of freshwater supply in many parts of the world. Unfortunately, these natural reserves are vulnerable to saltiness due to their proximity and the hydraulic contact to saline water, whether in the coastal area or adjacent to the deserts. In the coastal regions, the seawater concentration is almost constant and the water table is generally higher than the sea level. While in arid and semi-arid areas, the saline water concentration of desert varies from place to place, and there is the possibility of a drop in the aquifer water table to a level lower than the desert saline water, due to groundwater excessive extraction. The objectives for this research are: a) Evaluation of the transient movement of saltwater wedge and the mixing zone in coastal aquifers, b) Study on the shape of the interface of saline and fresh water and the mixing zone in the aquifers adjacent to deserts, in which the water table is lower than the saline water level of the desert. Seawater intrusion into coastal aquifers is inherently a transient process. But due to the limitations in acquiring and analysis of numerical and experimental results, less attentions has been paid to this transitory behavior. In this research data was collected automatically and without human intervention in both laboratory experiments and numerical model. Image processing techniques was used for acquiring of laboratory data and the results of numerical simulations was acquiring by algorithmic implementations. The results for saltwater wedge showed that: 1) Behavior of wedge area index is significantly similar to the index of toe wedge length in transient conditions. 2) In the advancing case, the wedge height reaches the steady state condition much sooner than the saltwater wedge toe length and the saltwater wedge area, while in the receding case, all three index stop at the same time. Also, the results for the mixing zone showed that: 1) at the early stages of the wedge receding due to washing and mixing processes, the thickness of the mixing zone increases. But continuing the receding stage, washing process is reduced and gradually stops. As a result, the dilute regions get closer to the dense regions of the mixing zone and thickness of the mixing zone is reduced again. 2) Speed of advancing and receding of saltwater wedge does not affect the mixing zone thickness in the steady state condition. The results of experimental and numerical studies on saltwater intrusion problem into the aquifers adjacent to the desert showed that: 1) as the concentration of desert saline water increases, the interface moves toward the aquifer with lower slope. Regardless of how much desert saline water concentration is, the slope of interface decreases over time