Seawater intrusion (SWI) is a phenomenon that has raised various concerns in recent past years, and it is described by the movement of saline water into freshwater coastal aquifers. The invasion and movement of saline water induce a significant degradation to groundwater quality. The majority of aquifers that are severely contaminated by SWI are unconfined coastal aquifers. In order to manage saline aquifers more effectively, it is crucial to study the dynamics of groundwater flow and contaminants transport. Consequently, remedial strategies/approaches need to be conducted, developed, and planned with high efficiency. While several studies have investigated various aspects of SWI using numerical models, physical sandbox experiments, field experiments and investigations, or a combination of two or all, none have specifically explored the dynamics of SWI under Aquifer Storage and Recovery (ASR) system using physical model (sandbox). ASR systems are used as part of the aquifer management process, in order to mitigate the salinization of groundwater reservoirs. Wells are used by ASR to inject freshwater into aquifers and to extract it when needed. The main objective of this thesis project is to investigate how fresh-saline water interface dynamics are affected by ASR systems using sandbox experiments with homogeneous and heterogeneous (layered) coastal aquifer settings. This study provides knowledge and understanding regarding the impact of ASR in managing unconfined coastal aquifers affected by SWI. Sandbox models has the ability to visualize the changes in the fresh-saline water interface directly along with allowing quantification of several parameters like saline water interface position, salinized area of the aquifer, etc. A Poly (methyl methacrylate) (PMMA) sandbox physical model used to mimic the unconfined homogenous and heterogeneous coastal aquifers using artificial white sand. In homogeneous aquifer setting, three injection and abstraction wells are installed in upstream (W1), midstream (W2) and downstream (W3). The heterogeneous (two layers) has four injection/abstraction wells, each installed in a layer: upstream wells (W1, lower layer & W1 upper layer) and midstream (W2, lower layer & W2 upper layer). Experiment analysis consist of qualitative (images) and quantitative data measured in laboratory such as water level and water salinity measurements. The primary finding of the study was that fresh water injection contributes to management of saline aquifer via causing retreat of the saline interface seaward direction.. This level of impact found to be a function of injection depth, injection to abstraction period, storage period of injected water and other factors as detailed later in the results chapter. Water injection near the saline interface toe was most effective scenario in reducing aquifer salinity by 76% for the homogeneous aquifer. Two storage periods were set to store water after injection: 10 minutes and 20 minutes. The longer storage period (before start of abstraction/recovery) resulted in higher reduction of saline area and salinity level. This is because injection helps to increase water level and hence the hydraulic gradient that controls ingression of saline interface. This illustrates the importance of identifying the specific storage period when ASR is practiced in salinized coastal aquifers. Aquifer salinity increased during the water abstraction phase for all abstraction scenarios (50%, 100%, 150%, and 200% of the injected volume) at both storage times when injection was at W1 (upstream) and W3 (downstream). In contrary, water abstraction, when injection into W2 (midstream) occurred, showed a reduction in aquifer salinity (compared to initial condition scenario) for all runs in both storage durations, except for 150% and 200% abstractions in 10-minute storage. In all runs in a homogeneous aquifer, the salinity of the water abstracted was within the freshwater range when abstraction took place from W1 and W2, while the water abstracted from W3 was saline water. The results of the heterogeneous aquifer were more realistic, helping us to better understand fresh-saline water dynamics in various geological structures. The W2 midstream injection was more effective in controlling aquifer salinity. Injection of fresh water into the W2 lower layer decreased salinity by 53.3%, whereas injection into the W2 upper layer decreased salinity by 55.8%. The aquifer remediation that involved injecting water into both layers at W1 resulted in a 17.5% decrease in salinity. The 20-minute storage period selected as the storage time to store injected water in heterogeneous aquifer setting. Water abstraction from different wells from both layers showed an increase in aquifer salinity but with different levels. The quality of water collected from all scenarios of the heterogeneous aquifer was within the acceptable range of fresh water. The ideal ASR scenario for a heterogeneous aquifer is represented by the case of injecting fresh water in the middle of the tank (W2) in the lower layer and abstracting water from the upstream (W1) of the upper layer. In general, the study illustrates clearly the impact of the ASR system in better sustaining the water supply from the coastal aquifers. The results illustrated that ASR allows to abstract more groundwater from the aquifer without jeopardizing the water quality compared with situation when ASR not practiced. Better planning and optimum operation of ASR will help to sustain the aquifer quality and hence the supply. This study helps to better understand the potential dynamics of groundwater under the ASR system in a layered system as it is the case in Al-Batinah North coastal aquifer where major abstraction is from the more conductive upper layer. The findings of this study will help to validate developed density-dependent numerical tools and represent a new benchmarking case study for those codes. This is important due to the complicated flow patterns of density-dependent flow and transport in a layered heterogeneous aquifer setting. There is a need for future studies about fresh-saline water dynamics, such as implementing ASR in confined aquifers, using the same well for injection and storage, and utilizing multiple wells for abstraction. Numerical modeling to mimic the presented sandbox experiments need to be conducted. This will allow to run more scenarios and analysis impact of different parameters on the SWI dynamics.