Groundwater regime has an important role in coastal sediment transport near the coast and beach profile changes. Hitherto, accurate and complete nature of the interaction between wave motions, underground water and beach sediment transport is not yet known. Most existing numerical models for studying the beach groundwater are related to the tidal forces. In this study, interaction of fresh groundwater, salt transport and wave motion was investigated via the process-based model. The hydrodynamic part is computed using the Navier-Stockes equations in conjunction with a k-ε closure turbulence model and Volume of Fluid (VOF) technique. The bed deformation is calculated using empirical sediment transport formula according the influence of watertable changes. Furthermore, the wave-induced watertable fluctuations and effects of infiltration/exfiltration on the nearshore sediment transport are discussed. The groundwater flow and salt transport are considered based on density-variable model. The results reveal that in the surf zone, the sediment transport rate increases towards the shore until the wave breaks whereas in the swash zone it decreases and the greatest erosion takes place in the vicinity of the wave breaking point.