Coastal dams are important infrastructure for ensuring freshwater security in the highly populated and economically significant coastal regions. In addition to the higher exposure to detrimental effects of the sea, an additional challenge in the design of coastal dams is ensuring that salination of the reservoir is within regulatory limits. The present study employs a three-phase coupled groundwater flow-solute transport Smoothed Particle Hydrodynamics (SPH) approach for the analysis of a typical cross-section of a coastal dam. The results show that due to the large width of the coastal dam, the amount of salt transported towards the reservoir under the influence of tidal fluctuations and seasonal variation of reservoir level is within acceptable limits set by the regulatory authority. Nevertheless, the efficacy of a plastic cutoff wall to further control the ingress of seawater towards the reservoir is also examined. The results of the seepage analysis without and with cutoff wall demonstrated that the SPH framework can accurately model the physical process and is a reliable tool for such analyses.