The tsunamis severely damaged several coastal structures in the past, including dykes, quay walls and breakwaters. The scouring of the foundation seabed has been identified as a key cause for the failure of many such structures during the tsunami. However, the scouring mechanisms involved with the response of these structures under tsunamis and possible methods to prevent such failures have not been well understood. Detailed numerical investigations are required to comprehend the dynamics underlying the foundation scouring of coastal structures. The complexity inherent in modelling a turbulent tsunami wave and its scouring effects on the seabed soil could be overcome by bridging multiple numerical analysis platforms. The present study thus attempts to quantify the scouring that occurred on the foundation soils of coastal structures through rigorous numerical simulations. Under the influence of the tsunami, significant scouring was seen on the seabed in the harbour side of the offshore structures, such as breakwaters. The depth of scouring depended on the overflowing velocity of tsunami waves and the impact stresses developed in the seabed. The addition of reinforcements has proven to be successful in lowering the scour depth by reducing the impact force of tsunami wave bore on the harbour side seabed. The efficiency of the suggested reinforcements has also been focused in the present study.