Low-lying beaches are highly dynamic and vulnerable coastal environments susceptible to flooding and erosion episodes, which will be exacerbated in the context of climate change. Highly complex processes take place during storms, and numerical models are useful tools to assess them. In this study, the XBeach model is applied to an idealised beach to analyse the role of the initial topobathymetry in the formation of washover deposits under an overwash episode caused by a storm event. Initial representative profiles were obtained from real measured 12-year time-lapse topobathymetries, after performing a PCA and a cluster analysis. Alongshore-periodic morphological patterns (mega-cusps, rhythmic dunes, and crescentic bars) of different realistic wavelengths were also included. After running the model with the storm, results of the different scenarios were compared. The washover volume deposited after the overwash event changed when different initial topobathymetries were used and when the morphological pattern wavelength was varied. These outcomes highlight the importance of using real, accurate and up to date topobathymetric data in numerical modeling studies. Also, it is important to consider the possible presence of morphological patterns, since not incorporating them in the initial topobathymetry or misrepresenting their wavelength, could lead to significant changes in washover deposit volumes, and in sediment transport processes in general.