This study investigates the effect of old river mouth and the Teizan Canal to the 2011 tsunami at Arahama and Akaiko, both part of Sendai Coast, Japan. At both locations, the Teizan Canal is situated parallel to the shoreline. This canal affected the tsunami inundation as well as the return flow, effectively draining the water back to the sea. In addition, there were old river mouths, which have been closed for many years in these locations. Nevertheless, the return flow of the 2011 tsunami caused the breaching of the sandy coast at the old river mouth locations. A detail topography analysis was carried out based on DEM data. The topography data show that this area is a river basin with mild slope towards the old river mouth location. The data was further analyzed by performing a flow accumulation analysis using GIS. The results confirm that the topographical features in both locations caused the flow to accumulate through the local channel and canal towards the locations of the old river mouth, which caused the breaching.