Coastal Protection for Tsunamis

Previous research showed that a tsunami similar to the 1755 event would inundate Caxias’ low-ground areas in Oeiras municipality, Portugal. However, the streets of downtown Caxias were not well reproduced, which is a limitation of the area’s mitigation strategies and evacuation plan. For these reasons, new Lidar data were used for the first time in Portugal. The new local topography data allowed the construction of a more accurate DEM, which was used in the tsunami numerical model to update and improve the inundation results. As a complement, a field survey was conducted in several locations to assess coastal features and protection. The numerical model results show that low-ground areas up to 6 m in height were inundated by the tsunami, including the residential area, the road, and the railway. To stop the tsunami waves from inundating these areas, it is proposed that the construction of more sea walls up to 7 m in height and a third bridge over the Barcarena Stream, only for pedestrians, ranging from 5 to 7 m in height, which will serve as a gate for the incoming tsunami waves. These coastal protections should be part of the strategy to mitigate coastal overtopping (winter storm surges and tsunamis) not only in Caxias but also in other coastal zones.