Prediction of Tsunami Inundation in the City of Lisbon (portugal)

Lisbon city is located inside the estuary of Tagus river, 20 km away from the Atlantic ocean. The city suffered great damage from tsunamis and its downtown was flooded at least twice in 1531 and 1755. Since the installation of the tide-gage network, in the area, three tsunamis caused by submarine earthquakes, were recorded in November 1941, February 1969 and May 1975. The most destructive tsunamis listed along Tagus Estuary are the 26th January 1531, a local tsunami event restricted to the Tagus Estuary, and the well known 1st November 1755 transoceanic event, both following highly destructive earthquakes, which deeply affected Lisbon. The economic losses due to the impact of the 1755 tsunami in one of Europe’s 18t century main harbor and commercial fleets were enormous. Since then the Tagus estuary suffered strong morphologic changes manly due to dredging works, construction of commercial and industrial facilities and recreational docks, some of them already projected to preserve Lisbon. In this study we present preliminary inundation maps for the Tagus estuary area in the Lisbon County, for conditions similar to the 1755 tsunami event, but using present day bathymetric and topographic maps. Inundation modelling is made using non linear shallow water theory and the numerical code is based upon COMCOT code. Nested grids resolutions used in this study are 800 m, 200 m and 50 m, respectively. The inundation is discussed in terms of flow depth, run up height, maximum inundation area and current flow velocity. The effects of estuary modifications on tsunami propagation are also investigated.