Development of a modelling strategy for simulation of coastal development due to tsunamis

The world’s coasts get more populated every year and most of them are under tsunami risk. Recently the 2004 Indonesia tsunami and the 2011 Japan tsunami have shown the destructive potential of tsunamis interacting with human settlements. Inundation of dry land is the most known tsunami damage but tsunamis also change the coastal morphology, at least temporally. In most of the cases, those changes disappear within several months or years. This work seeks to get a better understanding of the tsunami phenomenon and its consequences beyond wave height, by means of the modelling of tsunami morphodynamics. First, a modelling study was performed addressing the possible consequences of tsunamis at the North Sea and the German Bight, including a Storegga-like scenario. Tsunami current velocities were modelled and compared with those of storm surges at the North Sea and German Bight. Tsunami water levels were found to be smaller than those of storm surges, yet their flow velocities were comparable and tsunamis acted during a shorter period of time. Second, a parameterization of tsunamis was tried by means of N-waves. The morphological changes caused by the waves depended on their orientation. Tsunami flow velocities and morphological changes were more sensitive to the waveform than runup, making difficult to establish a generalization. And third, three-dimensional morphological changes were simulated in Tamil Nadu at the east coast of India by a tsunami similar to the 2004 Indian Ocean tsunami. The study region was an open coastline and the model results showed a flattening of the bed and a widening of the beach, both effects documented during the 2004 Indian Ocean tsunami. The results obtained in this thesis show that there is still much work to do on modelling tsunami morphodynamics. There are no specific equations for tsunami sediment transport and much more data is required for tsunami morphodynamics modelling than for hydrodynamics modelling