Evaluation of tsunami flooding using geomorphologic evidence

Whatever the generating mechanism of a tsunami may be, this event can discharge destructive energy along coastal areas and produce widespread inundation. The presence of large boulders along rocky coasts could be a useful indicator to understand the extent of the impact of past tsunami floods. A detailed study of the deposited boulder features – size, shape and rock density and their initial position prior to the transport – is extremely important when reconstructing the possible morphodynamic scenario(s); applying the appropriate equations is important when aiming to assess the maximum extent of flooding. The integration of morphological and hydrodynamic data allows for an estimation of the water level during the tsunami event responsible for boulder transport. Moreover, it is possible to calculate how far the impacting wave flooded inland; this is a function of the wave parameters and of the degree of roughness of the flooded terrain that is expressed by the Manning number. To evaluate its probable/average value, experimental data, computer simulations and post-tsunami surveys have been performed in two sectors of the Southern Apulia coastline, characterised by the presence of tsunami boulder fields and/or ridges. The surveys in each site have allowed for the calculation of the boulder sizes, the estimation of their pre-transport location and the extent of inland flooding. Data have been processed using a Geographic Information System (GIS). As a result a flooding map, useful in planning future possible actions for coastal area use, has been produced.