Estimation of the value of Manning’s coefficient using Terrestrial Laser Scanner techniques

The estimation of the inundation limit of a tsunami wave is, among other factors, influenced by coastal roughness as expressed by Manning's coefficient. The Manning number is an empirically derived coefficient, which is dependent on many features including surface roughness and sinuosity. It is calculated by using the empirical formula for open channel flow, or for free-surface flow driven by gravity. In this study, the Manning coefficient was estimated by directly measuring the roughness of a surface by means of a Terrestrial Laser Scanner. This kind of survey generates point clouds useful to obtain a digital elevation model (DEM) and the standard deviation of the surface micro-topography. Applying different hypothesized tsunami wave heights, it is possible to obtain a specific Manning number for each surface and material typology. This new methodology was tested in two coastal sectors of the Apulia region (Southern Italy) where, within previous studies, evidence of past tsunamis was found.