Investigation on the use of geomorphic approaches for the delineation of flood prone areas

•Mapping flood hazard on the Tiber River.•Comparative analysis of three different geomorphic approaches for the identification of flood prone areas.•New strategies for preliminary flood hazard mapping in ungauged basins.

SummaryThree different geomorphic approaches to the identification of flood prone areas are investigated by means of a comparative analysis of the input parameters, the performances and the range of applicability. The selected algorithms are: the method proposed by Manfreda et al. (2011) based on a modified version of the Topographic Index (TIm); the linear binary classifier proposed by Degiorgis et al. (2012), which uses different geomorphic features related to the location of the site under exam with respect to the nearest hazard source; the hydro-geomorphic method by Nardi et al. (2006) simulating inundation flow depths along the river valley with the associated extent of surrounding inundated areas. Comparison has been carried out on two sub-catchments of the Tiber River in Central Italy. The simulated flooded areas, obtained using the selected three methods, are evaluated using as a reference the Tiber River Basin Authority standard flood maps. The aim of the research is to deepen our understanding on the potential of geomorphic algorithms and to define new strategies for prompt hydraulic risk mapping and preliminary flood hazard graduation. This is of foremost importance when detailed hydrologic and hydraulic studies are not available, e.g., over large regions and for ungauged basins.