Comparing a Large‐scale Dem‐based Floodplain Delineation Algorithm With Standard Flood Maps: The Tiber River Basin Case Study

A large‐scale floodplain delineation algorithm is applied to identify potentially inundated areas at the basin scale. The model, which mainly uses a digital elevation model (DEM) and design flood peak discharge at the outlet as input data, is implemented within a geographic information system (GIS). It implements a preliminary GIS‐based terrain analysis framework for estimating the stream network, surface flow direction and drainage grids, while the core algorithm implements an automated fluvial cross‐section extraction for discharge and flow height estimation. The delineation is then implemented by filtering the floodplain cells as those cells whose elevation is lower than the corresponding channel flow height. The proposed ‘hydrogeomorphic floodplain’, obtained on the Tiber River basin (approx. 17 000 km 2 ) using the global NASA Shuttle Radar Topography Mission (SRTM) DEM at 90 m resolution, is compared to the official flood maps of the Tiber River Basin Authority to evaluate the model behaviour with respect to standard flood mapping results. The presented case study shows the potential of using an automated GIS algorithm and largely available remotely sensed data for the preliminary identification of the floodplain footprint at the global scale.