Comparison of one-dimensional and two-dimensional GRASS GIS models for flood mapping.

The first step of a risk assessment analysis is the evaluation of flood-prone areas. Nowadays, using Geographic Information System (GIS) technology for risk assessment analysis is very common. However, it is not widely used for defining inundated areas. LiDAR data, such as digital elevation models (DEM), makes GIS numerical models attractive methods for obtaining a flooded area automatically. A first approach (Federici & Sguerso, 2007; Marzocchi, 2009) uses a GIS module in order to simulate perifluvial flood maps, having as prerequisites (i) the conformation of the river floodplain by a high-resolution DEM and (ii) a water surface profile along the river axis calculated for a given water discharge through a generic one-dimensional (1D) hydraulic model (HEC-RAS, Basement, MIKE 11, etc.). On the other hand, a second approach uses a GIS-embedded two-dimensional (2D) model in order to simulate flooded areas due to a dam break (Cannata&Marzocchi, Nat Hazards 61(3):1143–1159, 2012). This module solves the conservative form of the 2D shallow water equations (SWE) using a finite volume method (FVM). We present a comparison between the two models mentioned above, and we analyse the possibility of integrating these two approaches.