GIS-based geomorphological map of the Calore R. alluvial plain near Benevento (southern Italy) overflooded by the 15th October 2016 event

Geomorphological maps play a fundamental role in mitigation of flood hazard and risk (Rinaldi et al., 2015; Magliulo & Valente, 2014). Classical geomorphological maps are nowadays generally replaced by GIS-based information layers. Using GIS, the space can be described by a series of “objects” discretized by points, lines or polygons (Dramis et al., 2011). Examples of GIS-based geomorphological maps of alluvial plains are provided, among others, by Valente & Magliulo (2012) and Magliulo & Cusano (2016). On 15th October 2015, the alluvial plain of the Calore R. underwent a destructive flood, with an increase of the river water level up to 10 m (Valente et al., 2016). In this paper, we describe the GIS-based, full coverage, object-oriented geomorphological map of the overflooded sectors of the Calore R. alluvial plain in the Benevento area. The map is the graphical representation of the results of a geomorphological study, that was carried out by introducing and analyzing into the ArcGIS 9.3 software: (a) 1:50,000-scaled historical topographic maps from 1870, 1909, 1936; (b) 1:25,000-scaled topographic maps from 1955; (c) 1:10,000 nominal-scaled orthophotos from 1998; and (d) 1:5,000 nominal scale orthophotos from 2011. Positional errors ranged from about 30 m to less than 3 m. The detected landforms were checked during a 1:10,000 geomorphological field survey. The alluvial plain was characterized by abandoned channels, anthropic landforms and several orders of river terraces, separated by strongly weathered, reshaped, very gently sloping and inactive fluvial scarps less than 1 m high. The proposed map could be a fundamental tool for a correct flood hazard assessment, which could avoid or reduce the negative effects of events such as that of the 15th October 2015.