Topographic predictors of susceptibility to alluvial fan flooding, Southern Apennines

Abstract

The flooding susceptibility of alluvial fans in the Southern Apennines has long been neglected. To partly address this oversight, we focus on the region of Campania which contains highly urbanized piedmont areas particularly vulnerable to flooding. Our findings are based on stratigraphic analysis of the fans and morphometric analysis of the basin‐fan systems. Using geomorphological analysis we recognized active alluvial fans while stratigraphic analysis together with statistical analysis of the morphometric variables was used to classify the fans in terms of the transport process involved. The results indicate that in the geological context examined, the best discrimination between debris flow (Df) and water flood (Wf) processes is achieved by means of two related variables, one for the basin (feeder channel inclination, Cg) and one for the fan (fan length, Fl). The probability that an unclassified fan belongs to group Wf is computed by applying a logistic function in which a P value exceeding 0.5 indicates that a basin/fan system belongs to group Wf. This important result led to the classification of the entire basin/fan system data. As regards process intensity, debris flow‐dominated fans are susceptible to the occurrence of flows with high viscosity and hence subject to more severe events than water flood‐dominated fans. Bearing this in mind, the data gathered in this study allow us to detect where alluvial fan flooding might occur and give information on the different degrees of susceptibility at a regional scale. Regrettably, urban development in recent decades has failed to take the presence of such alluvial fans into account due to the long recurrence time (50–100 years) between floods. This paper outlines the distribution of such susceptibility scenarios throughout the region, thereby constituting an initial step to implementing alluvial fan flooding control and mitigation. Copyright © 2012 John Wiley & Sons, Ltd.

A database on flash flood events in Campania, southern Italy, with an evaluation of their spatial and temporal distribution

“…Whilst in the Italian Alps, due to their high frequency, flash floods in small basins have been the subject of detailed studies for many decades (Crosta and Frattini, 2004;Sosio et al, 2007;Carrara et al, 2008;Simoni et al, 2011;Arattano et al, 2012Arattano et al, , 2015Marchi and Tecca, 2013;Berti and Simoni, 2014;Blahut et al, 2014;Tiranti et al, 2014), in the Apennines they have typically been analyzed with less attention (Sorriso Valvo et al, 1998;Zanchetta et al, 2004a;Santo et al, 2002Santo et al, , 2015Garfì et al, 2007;Cascini et al, 2008a;Santangelo et al, 2011Santangelo et al, , 2012Alessio et al, 2013;Antronico et al, 2015a, b;Scorpio et al, 2016).…”

“…The study area of this paper is situated in Campania, in the Southern Apennines of Italy, a region which in recent decades has been affected by severe flash floods with serious damage and fatalities (Calcaterra et al, 2000(Calcaterra et al, , 2003Santo et al, 2002Santo et al, , 2012Santo et al, , 2015Del Prete and Mele, 2006;Santangelo et al, 2006Santangelo et al, , 2011Santangelo et al, , 2012Chirico et al, 2012;Alessio et al, 2013). The focus of the study consisted of small catch- ments with intermittent flow, generally occurring during and after heavy rainstorms, which can be hydrologically defined as SMCs.…”

“…The focus of the study consisted of small catch- ments with intermittent flow, generally occurring during and after heavy rainstorms, which can be hydrologically defined as SMCs. All these basins are smaller than 10 km 2 , are characterized by low concentration times (from 30 min to several hours; Santo et al, 2002;Santangelo et al, 2012;Scorpio et al, 2016), and are highly prone to flash flood events. Aiming at collecting all the available information on floods occurring in such catchments, we consulted and scrutinized a variety of sources and scientific papers, with a view to building a reliable catalogue of these events.…”

Post flash flood survey: the 14th and 15th October 2015 event in the Paupisi-Solopaca area (Southern Italy)

“…Active fans generally have very small areas and the slope presents values ranging from 6°to 19°. Some of these morphometric attributes (feeder channel inclination and fan length) were assessed in order to classify the studied systems in terms of expected depositional processes, following Santangelo et al (2012), which proved to be debris flow dominated.…”

“…The alluvial fans are fed by drainage basins with high slopes, short response times and with a generally low runoff, occurring mainly during the most heavy rainfall periods. Recent studies have dealt with relationships between morphometric attributes of alluvial fans and those of the corresponding upslope basins, showing that this approach can be used effectively to classify alluvial fans with respect to the two dominant flooding mechanisms, namely debris flows and water floods (Santangelo et al, 2012).…”