Flood susceptibility assessment in a highly urbanized alluvial fan: the case study of Sala Consilina (southern Italy)

Abstract

Abstract. This paper deals with the risk assessment to alluvial fan flooding at the piedmont zone of carbonate massifs of the southern Apennines chain (southern Italy). These areas are prime spots for urban development and are generally considered to be safer than the valley floors. As a result, villages and towns have been built on alluvial fans which, during intense storms, may be affected by flooding and/or debris flow processes.The study area is located at the foothills of the Maddalena mountains, an elongated NW-SE trending ridge which bounds to the east the wide intermontane basin of Vallo di Diano. The area comprises a wide detrital talus (bajada) made up by coalescent alluvial fans, ranging in age from the Middle Pleistocene to the Holocene. Historical analysis was carried out to ascertain the state of activity of the fans and to identify and map the zones most hit by past flooding. According to the information gathered, the Sala Consilina fans would appear prone to debris flows; in the past these processes have produced extensive damage and loss of life in the urban area. The watershed basins feeding the fans have very low response times and may produce debris flow events with high magnitudes. Taking into account the historical damage, the fan surface morphology, and the present urban development (street orientation and hydraulic network), the piedmont area was zoned and various susceptibility classes were detected. These results may represent a useful tool for studies aiming at territorial hazard mapping and civil protection interventions.

Multiscale map analysis in alluvial fan flood-prone areas

“…We followed the method proposed by Santangelo et al (2011) which allows the construction of a flood susceptibility map by means of a map overlay procedure based on the susceptibility matrix. In particular, we discuss here the four 'base' maps required for this application: historical events map, recent lobes map, steepness map and hydraulic and road network conditions (see Main Maps 1b, 2b, 3b, and 4b).…”

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

“…In order to discriminate flash floods from other hydrogeological events, we first adopted a "geographical" approach. Based on the evidence that all the recently occurring and well-documented flash flood events (i.e., with accurate event description and availability of rainfall data; Alessio et al, 2013;Chirico et al, 2012;Santangelo et al, 2011Santangelo et al, , 2012Santo et al, 2002Santo et al, , 2012Santo et al, , 2015Scorpio et al, 2016) affected SMCs, we catalogued all the events recorded in the outlet zone of this kind of hydrographic basin as "flash floods".…”

“…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).…”

“…Due to the particular orography and climate of the country, they occur in many different settings, from mountain valleys (Crosta and Frattini, 2004;Tropeano and Turconi, 2004;Gaume et al, 2009) to coastal and inland plains Santangelo et al, 2011;Porfido et al, 2013), in volcanic areas (Alessio et al, 2013), and in semiarid and/or karst environments (Parise, 2003;Cossu et al, 2007;Delle Rose and Parise, 2010). Flash floods generally occur in ungauged watersheds where the lack of information on precipitation and discharge is significant due to the lack of spatially well-distributed rain or flow data.…”

“…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.…”