CONTRIBUTO ALLO STUDIO DELLA PERICOLOSITÀ ALLUVIONALE NEI BACINI TORRENTIZI DELLA REGIONE CAMPANIA

Questo progetto di Dottorato si è concentrato sui fenomeni di flash floods della Regione Campania e sullo studio della loro pericolosità. I fenomeni alluvionali torrentizi s’innnescano in seguito a precipitazioni brevi ed intense, concentrate nello spazio, ed interessano bacini idrografici caratterizzati da dimensioni limitate da pochi km2 a poche centinaia di km2 (Borga et al., 2007), elevate pendenze, basso tempo di corrivazione e portate a regime stagionale (Merheb et al., 2016). I bacini con tali caratteristiche in Campania hanno recapito sia in aree pedemontane che direttamente in mare. Le aree di deposizione di questi bacini sono spesso densamente abitate, per cui la popolazione ivi residente è esposta ad un rischio elevato. Attraverso un’analisi critica della letteratura esistente è stato costruito un database dedicato ai flash floods che hanno interessato la regione. Sono stati censiti 474 eventi, dal 1540 al 2015. Per ogni evento sono note le informazioni di occorrenza spaziale e temporale ed i danni prodotti. Inoltre, è stata inserita una classe di accuratezza relativa alle informazioni temporali, che consente in maniera immediata di comprendere il grado di conoscenza sul fattore tempo. Sono stati collezionati anche i dati pluviometrici relativi all’evento innescante qualora disponibili. I bacini interessati dagli eventi sono stati suddivisi in 5 tipologie, al fine di distinguere la tipologia di materiale presente nel bacino, e di ipotizzare la tipologia di trasporto prevalente. La classificazione è stata fatta considerando il substrato del bacino (carbonatico o vulcanico), la presenza o meno di coperture detritiche e la tipologia delle aree di deposito (conoide alluvionale o delta costiero). Le 5 classi sono le seguenti: bacino carbonatico con copertura piroclastica, bacino carbonatico senza copertura piroclastica, bacino carbonatico con copertura piroclastica e recapito a mare, bacino vulcanico, bacino vulcanico con recapito a mare. Sulla base delle dimensioni del bacino interessato dall’evento invece, sono state definite 3 classi: minori di 3 km2; comprese tra 3 km2 e 10 km2; maggiori di 10 km2 ma inferiori a 60 km2. Il database ha consentito di eseguire un’analisi sul dove e quando gli eventi di flash floods si sono verificati in Campania, nonché una stima dei danni prodotti. Sulla base dei dati a disposizione è stata inserita l’informazione relativa alla tipologia principale di flusso: water flood o debris flow. Tale distinzione è stata fatta principalmente su base morfometrica (Scorpio, 2011), nei rimanenti casi l’informazione è stata estratta dalla fonte d’informazione utilizzata solo nei casi in cui era chiara e precisa. Tra i numerosi eventi censiti sono stati selezionati diversi bacini per l’applicazione del software RAMMS (RApid Mass MovementS- Debris Flow runout model) che consente di simulare i deflussi nelle aree di conoide. Il software è stato utilizzato per simulare scenari d’evento nei bacini di Quadrelle (AV) e Castellammare di Stabia (NA), mentre per i bacini di Paupisi (BN ) e Buccino (SA) è stata eseguita una back analysis perché si avevano a disposizione i dati di campo relativi all’estensione e all’altezza dei depositi messi in posto durante gli eventi occorsi in queste aeree, rispettivamente nel 2015 e nel 2011. L’attenzione è stata concentrata sulla deposizione nelle aree di conoide urbanizzate. I risultati ottenuti sono stati analizzati in maniera oggettiva, attraverso l’applicazione dell’analisi quantitativa al fine di utilizzare i parametri corrispondenti ai test migliori a scopo previsionale in bacini con caratteristiche geomorfologiche simili

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

Abstract. This study presents an historical database of flash flood events in the Campania region of southern Italy. The study focuses on small catchments characterized by intermittent flow, generally occurring during and after heavy rainstorms, which can be hydrologically defined as small Mediterranean catchments. As the outlet zones of these catchments (consisting mainly of alluvial fans or fan deltas) are highly urbanized in Campania, the population living in the delivery areas is exposed to high risk. Detailed scrutiny and critical analysis of the existing literature, and of the data inventory available, allowed us to build a robust database consisting of about 500 events from 1540 to 2015, which is continuously updated. Since this study is the first step of a longer project to perform a hazard analysis, information about time and site of occurrence is known for all events. As for the hazard analysis envisaged, collecting information about past events could provide information on future events, in terms of damage and also spatial and temporal occurrence. After introducing the issue of flash floods in Italy we then describe the geological and geomorphological settings of the study area. The database is then presented, illustrating the methodology used in collecting information and its general structure. The collected data are then discussed and the statistical data analysis presented

Landslides, floods and sinkholes in a karst environment: the 1–6 September 2014 Gargano event, southern Italy

In karst environments, heavy rainfall is known to cause multiple geohydrological hazards, including inundations, flash floods, landslides and sinkholes. We studied a period of intense rainfall from 1 to 6 September 2014 in the Gargano Promontory, a karst area in Puglia, southern Italy. In the period, a sequence of torrential rainfall events caused severe damage and claimed two fatalities. The amount and accuracy of the geographical and temporal information varied for the different hazards. The temporal information was most accurate for the inundation caused by a major river, less accurate for flash floods caused by minor torrents and even less accurate for landslides. For sinkholes, only generic information on the period of occurrence of the failures was available. Our analysis revealed that in the promontory, rainfall-driven hazards occurred in response to extreme meteorological conditions and that the karst landscape responded to the torrential rainfall with a threshold behaviour. We exploited the rainfall and the landslide information to design the new ensemble-non-exceedance probability (E-NEP) algorithm for the quantitative evaluation of the possible occurrence of rainfall-induced landslides and of related geohydrological hazards. The ensemble of the metrics produced by the E-NEP algorithm provided better diagnostics than the single metrics often used for landslide forecasting, including rainfall duration, cumulated rainfall and rainfall intensity. We expect that the E-NEP algorithm will be useful for landslide early warning in karst areas and in other similar environments. We acknowledge that further tests are needed to evaluate the algorithm in different meteorological, geological and physiographical settings

Landslides, floods and sinkholes in a karst environment: the 1–6 September 2014 Gargano event, southern Italy

Abstract. In karst environments, heavy rainfall is known to cause multiple geohydrological hazards, including inundations, flash floods, landslides and sinkholes. We studied a period of intense rainfall from 1 to 6 September 2014 in the Gargano Promontory, a karst area in Puglia, southern Italy. In the period, a sequence of torrential rainfall events caused severe damage and claimed two fatalities. The amount and accuracy of the geographical and temporal information varied for the different hazards. The temporal information was most accurate for the inundation caused by a major river, less accurate for flash floods caused by minor torrents and even less accurate for landslides. For sinkholes, only generic information on the period of occurrence of the failures was available. Our analysis revealed that in the promontory, rainfall-driven hazards occurred in response to extreme meteorological conditions and that the karst landscape responded to the torrential rainfall with a threshold behaviour. We exploited the rainfall and the landslide information to design the new ensemble–non-exceedance probability (E-NEP) algorithm for the quantitative evaluation of the possible occurrence of rainfall-induced landslides and of related geohydrological hazards. The ensemble of the metrics produced by the E-NEP algorithm provided better diagnostics than the single metrics often used for landslide forecasting, including rainfall duration, cumulated rainfall and rainfall intensity. We expect that the E-NEP algorithm will be useful for landslide early warning in karst areas and in other similar environments. We acknowledge that further tests are needed to evaluate the algorithm in different meteorological, geological and physiographical settings

A Chronological Catalogue of Sinkholes in Italy: The First Step Toward a Real Evaluation of the Sinkhole Hazard

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A Chronological Database about Natural and Anthropogenic Sinkholes in Italy

Sinkholes are a widespread geological hazard, typical of karst lands, where they generally originate as collapse features related to presence of underground voids. Nevertheless, other types of sinkholes can be formed through solution, suffusion and sagging processes. Sinkholes can also be originated in relation to artificial cavities, excavated by man in past times. In Italy, sinkholes interest large sectors of the country, given the very long history of Italy with an intense utilization of the underground. They cause serious damage to infrastructures, economic activities, and human health every year. We present a catalogue on natural and anthropogenic sinkholes in Italy, as the first step toward evaluation of the sinkhole hazard. After introducing sinkholes, which is definitely a highly underrated type of disaster in Italy, we point out their occurrence in the country. We illustrate the methodology used to build the database, with particular focus on accuracy and reliability of the data. Collecting information from different types of sources, a catalogue of some 1190 sinkhole events is built. Database structure and data analysis are then illustrated. Eventually, we draw some conclusions on the likely uses of our work by providing recommendations for environmental management on this very delicate issue

Mimic expert judgement through automated procedure for selecting rainfall events responsible for shallow landslide: A statistical approach to validation

This paper proposes an automated method for the selection of rainfall data (duration, D, and cumulated, E), responsible for shallow landslide initiation. The method mimics an expert person identifying D and E from rainfall records through a manual procedure whose rules are applied according to her/his judgement. The comparison between the two methods is based on 300 D- E pairs drawn from temporal rainfall data series recorded in a 30 days time-lag before the landslide occurrence. Statistical tests, employed on D and E samples considered both paired and independent values to verify whether they belong to the same population, show that the automated procedure is able to replicate the expert pairs drawn by the expert judgment. Furthermore, a criterion based on cumulated distribution functions (CDFs) is proposed to select the most related D- E pairs to the expert one among the 6 drawn from the coded procedure for tracing the empirical rainfall threshold line