The research is conducted on the Albedosa River (northern Apennines, Italy) whose catchment was affected by an extreme flood on 21–22 October 2019. According to the observational data from meteorological and hydrometric stations, it was estimated the flood occurred with a return period of 500-years and originated from very intense rainfall. The catchment received in 12 hours more than 400 mm, which is nearly half of the mean annual rainfall. This study investigates the geomorphic response of the Albedosa River channel and its adjacent floodplain to the extreme flood by geomorphological post-flood field surveys and interpretation of pre-and post-flood aerial photographs. The evaluation is carried out by making a synergistic use of two methods, GIS remote sensing (Orthophotos, DTMs and cross-sections) and field surveys. Although the Albedosa catchment has a relatively sparse population, the flood of October 2019 caused significant damages to agriculture fields, buildings and infrastructures such as roads and bridges. In order to mitigate the risk of floods in the future, having an accurate map of flood-prone areas and using appropriate flood warning tools is crucial. Analyzing changes in planforms over time can provide a reliable estimation of system variability and valuable information about the potential rates and magnitude of future channel changes. To address assessments of large-scale past and future channel trajectories, the IDRAIM framework based on the integration of remote sensing analysis and field survey is applied. As a result of this research, undertaken within the framework of geomorphological analysis, we can get an important insight into the ongoing dynamics of the Albedosa River. The evidence shows that the Albedosa River floodplain experienced a reactivation of bank erosion after decades of stability, following the extreme flood of 2019. Since the analysis of the sinuosity index can provide information about morphological pattern changes over time in single-thread channels, by comparing historical maps and aerial photographs from 1900 to 2019, channel morphology in the Albedosa River has modified from straight to sinuous, and from sinuous to meandering in 10 reaches out of 28 total reaches. Based on aerial photographs taken before and after the flood, an analysis of the channel width represents widening occurred in 27 reaches out of 28, as well as, we can infer that there was no sign of braiding, or if there was, it was minimal. In addition, the largest width ratio (the channel width after the flood compared with the channel width before the flood) was attributed to the unconfined reaches. Furthermore, the MDI and EDC IDRAIM indicators associated with these highly widened reaches demonstrate high values, which indicate a relevant tendency to channel instability over the last decades and likely geomorphic processes changes during extreme events, respectively. Finally, the morphodynamic corridor concerning the area interested by the channel dynamic during extreme events showed the flood in 2019, occurred exactly in the channel mobility corridors defined accordingly to the IDRAIM procedure. Keywords: Albedosa River, Piedmont region, extreme flood, IDRAIM framework, geomorphological mapping, geomorphic changes.
Dinamiche fluviali e pericolosità in risposta ad eventi idrologici estremi: la piena di ottobre 2019 nel bacino del Torrente Albedosa (Piemonte, Italia). Questo lavoro si è focalizzato sul Torrente Albedosa (Appennino settentrionale, Italia), il quale in data 21-22 ottobre 2019 è stato interessato da un evento di piena ad alta magnitudo. Secondo i dati disponibili forniti da stazioni di monitoraggio meteorologico e idrometrico, l’evento di piena è stato indotto da precipitazioni molto intense ed è caratterizzato da un tempo di ritorno di circa 500 anni. Sul bacino idrografico sono caduti più di 400 mm di precipitazioni liquide in 12 ore, ovvero un valore prossimo alla metà del totale delle precipitazioni medie annue caratterizzanti l’area. Questo studio ha analizzato la risposta geomorfologica del Torrente Albedosa (alveo attivo e piana inondabile) indotta dalla piena ad alta magnitudo, utilizzando in sinergia dati ottenuti mediante rilievi geomorfologici di campo e da interpretazioni di fotografie aeree dell’area studio acquisite precedentemente e successivamente all’evento. Il bacino del Torrente Albedosa è relativamente poco abitato. Nonostante ciò, la piena del 2019 ha provocato danni significativi ai campi agricoli, ad edifici e a infrastrutture quali ponti e strade. Al fine di mitigare il rischio indotto dalle piene è fondamentale predisporre mappe relative alle aree propense ad essere inondate e adeguati strumenti di definizione del rischio. L’analisi delle modificazioni morfologiche indotte dalla piena rappresenta quindi un elemento utile alla definizione della dinamicità del sistema in risposta ad eventi idrologici intensi, fornendo elementi cruciali per l’individuazione di aree potenzialmente soggette a modificazioni morfologiche. Al fine di valutare la traiettoria evolutiva del corso d’acqua in esame è stato utilizzato il sistema integrato descritto in IDRAIM, il quale prevede l’impiego di dati acquisiti sia mediante remote sensing che sul terreno. I risultati di tale analisi forniscono importanti informazioni circa le dinamiche attualmente attive lungo il Torrente Albedosa. I dati evidenziano come la piana inondabile del Torrente Albedosa, dopo alcuni decenni di stabilità, abbia subito durante la piena del 2019 una riattivazione indotta dall’erosione spondale. L’analisi della sinuosità può fornire informazioni utili circa le modificazioni morfologiche di un corso d’acqua monocursale. Confrontando materiale cartografico e fotografie aeree prodotti fra il 1900 e il 2019 è possibile osservare come la configurazione planimetrica del Torrente Albedosa sia mutata da rettilinea a sinuosa o da sinuosa a meandriforme in 10 tratti su un totale di 28 tratti analizzati in questo lavoro. Sulla base delle fotografie aeree acquisite precedentemente e successivamente alla piena del 2019, un allargamento del canale si è verificato in 27 tratti su un totale di 28 tratti, tuttavia senza generazione di morfologie a canali multipli. Inoltre, i maggiori allargamenti in termini di rapporto fra la larghezza del canale post e pre-evento si è verificata nel tratti non confinati. Gli indicatori di IDRAIM MDI e EDC associati a questi tratti soggetti a maggiori allargamenti mostrano valori elevati che indicano rispettivamente un’elevata tendenza all’instabilità del canale avvenuta nel corso degli ultimi decenni e probabili variazioni morfologiche significative in risposta ad eventi idrologici intensi. Infine, il corridoio interessato dalle modificazioni avvenute durante la piena ad alta magnitudo del 2019 corrisponde esattamente alla fascia di potenziale dinamica individuata mediante l’applicazione di IDRAIM. Parole chiave: Torrente Albedosa, Regione Piemonte, eventi idrologici estremi, , sistema IDRAIM, rilevamento geomorfologico, modificazioni morfologiche.
Fluvial dynamics and hazard in response to extreme events: the October 2019 flood in the Albedosa River catchment (Piedmont, Italy)
VALIZADEH, MEHDI
2020/2021
Abstract
The research is conducted on the Albedosa River (northern Apennines, Italy) whose catchment was affected by an extreme flood on 21–22 October 2019. According to the observational data from meteorological and hydrometric stations, it was estimated the flood occurred with a return period of 500-years and originated from very intense rainfall. The catchment received in 12 hours more than 400 mm, which is nearly half of the mean annual rainfall. This study investigates the geomorphic response of the Albedosa River channel and its adjacent floodplain to the extreme flood by geomorphological post-flood field surveys and interpretation of pre-and post-flood aerial photographs. The evaluation is carried out by making a synergistic use of two methods, GIS remote sensing (Orthophotos, DTMs and cross-sections) and field surveys. Although the Albedosa catchment has a relatively sparse population, the flood of October 2019 caused significant damages to agriculture fields, buildings and infrastructures such as roads and bridges. In order to mitigate the risk of floods in the future, having an accurate map of flood-prone areas and using appropriate flood warning tools is crucial. Analyzing changes in planforms over time can provide a reliable estimation of system variability and valuable information about the potential rates and magnitude of future channel changes. To address assessments of large-scale past and future channel trajectories, the IDRAIM framework based on the integration of remote sensing analysis and field survey is applied. As a result of this research, undertaken within the framework of geomorphological analysis, we can get an important insight into the ongoing dynamics of the Albedosa River. The evidence shows that the Albedosa River floodplain experienced a reactivation of bank erosion after decades of stability, following the extreme flood of 2019. Since the analysis of the sinuosity index can provide information about morphological pattern changes over time in single-thread channels, by comparing historical maps and aerial photographs from 1900 to 2019, channel morphology in the Albedosa River has modified from straight to sinuous, and from sinuous to meandering in 10 reaches out of 28 total reaches. Based on aerial photographs taken before and after the flood, an analysis of the channel width represents widening occurred in 27 reaches out of 28, as well as, we can infer that there was no sign of braiding, or if there was, it was minimal. In addition, the largest width ratio (the channel width after the flood compared with the channel width before the flood) was attributed to the unconfined reaches. Furthermore, the MDI and EDC IDRAIM indicators associated with these highly widened reaches demonstrate high values, which indicate a relevant tendency to channel instability over the last decades and likely geomorphic processes changes during extreme events, respectively. Finally, the morphodynamic corridor concerning the area interested by the channel dynamic during extreme events showed the flood in 2019, occurred exactly in the channel mobility corridors defined accordingly to the IDRAIM procedure. Keywords: Albedosa River, Piedmont region, extreme flood, IDRAIM framework, geomorphological mapping, geomorphic changes.È consentito all'utente scaricare e condividere i documenti disponibili a testo pieno in UNITESI UNIPV nel rispetto della licenza Creative Commons del tipo CC BY NC ND.
Per maggiori informazioni e per verifiche sull'eventuale disponibilità del file scrivere a: unitesi@unipv.it.
https://hdl.handle.net/20.500.14239/14476