Abstract

San Fruttuoso of Camogli is not only the most popular subject of discussion of Portofino Park – internationally well-known for the historical and architectural value of its hamlets and for the environmental qualities of the landscape – but the village is also recognised in progress as a UNESCO World Heritage site.

Various natural hazards threaten these cultural and landscape assets. This study focuses on the debris flows that occurred here on 25th September 1915, when the Abbey complex was damaged and a beach was formed in less than 24 hours.

A number of methods were used to reconstruct the event, following both the scientific approach and the historical-geographical model. Archive research allows us to say that the event involved a rainfall of about 310 mm at Chiavari and of more than 400 mm at nearby areas over less than 4 hours.

The data collected lead us to think that the 25th September 1915 rainfall triggered a debris flow, whose geometrical, sedimentology and magnitude features can be compared to those typical of the alpine environment.

According to the thermo-pluviometrical data recorded at the Chiavari weather station, such an event should have a recurrence time of at least 100 years. However, the unfavourable geomorphological features of the valley related to the present climate trends make the statistical approach less accurate. The mean annual temperature together with dry days shows a positive trend. Therefore, the daily rainfall rate causes a rainfall tropicalisation effect and thus leads to the possibility of heavy rainfall, including triggering shallow instabilities thresholds.

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