The 4th October 2010 flash flood event in Genoa Sestri Ponente (Liguria, Italy)

The Mediterranean Sea and in particular the Liguria region have always been suffering from severe geohydrological events. Landform features and autumnal atmospheric circulation deeply influence the hazard in Genoa city, the capital of Liguria, crossed by many streams: heavy rainfall can trigger flash floods involving structures and infrastructures, often causing fatalities. The recent growth of events characterized by intense rainfall and floods has been amplified by the urban sprawl of flood-plain: these factors seem to be the most important causes in the increase of damage related to geo-hydrological events. In this case, typical of the whole Genoan Metropolitan area, a severe event occurred in Sestri Ponente district on October 4th 2010: a critical rainfall, over 400 mm/6 hours, a peak of 125 mm/h, triggered shallow landslides and flash floods in the Molinassi and Chiaravagna catchments crossing Sestri Ponente, causing one fatality and damage of over 60 million euros. These watercourses show the typical features of Ligurian basins: small areas, steep slopes, proximity of watersheds to the coastline and intense urbanization of the plain. During this event, the hydrological response to rainfall was almost immediate, with times of concentration shorter than 25 minutes. The narrow plain on which Sestri Ponente rises was completely flooded.