Heavy rains triggering flash floods in urban environment: A case from Chiavari (Genoa metropolitan area, Italy)

Between 10th and 11th November, 2014, heavy rainfall over a short period fell on the eastern Genoa metropolitan area. The geohydrological event had important ground effects, among them the simultaneous flooding of Entella and Rupinaro streams, in Chiavari city. In lower Lavagna valley, the main tributary of the Entella, a landslide caused two casualties, while serious damage to buildings and infrastructures were registered in Chiavari's Old Town and in the nearby communities of Carasco and Cogorno. In the Entella basin, the rainfall peaked at 60 mm/hour and accumulated 220 mm in six hours. The levels of the streams rose instantly, showing concentration times of less than an hour. The Entella rose seven meters, flooding Carasco, Cogorno, and the Caperana neighborhood of Chiavari. Flash flooding of the Rupinaro stream caused water to rise to 1.5 m in Chiavari's historic core. Analyses were carried out of the weather conditions and the ground effects of the events; in addition, studies were made of the main causes of the geo-hydrological risk. In particular, variations in climate and uncontrolled urban development were the cause of increased geo-hydrological hazards and vulnerability of this area, historically subject to flooding. Such conditions of risk are unacceptable, and urgent measures are required to mitigate the effects of heavy rainfall events. © Sapienza Università Editrice.