Lorenzo Marchi, Marco Cavalli, William Amponsah, Marco Borga, Francesco Comiti, Stefano Crema, Alberto Mazzali, Alessandro Mondini, Giovanni Saulle, Ana Lucía Vela, Alessia Viero, 2013, Documentation and analysis of a flash flood in a test catchment (Pogliaschina Creek, eastern Liguria, Italy), Florisa Melone Memorial Conference, Assisi (Perugia), October 10-11, 2013,
URL: http://www.cnr.it/prodotto/i/277986

Flash floods in mountainous catchments are often associated to intense geomorphic processes, which encompass changes in the morphology of channels (bed erosion and aggradation, channel widening) directly caused by flood discharge, and rainfall-triggered instability phenomena on the slopes. When forest cover is present on catchments slopes and in the valley floor, entrainment and transport of large wood occur, increasing the probability of channel obstruction. The interaction of hazardous hydraulic and geomorphic processes results in multiple risks for human settlements and transport routes and urges an integrated approach to the documentation and analysis of flash floods. The catchment of the Pogliaschina Creek (drainage area 25 km2), a tributary of the Vara River (eastern Liguria, northwest Italy), which was severely hit by a flash flood on 25 October 2011, was selected for a pilot study aimed at defining the procedures for the documentation of flash floods and related geomorphic processes. The Pogliaschina catchment is representative of conditions often occurring in Italy as to availability of geographical and meteorological data and studies and documents for watershed planning. The approach devised includes reconstruction of peak discharge from high water marks at several cross-sections, assessment of the time evolution of the flood from interviews to eye-witnesses of the event, implementation of an inventory of landslides, evaluation of morphological changes of channels, and establishment of an approximate budget of large wood. The consistency of peak discharges reconstructed by means of post-flood field observations with rainfall data resulting from raingauges and radar data was checked through the application of a rainfall-runoff model. The inventory of landslides implemented through aerial photo interpretation was integrated with semi-automated identification of landslides on satellite images using remote sensing techniques.

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