Geomorphic effects of large floods: some examples from Italian rivers

Abstract

An increasing number of heavy precipitation events causing flash floods, debris flows and other types of landslides, as well as severe morphological effects on changes have affected Italy and Europe over the last years (Tarolli et al., 2012). Italian territory is particularly prone to these types of phenomena, due to a combination of distinctive topographic and meteorological characteristics (Rinaldi et al., 2016). Extreme events induce physical impacts on rivers and valley bottoms, consisting in channel widening (due to bank erosion and overbank deposition), changes in bed level, avulsions, huge amount of sediment transport, as well as recruitment of large wood. On overall, channel widening is the dominant geomorphic effect observed in many rivers. If on one hand channel widening represents an essential process to sustain channel morphology and fluvial ecosystems, on the other hand, in highly populated fluvial corridors, it can result in the loss of agricultural land and damages to buildings and infrastructures; thus, it should be considered a natural hazard and a major management problem. Interests in geomorphic effects of large floods have been intensively increasing over the recent decades. At Italian level, several case study papers were published, and new integrated approaches were proposed (Rinaldi et al., 2016). Even, the Italian Istituto Superiore per la Protezione e la Ricerca Ambientale (ISPRA) have proposed a method (the Event Dynamics Classification - EDC, Rinaldi et al., 2015) which provides tools to predict the geomorphic flood hazards, and supports the definition of morphological river corridors, meant to be complementary to inundation maps determined by “classical” hydraulic modelling. In light of this, an overview of recent studies on flood events at Italian level is presented, with the aims to highlight similar trends in channels changes induced by large floods and to assess the relative role of the different hydrological and morphological factors controlling the flood geomorphic effectiveness.