Understanding patterns and processes of channel response to a large flood and their relations with the evolutionary morphological trajectory is important in order to predict future changes, assess channel dynamics hazards, and identify possible management options. This study aims to document channel changes occurred during a large flood and analyze them in the context of the longer term (last 150 years) evolutionary trajectory. The Magra River catchment experienced an extreme flood event (return periods ranging from about 100-200 years along the Magra, and to 500 years along some tributaries) in October 2011 which resulted in morphological changes, flooding, damage and loss of human lives. Analysis of past channel changes are based on multi-temporal series of aerial photos, cross-sections, longitudinal profiles, and field surveys. Morphological changes consequent to the flood event were investigated by: (1) field survey, including a reconstruction of the peak stage profile; (2) analysis of aerial photos and LiDAR before and after the event; (3) topographic survey of cross-sections. Results of the evolutionary trends show a recent phase (last 10-15 years) of dominant aggradation and widening, following previous phases (last 100-150 years) of progressive narrowing and incision. The October 2011 produced a complex pattern of changes, but with prevailing aggradation of the channel bed alternated to erosion. Comparison of aerial photos before and after the flood event clearly shows an important channel widening, related to two different processes: (1) bank retreat; (2) overbank sedimentation of bedload. Comparison with the longer term evolutionary trajectory shows that the channel width is still in the range of variations occurred during the last 50-60 years. Changes in channel width occurred along a series of partly-confined tributaries are more impressive, with frequent avulsions and, in some cases, a complete aggradation of the available alluvial plain.
Morphological effects of a large flood: the case study of the Magra River (Italy) / Rinaldi M.; Nardi L.. - STAMPA. - (2013), pp. 808-808. (Intervento presentato al convegno 8th International Conference (IAG) on Geomorphology tenutosi a Paris, Francia nel 27-31 August, 2013).