Valutazione della pericolosità da dinamica morfologica nei fiumi Tagliamento e Fella (Friuli Venezia Giulia).

The study originates from the need to investigate and monitor rivers in order to manage and mitigate fluvial dynamics and prevent flood adverse effects. This research tests two survey and classification tools, the Morphological Dynamics Index (MDI) and the Event’s Dynamics Classification (EDC), recently developed in the IDRAIM methodology (Rinaldi et al., 2013). A further purpose is to assess the morphologic indexes integrability with the hydraulic hazard estimations commonly used. The indexes, which are applied by using GIS-remote sensing analysis and field geomorphologic surveys on 20 reaches belonging to the Tagliamento and Fella rivers (Friuli Venezia Giulia, northeastern Italy), are based on indicators examining rivers processes (e.g. bank erosion) and primary attributes (e.g. type of sediment transport), protection works, morphological variations and channel obstruction probability. The enquired temporal scales are about the last 10-15 years and the last 60 years for the MDI, whereas the EDC refers to extreme flood events. The results obtained allowed to define medium and high morphological dynamic classes (with a single reach hallmarked by low dynamics) for the MDI and high and very high for the EDC. High values for the MDI are located especially on the medium Tagliamento reaches, whereas a very high EDC is localized on the alpine reaches. The limited range of values obtained depends mainly on bed erosion indicators, which homogenized the resulting classes smoothing the morphologic dynamic differences among different landscape segments. On the other hand, overall the results obtained are in accordance with the expectations for these two rivers, which are characterized on many reaches by high energy, braided morphology and high bed-load transport rates. A comparison of the obtained results and the PAI mapping (i.e. maps of flood-prone areas) denoted a substantial similarity in the hazard evaluation on the studied reaches, with only two cases hallmarked by high MDI and EDC and low hydraulic hazard. These situations put evidence on the need of integrating hydraulic studies with a geomorphologic approach aimed at defining morphological dynamic hazard.