Preliminary characterization of the October 2018 event (Vaia storm) in the Rio Cordon catchment

Abstract: In October 2018, the Vaia storm affected large part of the mountain area of northeastern Italy. The main damages were caused by strong winds that produced large windthrows, but significant disturbances were observed also along the river network. Between October 27 and October 30, the cyclonic event led to heavy rainfall in many mountain watersheds triggering floods, sediment- and wood-laden fluxes. The Rio Cordon is a small dolomitic catchment (5 km2) located in the Agordino region. Since 1986, it is instrumented with a permanent monitoring station, which continuously measures the water and sediment fluxes as well the climatic conditions. The Vaia storm hit the Rio Cordon catchment severely and this work presents a first characterization about the effects induced. During the event, a rainfall amount of 331 mm was recorded, which corresponds approximately to the 28% of average annual precipitation. These conditions caused a massive runoff. Based on post-event field surveys, the peak of water discharge has been estimated between 16.2 – 18.8 m3 s-1, while the computed event-hydrograph suggests that the water discharge showed over bankfull values for approximately 22 h. The event-magnitude can be appreciated even in terms of bedload transport, as about 8000 m3 were transported to the monitoring station. In this sense, the above-mentioned rainfall and runoff favored an intense erosive activity over the entire catchment that led, in turn, to the reactivation of several sediment source areas and to the creation of new ones.