Sediment transfer in mountain streams occurs by transport processes classified as debris flows, debris floods,and water flows. Debris floods are water-driven flood flows with high bedload transport, during which astreambed may be destabilized causing massive movement of sediment. This study aims at testing how theenergy of water and the amount of sediment involved during a high-magnitude hydrological event can modify themechanisms of sediment transfer promoting the occurrence of debris floods in mountain streams. We developeda post-flood survey protocol for distinguishing various flow types on the basis of the geomorphological andsedimentological features of flood deposits. This protocol was applied in the Tegnas catchment (Dolomites, Italy)to determine the transport processes activated in October 2018 by the severe Vaia storm. Additionally, we tookinto account the unit stream power that occurred at the flood peak. Water flow was the dominant process in theTegnas main steam, but debris flood deposits were documented at a number of channel sites. Most of the steeptributaries were affected by debris flows, but also debris floods were recognized at three steep channels. Theseresults enabled us to gain new insights on the poorly explored debris flood processes. In particular, the upheavalfrom ordinary water flows to debris floods appeared to be promoted by (1) the presence of tributaries prone todebris flow occurrence connected to a receiving stream and/or (2) channel sites characterized by high slope andnarrow section, where the unit stream power exceeded about 5000 Wm-2.
THE OCCURRENCE OF DEBRIS FLOODS DURING HIGH-MAGNITUDE HYDROLOGICAL EVENTS:INSIGHTS FROM THE VAIA STORM (OCTOBER 2018) IN THE TEGNAS TORRENT (DOLOMITES, ITALY)
Marchi;Lorenzo;
2023
Abstract
Sediment transfer in mountain streams occurs by transport processes classified as debris flows, debris floods,and water flows. Debris floods are water-driven flood flows with high bedload transport, during which astreambed may be destabilized causing massive movement of sediment. This study aims at testing how theenergy of water and the amount of sediment involved during a high-magnitude hydrological event can modify themechanisms of sediment transfer promoting the occurrence of debris floods in mountain streams. We developeda post-flood survey protocol for distinguishing various flow types on the basis of the geomorphological andsedimentological features of flood deposits. This protocol was applied in the Tegnas catchment (Dolomites, Italy)to determine the transport processes activated in October 2018 by the severe Vaia storm. Additionally, we tookinto account the unit stream power that occurred at the flood peak. Water flow was the dominant process in theTegnas main steam, but debris flood deposits were documented at a number of channel sites. Most of the steeptributaries were affected by debris flows, but also debris floods were recognized at three steep channels. Theseresults enabled us to gain new insights on the poorly explored debris flood processes. In particular, the upheavalfrom ordinary water flows to debris floods appeared to be promoted by (1) the presence of tributaries prone todebris flow occurrence connected to a receiving stream and/or (2) channel sites characterized by high slope andnarrow section, where the unit stream power exceeded about 5000 Wm-2.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
