Abstract
On 4 August 2015, a very high intensity storm, 31.5 mm in 20 minutes (94.5 mm/h), hit the massif of Mount Antelao on the Venetian Dolomites triggering three debris flows characterized by high magnitude. Two of them occurred in the historical sites of Rovina di Cancia and Rudan Creek and were stopped by the retaining works upstream the inhabited areas, while the third routed along the Ru Secco Creek and progressively reached the resort area and the village of San Vito di Cadore, causing fatalities and damages. The main triggering factor of the Ru Secco debris flow was a large rock collapse on the northern cliffs of Mount Antelao occurred the previous autumn. The fallen debris material deposited on the Vallon d’Antrimoia inclined plateau at the base of the collapsed cliffs and part reached the Ru Salvela Creek, covering it from the head to the confluence with the Ru Secco Creek. The abundant runoff, caused by the high intensity rainfall on 4 August 2015, mobilized about 52500 m^3 of the debris material laying on the Vallon d’Antrimoia forming a debris flow surge that hit and eroded the debris deposit covering the downstream Ru Salvela Creek, increasing its volume. This debris flow routed downstream the confluence, flooding the parking of a resort area where three people died, and reached the village downstream damaging some buildings. A geomorphological analysis was initially carried out after surveying the whole basin. All liquid and solid-liquid contributions to the phenomenon were recognized together with the areas subjected to erosion and deposition. The elaboration of pre and post-event topographical surveys, provided the map of deposition-erosion depths. Using the rainfall estimated by weather radar and corrected by the nearest rain gauge, about 0.8 km far, we estimated runoff by using a rainfall-runoff model designed for the headwater rocky basins of Dolomites. A triggering model provided the debris flow hydrographs in the initiation areas, routed downstream by means of a cell model. The comparison between the simulated and estimated deposition-erosion pattern resulted satisfactory. The results of the simulation captured, in fact, the main features of the occurred phenomenon.
Highlights
The Boite Valley in Venetian Dolomites (Northestern Italian Alps) was affected by several runoff generated debris flows during the summer of 2015 (Baglioni and De Marco, 2015)
The simultaneous availability of pre and post-event data is not frequent but rare because in many cases the pre event terrain topography is usually unknown: previous occurred debris flow phenomena, of small magnitude, and local instability phenomena can significatively change the flow path morphology, and debris flow routing could not be captured by simulations
The 4th of August 2015, a high intensity storm concentrated on a square of about two kilometers and triggered some inchannel debris flows on Venetian Dolomites
Summary
The Boite Valley in Venetian Dolomites (Northestern Italian Alps) was affected by several runoff generated debris flows during the summer of 2015 (Baglioni and De Marco, 2015). After the debris flow occurrence, all the areas surrounding the Ru Secco Creek were carefully surveyed with the scope of identifying the development of the phenomenon and its characteristics This field survey gave the general view of all the single phenomena that contributed to the formation and routing of the solid-liquid surge along the Ru Secco Creek. We used an updated version of the GIS-based cell model of Gregoretti et al (2016b) that ensures a fully bi-phase routing for modeling the debris flow propagation downstream the initiation areas This updated version, proposed by Gregoretti et al (2018), allows a better simulation of the entrainment processes that have a crucial role in the estimation of the sediment volume transported by a debris flow that is needed for an efficient hazard assessment. The comparison between the simulation results with the deposition-erosion depth map accounts for the reliability of the phenomenon reconstruction, that is the capturing of its main features
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