Abstract
Abstract. The use of remotely piloted aircraft systems (RPASs) in geosciences is often aimed at the acquisition of an image sequence to produce digital models and orthophotographs of the topographic surface. The technology can be applied for rockfall hazard and risk assessment. To study rockfalls, an approach consists in the application of numerical models for the computation of rockfall trajectories. Data required for such simulations include digital terrain models, location of the instability source areas, and the mechanical properties of the terrain. In this article, we present an analysis of the earthquake-triggered rockfall that occurred along the SP18 in Villanova di Accumoli (Lazio, central Italy) during the seismic sequence that started on 24 August 2016. A survey with a multicopter was carried out to obtain a surface model of the terrain and identify and characterize the source areas and other instable blocks in areas not accessible in the field. The investigated area extends for 6500 m2 and was covered by 161 photographs that were used to obtain an orthophoto with a ground resolution of 2.5 cm and a digital surface model with a ground resolution of 20 cm × 20 cm, which was processed and fused with GNSS real-time kinematic data. To obtain a map of potential rockfall trajectories, we run the numerical model STONE, using as origin of the boulders both source areas mapped in the field and pixels with a slope angle above a selected threshold. Results showed that only the part of the road SP18 already affected by the rockfall was exposed to further rockfall impacts. In particular, it was observed that 29.2 % (i.e. 12 123) of the 41 500 simulated trajectories may potentially reach or cross this tract of the road. Based on these data, limited protection measures were suggested. The combined use of RPAS data, fused with ground GPS points, an accurate geomorphological survey, and terrain static and dynamic parameters from the literature allows fast, low-cost, and replicable rockfall numerical modelling useful for emergency response and adoption of proper protection measures.
Highlights
Rockfall is a widespread natural hazard that poses continuous risk to the population in mountain areas worldwide (Whalley, 1984; Guzzetti et al, 2002)
This is confirmed by the STONE simulations, which reveal a total of 957 pixels affected by possible trajectories with a mode value of 1 within the road or downhill of it
The portion of the SP18 downhill from site 2” (S2), and which was hit by the rockfall during the seismic sequence, is correctly predicted by the model as subject to rockfall hazard
Summary
Rockfall is a widespread natural hazard that poses continuous risk to the population in mountain areas worldwide (Whalley, 1984; Guzzetti et al, 2002). The elements most exposed to rockfall hazard are transport corridors (Guzzetti et al, 2002; Budetta, 2004; Guzzetti et al, 2004), which often cross hazardous areas. Rockfalls cause relevant damage to structures and infrastructures along secondary and minor transport networks, where adequate protection measures are not economically sustainable. M. Santangelo et al.: RPAS for rockfall modelling (Corominas et al, 2005; Ferlisi et al, 2012), and pose a severe risk to people
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