![]() , and erosion processes will confound the results. Otherwise, anthropogenic influences, as shown by Bull et al. However, these data should not be collected at long intervals from the event, but must be carried out closely before and immediately afterwards. In order to analyse the spatial effects and the accumulation volumes of a single debris flow event, pre- and post-event data acquisition is necessary (e.g., ). Therefore, in recent years, debris flow transported volumes have increasingly been measured in more direct ways using highly-precision methods such as terrestrial laser scanning (TLS) and airborne laser scanning (ALS), or photogrammetric techniques using uncrewed aerial systems (UAS). However, accurate volume data are crucial for the calibration and validation of models. In addition, permanently installed monitoring systems often do not measure the deposition volumes, but use empirical relationships to calculate debris flow magnitudes as, e.g., in Comiti et al. Therefore, it is difficult to determine the spatial characteristics of a single large-scale debris flow event that triggers multiple debris flows in the surrounding area. However, these installations focus mainly on channelised debris flows at medium-to-low altitudes and provide detailed information only about a single torrent or debris flow system. In such systems, a wide range of precise instruments provide accurate data on e.g., rainfall conditions, flow dynamics and velocities. Permanently installed debris flow monitoring systems have been established in some parts of the Alps, such as Italy, France and Switzerland, to gain observational data. Because of the rare occurrence of debris flow events, there is a lack of direct observations of the process and its consequences. Thus, it is of great importance to acquire in situ field data of debris flow systems especially after large-scale events. ![]() Due to the high-risk potential of debris flows, it is necessary to understand their triggering mechanisms as well as their flow dynamics. The gridded area-wide INCA (Integrated Nowcasting through Comprehensive Analysis) rainfall data further point to a local convective event on 20 July 2022, with a maximum rainfall intensity of 44 mm/h.Įspecially during such heavy precipitation events, debris flows occur as a natural hazard in all mountainous regions around the world. This is further supported by the measurements from three meteorological stations and four discharge gauges within the study area. The spatial appearance of the debris flows shows a concentration of processes in a particular area rather than a uniform distribution, suggesting a local nature of the triggering event. ![]() The calculated debris flow deposition volumes also show a power-law relationship with the total amount of rainfall in the respective debris flow catchments. ![]() Pre- and post-event airborne LiDAR (light detection and ranging) data with a high spatial resolution reveal that 156 different debris flow processes were initiated during these events, with accumulation volumes of up to approximately 40,000 m³. In this study, we present quantitative analyses of a single extreme debris flow event in the Horlachtal, Austria, triggered by local high-intensity short-duration precipitation events on 20 and 23 July 2022. However, precise data on debris flow triggering thresholds, accumulation volumes and spatial characteristics of large-scale events on catchment scale are scarce due to the rare occurrence of debris flows and the challenges of acquiring accurate data for a larger area. High-quality in situ measurements are essential for hazard assessment of debris flow events. ![]()
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